International Journal of Thermal Sciences (12900729)203
The comprehension of heat transfer mechanisms and their profound implications on biological heat transfer is of paramount importance in the advancement of cancer treatments across all types of malignancies. In the present study, the intricate interplay between Pennes' biothermal principles, Maxwell's electromagnetic equations, and heat generation via a one-slot microwave antenna is resolved numerically. By administering magnetite nanoparticles into malignant tumors, an induced field is engendered, ultimately leading to tumor ablation. By manipulating the microwave frequency, the resultant field is assessed to ascertain the optimal therapeutic modality for this dangerous ailment. The investigation incorporates varying volume percentages of nanoparticles, namely 0.1, 0.05, 0.01, and 0.005 percent, yielding tumor necrosis durations of 2.8, 7.3, 34, and 69 s, respectively. Furthermore, the loss of healthy tissue is quantified as 4.8 %, 15.4 %, 65 %, and 139 %, respectively. Consequently, a direct correlation emerges between the percentage of nanoparticles employed and the diminished treatment duration, as well as reduced adverse effects on healthy tissues, leading to improved patient comfort and minimized thermal-induced injury. Additionally, the influence of frequency within the microwave range (0.3–10 GHz) is probed. Accordingly, when the nanoparticles are injected into the tumor, the frequency has no meaningful difference in the treatment result. © 2024
Heat and Mass Transfer (09477411)60(7)pp. 1235-1250
One of the most effective parameters in the thermal treatment of liver cancer by microwave heating method is the changes in the input power to the antenna. This study aims to numerically investigate the effects of the change in the input power to the microwave antenna in the presence of magnetic nanoparticles using the finite element method in liver tumors. Also, the importance of the type of nanoparticles, treatment time and side effects were investigated. According to the results, after the injection of maghemite nanoparticles, the purification time is 7.35 s at a power of 10 W and reaches 6.1 s when the power is increased to 100 W. Also, the ratio of the destroyed healthy volume of the tissue to the tumor volume is less than 20% in the mentioned powers, and the treatment can be considered independent of the power. After the injection of magnetite and FccFePt nanoparticles at a power of 10 W, the treatment time was calculated as 176 s and 295 s, respectively, and with the increase of the input power, the reduction of the treatment time was observed. So that the treatment time was reduced to 58 s and 74 s, respectively, at 100 W. In terms of side effects, for the mentioned nanoparticles, 4.89 and 8.93 times the volume of the tumor with a power of 10 W and when the power reaches 100 W, 4.05 and 5.6 times the volume of the tumor is destroyed from the healthy tissue, respectively. However, the lowest amount of healthy tissue destruction in these two nanofluids occurs at moderate powers—60 W and 50 W, respectively—so the dependence of treatment time and side effects on input power was observed. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Journal of Thermal Biology (18790992)112
An extensive algorithm based on both analytical and numerical solution methodologies is proposed to obtain transient temperature distributions in a three-dimensional living tissue subjected to a moving single-point and multi-point laser beam by considering metabolic heat generation and blood perfusion rate. Here, the dual-phase lag/Pennes equation is analytically solved by using the method of Fourier series and the Laplace transform. The ability to model single-point or multi-point laser beams as an arbitrary function of place and time is a significant advantage of the proposed analytical approach, which can be used to solve similar heat transfer problems in other living tissues. Besides, the related heat conduction problem is numerically solved based on the finite element method. The effects of laser beam transitional speed, laser power, and the number of laser points on the temperature distribution within the skin tissue are investigated. Moreover, the temperature distribution predicted by the dual-phase lag model is compared with that of the Pennes model under different working conditions. For the studied cases, it is observed that the maximum tissue temperature decreased about 63% by an increase of 6mm/s in the speed of the laser beam. An increase in the laser power from 0.8W/cm3 to 1.2W/cm3 results in a 28 °C increase in the maximum temperature of the skin tissue. It is observed that the maximum temperature predicted by the dual-phase lag model is always lower than that of the Pennes model and the temperature variations over time are sharper, while their results are entirely consistent over the simulation time. The obtained numerical results indicated that the dual-phase lag model is preferred in heating processes occurring at short intervals. Among the investigated parameters, the laser beam speed has the most considerable effect on the difference between the results of the Pennes and the dual-phase lag models. © 2022 Elsevier Ltd
Malekmohamadi, M.H.,
Ahmadikia, H.,
Golmohamadi, S.,
Khodadadi, H. ARCHIVE OF MECHANICAL ENGINEERING (00040738)70(1)pp. 129-149
Water resources are the main component of natural systems affected by climate change in the Middle East. Due to a lack of water, steam power plants that use wet cooling towers have inevitably reduced their output power. This article investigates the replacement of wet cooling towers in Isfahan Thermal Power Plant (ITPP) with Heller natural dry draft cooling towers. The thermodynamic cycle of ITPP is simulated and the effect of condenser temperature on efficiency and output power of ITPP is evaluated. For various reasons, the possibility of installing the Heller tower without increasing in condenser temperature and without changing the existing components of the power plant was rejected. The results show an increase in the condenser temperature by removing the last row blades of the low-pressure turbine. However, by replacing the cooling tower without removing the blades of the last row of the turbine, the output power and efficiency of the power plant have decreased about 12.4 MW and 1.68 percent, respectively.
International Journal of Thermal Sciences (12900729)184
Blood flow greatly affects heat transfer in living tissue and has many applications in medical treatments. The existence of vessels has always been a challenge for modeling living tissue analytically in engineering studies related to bioheat transfer. In this article, the vessels are considered a heat source or sink, and the heat from the bloodstream is given or taken to the tissue. The heat generated in living tissue by continuous and pulsed lasers during the hyperthermia process and the effect of blood flow within the arteries and veins on tissue temperature distribution are solved analytically. The unsteady Fourier and non-Fourier equations for tissue are analytically solved by considering the vessels and blood perfusion within the tissue. The analytical solution results in both Fourier and non-Fourier models showed that the vessel could be modelled as a heat source/sink inside the tissue. The temperature distributions in the numerical and analytical solutions are completely similar. The results show that vessels have an effect of about ±0.6 °C on tissue during laser therapy. © 2022
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine (9544119)237(12)pp. 1366-1376
In order to design shoes suitable for cold environments, knowledge of the thermal conditions inside the shoes and the variables affecting those conditions is necessary. A two-dimensional model of a boot and sock was developed to investigate the effect of the materials and dimensions of various parts of shoes and to design geometry for them to prevent foot frostbite. The optimization algorithm was used to optimize the dimensions of the boots to maximize the minimum foot temperature with the lowest boot weight. Two types of shoe soles and two kinds of shoe uppers were used to design suitable shoes. The results show the following: (1) In the design boots, the thermal insulation of the toe area plays an essential role in preventing frostbite. Two variables of the thickness of the toe cap and the length of the shoe sole had the greatest impact on the design of shoes with the least weight and the most protection against frostbite. So that to increase minimum foot temperature from 7°C to 15°C, 16°C, or 17°C, only the amounts of these variables should increase. (2) In designing the suitable boot, choosing the proper shoe sole had a significant effect on increasing the thermal insulation in the shoe and reducing its weight. So, for the boot with a minimum foot temperature of 20°C, by changing the shoe sole from EVA08 to EVA12, the weight is reduced by 42%. (3) To maximize the minimum foot temperature, it is necessary to use thick socks. © IMechE 2023.
Journal Of Lasers In Medical Sciences (22286721)14
Introduction: There are some ways to examine heat transfer in tumor tissue, which is an important issue in bioengineering. One of these ways uses the bioheat equation, proposed by Pennes, in a continuous medium. Another one uses a porous medium to model heat transfer in living tissues. The objective of this paper was to study an approach to modelling the temperature distribution and tumour ablation in brain tissue and compare results to Pennes’ approach. Methods: This approach presents and uses a porous medium as the tissue instead of a continuous medium. In addition, the two approaches (simulation in continuous and porous medium) are compared in terms of temperature simulation and amount of cell ablation. The density, heat conduction factor, and blood perfusion rate are considered functions of temperature. Results: In these approaches, after an 85-second treatment, the temperature increases to about 90°C. The temperature increase of the porous medium is relatively the same as that of the continuous medium and for this reason, the amount of cancerous cells that are ablated in a porous medium is approximately the same as that in a continuous medium. The volume of cell ablation is about 6500 mm3 for two ideas. In addition, the degree of damage, computed from the Arrhenius integral method, and the ablated volume of the tumour endorse equality at the end of treatment. According to the results, similar to the continuous approach, the porous approach predicts the temperature and amount of volume of damaged cells. Conclusion: Therefore, it is possible to use the porous approach instead of the Pennes approach for tumour treatment. © (2023), (Laser Application in Medical Sciences Research Center). All Rights Reserved.
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)46(4)pp. 1261-1273
Accurate prediction of temperature distribution during thermotherapy is a significant factor in the thermotherapy process. Thermotherapy equipment produces a different distribution spatial and time-dependent heat fluxes in the thermotherapy processes. This paper presents an exact analytical solution of steady and unsteady Pennes and porous bioheat equations in a cylindrical coordinate system for multi-layer skin with different spatial and time-dependent heat fluxes on the surface. The proposed analytical solutions are useful to make accurate temperature distribution in multi-layer skin tissue with various properties. The results show that the unsteady temperature distributions in both Pennes and porous models are the same in the initial times of process. When the temperature rises, the cooling effect of blood perfusion in the Pennes model increases the difference in temperature distribution for these two models. The skin surface temperature is linear versus time in constant and linear fluxes, and skin temperature increment has a second-degree trend versus time in the quadratic flux. The magnitude of the flux coefficient and the time of applying flux to the tissue are effective in increasing the temperature of the tissue and the skin surface. © 2021, Shiraz University.
Urban Climate (22120955)44
Large urban areas are typically subjected to excessive levels of heat and pollution. The formation of an urban-scale plume would arise from releasing heat in a stable atmosphere. The presence of wind may disrupt the pattern of the plume. This study explores the effect of wind intensity and ambient stability on the plume structure and pollution dispersion numerically. A metropolitan has been selected as the urban, and the average heat and pollution release rate is calculated based on a typical megacity. It has been found that for buoyancy ratios (the ratio between the horizontal velocity of the urban plume to wind speed) smaller than 0.5, the wind is the governing mechanism. For buoyancy ratio higher than 2, the urban heat island is governing mechanism. In stable conditions and the ratios smaller than 0.5, the urban average temperature difference reduces by about 0.125 K for a unit increase in wind speed. When the ratios are less than 0.2, there are 0.5 K temperature differences between urban and rural, and 0.072 μg/m3 averaged pollution for all stability conditions. It is also found that for ratios higher than 0.5, any increase in wind velocity does not reduce the pollution concentration significantly. For values smaller than 0.5, any increase in wind speed would result in a considerable drop in pollution concentration if the radiative effect of pollutants is ignored. © 2022
Journal of Building Engineering (23527102)50
In this paper, a mathematical model is developed for the simulation of encapsulated phase change material as a thermal energy storage tank. The model is modified for the TRNSYS software to enable researchers for investigating the performance of a latent heat energy store system integrated with solar energy systems and buildings. The model is validated against experimental and numerical studies and the error is found to be less than 2% and 10% for 1-D and 2-D models, respectively. The new component is applied for solar energy storage and it is concluded that it effectively follows the variation of solar irradiation. The application of a PCM tank for daily energy storage reduces the cooling and heating loads by 22.5% and 18%, respectively. The energy-saving with seasonal cooling storage using a PCM tank is about 7% of the total energy consumption. © 2022 Elsevier Ltd
Journal of Engineering Mathematics (15732703)131(1)
In the present study, the temporal and spatial variation of temperature in a three-dimensional triple-layer skin tissue under the laser heating is determined. Using the method of separation of variables along with the Laplace transform, the so-called Pennes bio-heat equation is analytically solved in a 3D triple-layer tissue in which each layer has its own thermo-physical properties. The laser heating of the skin, with both single and multiple laser beams, is modelled based on time-dependent Gaussian-shaped irradiance distributions with exponential axial attenuation. For the presented solution approach, it can be shown that the laser can be considered as an arbitrary function of time such as pulses with a specified time interval with each desired spatial distribution. Besides the analytical solution, the governing equations are solved numerically by using the standard finite element method and the results are compared with the analytical solution to investigate the effects of laser heating on human skin. The effects of using single and multiple-point laser beams on the temperature increment are investigated. A good agreement between both analytical and numerical solutions is observed. The obtained results indicate that a better temperature distribution in the skin tissue is obtained; whenever, a multi-point laser is employed. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
Ghaffarpasand o., O.,
Talaie m.r., M.R.,
Ahmadikia, H.,
Talaiekhozani, A.,
Shalamzari, M.D.,
Majidi, S. Sustainable Cities and Society (22106707)72
Poor urban development and social instability are the results of unsustainable urbanization. These urban risks could significantly influence public culture and might even lead to aggressive driving styles. A practical approach comprising of model estimation and real-world measurements is applied here to discuss the role of urban development and public culture in the driving behavior and vehicle emissions in an unsustainable urbanized city, i.e. Isfahan, Iran. Over 60,000 speed-time data were collected from the streets for several time slices to develop the ISFahan Driving Cycle (ISFDC). ISFDC is assessed against the DCs of foreign countries and other Iranian cities to discuss the contribution of the studied factors to driving behavior. ISFDC is then entered into the IVE model to estimate the exhaust emission factors (EFs) under real-urban conditions, while IVE is primarily adjusted to the real-world experiments. Also, several emission mitigation scenarios that are likely to mitigate vehicular emissions are evaluated. Results show that ISFDC is already unique around the world, but unsustainable urbanization in terms of poor urban development and aggressive actions/reactions plays a vital role in the driving behavior of Iranian drivers. Unsustainable urbanization causes the CO and NOx EFs of Isfahan vehicles to be 40 and 25.47 % higher than those in Tehran, and 60 and 57 % higher than those in Beijing, respectively. Among the studied EFs, CO EF is more affected by the level of urban development. Ammonia, Formaldehydes, and Benzene are consecutively ranked as the major toxic gases in the Isfahan vehicle exhausts. © 2021 Elsevier Ltd
Computer Methods in Biomechanics and Biomedical Engineering (10255842)24(11)pp. 1221-1227
There are some techniques to ablate tumours of brain, breast and liver. One of them is laser irradiation. The most important problem of this technique is to injure noncancerous tissues. It is a challenging work to control the domain of laser effects. In other words, it is hard to ablate cancerous tissue without ablating noncancerous. To gain this goal, some researchers have been proposed some ways, such as using two or three applicators or moving applicator. The objective of this paper is to present an approach to control the temperature distribution and heat affected zone in brain tumours when irradiated by shielded laser beam, 1064 nm ND-YAG. The effects of laser beam, resulting in tissue temperature increasing, follows the border of tumour by defining of a dual intensity distribution. This is included two distinct intensity distributions of laser on the applicator by shielding. Treatment of an arbitrary topology of tumour will be simulated irradiation of laser by two different distributions through numerical method. Results show when dual distribution on the tumour border is used, the pattern of photon distribution is coincident by the tumour and the affected zone and temperature increasing follows the borderline of tumour, qualitatively. It shows that the ablated volume of tumour will be 53% more than when the unique distribution is used and the treatment time is shorter, resultantly. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
Ghaffarpasand o., O.,
Talaie m.r., M.R.,
Ahmadikia, H.,
Khozani, A.T.,
Shalamzari, M.D.,
Majidi, S. Atmospheric Pollution Research (13091042)12(3)pp. 113-124
In the present study, we seek to conduct a real-world assessment of the driving behavior, emission performance, and fuel consumption of urban buses in a medium-sized city in the Middle East, i.e. Isfahan, Iran. A comprehensive data collection was conducted within the main routes of the city and then the ISFahan Bus Driving Cycle (ISFBDC) was developed using a micro-trips random selection approach. On-board experiments were carried out on 20 urban buses to analyze the emission performance of the fleet in real-world conditions. The effects of bus speeds, after-treatment systems, and passenger load on emission performance and fuel consumption (FC) were also discussed. Meanwhile, the contribution of different driving modes to the CO, HC, NOx, and CO2 mileage(M)/fuel(F)-based(B) EFs and FC rates were investigated. Our results show that ISFBDC is unique in the world. FBEFs are strongly correlated with the speed, so much so that HC FBEFs were reduced by over 70% with increasing 30 km/h in the bus speed. Idling status contributes over 70%, 50%, 30%, and 30% to the NOx, CO2, and HC emission, and FC of the studied fleet, respectively. Although DPF filters in Euro IV buses could significantly reduce the NOx emission, they have no considerable impact on the emission of the other studied pollutants. Per-passenger EFs and FCF are more than halved by 1.5 T increase in passenger loads. Euro IV buses with DPFs had better per-passenger/accumulated emission performance and fuel consumption than the others. CO2 MBEFs of Isfahan buses are nearly twice that of Beijing buses. © 2021 Turkish National Committee for Air Pollution Research and Control
Ghaffarpasand o., O.,
Talaie m.r., M.R.,
Ahmadikia, H.,
Khozani, A.T.,
Shalamzari, M.D.,
Majidi, S. Urban Climate (22120955)39
The present study aims at a real-world assessment of the driving behaviour and exhaustive emission performance of motorcycle (MC) driving in a middle-sized city of a developing country, i.e. Isfahan, Iran. We developed the Isfahan Motorcycle Driving Cycle (IMDC) using comprehensive data collection and then compared it with the available overseas MCDCs and DC of local LDVs. Onboard experiments were also conducted on 20 test motorcycles to analyze emission performance, emission characteristics, and combustion quality of motorcycles under real-world conditions. IVE model was used to estimate the MC emission factors (EFs) according to the real-urban conditions, but it was first adjusted to the real-world measurements. Results show that MC EFs steadily decrease with vehicle speeds. Apparent discrepancies were observed between IMDC and the MC DCs overseas, while local DCs of motorcycles and LDVs follow a prevailing trend determined by the new factors of public culture and urban development. CO was the major criteria pollutant of the MCs exhaust, and formaldehyde and benzene were ranked as the first and second principal toxic gases, respectively. The air-fuel mixture control system and combustion quality of 150 and 200 cc MCs were impaired with the vehicle speed, but the same is not true for the 125 cc MCs. © 2021 Elsevier B.V.
Journal of Engineering Mathematics (15732703)130(1)
Although many models have been derived for heat transfer in the skin, analytical solutions for heat transfer provide more reliable results than numerical approaches. Due to the limitations of the in-vivo experiments, it is of great value to describe the thermal behavior of living tissues. In this paper, heat transfer in a multi-layer living tissue with different thermophysical properties in both steady and unsteady states are analyzed by using the Pennes’ and porous media models. Convective heat transfer in a three-layer skin is considered. It is found that both the results of the Pennes’ and porous models are almost identical. That is, by ignoring the blood perfusion term in the Pennes model, and instead, using the porous tissue properties similar results can be achieved, especially in the early stages of transient processes. It is also depicted that the magnitude of the blood temperature convection term is negligible compared to the temperature diffusion in the porous equation model. This indicates that the blood velocity within different layers of the skin can be ignored and only the thermophysical properties of the porous model can be considered in performing the analysis, which has less than a 3% difference compared to the Pennes model results. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
Journal of Thermal Biology (18790992)99
Proper analysis of the temperature distribution during heat therapy in the target tissue and around it will prevent damage to other adjacent healthy cells. In this study, the exact solution of steady and unsteady of the hyperbolic bioheat equations is performed for multilayer skin with tumor at different heat fluxes on its surface and the generation of internal heat in the tumor. By determining the temperature distribution in three modes of constant heat flux, parabolic heat flux and internal heat generation in tumor tissue, the amount of burn in all three modes is evaluated. The results indicated that the Fourier or non-Fourier behavior of tissue has no role in the rate of burns in thermotherapy processes. At equal powers applied to the tissue, the internal heat generation in the tumor, constant flux and parabolic flux on the skin surface have the most uniform and most non-uniform temperature distribution, respectively and cause the least and the most thermal damage in the tissue. © 2021 Elsevier Ltd
Ghaffarpasand o., O.,
Talaie m.r., M.R.,
Ahmadikia, H.,
Khozani, A.T.,
Shalamzari, M.D. Atmospheric Pollution Research (13091042)11(9)pp. 1598-1609
The present study is primarily aimed to establish a detailed exhaustive emission inventory of urban motor vehicles in a medium-sized city, i.e. Isfahan. The International Vehicle Emission (IVE) model was utilized to estimate the motor vehicle Emission Factors (EFs) in different areas of Isfahan. IVE was adjusted using the results obtained by on-board real-world EF measurements. A high resolution 1 km × 1 km vehicle emission inventory for the year 2018 was then developed in a bottom-up approach. The method was employed based on the influencing factors such as the collected hourly-data on road network, traffic flow, vehicle driving cycles, and the vehicle population in Isfahan. Moreover, the variations of EFs with vehicle speed were investigated for different vehicle categories to assess the emission rates through Isfahan transportation fleet. The results showed that EFs of all pollutants emitted from vehicle exhausts usually decrease with vehicle speed. Also, gasoline vehicles have larger CO and VOCs EFs than the others, whereas vehicles fueled by diesel have the largest NOx, SOx, and PM10 EFs. The established emission inventory revealed that the annual amount of CO, VOCs, NOx, SOx, and PM10 emitted from Isfahan on-road mobile sources in 2018 are 267.6, 12.6, 20.3, 0.3, and 2.3 kt, respectively. The gasoline vehicles including cars and motorcycles were the main sources of CO, VOCs, and SOx, whereas the heavy-duty vehicles and buses equipped with diesel engines were the main sources of NOx and PM10. The hourly variations of EFs ensure an acceptable consistency with the hourly variation of the traffic flow at different areas. Moreover, the high-resolution spatial distribution of vehicle emission inventory represented that emissions were concentrated on the downtown, esp. on underdeveloped historical area of the city, where the most of the governmental and administrative departments are concentrated. © 2020 Turkish National Committee for Air Pollution Research and Control
Computer Methods in Biomechanics and Biomedical Engineering (14768259)23(13)pp. 987-1004
An image-based numerical algorithm is presented for simulating blood flow through the liver tissue. First, a geometric model is constructed by applying image processing techniques on a real microscopic image of a liver tissue. Then, incompressible blood flow through liver lobules is simulated. Effects of tissue heterogeneity and deformity, presence/absence of the second central vein in a particular lobule, and apparent sinusoids density in the liver cross section on the blood flow are investigated. Numerical results indicate that the existence of thick low permeability vascular septum, high permeability sinusoids, and lobule tissue heterogeneity can considerably affect interlobular and intralobular blood flow. . © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Askarizadeh, H.,
Ahmadikia, H.,
Ehrenpreis, C.,
Kneer, R.,
Pishevar, A.,
Rohlfs, W. International Journal of Heat and Mass Transfer (00179310)146
Because of its high heat transfer potential, liquid jet impingement is broadly used in cooling applications. As a free-surface jet spreads radially after impinging on a flat surface, a hydraulic jump can occur that severely affects the heat transfer. This study numerically scrutinizes the effects of different flow structures within the jump on the local heat transfer of the impinged plate subjected to a uniform heat flux. For the numerical simulations, a modified version of the interFoam solver of OpenFOAM is used, in which the interface compression scheme is amended implementing the continuum surface stress method. To create different flow structures in the jump region, an obstacle with a varying height is placed at the edge of the impinged plate. Jump structures and the transitions between them are distinguished by virtue of the appearance of a separation bubble on the bottom surface and/or a roller underneath the interface in the jump region. The results show that the hydraulic jump in itself reduces the local Nusselt number, whereas the roller underneath the free surface slightly improves the heat transfer. The minimum heat transfer rate occurs right before the separation bubble (at the separation point); however, the local stagnation point ahead of the separation bubble increases the Nusselt number. © 2019
Ghaffarpasand o., O.,
Talaie m.r., M.R.,
Ahmadikia, H.,
Talaiekhozani, A.,
Shalamzari, M.D.,
Majidi, S. Atmospheric Pollution Research (13091042)11(10)pp. 1743-1753
The real-world emission factors (EFs) and emission performance of bi-fuel (CNG/GAS) vehicles have been seriously investigated by the emission scientists and urban planners. In the present study, we propose an almost new practical methodology and perform on-road experiments on 60 bi-fuel vehicles to discuss the impacts of vehicle speed, fuel type, usage, and accumulated mileage on the CO, HC, and NOx EFs. 80% and 20% of the tested vehicles were private cars (PCs) and taxis (TXs), respectively. TXs and PCs are compared together based on their emission performances, emission characteristics, vehicular specific power (VSP) distributions, and type of fuel. The results show that in the entire cases except for GAS-PCs, CO EFs increased with vehicle speed. Although CNG vehicles show less HC EFs, they produce higher NOx mileage-based EFs compared to gasoline ones. NOx mileage-based EFs decrease with vehicle accumulated mileage, whereas the opposite trend was observed for the CO and HC EFs. Burning CNG rather than gasoline decreases 70% and 42% of CO, and 70% and 85% of HC mileage-based EFs in PCs and TXs, respectively. The influence of burning CNG on NOx emission of TXs seems to be insignificant, but NOx was more emitted by a factor of 1.7 in CNG PCs. Accumulated mileage has a destructive effect on combustion quality, especially in CNG vehicles. The factors of usage and accumulated mileage could considerably develop the VSP distribution and fuel consumption rate of GAS vehicles, while they have no detectable impact on that of CNG vehicles. © 2020 Turkish National Committee for Air Pollution Research and Control
Building and Environment (03601323)168
The background atmospheric stratification with inversion layers in association with urban heat island phenomena affects the city ventilation and pollution transport. In this study, the effects of different stratification including ground inversion, isotherm, sub-adiabatic and super-adiabatic profiles with an inversion layer on pattern, intensity and extend of urban heat island induced circulation (UHIC) are investigated. The effect of the UHIC pattern on pollutant transport for two different scenarios are studied. The study is conducted using a modified CFD model that is adopted to include temperature background layers, compressibility and anelasticity of the atmosphere. The modified CFD model and results of simulation are validated against the available data in literature for UHIC pattern and pollution transport scenarios. The results indicate that background temperature profile controls the convergence and divergence of flow, and it affects the mixing height of flow inside of urban area, significantly. The flow speed at the urban border for inversion, isotherm, and sub-adiabatic stratification is 55%, 52%, and 40% less than super-adiabatic stratification, respectively. It is observed that the existence of inversion layer is essential for convergence of flow in case of super-adiabatic stratification. In case of ground inversion, pollutants that are released inside urban area are transferred to higher levels in rural area. The induced flow due to ground inversion transfers thepollutant in rural area into the urban dome. The pollutant concentration for inversion, isothermal and super-adiabatic profiles is 350%, 200%, and 150% more than sub-adiabatic stratification, respectively. © 2019 Elsevier Ltd
International Journal of Thermal Sciences (12900729)156
This study concerns with the effect of transverse vibration of an internal plate on mixed convection heat transfer inside a square enclosure of a glass recycling process dryer. The plate can oscillate in horizontal and vertical directions. The Reynolds-averaged Navier-Stokes equations are used to describe the unsteady turbulent flow field. The governing equations are solved numerically applying a finite-volume approach. OpenMP Parallel SIMPLE algorithm is employed with power-low scheme for the convective terms. Also, the turbulent flow properties are estimated by a two-layer zonal model based on k−εmodel and Wolfstein near wall treatment. Dimensionless effective parameters including Reynolds number (Re), Grashof number (Gr) and vibration angular frequency (ω) are varied to investigate inherent flow structures and the heat transfer rate. It was deduced from the results that at high Gr and low Re numbers, the effect of internal plate vibrations is negligible and the fluid flow is induced only by the buoyancy force. As Re and ω are increased, the effect of internal plate vibration becomes dominant. At high Re and ω values while Gr kept low, benchmark cavity heat transfer is increased up to 90 and 80 times due to the vibration of internal horizontal and vertical plates, respectively. The obtained results can be beneficial for the dryers of glass recycling industries in order to heat and smash the glass particles without a significant heat loss. Desired condition occurs at high Gr and ω when the flow Re number is comparatively low. © 2020
Askarizadeh, H.,
Ahmadikia, H.,
Ehrenpreis, C.,
Kneer, R.,
Pishevar, A.,
Rohlfs, W. Physical Review Fluids (2469990X)4(11)
In almost all of the studies on the circular hydraulic jump (CHJ), gravity had been considered as a significant variable that affects the formation of the jump. Most recently, gravity was deprived of being important in the origin of the CHJ, which challenged researchers in this field of fluid mechanics. This study addresses in detail the physical concepts behind this intriguing phenomenon occurring in the radial outspreading of a vertically downward free-surface liquid impinging jet upon a horizontal plate. The aim is to find out whether gravity plays any role in the origin of the CHJ. Accordingly, the jump evolution is investigated in two cases: First, the initial formation of the CHJ in which the subcritical flow downstream from the jump is approaching the outlet boundary (developing jump). Second, the final evolution of the CHJ in which a steady-state flow is circumventing an obstacle at the edge of the impinged plate and falling uniformly down from the outlet boundary (developed jump). The results indicate the existence of two different flow regimes in the jump formation: Gravity- A nd capillary-dominant flow regimes. In general, the role of gravity in the formation of developing or developed jumps cannot be eliminated; however, its importance lies in the fact of which regime dominates the flow. Intensification of gravitational effects is observed when capillary waves are dampened by increasing viscosity, density, or volume flow rate as well as by decreasing surface tension. Finally, a generalized scaling relation for the jump radius is obtained considering both capillary and gravitational effects in the critical flow condition. In contrast to the previous results, this generalized scaling relation predicts more accurately the radius of both a developing and a developed jump. © 2019 American Physical Society.
Journal of Heat Transfer (221481)140(8)
This study introduces an analysis of high-order dual-phase-lag (DPL) heat transfer equation and its thermodynamic consistency. The frameworks of extended irreversible thermodynamics (EIT) and traditional second law are employed to investigate the compatibility of DPL model by evaluating the entropy production rates (EPR). Applying an analytical approach showed that both the first- and second-order approximations of the DPL model are compatible with the traditional second law of thermodynamics under certain circumstances. If the heat flux is the cause of temperature gradient in the medium (over diffused or flux precedence (FP) heat flow), the DPL model is compatible with the traditional second law without any constraints. Otherwise, when the temperature gradient is the cause of heat flux (gradient precedence (GP) heat flow), the conditions of stable solution of the DPL heat transfer equation should be considered to obtain compatible solution with the local equilibrium thermodynamics. Finally, an insight inspection has been presented to declare precisely the influence of high-order terms on the EPRs. © 2018 by ASME.
Applied Thermal Engineering (13594311)144pp. 769-778
This paper concerns with the problem of natural convection heat transfer inside an industrial oven with an internal plate. The model is simulated numerically as a square cavity with an isolated plate laid horizontally or vertically inside it. Different ranges of Rayleigh number from laminar to turbulent flow regimes were investigated numerically and inherent flow structures and the amount of transferred heat were obtained. The governing Reynolds-averaged Navier-Stokes and energy equations are discretized and solved applying finite-volume method. Moreover, a two-layer zonal model is applied for near-wall turbulent properties. Comparing the present results with similar previous studies and experimental data shows that the employed zonal model is more accurate than other existing turbulent models. Our results also demonstrate that the total rate of heat transferred by a cavity with internal isolated plate is always lower than that of a bare cavity. As the distance of internal plate from the cavity wall decreases, its effect on the reduction of overall heat transfer increases accordingly. We also determined a distance between the plate and the cavity wall with less than 2% change in relative Nusselt number and deduced that the maximum distance of vertical plate is always greater than that of the horizontal plate at each Rayleigh number. Furthermore, a dead zone is created between the hot wall and the plate with low velocities, the temperatures close to the hot wall temperature, and very weak circulation, which can significantly reduce the overall heat transfer in the cavity. The results of this work can be used in glass industries and reduction of heat loss in industrial ovens by placing the glass sheets inside them in appropriate position. © 2018 Elsevier Ltd
Energy and Buildings (03787788)150pp. 37-51
The transient performance of different configurations of solar desiccant cooling systems is analyzed and compared based on the concept of Finite Time Thermodynamics. The TRNSYS software is used to conduct the transient simulation, and the results are compared with the experimental data in literature. Solar desiccant cooling systems are studied in 3 different configurations, in which fresh air, conditioned air, and a mixture of fresh air and conditioned air enter the dehumidifier wheel, respectively. Also, the performance of desiccant cooling system is investigated in single-stage and double-stage configurations to consider the effect of the number of dehumidifier wheels. The coefficient of performance (COP) and exergy efficiency of different configurations are evaluated to determine the optimum arrangement. The highest COP is achieved for Dunckle configuration in ventilation mode and for Uçkan configuration in recirculation mode. The results indicate that the COP of single-stage systems is higher than double-stage in both recirculation and ventilation modes. The highest COP and exergy efficiency are achieved for Dunckle configuration in ventilation mode as 0.6 and 35%, respectively. Implementation of heat recovery system improves the performance of double-stage configuration more than the single-stage system. An economic analysis is performed to compare different configurations based on electrical energy saving and payback period. The result indicates that the Uckan and Dunckle configurations consume 50% lower electrical energy compared to air conditioning heat pumps with payback period of about 4 years. © 2017 Elsevier B.V.
International Journal of Heat and Mass Transfer (00179310)104pp. 301-309
The compatibility of dual-phase-lag (DPL) heat conduction with the hypothesis of local thermodynamic equilibrium (LTE) and extended irreversible thermodynamic is investigated. The analysis is based on evaluating the entropy production rate (EPR) for a solid slab that is exposed to a sudden temperature gradient at its boundaries. In this regard, an analytical solution is presented for the first-order and second-order approximations of the DPL model. It is shown that by extending the non-Fourier Cattaneo–Vernotte (C–V) wave model to the high-order DPL model, the unphysical values of the slab temperature that exist in the solution of C–V wave model cannot be generally eliminated. However, a set of phase lag times for the DPL model exist based on which these unphysical values can be omitted by increasing the diffusion versus the wavelike features. © 2016
Heat Transfer - Asian Research (10992871)46(1)pp. 29-48
Thermal wave and dual phase lag bioheat transfer equations are solved analytically in the skin tissue exposed to oscillatory and constant surface heat flux. Comparison between the application of Fourier and non-Fourier boundary conditions on the skin tissue temperature distributions is studied. The amplitude of temperature responses increases and also the phase shift between the temperature responses and heat flux decreases under the non-Fourier boundary conditions for the case of an oscillatory surface heat flux. It is supposed the stable temperature cycles in order to estimate the blood perfusion rate via the existing phase shift between the surface heat fluxes and the temperature responses. It is shown that the higher rates of the blood perfusion correspond to lower phase shift between the surface temperature responses and the imposed heat flux. © 2015 Wiley Periodicals, Inc.
Applied Thermal Engineering (13594311)112pp. 100-110
In this paper, a single stage and double stage mechanical vapor recompression (MVR) system are designed and their performances are analyzed at different working conditions. The main purpose is to recycle water from the Reverse Osmosis rejected brine that is one of the main environmental challenges. A mathematical model for the MVR system is implemented and a sensitivity analysis is performed to investigate the effect of operational variables on the system power consumption and heat transfer area in both single stage and double stage MVR. An exergy analysis is performed to evaluate the improvement potential of the system performance based on the second law of thermodynamics. The results show that by increase of the saturation temperature difference of the single stage MVR from 10 °C to 15 °C, the total heat transfer area of the system decreases and the compressor power consumption increases by 50%. Almost 3.3% energy saving is achieved using the double-stage MVR instead of the single-stage MVR and the total heat transfer area is decreased by about 5.6 m2. The coefficients of performance of the single stage and double-stage MVR are 16.2 and 15.12, and the exergy efficiencies are 3.51% and 9.52%, respectively. © 2016 Elsevier Ltd
Applied Thermal Engineering (13594311)125pp. 1002-1014
A Parallel Path Wet/Dry configuration and a high-precision airflow regulation method are implemented in order to retrofit an existing wet cooling tower. The modifications are intended to reduce water requirements and fan power consumption of a 12-cell wet tower. The proposed method of airflow control takes advantage of fans with variable frequency drive to regulate airflow with high accuracy. A number of simulations are carried out to predict different operating factors of the wet and hybrid towers. Experimentally obtained values of water consumption demonstrate the validity of those obtained using the computer simulations. According to the results, the accurate airflow control prevents sudden fluctuations in requisite fan power and water consumption rate and causes up to 64.6% decrease in fan power consumption. The results reveal that using the proposed wet/dry approach results in an average 9.4% decrease in water consumption. Given the relatively low degree of modifications made to the original wet tower and preserving the condenser operating condition, the accomplished amount of water conservation is satisfactory. © 2017 Elsevier Ltd
Heat Transfer Engineering (1457632)37(12)pp. 1038-1049
Applying a constant or transient heat flux on a plane slab is a common technique in microelectronics technology and material processing, including laser patterning, micromachining, and laser surface treatment processes. Although Fourier's law is typically very precise for evaluating temperatures in solids, a number of experimental observations suggest the existence of non-Fourier transient conduction in these applications. Since the dual-phase-lag (DPL) model of heat conduction can be compatible with the hypothesis of local equilibrium thermodynamics (as shown here), the effects of temperature gradient relaxation time on the non-Fourier hyperbolic conduction in a finite slab subjected to an arbitrary time-dependent surface heat flux is examined by this model. The combination of diffusion-and wave-like features in heat conduction process is properly monitored by the DPL model for two types of heat flow regimes, namely, gradient precedence and flux precedence. The results indicate considerable deviations between the predictions of these regimes. © 2016 Taylor and Francis Group, LLC.
International Journal Of Chemical Engineering (1687806X)2016
This paper investigates the performance of a ground source heat pump that is coupled with a photovoltaic system to provide cooling and heating demands of a zero-energy residential building. Exergy and sustainability analyses have been conducted to evaluate the exergy destruction rate and SI of different compartments of the hybrid system. The effects of monthly thermal load variations on the performance of the hybrid system are investigated. The hybrid system consists of a vertical ground source heat exchanger, rooftop photovoltaic panels, and a heat pump cycle. Exergetic efficiency of the solar-geothermal heat pump system does not exceed 10 percent, and most exergy destruction takes place in photovoltaic panel, condenser, and evaporator. Although SI of PV system remains constant during a year, SI of GSHP varies depending on cooling and heating mode. The results also show that utilization of this hybrid system can reduce CO2 emissions by almost 70 tons per year. © 2016 Yasser Abbasi et al.
Journal of Thermophysics and Heat Transfer (8878722)30(2)pp. 359-368
Heat transfer enhancement through extended surfaces is crucial in modern engineering applications such as microelectromechanical systems and electronic components. Conduction heat transfer is the only way to achieve this objective when the mixing augmentation is not possible. This paper investigates the effects of non-Fourier thermal conduction in convective straight fins with arbitrary constant cross section under periodic boundary conditions by introducing the exact analytical solution for the dual-phase-lag heat conduction. The corresponding analytical approach is developed through the Laplace transform method and inversion theorem. To help advance the understanding of fin thermophysical behavior, a generalized model of conduction heat transfer equation is used for studying all of the interpretations to Fourier-based model, namely, parabolic thermal diffusion, hyperbolic thermal wave, and dual-phase-lag models. Heat flux and temperature gradient relaxation times are the characteristics of the dual-phase-lag model, and the simulation results are strictly a function of these two parameters. Therefore, fin temperature distributions are presented for flux precedence and gradient precedence heat flow regimes. Calculations are performed to investigate the influence of temperature gradient relaxation time on the hyperbolic heat conduction characteristics of non-Fourier fins. © Copyright 2015 by the American Institute of Aeronautics and Astronautics, Inc.
Applied Mathematical Modelling (0307904X)39(13)pp. 3704-3720
In this study, exact analytical analysis of two-dimensional Fourier and non-Fourier bioheat transfer equations in skin tissue exposed to an instantaneous heating condition is presented. The effects of blood perfusion and metabolic heat generation on the tissue thermal behavior are considered. Corresponding analytical approach is developed through Laplace transform (LT) technique in conjunction with the separation of variables method and inversion theorem. The dual-phase-lag (DPL), thermal wave (TW) and Pennes models of bioheat transfer equation are studied by utilizing a generalized model. The reliability of the presented results has been evidenced through enforcing appropriate circumstances on the DPL model and comparing the outcome results with that of predicted by the Pennes and TW models. It is proved that the DPL bioheat transfer equation with the effects of blood perfusion and metabolic heat generation can be reduced to the Pennes bioheat transfer equation when τq=τT. The effects of local non-equilibrium on the tissue thermal behavior are examined and discussed by comparing the gradient precedence (GP) and flux precedence (FP) heat flow regimes of the DPL model. The first- and second-degree burn times of a 2D skin tissue for different bioheat models are introduced and compared with the 1D case. © 2014 Elsevier Inc..
Journal of Porous Media (1091028X)18(1)pp. 57-69
To describe nonequilibrium heat transfer in living biological tissues as porous mediums, the recently developed generalized dual-phase-lag (DPL) model of bioheat transfer equation is studied analytically. An arbitrary time-dependent surface heat flux is considered. In order to compare the tissue thermal behavior, when it is considered as porous and nonporous media, the classical DPL model of bioheat transfer equation is studied as well. Analytical expressions for the DPL model are obtained by applying the Laplace transform (LT) method with the aid of the inversion theorem. The reliability of the present results has been evidenced through comparison with the literature. Since the classical DPL model under certain circumstances can be reduced to the traditional Pennes and thermal wave (TW) models, comparisons between the tissue temperatures and damages predicted by the aforementioned models are carried out. The influences of porosity factor (ε), coupling factor between blood and tissue (G), and various thermal relaxation times on the thermal behavior of biological tissues are investigated and discussed. © 2015 by Begell House, Inc.
Heat and Mass Transfer (09477411)50(12)pp. 1673-1684
Dual-phase-lag model of bioheat transfer equation is utilized in treating the transient heat transfer problems in skin tissue considering prevalent heating conditions in thermal therapy applications, namely, pulse train and periodic heat flux. Comparisons between the presented analytical results for limiting cases and previous studies display an excellent agreement. The effects of temperature gradient relaxation time on the tissue temperature, damage, and also on the blood perfusion in skin tissue are studied. © 2014, Springer-Verlag Berlin Heidelberg.
Applied Thermal Engineering (13594311)71(1)pp. 410-418
In this study, a CFD model is adopted for investigating the effects of the four important ejector geometry parameters: the primary nozzle exit position (NXP), the mixing tube length (Lm), the diffuser length (L d), and the diffuser divergence angle (θ) on its performance in the PEM fuel cell system. This model is developed and calibrated by actual experimental data, and is then applied to create 141 different ejector geometries which are tested under different working conditions. It is found that the optimum NXP not only is proportional to the mixing section throat diameter, but also increases as the primary flow pressure rises. The ejector performance is very sensitive to the mixing tube length while the entrainment ratio can vary up to 27% by change in the mixing tube length. The influence of θ and Ld on the entrainment ratio is evident and there is a maximal deviation of the entrainment ratio of 14% when θ and Ld vary from 2° to 8° and 6Dm to 24Dm, respectively. To make sure the correlation of all geometric parameters on the ejector performance, the artificial neural network and genetic algorithm are applied in obtaining the best geometric. © 2014 Elsevier Ltd. All rights reserved.
Journal Of Applied Fluid Mechanics (17353572)7(2)pp. 197-208
Superheaters are among the most important components of boilers and have major importance due to this operation in high temperatures and pressures. Turbines are sensitive to the fluctuation of superheaterstemperature;therefore even the slightest fluctuation in the outlet vapor temperature from the superheaters does damage the turbine axis and fins. Examining the potential damages of combustion in the boilers and components such as the superheaters can have a vital contribution to the progression of the productivity of boiler, turbine and the power plant altogether it solutions are to be fund to improve such systems. In this study, the focus is on the nearest tube set of superheaters to the combustion chamber.These types of tubes are exposed to a wide range ofcombustion flames such that the most heat transfer to them is radiation type.Here, the 320 MW boiler of Isfahan power plant (Iran), the combustion chamber, 16 burners and the platensuperheater tubes were remodeled by CFD technique. The fluid motion, the heat transfer and combustion processes are analyzed. The two-equation turbulence model of k-eis adopted to measure the eddy viscosity. The eddy dissipation model is used to calculate the combustion as well as the P-1 radiation model to quantify the radiation. The overheated zones of superheater tubes and the combustion chamber are identified in order toimprove this problem by applying the radiation thermal shields and knees with porous crust which are introduced as the new techniques.
International Journal of Thermophysics (0195928X)34(1)pp. 139-159
Modeling and understanding the heat transfer in biological tissues is important in medical thermal therapeutic applications. The biothermomechanics of skin involves interdisciplinary features, such as bioheat transfer, biomechanics, and burn damage. The hyperbolic thermal wave model of bioheat transfer and the parabolic Pennes bioheat transfer equations with blood perfusion and metabolic heat generation are applied for the skin tissue as a finite and semi-infinite domain when the skin surface temperature is suddenly exposed to a source of an arbitrary periodic temperature. These equations are solved analytically by Laplace transform methods. The thermal wave model results indicate that a non-Fourier model has predicted the thermal behavior correctly, compared to that of previous experiments. The results of the thermal wave model show that when the first thermal wave moves from the first boundary, the temperature profiles for finite and semi-infinite domains of skin become separated for these phenomena; the discrepancy between these profiles is negligible. The accuracy of the obtained results is validated through comparisons with existing numerical results. The results demonstrate that the non-Fourier model is significant in describing the thermal behavior of skin tissue. © 2013 Springer Science+Business Media New York.
International Journal of Thermal Sciences (12900729)64pp. 129-136
This article looks at the thermal analysis of the mixed convection-radiation of an inclined flat plate embedded in a porous medium. The boundary-layer equations are reduced to the nonlinear ordinary differential equations (ODEs) using similarity transformations. The governing equations are solved using the homotopy analysis method (HAM). The dimensionless velocity and temperature profiles are obtained for different values of emerging parameters. The obtained results without the radiation effect are compared with the existing results. Such results show the performance and reliability of HAM. The present results in comparison with the existing solutions admit an excellent accuracy. © 2012 Elsevier Masson SAS. All rights reserved.
Thermal Science (3549836)17(2)pp. 443-455
To investigate the effect of water spray and crosswind on the effectiveness of the natural draft dry cooling tower, a 3-D model has been developed. Efficiency of natural draft dry cooling tower is improved by water spray system at the cooling tower entrance for high ambient temperature condition with and without crosswind. The natural and forced heat convection flow inside and around the natural draft dry cooling tower is simulated numerically by solving the full Navier-Stokes equations in both air and water droplet phases. Comparison of the numerical results with 1-D analytical model and the experimental data illustrates a well-predicted heat transfer rate in the cooling tower. Applying water spray system on the cooling tower radiators enhances the cooling tower efficiency at both no wind and windy conditions. For all values of water spraying rate, natural draft dry cooling tower operate most effectively at the crosswind velocity of 3 m/s and as the wind speed continues to rise to more than 3 m/s up to 12 m/s, the tower efficiency will decrease by approximately 18%, based on no-wind condition. The heat transfer rate of radiator at wind velocity 10 m/s is 11.5% lower than that of the no wind condition. This value is 7.5% for water spray rate of 50 kg/s.
Journal of Mechanical Science and Technology (1738494X)26(6)pp. 1937-1947
The thermal wave and the Pennes bioheat transfer models are solved analytically by employing the Laplace transform method for small and large values of reflection power (albedo) during laser irradiation. Most of the previous studies have been based on the infinite heat diffusion velocity, but non-Fourier thermal behavior has been observed experimentally in biological tissue. At low initial albedo values, the temperature in the skin depth that directly results from conduction heat transfer process is caused by the lengthy thermal relaxation time in skin tissue. This condition generates a big difference between the thermal wave and Pennes results at the beginning of the heating process. This difference increases under short-time heating condition and high heat flux. However, with high initial albedo, the temperature distribution in the skin depth becomes negligible because of the skin absorption of laser beams. The non-Fourier effect should be considered during laser heating with low albedo, because errors in the predicted temperature values may occur. © 2012 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
International Communications in Heat and Mass Transfer (7351933)39(1)pp. 121-130
In this article, the parabolic (Pennes bioheat equation) and hyperbolic (thermal wave) bioheat transfer models for constant, periodic and pulse train heat flux boundary conditions are solved analytically by applying the Laplace transform method for skin as a semi-infinite and finite domain. The bioheat transfer analysis with transient heat flux on skin tissue has only been studied by Pennes equation for a semi-infinite domain. For modeling heat transfer in short duration of an initial transient, or when the propagation speed of the thermal wave is finite, there are major differences between the results of parabolic and hyperbolic heat transfer equations. The non-Fourier bioheat transfer equation describes the thermal behavior in the biological tissues better than Fourier equation. The outcome of transient heat flux condition shows that by penetrating into the depths beneath the skin subjected to heat, the amplitude of temperature response decreases significantly. The blood perfusion rate can be predicted using the phase shift between the surface temperature and transient surface heat flux. The thermal damage of the skin is studied by applying both the parabolic and hyperbolic bioheat transfer equations. © 2011 Elsevier Ltd.
Numerical Heat Transfer; Part A: Applications (15210634)61(3)pp. 220-240
This study aims to estimate unknown base temperature distribution in different non-Fourier fins. The Cattaneo-Vernotte (CV) heat model is used to predict the heat conduction behavior in these fins. This inverse problem is solved by the function-estimation version of the Adjoint conjugate gradient method (ACGM) based on boundary temperature measurements. The ACGM includes direct, sensitivity, and adjoint problems. For each of these problems, a one-dimensional general formulation of the non-Fourier model for longitudinal fins with arbitrary profile is driven and solved by an implicit finite difference method. In this study, three different profiles are considered: triangular, convex parabolic, and concave parabolic. For each of them, two different base temperature distributions are estimated using an inverse method. Moreover, the effects of sensor positions at the fin tip and a specific place in-between are considered on the base temperature estimation. A close agreement between the exact values and the estimated results is found, confirming the validity and accuracy of the proposed method. The results show that the ACGM is an accurate and stable method to determine the thermal boundary conditions in different non-Fourier fin problems. © 2012 Copyright Taylor and Francis Group, LLC.
Heat and Mass Transfer/Waerme- und Stoffuebertragung (14321181)48(9)pp. 1559-1568
The phase change in biological tissues during a freezing process is simulated by hyperbolic and parabolic heat equations with temperature-dependent enthalpy. It is observed that the experimental results are in a good agreement with that the calculated results by the enthalpy method. The results shown that the Fourier model predicts tissues temperature lower than of the non-Fourier model. Further decrease in freezing rate and freezing velocity is noticed with an increase in relaxation time value. © Springer-Verlag 2012.
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine (20413033)226(5)pp. 406-416
The bioheat transfer with phase change in biological tissues during the freezing process is simulated by the dual phase lag conduction heat transfer model. A numerical algorithm based on the enthalpy method is established to solve the solidification of biological tissues. The linearly temperature-dependent enthalpy (non-isothermal phase change) is considered here. The results of the parabolic heat conduction model for a slice of cucumber are compared with the experimental data. A comparison between dual phase lag and hyperbolic solutions with small values of relaxation times is applied in order to verify the corresponding parabolic solutions accuracy of the dual phase lag and hyperbolic solutions. The heating source effect owing to blood perfusion and metabolic heat on the heat transfer in a biological tissue subject to freezing process is studied. The relaxation time has an important influence on the transient temperature and temperature gradient. A major discrepancy among bioheat transfer models is found for zones closer to the cooling boundary. The heat source term, owing to blood flow and metabolism in a phase change problem in the biological tissue, has a significant influence on thermal effects of the subject tissue. © IMechE 2012.
International Journal of Green Energy (15435083)9(2)pp. 160-173
Wind-catchers have been serving as a cooling system for providing acceptable natural ventilation using the renewable energy of wind. The effects of wind velocity and mass flow rate of water spray are investigated regarding the relative humidity and temperature of a wind-catcher in a hot and dry climate. Water spray increases the relative humidity and decreases the air temperature inside the wind-catcher. With an increase in the mass flow rate of water spray, the average relative humidity and temperature of indoor-space increase and decrease, respectively. Low wind speed with the same water spray mass flow rate provides a more pleasant air condition in comparison with that of the high wind speed. Adding water spray systems to wind-catchers contribute to pleasant air condition in hot and arid regions. © 2012 Copyright Taylor and Francis Group, LLC.
Journal of Engineering Mathematics (15732703)76(1)pp. 181-193
The thermal performance of variable cross-section fins is considered using the Maxwell-Cattaneo-Vernotte (MCV) heat conduction model. Four different fins, namely rectangular, triangular, convex, and concave fins, with a periodic thermal condition are examined. The governing equations are hyperbolic and are solved numerically using an implicit finite difference method. In the MCV model, the thermal wave propagates with a finite speed, and hence sharp discontinuities appear in the temperature profiles. In this study, temperature profiles at various times, heat transfer rates, and thermal efficiencies of Fourier and non-Fourier fins are presented. In addition, the effect of relaxation time is considered. The results show that the effects of cross-sectional area and relaxation time are considerable on the thermal performance of various non-Fourier fins. To validate our findings, the results for non-Fourier fins with constant cross-sectional area obtained from this study are compared to those of other numerical solutions. This comparison confirms the correctness of the current results. © 2012 Springer Science+Business Media B.V.
Journal of Mechanical Science and Technology (1738494X)25(11)pp. 2919-2926
Fourier and hyperbolic models of heat transfer on a fin that is subjected to a periodic boundary condition are solved analytically. The differential equation in Fourier and non-Fourier models is solved by the Laplace transform method. The temperature distribution on the fin is obtained using the residual theorem in a complex plan for the inverse Laplace transform method. The thermal shock is generated at the base of the fin, which moves toward the tip of the fin and is reflected from the tip. The current study of various parameters on the thermal shock location shows that relaxation time has a great influence on the temperature distribution on the fin. An unsteady boundary condition in the base fin caused the shock, which is generated continuously from the base and has interacted with the other reflected thermal shocks. Results of the current study show that the hyperbolic heat conduction equation can violate the second thermodynamic law under some unsteady boundary conditions. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Mathematical Problems in Engineering (15635147)2010
Three different profiles of the straight fin that has a temperature-dependent thermal conductivity are investigated by differential transformation method (DTM) and compared with numerical solution. Fin profiles are rectangular, convex, and exponential. For validation of the DTM, the heat equation is solved numerically by the fourth-order Runge-Kutta method. The temperature distribution, fin efficiency, and fin heat transfer rate are presented for three fin profiles and a range of values of heat transfer parameters. DTM results indicate that series converge rapidly with high accuracy. The efficiency and base temperature of the exponential profile are higher than the rectangular and the convex profiles. The results indicate that the numerical data and analytical method are in agreement with each other. © 2010 A. Moradi and H. Ahmadikia.
2025 29th International Computer Conference, Computer Society of Iran, CSICC 20252pp. 497-503
In this paper, the steady/unsteady heat conduction in the longitudinal fins with variable cross sectional area under the periodic thermal conditions is examined. Three different one-dimensional fins are considered and solved numerically by implicit finite difference method. In the hyperbolic equation the heat wave propagates with the finite speed hence the sharp discontinuities appear at the temperature distributions. In the explicit solution oscillations appear at discontinuity point which is greatly improved at the implicit method. In the present study temperature distributions are obtained for non-Fourier fins with different profiles. The effects of frequency of temperature oscillation, relaxation time and fin cross sectional area are studied on the temperature and location of the discontinuity of temperature. In order to validate the obtained results of the present study, these results have been compared to those of numerical solutions of the non-Fourier fin with constant cross sectional area. This comparison confirms the correctness of the current results. Copyright © 2010 by ASME.
In this paper, the 3D finite-element simulation of ultrasound brain surgery is demonstrated. The pressure variations are obtained using Helmholtz equation and temperature distributions resulting from acoustic absorption are calculated by employing bioheat equation. Our results show that with increase of the pressure, focal temperature is increased. With using appropriate pressure amplitude, surgical time duration could be decreased and this could lead to minimal side effect of ultrasound heating of the surrounded healthy tissue. © 2010 IEEE.
