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International Communications in Heat and Mass Transfer (07351933)
Electrochromic windows stand out as a subset of smart windows that effectively manage sunlight, thereby contributing significantly to energy efficiency and occupant comfort. In this paper, a methodology is presented for determining the optimal properties of electrochromic windows in six distinct cities characterized by varying climates. The cities under examination include Tehran, Sari, Yazd, Shiraz, Esfahan, and Tabriz. The optimization method uses a multi-objective approach to optimize various design variables for electrochromic windows, such as thickness of glass panes, gas layer properties, and window-to-wall ratio. Additionally, it identifies optimal illuminance, heating, and cooling setpoints to enhance electrochromic window performance. The objectives under consideration include the total annual electricity consumption (E) and the Predicted Percentage of Dissatisfied (PPD) coefficient. To facilitate this optimization, Non-Dominated Sorting Genetic Algorithm II (NSGA-II) is employed, generating a Pareto front. The Discomfort Glare Index (DGI) parameter is subsequently computed at the Pareto points to determine the final optimal solution. The results demonstrate that in Esfahan, the implementation of optimum electrochromic windows yields the most substantial reductions in electricity consumption (27.6 %) and PPD coefficient (29.7 %). Furthermore, Krypton gas is identified as the most suitable gas for deployment in optimal electrochromic windows. © 2025 Elsevier Ltd
Journal of Building Engineering (23527102)
A solar combisystem is utilized to supply domestic hot water (DHW) and heat a residential building. This system decreases the fossil fuel consumption and, hence, reduces air pollution and global warming. This paper proposes an innovative method to design and optimize a suitable solar combisystem for a residential building with respect to technical and economic parameters. First, different configurations of solar combisystems, including various components, are considered. Then, the optimum design variables are determined for each configuration using Grouped Method of Data Handling (GMDH) type of Artificial Neural Network (ANN) and Non-Dominated Sorting Genetic Algorithm II (NSGA-II). Total Solar Fraction (TSF) and Life Cycle Cost (LCC) are considered as objective functions. Finally, the optimum design is chosen for the solar combisystem. Typically, researchers have focused on evaluating the performance of a single solar combisystem configuration in each study. However, this research takes a different approach by optimizing multiple configurations, resulting in a significant improvement in the total solar fraction by 7.3%. This is the main novelty of this paper. Based on the results, the optimum configuration of the solar combisystem includes 17.91 m2 of evacuated-tube collectors with a tilt angle of 50°. Also, the volume of the hot water tank and heating buffer tank are, respectively, equal to 204 and 500 L (L). In this system, solar energy provides 94% of the required energy for supplying DHW and 23% of the energy for heating the building. Moreover, reduction of annual CO2 emissions is 1806 kg. This paper presents a guideline to design solar systems for the residential buildings considering technical and economic aspects. © 2023 Elsevier Ltd
This article presents a modified version of the WENO numerical method with an increased order of accuracy over critical points and higher resolution in detecting shock-turbulence interactions. The proposed method is an improved version of the WENO-η-Z scheme. The optimization is based on a new Global Smoothness Indicator definition that produces less numerical error at relative extremum points as an indicator of fluctuations in the flow field. Both 1-D and 2-D benchmark problems are implemented to verify the proposed scheme's accuracy. The convergence of the presented scheme is compared with that of a standard and optimal WENO-η-Z, in the linear wave transfer problem, which shows better convergence for the proposed method. The modified method's capability to detect discontinuity and shocks in the flow-field has been evaluated by solving two shock-tube problems, namely the Lax shock tube problem and Sod's problem. The proposed method's ability to detect fluctuations and disturbances in the flow-field in the presence of shocks has also been assessed in two problems, including the 1-D Shu-Osher shock-disturbance interaction and the 2-D shock-turbulence interaction. Improvements is observed in convergence and reduction in numerical errors in the proposed method compared to the standard WENO and WENO-η-Z method, whilst the capability to detect shocks has not reduced in the modified version. © 2022 Elsevier GmbH
Energy and Buildings (03787788)
Determination of the optimum setpoint temperature of thermostats in various climates is a problem in air conditioning of residential buildings. In this paper, a new method is developed to optimize the setpoint temperature of thermostats in different climates of Iran. Design variables in the optimization process are heating setpoint, cooling setpoint, thickness, and thermal conductivity of insulations in the building envelopes. The optimization goals are minimizing energy consumption and cost of insulations in addition to maximizing thermal comfort of occupants. Thus, the static payback period (SPP) and the predicted percentage dissatisfied (PPD) indices are selected as objective functions which should be minimized in the optimization process. The methods applied to attain these objectives are numerical modeling by EnergyPlus software, Grouped Method of Data Handling (GMDH) type of Artificial Neural Network (ANN), and Non-Dominated Sorting Genetic Algorithm II (NSGA-II). Therefore in this process, first, EnergyPlus is used to train the neural network. Afterward, the GMDH-type neural network is applied to derive polynomials computing the objective functions from the design variables. Then, Pareto optimal points for the objective functions are obtained through using these polynomials and NSGA-II multi-objective optimization. Finally, the optimum design point is selected for different cities. According to the results, type and thickness of insulation integrated in the building envelopes affect the static payback period and thermal comfort of occupants. For all the climates of Iran, the most appropriate insulation is XPS and the optimum heating setpoint of thermostat is 22 °C. Also, the optimum value for the cooling setpoint pertains to the type of climate, so that this value for Bandar Abbas, Yazd, Tehran, Rasht and, Tabriz is, respectively, equal to 24.5, 24.7, 25.2, 25.3, and 25.6 °C. Moreover, thermal comfort of occupants increases with thickness of insulation, except for Bandar Abbas whose PPD is almost constant. The most value of PPD reduction with insulation thickness is related to Tehran where by increasing the insulation thickness from 1 cm to 5 cm, PPD decreases up to 53%. © 2022 Elsevier B.V.
International Journal of Computational Fluid Dynamics (10618562) (5)
Canard is one of the aerodynamic add-on devices which can reduce drag coefficient of the car. In this paper, different parameters of the canard geometry are determined using a multi-objective optimisation. Design variables are entrance velocity (U), geometrical parameters of canard (L 1, L 2, r, α) and canard angle from horizontal axis (θ). The objective functions include magnitude of drag and lift coefficients that should be minimised and maximised, respectively. First, the neural network is trained by means of a series of ANSYS Fluent-based CFD calculations. A GMDH-type neural network is then applied to derive polynomials that compute the objective functions from input variables. Finally, Pareto optimal points for objective functions are obtained through using these polynomials and NSGA-II multi-objective optimisation. According to the results, the canard’s optimum state is specified as L 1 = 0.37 m, L 2 = 0.18 m, r = 0.09 m, α = 25°, θ = 20° with potential drag reduction of 4.5%. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.
International Journal of Engineering, Transactions A: Basics (17281431) (1)
In the present paper, a supersonic wind-tunnel is designed to maintain a flow with Mach number of 3 in a 30cm×30cm test section. An in-house CFD code is developed using the Roe scheme to simulate flow-field and detect location of normal shock in the supersonic wind-tunnel. In the Roe scheme, flow conditions at inner and outer sides of cell faces are determined using an upwind biased algorithm. The in-house CFD code has been parallelized using OpenMp to reduce the computational time. Also, an appropriate equation is derived to predict the optimum number of cores for running the program with different grid sizes. In the design process of the wind-tunnel, firstly geometry of the nozzle is specified by the method of characteristics. The flow in the nozzle and test section is simulated in the next step. Then, design parameters of the diffuser (convergence and divergence angles, area of the throat, and ratio of the exit area to the throat area) are determined by a trial and error method. Finally, an appropriate geometry is selected for the diffuser which satisfies all necessary criteria. © 2018 Materials and Energy Research Center. All rights reserved.
Scientia Iranica (10263098) (2)
In the present paper, an in-house CFD code is developed using Roe scheme to simulate a condensing two-phase flow in blade to blade passage of a steam turbine. Effects of condensation on the flow field of steam turbine rotor tip section are investigated for different outlet pressures. Firstly, comparison is performed between results of wet and dry cases. Then, effects of outlet pressure variations on the flow field are studied. Finally, effects of condensation on different specifications of the flow field (total pressure loss coefficient, entropy generation, and deviation angle) are investigated. Also, the mechanism of flow deviation in the cascade flow field is described. Condensation has a great influence on the behavior of the flow field based on the numerical results of this paper. It changes the out-flow direction, and consequently the flow entering to the next blade deviates from its on-design condition; thus, additional losses are produced. For example, the value of deviation angle reaches 7:62° for wet case and exit Mach number Me = 1:45. Also, there are stagnation pressure loss and entropy generation due to non-equilibrium condensation that reduce the efficiency of the steam turbine. © 2017 Sharif University of Technology.
Neural Computing and Applications (09410643)
In the present study group method of data handling (GMDH) type of artificial neural networks are used to model deviation angle (θ), total pressure loss coefficient (ω), and performance loss coefficient (ξ) in wet steam turbines. These parameters are modeled with respect to four input variables, i.e., stagnation pressure (Pz), stagnation temperature (Tz), back pressure (Pb), and inflow angle (β). The required input and output data to train the neural networks has been taken from numerical simulations. An AUSM–Van Leer hybrid scheme is used to solve two-phase transonic steam flow numerically. Based on results of the paper, GMDH-type neural networks can successfully model and predict deviation angle, total pressure loss coefficient, and performance loss coefficient in wet steam turbines. Absolute fraction of variance (R2) and root-mean-squared error related to total pressure loss coefficient (ω) are equal to 0.992 and 0.002, respectively. Thus GMDH models have enough accuracy for turbomachinery applications. © 2016, The Natural Computing Applications Forum.
Journal of Mechanical Science and Technology (1738494X) (3)
In this paper, the AUSM-van Leer hybrid scheme is extended to solve the governing equations of two-phase transonic flow in a steam turbine stage. The dominant solver of the computational domain is the non-diffusive AUSM scheme (1993), while a smooth transition from AUSM in regions with large gradients to the diffusive scheme by van Leer (1979) guarantees a robust hybrid scheme throughout the domain. The steam is assumed to obey non-equilibrium thermodynamic model. The effects of condensation on different specifications of the flow field are studied at subsonic/supersonic flow regimes. It is observed that as a result of condensation, the aerothermodymics of the flow field changes. For example in supersonic wet case (Pb = 14.55 kPa), pressure loss coefficient of rotor and total entropy generation are, respectively, 77% and 29% more than those in dry conditions. Also the value of rotor deviation angle reaches 6.27° in wet case and Pb = 14.55 kPa. © 2016, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Journal Of Applied Fluid Mechanics (17353572) (2)
In the present paper, the hybrid AUSM-van Leer scheme is extended to solve the governing equations of twophase condensing flows. The method of moments with the classical homogeneous nucleation theory is used to model the non-equilibrium condensation phenomenon. Firstly, the hybrid method is validated using two test cases (i.e. Laval nozzle and rotor-tip cascade) and the results are compared with the MacCormack method. Then the hybrid method is used to solve two other problems (i.e. wavy channel and VKI stage). Based on the numerical results of the paper, the hybrid AUSM-van Leer scheme is an accurate method to simulate twophase transonic flows with nucleation. If the super cooling degree reaches to its maximum value, the nonequilibrium condensation begins and wetness fraction increases suddenly. Also across a shock the wetness fraction decreases due to evaporation of the droplets.
Scientia Iranica (10263098) (6)
Petroleum Refinery Wastewaters (PRW) contain water-soluble hydrocarbons which cannot be separated by physical methods. In recent years, there have been enormous approaches to treat PRW. The most outstanding methods involve biological, photocatalytic, electro-and photo-Fenton, etc. Using microbial fuel cell is a new method to treat PRW. In this paper, PRW treatment in MFC was studied using oxygen and permanganate as cathodic electron acceptors. Also, effects of temperature and external resistance on MFC performance and PRW treatment were investigated. Finally, an electrochemical model was fitted on empirical polarization curves to evaluate activation, ohmic, and mass transfer losses. Maximum power production was 0.03 W/m2 at 33°C using oxygen as cathodic electron acceptor. Also, COD removal eficiency was 49.27% during 44 h. To enhance power production of the MFC, potassium permanganate was used as cathodic electron acceptor. At the temperature of 33°C and 0.2 g/L of permanganate concentration, the maximum power density was 0.95 W/m2 and COD removal eficiency was 78% during 44 h. © 2016 Sharif University of Technology. All rights reserved.
Applied Thermal Engineering (13594311)
In this paper, effects of turbine blade roughness and steam condensation on deviation angle and performance losses of the wet stages are investigated. The steam is assumed to obey non-equilibrium thermodynamic model, in which abrupt formation of liquid droplets produces condensation shocks. An AUSM-van Leer hybrid scheme is used to solve two-phase turbulent transonic steam flow around turbine rotor tip sections. The dominant solver of the computational domain is taken to be the AUSM scheme (1993) that in regions with large gradients smoothly switches to van Leer scheme (1979). This guarantees a robust hybrid scheme throughout the domain. It is observed that as a result of condensation, the aerothermodymics of the flow field changes. For example for a supersonic wet case with exit isentropic Mach number Me,is = 1.45, the deviation angle and total pressure loss coefficient change by 65% and 200%, respectively, when compared with dry case. It is also observed that losses due to surface roughness in subsonic regions are much larger than those in supersonic regions. Hence, as a practical guideline for maintenance sequences, cleaning of subsonic parts of steam turbines should be considered first. © 2015 Published by Elsevier Ltd.
Journal Of Applied Fluid Mechanics (17353572) (3)
In this paper vorticity confinement parameters are successfully developed for compressible flows. The first new confinement parameter is proportional to spectral radii of the flux Jacobian matrix. Therefore, the confinement parameter implicitly contains the local conditions of the flow field. This new method is named as lambda vorticity confinement method. In order to gain confidence in the applicability of vorticity confinement, it would be ideal to completely eliminate constant coefficients from confinement parameters. Because these constant coefficients should be determined for every problem by trial and error and it takes a long time. In the next part of this paper, a suitable relation is introduced for the vorticity confinement parameter that doesn't need any constant coefficient. This new method is named as adaptive vorticity confinement method. Then the capability of these new methods is compared with the other vorticity confinement methods for solving shock-vortex interaction and three dimensional moving vortex problems.
International Review of Mechanical Engineering (19708734) (1)
The SCalar Dissipation Scheme (SCDS-1) and MAtrix Dissipation Scheme (MADS-1) are two common artificial dissipation schemes that have been used for several years. Two new artificial dissipation schemes are introduced by using the QUICK scheme in this paper (SCDS-2, MADS-2). The capability of these four artificial dissipation schemes is compared for two different problems. First for the channel flow problem and then for the moving vortex problem. The results of two problems show that the accuracy of these new artificial dissipation schemes (SCDS-2, MADS-2) are almost equal to two other schemes (SCDS-1, MADS-1). The implementation of the boundary conditions is more convenient in the new schemes. Also the new artificial dissipation schemes don't need any sensor. © 2011 Praise Worthy Prize S.r.l. - All rights reserved.
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (20413025) (8)
The conventional vorticity confinement methods have a constant confinement parameter that should be determined for every problem by trial and error. In this article, vorticity confinement parameters are successfully developed for compressible flows. The first new confinement parameter is proportional to spectral radii of the flux Jacobian matrix. Therefore, the confinement parameter implicitly contains the grid size and the other local fluid properties. In order to gain confidence in the applicability of vorticity confinement, it would be ideal to completely eliminate such constant parameters. In the next part of this article, a suitable relation is introduced for the vorticity confinement parameter that does not need any constant coefficient. The scalar dissipation scheme (SCDS-1) and matrix dissipation scheme (MADS-1) are two common artificial dissipation schemes that have been used for several years. Two new artificial dissipation schemes are introduced by using the QUICK scheme in this article (SCDS-2, MADS-2). The capabilities of these four artificial dissipation schemes are compared for channel flow problem. Then, the new confinement parameters and artificial dissipation schemes are used for solving moving vortex in a uniform flow and supersonic shear layer problems. The methods have been shown to be very effective at treating shock waves and vortex dominant flows. © Authors 2011.
