filter by:
Articles
Journal of Thermal Biology (18790992)129
Microwave thermal therapy for liver cancer presents challenges due to the potential for healthy tissue damage. This study explores the use of hybrid magnetic nanofluids to optimize treatment effectiveness while minimizing side effects. Preoperative modeling was employed to determine the optimal nanoparticle type, concentration, and combination for enhanced thermal efficiency. Three magnetic nanoparticles—maghemite, magnetite, and FccFePt—were analyzed, both individually and in hybrid compositions. Results demonstrated that increasing nanoparticle concentration significantly reduced treatment duration and minimized healthy tissue necrosis. At 0.1 % concentration, treatment times for maghemite, magnetite, and FccFePt were 3, 67, and 90 s, with corresponding healthy tissue loss-to-tumor volume ratios of 0.06, 3.08, and 4.36. Lowering the concentration to 0.05 % increased treatment times to 46, 126, and 129 s, raising tissue loss ratios to 1.88, 6.65, and 8.36. Notably, hybrid nanoparticle compositions showed divers but non-uniform effects, with some combinations marginally improving treatment efficacy while others had negligible impact. The hybridization of maghemite and FccFePt reduced necrosis time, but its influence on overall treatment efficiency was inconsistent. These findings underscore the potential of hybrid nanoparticles to enhance microwave ablation therapy; however, they also highlight the complexity of nanoparticle interactions, emphasizing the need for precise selection and concentration optimization to achieve superior treatment outcomes while preserving healthy tissue. © 2025 Elsevier Ltd
Amirkabir Journal of Mechanical Engineering (20086032)56(12)pp. 1609-1628
One of the methods for producing hydrogen is using a polymer membrane electrolyzer with photovoltaic panels. To avoid hydrogen storage and achieve decarbonization, injecting hydrogen into the urban gas pipeline is an effective solution. This study examines the injection of hydrogen into the urban gas pipeline and determines that to keep the injected hydrogen flow rate below 10% of the gas flow rate, a production of 20.69mole/s of hydrogen is required. According to mathematical modeling, to produce the necessary hydrogen, 3,230 cells with an area of 2,500cm2 should be used. The injection pressure of hydrogen is 17.23 bar. To achieve this pressure, an electrochemical compressor with 1,600 cells and an area of 2,500cm2 is used. The power consumption of the electrolyzer and compressor for injecting 9.5% hydrogen during maximum solar radiation, accounting for losses, is 6.64MW. To generate this power with a photovoltaic system, 12,991 STP550S-C72/Vmh panels are needed. Considering the electrolyzer pressure of 17.23 bar, the compressor can be eliminated, allowing the use of a high-pressure electrolyzer. © 2025, Amirkabir University of Technology. All rights reserved.
Computer Methods in Biomechanics and Biomedical Engineering (14768259)
Many living tissues can be modelled as porous media containing blood vessels and numerous capillaries that act as flow channels. Although direct simulation using the Navier–Stokes equations in flow channels coupled with the Brinkman equations in porous regions offers high accuracy, it is computationally expensive. This study proposes a virtual porous medium (VPM) model that approximates capillaries as virtual porous regions with estimated porosity and permeability fields. By employing Darcy’s law instead of the Navier–Stokes equations, the VPM model significantly reduces computational cost. To evaluate its accuracy and efficiency, several 2D and 3D test cases related to interlobular blood flow in the liver are presented. Each case, in fact, features blood vessels surrounding a channelised porous medium, representing liver tissue embedded with capillaries. Numerical results indicate that the VPM model generally produces acceptable predictions, with 2-norm errors for pressure and velocity fields at 3 and 2.2%, respectively. Additionally, the CPU time required is approximately 60% less compared to the direct pore-scale approach. Furthermore, the VPM model accurately captures the primary flow characteristics in channelised porous media, demonstrating its effectiveness for simulating coupled free and porous media flows. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
Journal of Food Process Engineering (01458876)48(2)
Energy and water consumption are critically important in the sugar industry. In this context, the heat exchanger network of a target sugar factory has been modeled and optimized, as this sector is the primary consumer of energy and water. A key innovation of this work lies in the coupling of interacting components within the model, leading to a more comprehensive framework compared to previous models in the literature. Some sections of the system are modeled using analytical interpretations, while others are developed through a regression learning process utilizing statistical data. This integration of analytical formulation and data-driven modeling represents another significant advancement in this research. The resulting model demonstrates acceptable accuracy for most measurable parameters, with an average deviation of approximately 4%. The optimization results indicate that certain parameters, such as the cooling pool evaporation rate, exhibit considerable flexibility, allowing optimization algorithms to converge more easily. Conversely, other parameters, such as the vapor fed to the exchangers, are more rigid, which restricts the freedom of the optimization process. Moreover, the effectiveness of the elements within the optimization target function is crucial for identifying the optimal point. Overall, minimizing energy consumption and water usage simultaneously presents a significant challenge, necessitating careful consideration in determining which optimal point is most practical. © 2025 Wiley Periodicals LLC.
Journal of Food Process Engineering (01458876)47(4)
A hybrid model is developed and evaluated to simulate the heat and mass transfer in the crystallization unit of a sugar factory. While the mass transfer is modeled by using the kinetic growth rate model, the heat transfer is simulated by applying the energy balance to the model. Here, the overall convection heat transfer coefficient of the crystallizer's heat exchanger is considered as a temperature-dependent function. As this makes the governing equations more realistic, it can help to increase the model accuracy. Additionally, a thorough examination of key practical equations and principles governing the sugar crystallization process is presented. A regression learner method is applied to extract the pattern of the overall heat transfer coefficient. According to our results, the regression learning model successfully predicts the heat transfer coefficient with an average 7% deviation from experimental results. For the hybrid model, an average deviation of about 10% is observed. The crystallizer's behavior is somehow linear, indicating a constant growth rate of sugar crystals. Furthermore, the heat transfer in the crystallizer is improved by increasing the working temperatures. Practical applications: The method and obtained results of this work could be used in the following practical purposes: to find the optimum working temperatures of crystallizers used in sugar industry and to predict total working time of batch crystallizers versus working parameters. © 2024 Wiley Periodicals LLC.
International Communications in Heat and Mass Transfer (07351933)159
The present paper uses computational fluid dynamics (CFD) and the response surface method (RSM) to optimize the performance of a novel high-throughput recycle micromixer. The micromixing of DI water and blood plasma with various thermophysical properties is simulated for a broad range of DI water Reynolds numbers (50 < ReDI< 400). The impacts of geometrical parameters and ReDI are assessed on the mixing index (MI) and pressure drop (Δp). It is found that the chaotic advection can be enhanced by changing effective parameters due to the recirculating flow in feedback channels and vortex generation in mixing chambers. Accordingly, the channel depth has a major effect on MI and Δp in such a way that when the channel depth changes from 50 to 1000 μm, MI is augmented from 23 % to 73.25 % and Δp is reduced from 75.171 kPa to 12.85 kPa when ReDI= 400. It is revealed that MI is an enhancing function of ReDIand the number of mixing units. Besides, the figure-of-merit (FoM) analysis shows that the proposed micromixer gives a much greater FoM compared to the micromixers with ordered flow patterns when Re is an order of 50. The RSM provides two mathematical correlations for MI and Δp to obtain an optimal recycle micromixer that can be efficiently utilized in biological and clinical applications. © 2024
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
Chemical Engineering and Processing - Process Intensification (02552701)201
Micromixers are critical parts of integrated microfluidic systems and their performance improvement has been a crucial problem for many investigators. Since the mixing enhancement in passive micromixers is hindered by the low-Reynolds number regime, multiple inlets have been recommended to create chaotic advection and improve the mixing quality. In this paper, a novel T-arrow micromixer is introduced to augment the mixing index (MI) of two liquids with different thermophysical properties. Numerical and experimental investigations are carried out by changing the distance between the inlets (a), the angle of the arrow-shaped inlet (α), the velocity ratio (VR), and the width-to-height aspect ratio (AR). Five optimization algorithms are also utilized to optimize the micromixer performance to achieve the most appropriate geometrical characteristics. It is found that MI is enhanced significantly by adding a Y-type inlet compared to a T-shaped mixer. The results demonstrate that while MI declines with a, there are optimal values for α, VR, and AR. Besides, parallel optimization of MI and pressure drop recommends two optimal micromixers with mixing energy cost (MEC) of 2841 Pa and 3370 Pa. © 2024 Elsevier B.V.
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
Technological Forecasting and Social Change (00401625)195
The concept of Explainable Artificial Intelligence (XAI) provides a clear and comprehensible explanation for the reasoning behind a system's output, allowing users to understand the context in which it operates. In the realm of Clinical Decision Support Systems (CDSS), XAI is particularly crucial, as it helps healthcare professionals (HCPs) in their decision-making processes. Without XAI, there is a risk of over-reliance on the system's output, potentially leading to subpar results. Despite the numerous benefits that XAI-enhanced CDSS hold in the healthcare industry, there has been a limited number of studies examining their implementation and acceptance. Thus, the objective of this study was to examine the adoption of XAI-based CDSS through the Stimulus-Organism-Response model. The sample consisted of 172 HCPs from Malaysian public and private hospitals, and the research model was tested using Partial Least Squares Structural Equation Modeling (PLS-SEM) in conjunction with the bootstrapping method. The results showed a significant positive correlation between the stimulus factors of informed action, transparent interaction, and representational fidelity and the positive attitude towards XAI-based CDSS as an organism factor. Additionally, the study found that attitude was a significant predictor of the intention to adopt as a response factor. The analysis also revealed a negative and significant moderation effect of perceived performance risk on the relationship between attitude and intention, while the positive moderating effect of perceived fairness was not supported. The findings of this study have significant implications for both theoretical and practical considerations and highlight the importance of XAI in the field of Clinical Decision Support Systems. © 2023 Elsevier Inc.
Journal of Computational Physics (10902716)462
An enhanced Multi-scale Finite Volume (MsFV) method is proposed to efficiently simulate two phase flow through highly heterogeneous porous media. Here, the accuracy of the MsFV method is significantly improved by enhancing its so-called basis functions, while its computational cost remains in the same order of the basic MsFV method. First, a fixed point is defined along each edge of local problems producing the basis functions and a proper basis function value at this point is estimated based on the local absolute permeability data. Then, the variable boundary condition is independently calculated for both sides of each fixed point. The proposed numerical method is validated by using the analytic solution of a heterogeneous problem. In addition, the convergence of the MsFV method is discussed. Considering highly heterogeneous permeability domains derived from 35 top layers of the tenth SPE comparative study problem, the accuracy of different localization schemes is compared for a set of imbibition problems with different global boundary conditions and mobility ratios. Numerical results have indicated that the overall accuracy of multi-scale velocity solutions is increased noticeably (up to 45%) by using the proposed localization scheme in the MsFV method. © 2022 Elsevier Inc.
Advances in Water Resources (03091708)162
Accurate two-phase flow modeling has a crucial role in detecting pollution in aquifers and/or in the simulating immiscible flow through porous media. In this research, a new hybrid numerical method based on the lower order non-conforming finite element method (NCFEM) and interior penalty discontinuous Galerkin (DG) method is proposed to simulate two-phase incompressible flow in heterogeneous porous media. The pressure and transport saturation equations are discretized by using the non-conforming Crouzeix-Raviart (CR) finite element and the symmetric weighed interior penalty discontinuous Galerkin (SWIPM). As a result of determining the degrees of freedom at the midpoint of neighboring element edges, a consistent set of pressure and velocity fields is obtained via the NCFEM. An H(div) projection based on the Raviart-Thomas (RT) element is implemented to improve the results resolution and preserve the continuity of the normal component of the velocity field. Besides, the spurious numerical oscillations of the saturation solution at the end of each time step are removed by using a novel vertex-based slope limiter, named the modified Chavent-Jaffre limiter. The accuracy and performance of the proposed numerical method are assessed by solving the Buckley-Leverett and McWhorter-Sunada benchmark problems, along with two test problems associated with highly heterogeneous porous media. The numerical results indicate that the proposed scheme has a remarkable potential to accurately capture the shock front and sharp interface zone of immiscible phases in the heterogeneous aquifers and other porous media. © 2022
Jamei, M.,
Karbasi, M.,
Mosharaf dehkordi, M.,
Adewale olumegbon, I.,
Abualigah, L.,
Said, Z.,
Asadi, A. Measurement: Journal of the International Measurement Confederation (02632241)189
There is no doubt that density is one of the most crucial thermophysical properties of hybrid nanofluids in thermal energy applications. Various research papers have been devoted to thermophysical properties of various hybrid nanofluids. However, a few of them focused on the simultaneous effects of nanoparticles, base fluids, and other factors on the density of hybrid nanofluids. In this research, a comparative study was conducted on non-parametric and evolutionary machine learning paradigms, namely, Multivariate Adaptive Regression Spline (MARS) and Evolutionary Polynomial Regression (EPR) models to accurately predict the density of a wide variety type of nanofluids in thermal energy applications. Here, for providing the predictive models, 501 data points were collected from the reliable recent literature. Besides, the Gene Expression Programming (GEP) and Multivariate Linear Regression (MLR) models were examined for validating the outcomes of MARS and EPR models. The comprehensive assessment demonstrated that the MARS outperformed the other models. © 2021 Elsevier Ltd
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.
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.
Applied Thermal Engineering (13594311)196
Inhalation gas humidification is a kind of major matter for patients using mechanical ventilation systems due to the necessity of keeping mucus layer at the suitable thickness and wetness. The performance of membrane humidifier with partially blocked gas channels, is investigated in this study. Three types of membrane humidifier channel arrangement, including a normal, wet channel with obstacles, and similar ones in both channels (wet and dry) are studied under various mass flow rates and temperatures. Flanged obstacles improve the thermal efficiency of the humidifier so that in this case the outlet dry air temperature can be increased about 4°by using 10 obstacles in both channels but they increase the pressure drop noticeably. PEC is calculated as a dimensionless parameter to compare the performance enhancement with pressure drop increment, simultaneously. Higher water recovery rate (WRR) and dew point temperatures at the dry side channel outlet, indicate the higher humidifier performance. At all mass flow rates, presence of obstacles improves the performance of the humidifier by increasing the dew point temperature and water recovery rate (WRR). Overall, the presence of obstacles on both channels amplifies the overall performance of the membrane humidifier in almost all cases. © 2021 Elsevier Ltd
Amirkabir Journal of Mechanical Engineering (20086032)53(9)pp. 1153-4924
The heat pipes are usually simulated by using a two phase model and a model describing the phase-change process. The computational costs of the two-phase approaches are relatively high and the model generally needs small-size time steps, which leads to a long simulation run times in the order of several days. In the present study, a variable conductance heat pipe is simulated by using a set of single-phase fluid flow models. It is shown that the proposed approach needs to a simulation time in the order of minutes that considerably facilitates the parametric study process of the variable conductance heat pipe. The effect of heat rate, sink temperature, mass of non-condensable gas, vapor radius, and wick porosity on the performance of variable conductance heat pipe are investigated. For the considered variable conductance heat pipe, the obtained numerical results indicate that sink temperature has the greatest effect on distributions of average wall temperature, overall heat transfer coefficient, the active length of condenser, and its average temperature. By increasing the sink temperature of 10 K, the active length of condenser is increased about 48 mm and average wall temperature is increased about 6.4 K. © 2021, Amirkabir University of Technology. All rights reserved.
Jamei, M.,
Olumegbon, I.A.,
Karbasi, M.,
Ahmadianfar, I.,
Asadi, A.,
Mosharaf dehkordi, M. International Journal of Heat and Mass Transfer (00179310)172
Regarding their ability to enhance conventional thermal oils' thermophysical properties, oil-based hybrid nanofluids have recently been widely investigated by researchers, especially on lubrication and cooling application in the automotive industry. Thermal conductivity is one of the most crucial thermophysical properties of oil-based hybrid nanofluids, which has been studied in a minimal case of studies on the specific types of them. In this research, for the first time, a comprehensive data-intelligence analysis performed on 400 gathered data points of various types of oil-based hybrid nanofluids using a novel hybrid machine learning approach; the Extended Kalman Filter-Neural network (EKF-ANN). The genetic programming (GP) and response surface methodology (RSM) approaches were examined to appraise the main paradigm. In this research, the best subset regression analysis, as a novel feature selection scheme, was provided for finding the best input parameter among all existing predictive variables (the volume fraction, temperature, thermal conductivity of the base fluid, mean diameter, and bulk density of nanoparticles). The provided models were examined using several statistical metrics, graphical tools and trends, and sensitivity analysis. The results assessment indicated that the EKF-ANN in terms of (R = 0.9738, RMSE = 0.0071 W/m.K, and KGE = 0.9630) validation phase outperformed the RSM (R = 0.9671, RMSE = 0.0079 W/m.K, and KGE = 0.9593) and GP (R = 0.9465, RMSE = 0.010 W/m.K, and KGE = 0.9273), for accurate estimation of the thermal conductivity of oil-based hybrid nanofluids. © 2021
Applied Mathematics and Computation (18735649)390
Two-phase incompressible fluid flow through highly heterogeneous porous media is simulated by using the Multiscale Finite Volume (MsFV) method. Effects of the localization assumption on the accuracy of the MsFV are investigated by comparing the results associated with different boundary conditions of local problems producing the basis functions. The total number of six boundary conditions of two general types, including Dirichlet and Dirichlet-Neumann types, are compared. For the former, the linear, variable (reduced), and step-type boundary conditions are considered and a modified variable boundary condition is proposed. For the latter, a basic and a step-type Neumann-Dirichlet boundary condition are suggested. To estimate the errors in the MsFV solutions for continuous problems, a heterogeneous two-dimensional problem with continuous permeability field is designed and solved analytically. Synthetic two-scale permeability fields as well as highly heterogeneous random fields are used to assess the accuracy of the MsFV solutions with different localization schemes, in comparison with the fine-scale reference solution. Numerical results indicate that the modified variable boundary condition, with a proper value of its weighting factor, can generally produce the most accurate results, when compared with the other localization schemes. © 2020
Jamei, M.,
Karbasi, M.,
Adewale olumegbon, I.,
Mosharaf dehkordi, M.,
Ahmadianfar, I.,
Asadi, A. Journal of Molecular Liquids (18733166)335
The quantitative determination of specific heat capacity (SHC) of molten (nitrate) salt-based nanofluids helps to control the start-up heat and prevent overheating when deployed as a working heat transfer fluid in a wide range of solar thermal applications. Thus, accurate measurement of the SHC and capturing the melting point is of paramount importance in the molten salt-based nanofluids’ characterization analyses applied in solar collectors. In this research, two modern ensemble machine learning models, Extra Tree Regression (ETR) and AdaBoost Regression (ABR), were developed based on 2,384 datasets, including solid mass fraction (w), temperature (T), SHC of base fluid (CPBase), mean diameter (Dp), and density (ρp) of nanoparticle as all independent input variables and the SHC of molten salt-based nanofluids (CPMS-nf) as the target. Herein, the stepwise forward method and mutual information were addressed to determine the best input combination and sensitivity analysis. The provided models were validated using Random Forest (RF) and Boosted Regression Tree (BRT) as two powerful other ensemble models. The results demonstrated that ETR model in terms of (R = 0.9964, RMSE = 0.1566, and U95%=3.6062) outperformed the ABR (R = 0.9949, RMSE = 0.1855, and U95%=3.6009), RF (R = 0.9922, RMSE = 0.2326, and U95%=3.5904), and BRT (R = 0.9907, RMSE = 0.2508, and U95%=3.5857). The SHC of molten salt base fluid was identified as the most significant factor in estimating the SHC of molten salt-based nanofluids. © 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
Journal of Hydrology (00221694)585
Horizontal wells have gained considerable interest among petroleum engineers and hydrologists in the last decades. Many attempts were made to reach a better understanding of fluid flow behaviour inside the reservoir/aquifer, especially in the near-wellbore regions. In most of the previous studies on horizontal wells, each well is treated as a volumetric source term in governing equations describing the fluid flow in the main reservoir/aquifer. Many important features affecting the fluid flow, such as the realistic wellbore geometry, have been ignored for mathematical convenience. In the present study, the three-dimensional single-phase fluid flow through a large size reservoir block is coupled to wellbore flow through imposing the pressure and flux continuity at the reservoir-well interface. As the momentum equations, the Darcy and turbulent Navier–Stokes equations are used in the reservoir block and wellbore, respectively. The governing equations are discretized on unstructured grids and solved by using the finite volume method. Using the computed pressure and velocity distributions, the horizontal well characteristics are numerically estimated and compared with available analytic data for various cases. It is shown that the calculated well index, a coefficient in reflecting the geometric features of the well-reservoir system, deviates from its analytic value, as a result of reservoir block boundary condition, the pattern of the wellbore open intervals, the horizontal well drilling path, and its vertical eccentricity. In addition, the proposed approach is used to improve Economides model, an analytical model for horizontal well index, by estimating its pseudo-skin factor in various cases of the well vertical eccentricity, horizontal orientation, and reservoir block conditions. © 2020 Elsevier B.V.
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.
Computer Methods in Biomechanics and Biomedical Engineering (14768259)22(9)pp. 901-915
Two dimensional, steady state, and incompressible blood and bile flows through the liver lobules are numerically simulated. Two different geometric models A and B are proposed to study the effects of lobule structure on the fluid flow behaviour. In Model A, the lobule tissue is represented as a hexagonal shape porous medium with a set of flow channels at its vertices accounting for the hepatic artery, portal and central veins along with bile ductules. Model B is a channelized porous medium constructed by adding a set of flow channels, representing the bile canaliculies and lobule sinusoids, to Model A. The bile and blood flow through the lobule is simulated by the finite element approach, based on the Darcy/Brinkman equations in the lobule tissue and the Navier-Stokes (or Stokes) equations in the flow channels. In Model B, a transmission factor on the boundaries of the bile canaliculies is introduced to connect the bile and blood flows. First, a single regular lobule is utilized to exhibit the fluid flow pattern through the liver lobule represented by proposed geometric models. Then, the model is extended to a group of liver lobules to demonstrate the flow through a liver slice represented by irregular lobules. Numerical results indicate that the Darcy and Brinkman equations provide nearly the same solutions for Model A and similar solutions with a little difference for Model B. It is shown that the existence of sinusoids and bile canaliculies inside the liver lobules has noticeable effects on its fluid flow pattern, in terms of pressure and velocity fields. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.
International Journal of Numerical Methods for Heat and Fluid Flow (09615539)28(11)pp. 2506-2530
Purpose: The purpose of this paper is to present detailed algorithms for simulation of individual and group control of production wells in hydrocarbon reservoirs which are implemented in a finite volume-based reservoir simulator. Design/methodology/approach: The algorithm for individual control is described for the multi-lateral multi-connection ones based on the multi-segment model considering cross-flow. Moreover, a general group control algorithm is proposed which can be coupled with any well model that can handle a constraint and returns the flow rates. The performance of oil production process based on the group control criteria is investigated and compared for various cases. Findings: The proposed algorithm for group control of production wells is a non-optimization iterative scheme converging within a few number of iterations. The numerical results of many computer runs indicate that the nominal power of the production wells, in general, is the best group control criterion for the proposed algorithm. The production well group control with a proper criterion can generally improve the oil recovery process at negligible computational costs when compared with individual control of production wells. Research/limitations/implications: Although the group control algorithm is implemented for both production and injection wells in the developed simulator, the numerical algorithm is here described only for production wells to provide more details. Practical/implications: The proposed algorithm can be coupled with any well model providing the fluid flow rates and can be efficiently used for group control of production wells. In addition, the calculated flow rates of the production wells based on the group control algorithm can be used as candidate solutions for the optimizer in the simulation-optimization models. It may reduce the total number of iterations and consequently the computational cost of the simulation-optimization models for the well control problem. Originality/value: A complete and detailed description of ingredients of an efficient well group control algorithm for the hydrocarbon reservoir is presented. Five group control criteria are extracted from the physical, geometrical and operating conditions of the wells/reservoir. These are the target rate, weighted potential, ultimate rate and introduced nominal power of the production wells. The performance of the group control of production wells with different group control criteria is compared in three different oil production scenarios from a black-oil and highly heterogeneous reservoir. © 2018, Emerald Publishing Limited.
International Journal of Engineering, Transactions B: Applications (1728144X)31(5)pp. 812-819
The performance of proton-exchange membrane fuel cell cooling system using coolant flow channels enhanced with baffles was numerically investigated. To do this, the maximum temperature of the cooling plate, temperature uniformity and also pressure drop along the flow channels were compared for different cases associated with number of baffles and their dimensions inside the channels. The governing equations by the finite-volume approach in three dimensions were solved. Numerical results indicate that the baffle-restricted cooling flow channels, generally improved the performance of the fuel cell in such a way that a reduced maximum temperature of the cell and a better temperature uniformity in the cooling plates were determined. As the pressure drop increases by incorporating the baffles inside the coolant flow channels, one needs to compromise between the improvement of cooling system performance and the total pressure drop. © 2018 Materials and Energy Research Center. All Rights Reserved.
Solar Energy (0038092X)170pp. 594-605
This paper presents the numerical analysis of a novel thermal energy storage (TES) system using phase change material (PCM) for direct steam solar power plants. The energy storage system consists a preheater, steam generator and superheater in a cascade arrangement. The performance of the integrated system that constitutes a novel concept of thermal storage system is analyzed, numerically. The numerical model is verified against experimental data and the realistic effects of the operating conditions on the energy storage system performance are considered. The effects of different design parameters on the performance of the system are investigated. The effects of thermal conductivity of PCM, heat transfer fluid (HTF) flow rate and the diameter of heat exchanger tubes are analyzed during the entire thermal cycling of the evaporator. The effects of HTF flow rate and temperature on the exergy efficiency of TES system are analyzed. The results indicate that thermal conductivity of PCM is the most effective parameter, and increase of this parameter from 0.5 to 5 W K−1 m−1 leads to decrease of charging time from 25 to 4.5 h and increase of output steam quality from 0.2 to 0.5 during the discharging process. It is observed that cascade arrangement in preheater and superheater heat exchangers results in lower temperature gradient of the output HTF. © 2018 Elsevier Ltd
International Journal of Pressure Vessels and Piping (03080161)165pp. 1-10
Different families of the Discrete Vapour Cavity Model (DVCM) are developed, including the frictionless, steady and quasi-steady friction models. A relaxation-dissipation approach is proposed to improve the timing of pressure pulses predicted by the classic DVCM. In this approach, a friction correction factor is introduced into the steady/quasi-steady friction term to reduce the local value of the dissipation term in regions facing with cavitation. The proposed approach is completely consistent with the classical water-hammer framework. The importance of the steady/quasi-steady friction term is investigated by comparing numerical results of different DVCMs with the experimental data for various cavitation problems. Based on a frictionless study, it is shown that there exists an unrealistic attenuation in pressure pulses of the classic DVCM. For problems with high-intensity cavitation, it is shown that the frictionless, steady and quasi-steady friction models generally produce different results, especially in terms of the pressure pulses timing. Within the range described in the manuscript, the timing of the classic DVCM pressure pulses can generally be improved by applying the proposed relaxation-dissipation approach on the steady/quasi-steady friction term. © 2018 Elsevier Ltd
Energy (18736785)118pp. 705-715
In the present work, the performance of proton exchange membrane fuel cells is studied for three cases; A fuel cell with two parallel flow channels (model A), locally baffle restricted flow channels (model B), and metal foam as a flow distributor (model C). The fully coupled thermal-electrochemical equations are numerically solved in three dimensions, based on the macroscopic, single-domain, and finite-volume approaches. While having no significant effect on temperature distribution, the existence of baffles inside flow channels results in more oxygen penetration into gas diffusion and catalyst layers at the cathode side of the cell. This improves the chemical reaction rate, current density and cell performance. Using metal foam increases oxygen concentration and current density at the cathode catalyst surface, and improves the uniformity of their distributions. Furthermore, a more uniform temperature distribution is achieved, when compared with the other cases. For the considered dimensions, it is observed that decreasing the flow channel depth results to an increase in current density and also in pressure drop along channels (models A and C). Moreover, increasing metal foam porosity can increase the current density value and decrease pressure drop in model C, while it has nearly no effects on temperature distribution. © 2016 Elsevier Ltd
Journal of Contaminant Hydrology (01697722)202pp. 33-46
A simulation-optimization model is proposed for identifying the characteristics of local immiscible NAPL contaminant sources inside aquifers. This model employs the UTCHEM 9.0 software as its simulator for solving the governing equations associated with the multi-phase flow in porous media. As the optimization model, a novel two-level saturation based Imperialist Competitive Algorithm (ICA) is proposed to estimate the parameters of contaminant sources. The first level consists of three parallel independent ICAs and plays as a pre-conditioner for the second level which is a single modified ICA. The ICA in the second level is modified by dividing each country into a number of provinces (smaller parts). Similar to countries in the classical ICA, these provinces are optimized by the assimilation, competition, and revolution steps in the ICA. To increase the diversity of populations, a new approach named knock the base method is proposed. The performance and accuracy of the simulation-optimization model is assessed by solving a set of two and three-dimensional problems considering the effects of different parameters such as the grid size, rock heterogeneity and designated monitoring networks. The obtained numerical results indicate that using this simulation-optimization model provides accurate results at a less number of iterations when compared with the model employing the classical one-level ICA. © 2017 Elsevier B.V.
Journal of the Energy Institute (17460220)90(5)pp. 752-763
This paper concerns with numerical modeling of fluid flow through a zigzag-shaped channel to be used as the cooling plate for polymer electrolyte membrane fuel cells. In general, large scale PEM fuel cells are cooled by liquid water flows through coolant flow channels, and the shape of these channels has a key role in the cooling performance. We perform a three-dimensional numerical simulation to obtain the flow field and heat transfer rate in square area cooling plates. The performance of zigzag flow channels is evaluated in terms of maximum surface temperature, temperature uniformity and pressure drop. The results indicate that in the zigzag channels model, maximum surface temperature, surface temperature difference and temperature uniformity index, respectively, reduce about 5%, 23%, and 8% with respect to straight channels model. Hence, the cooling performance of fuel cells can be improved by implementing the zigzag channels model as the coolant fluid distributors, although the coolant pressure drop is higher than straight channels in this model. © 2016 Energy Institute
International Journal of Numerical Methods for Heat and Fluid Flow (09615539)24(8)pp. 1831-1863
Purpose: The purpose of this paper is to present a detailed algorithm for simulating three-dimensional hydrocarbon reservoirs using the blackoil model. Design/methodology/approach: The numerical algorithm uses a cell-centred structured grid finite volume method. The blackoil formulation is written in a way that an Implicit Pressure Explicit Saturation approach can be used. The flow field is obtained by solving a general gas pressure equation derived by manipulating the governing equations. All possible variations of the pressure equation coefficients are given for different reservoir conditions. Key computational details including treatment of non-linear terms, expansion of accumulation terms, transitions from under-saturated to saturated states and vice versa, high gas injection rates, evolution of gas in the oil production wells and adaptive time-stepping procedures are elaborated. Findings: It was shown that using a proper linearization method, less computational difficulties occur especially when free gas is released with high rates. The computational performance of the proposed algorithm is assessed by solving the first SPE comparative study problem with both constant and variable bubble point conditions. Research limitations/implications: While discretization is performed and implemented for unstructured grids, the numerical results are presented only for structured grids, as expected, the accuracy of numerical results are best for structured grids. Also, the reservoir is assumed to be non-fractured. Practical implications: The proposed algorithm can be efficiently used for simulating a wide range of practical problems wherever blackoil model is applicable. Originality/value: A complete and detailed description of ingredients of an efficient finite volume-based algorithm for simulating blackoil flows in hydrocarbon reservoirs is presented. © Emerald Group Publishing Limited.
Journal of Computational Physics (10902716)248pp. 339-362
This paper presents an extension of the multiscale finite volume (MsFV) method to multi-resolution coarse grid solvers for single phase incompressible flows. To achieve this, a grid one level coarser than the coarse grids used in the MsFV method is constructed and the local problems are redefined to compute the basis and correction functions associated with this new grid. To construct the coarse-scale pressure equations, the coarse-scale transmissibility coefficients are calculated using a new multi-point flux approximation (MPFA) method. The estimated coarse-scale pressures are utilized to compute the multiscale pressure solution. Finally a reconstruction step is performed to produce a conservative velocity field which is used to solve the transport equations. The computational cost of the proposed method is compared with that of the MsFV method and the relevant time complexity formulas are given. Several two-dimensional test cases with permeability fields ranging from two-scale to multi-scale problems are solved. The performance of the proposed method in handling problems with shale layers or discrete fractures is assessed. Also, a number of layers from the tenth SPE comparative study problem are used to examine general abilities of the method when facing realistic reservoir problems. The results are compared with fine-scale reference solutions to assess the accuracy of the proposed method. © 2013 Elsevier Inc.
Advances in Water Resources (03091708)59pp. 221-237
In the present work, the multiscale finite volume (MsFV) method is implemented on a new coarse grids arrangement. Like grids used in the MsFV methods, the new grid arrangement consists of both coarse and dual coarse grids but here each coarse block in the MsFV method is a dual coarse block and vice versa. Due to using the altered coarse grids, implementation, computational cost, and the reconstruction step differ from the original version of MsFV method. Two reconstruction procedures are proposed and their performances are compared with each other. For a wide range of 2-D and 3-D problem sizes and coarsening ratios, the computational costs of the MsFV methods are investigated. Furthermore, a matrix (operator) formulation is presented. Several 2-D test cases, including homogeneous and heterogeneous permeability fields extracted from different layers of the tenth SPE comparative study problem are solved. The results are compared with the fine-scale reference and basic MsFV solutions. © 2013 Elsevier Ltd.
Scientia Iranica (23453605)17(1 B)pp. 13-24
The condition known as a water-hammer problem is a transient condition that may occur as a result of worst-case loadings, such as pump failures, valve closures, etc. in pipeline systems. The pressure in the water hammer can vary in such a way that in some cases it may increase and cause destruction to the hydraulic systems. The pressure in the water hammer can also be decreased to the extent that it can fall under the saturation pressure, where cavitation appears. Therefore, the liquid is vaporized, thus, making a two-phase flow. This pressure decrease can be as dangerous as the pressure rise. As a result of the pressure drop and vaporization of the liquid, two liquid regions are separated, which is referred to as column separation. In almost all standard methods for simulation of column separation, the steady friction factor was used, but in reality, the quantity of the friction factor is variable. In this work, the unsteady friction factor has been applied in the Discrete Gas Cavity Model (DGCM), which is a standard method of column separation prediction. Through comparisons with experimental data, results showed that applying the unsteady friction factor can improve the magnitude of the predicted duration shape and the timing of the pressure pulse in all of the case studies. © Sharif University of Technology, February 2010.
