Journal of Heat and Mass Transfer ResearchJournal of Heat and Mass Transfer Research
http://jhmtr.journals.semnan.ac.ir/
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http://jhmtr.journals.semnan.ac.ir/
Feed provided by Journal of Heat and Mass Transfer Research. Click to visit.Spectral quasi-linearization approach for unsteady MHD boundary layer flow of casson fuid due ...
http://jhmtr.journals.semnan.ac.ir/article_422_0.html
The present paper seeks to examine a numerical method of solution called spectra quasi-linearization method (SQLM) to the problem of unsteady MHD boundary layer flow of Casson fluid due to an impulsively stretching surface under the influence of a transverse magnetic field, which is an important physical phenomena in engineering applications.The study extends the previous models to account for a classical non-newtonian fluid called Casson fluid under the influence of a transverse magnetic field. The flow model is described in terms of a highly nonlinear partial differential equations. The method of solution Spectral quasi-linearization methods(SQLM) seeks to linearised the original system of PDEs using the Newton-Raphson based quasilinearization method (QLM). The numerical resultsfor the surface shear stress are compared with those of the analytical approach results, and they are found to be in good agreement. The flow controlling parameters are found to have a profound effect on the resulting flow profiles.It is observed that there is a smooth transition from the small time solution to the large time solution. The magnetic field significantly affects the flow field and skin friction coefficient. Indeed, skin friction coefficient is found to decreaserapidly, initially, in small time interval before attaining a steady state for large time.Sun, 19 Jun 2016 19:30:00 +0100Performance Investigation of Two Modified Two-Stage Trans-Critical Carbon Dioxide Refrigeration ...
http://jhmtr.journals.semnan.ac.ir/article_2894_0.html
In the present work, the performances of two new two-stage multi inter-cooler trans- critical carbon dioxide (CO2) refrigeration cycle with ejector and internal heat exchanger have been studied. In the new modified cycles, an internal heat exchanger is added to the cycles. Also second inter-cooler in modified cycles, cooled with the refrigeration of the cycle, so that in first cycle it is a branch of saturated vapour flow from separator and also in second cycle it is a branch of supersaturated steam from internal heat exchanger. Results are validated against those available in the literature. Comparisons of the results show that there is excellent agreement between them. The influences of important operational parameters in the cycle performance such as gas-cooler pressure, evaporator temperature and gas-cooler temperature on the cycle performance have been analysed. The obtained results show that if the cooling flow for second inter-cooler supply from saturated vapour from separator, maximum coefficient of performance can be improved 25% compared to the original cycle at the considered particular conditions for operation.Thu, 22 Feb 2018 20:30:00 +0100Influence of inclined Lorentz forces on entropy generation analysis for viscoelastic fluid over ...
http://jhmtr.journals.semnan.ac.ir/article_3084_453.html
In the present study, an analytical investigation on the entropy generation examination for viscoelastic fluid flow involving inclined magnetic field and non-linear thermal radiation aspects with the heat source and sink over a stretching sheet has been done. The boundary layer governing partial differential equations were converted in terms of appropriate similarity transformations to non-linear coupled ODEs. These equations were solved utilizing Kummer's function so as to figure the entropy generation. Impacts of different correlated parameters on the profiles velocity and temperature, also on entropy generation were graphically provided with more information. Based on the results, it was revealed that the existence of radiation and heat source parameters would reduce the entropy production and at the same time aligned magnetic field, Reynolds number, dimensionless group parameter, Hartmann number, Prandtl number, and viscoelastic parameters would produce more entropy. The wall temperature gradient was additionally computed and compared with existing results from the literature review, and demonstrates remarkable agreement.Tue, 30 Apr 2019 19:30:00 +0100Numerical study of flow and heat transfer characteristics of CuO/H2O nanofluid within a mini tube
http://jhmtr.journals.semnan.ac.ir/article_3091_453.html
Nanofluids are new heat transfer fluids, which improve thermal performance while reducing the size of systems. In this study, the numerical domain as a three-dimensional copper mini tube was simulated to study the characteristics of flow and heat transfer of CuO/H2O nanofluid, flowed horizontally within it. The selected model for this study was a two-phase mixture model. The results indicated that nanofluids with the platelet nanoparticles have better thermal performance than other shapes of nanoparticles such as cylindrical, Blade, Brick, and spherical nanoparticles, respectively. By studying the flow characteristics, it was found that the pressure drop and friction factor of the nanofluids are dependent on the shape of the nanoparticles so that the nanofluids containing spherical nanoparticles have the lowest reduction in the friction factor and nanofluids containing platelet-shaped nanoparticles have the highest reduction in friction factor. Furthermore, as new formulas, two correlations were suggested to calculate the Nusselt number of nanofluids according to the effect of nanoparticle shape on the laminar and turbulent flow regimes.Tue, 30 Apr 2019 19:30:00 +0100Investigating Tubes Material Selection on Thermal Stress in Shell Side Inlet Zone of a Vertical ...
http://jhmtr.journals.semnan.ac.ir/article_3100_453.html
In this study, the effect of the tube material on the thermal stress generated in a vertical shell and tube heat exchanger is investigated. Shell and tube heat exchangers are the most common heat exchangers used in industries. One of the most common failures in these exchangers in the industry is the tube failure at the junction of the tube to tubesheet. When the shell side and the tube side fluid with temperature difference, flow in the heat exchangers, a temperature gradient occurs in the tube. Temperature gradients cause thermal stress in the tube, especially at the junction of the tube to tubesheet where there is no possibility of expansion and contraction. Therefore, in this study, it was tried to make changes in order to reduce the effect of thermal stress in the failure. For this purpose, temperature distribution, thermal stress distribution, and its effects on failure were investigated by changing the material. In order to perform the required analysis, three dimensional models of the inlet zone of the shell side were created, and steady state temperature distribution was obtained, and the stress caused by temperature gradient was analyzed. Because of the interference between fluid and structure in this study, the indirectly coupled field analysis was used. In this way, the thermal analysis results were converted into indirect couple structural analysis as loading. Among the analyzed materials, the lowest rate of stress is for the copper tubes. However, steel tubes have the best safety factor regarding thermal stress.Tue, 30 Apr 2019 19:30:00 +0100Investigation on Turbulent Nanofluid Flow in Helical Tube in Tube Heat Exchangers
http://jhmtr.journals.semnan.ac.ir/article_3101_453.html
In this study, the thermal characteristics of turbulent nanofluid flow in a helical tube in the tube heat exchanger (HTTHE) were assessed numerically through computational fluid dynamics (CFD) simulation. The findings of both the turbulent models: realizable k-epsion (k-ε) and re-normalisation group (RNG) k-epsilon were compared. The temperature distribution contours show that realizable and RNG k-ε models, together with the swirl dominated flow are of more uniform temperature distributions. The proper prediction of two layer theory leads to having a uniform temperature distribution and proper dimensionless wall distance (Y+). The turbulent flow and heat transfer of two nanofluids (SiO2, Al2O3) and base fluid with respect to swirl dominated flow was simulated through the RNG model. The effects of the concentration of nanoparticles on heat transfer characteristics in HTTHE and two turbulent models were analyzed in a comprehensive manner. It is concluded that up to 1% concentration of SiO2 and 1% concentration of Al2O3, similar heat transfer characteristics are observed. Comparison between the CFD results with the predicted values for friction factor coefficient (f) and Nusselt number (Nu) calculated through experimental correlations indicate the maximum errors of 6.56% and 0.27%, respectively.Tue, 30 Apr 2019 19:30:00 +0100Numerical Investigation of Roofing Materials Effect on Solar Heat Gain in Different External ...
http://jhmtr.journals.semnan.ac.ir/article_3155_453.html
In this study, the thermal performance of three kinds of roofs with different heat capacity and thermal conductivity under different external conditions has been investigated using a numerical method. For this purpose, the combined solar radiation, conduction and convection heat transfer were calculated implicitly in terms of a one-dimensional finite difference method. Different high and low solar radiation conditions in two common climates in the Middle East, including hot-humid and hot-dry, were considered. The effect of roofing materials was investigated in terms of their thermal storage and overall heat transfer coefficient. Moreover, the time lags and decrement factors were evaluated to compare the performance of the roof. The numerical model has been validated using EnergyPlus. The results indicate that the roof with high thermal storage and low thermal conductivity has better performance in comparison to others. However, the total heat gains are not linearly proportional to the overall heat transfer coefficients, e.g. here, the ratios of a total load of roof 1 to roofs 2 and 3 are about 12 percent lower than the ratio of overall heat transfer coefficients. Furthermore, the solar radiation intensity had considerable effects on time lags. Finally, it can be concluded that the external conditions have no significant effect on the decrement factor.Tue, 30 Apr 2019 19:30:00 +0100Mixed convection study in a ventilated square cavity using nanofluids
http://jhmtr.journals.semnan.ac.ir/article_3485_0.html
This work shows a numerical study on the laminar heat transfer mixed convection in a square cavity with openings on the vertical walls through which nanofluid flows. The intention is to cool a square heat source placed at the center of the geometry. The nanofluid has Copper nanoparticles and water as its base-fluid. The velocity and temperature of the entrance flow are known. Some results are experimentally and numerically validated. A mesh independency study is carried out. Some parameters are ranged as follows: i) the Reynolds number from 50 to 500, the nanofluid volume fraction from 0 to 1%, the Grashof number from 1000 to 100000. Two main directions of the flow are studied: i) the ascending flow which goes from the bottom to the upper openings; ii) the descending flow which goes from the upper to the bottom openings. In some cases, the fluid seems to be stuck inside the cavity which weakens the heat transfer. The presence of nanoparticles also increases the heat transfer of 4% for the ascending primary flow inside the cavity.Sun, 02 Dec 2018 20:30:00 +0100Experimental Investigation of Thermal Conductivity of Liquid Paraffin/Alumina Nanofluids with a ...
http://jhmtr.journals.semnan.ac.ir/article_3489_0.html
Liquid paraffin as a coolant fluid can be used in electronic devices due to its suitable capabilities such as electrical insulating, high heat capacity, chemical and thermal stability, and high boiling point. However, the poor thermal conductivity of paraffin has been confined its thermal cooling application. Addition of high conductor nanoparticles to paraffin can fix this drawback properly. In this study, the influence of the nanoparticles on the thermal conductivity of base material was assessed. The effects of temperature (20 °C ≤ T ≤ 50 °C) and volume fraction (0 ≤ ϕ ≤ 3%) on the thermal conductivity of paraffin/alumina nanofluids have been presented. Nanofluid samples were prepared by the two-step method and thermal conductivity measurements were done by a KD2 pro instrument. The results showed that the thermal conductivity increased uniformly with the increase of solid volume fraction and temperature. Moreover, it can be observed that for more concentrated samples, the effect of temperature was more tangible. Thermal conductivity enhancement (TCE) and effective thermal conductivity (ETC) of the nanofluid was calculated and new correlations were reported to predict the values of them based on the volume fraction of nanoparticles and temperature of composite accurately.Sat, 08 Dec 2018 20:30:00 +0100Rapid mixing of Newtonian and non-Newtonian fluids in a three-dimensional micro-mixer using ...
http://jhmtr.journals.semnan.ac.ir/article_3504_453.html
The mixing of Newtonian and non-Newtonian fluids in a magnetic micro-mixer was studied numerically using ferrofluid. The mixing process was performed in a three-dimensional steady-state micro-mixer. A magnetic source was mounted at the entrance of the micro-channel to oscillate the magnetic particles. The effects of electric current, inlet velocity, size of magnetic particles, and non-Newtonian fluid were examined on the mixing efficiency. It was demonstrated that the mixing efficiency would increase with applied current and the size of magnetic particles. The inlet velocity has an inverse effect on the enhancement of the mixing efficiency. It is found that electric currents of 0A and 50A would lead to the mixing efficiency of 10% and 83%, respectively. In addition, the results of the present work revealed that the mixing efficiency of a non-Newtonian fluid (blood) is smaller than that of a Newtonian one. Tue, 30 Apr 2019 19:30:00 +0100Numerical investigation of heat transfer in a sintered porous fin in a channel flow with the ...
http://jhmtr.journals.semnan.ac.ir/article_3534_453.html
Extended surfaces are one of the most important approaches to increase the heat transfer rate. According to the Fourier law, the heat transfer increases by increasing the contact surface of body and fluid. In this study, the effect of heat transfer has been investigated on two sets of engineered porous fins, in which the balls with different materials are sintered together. The fluid flow through the channel is considered incompressible, steady and three-dimensional. In this study, fins made of copper, aluminum and steel balls with 0.6 and 1.7 mm diameters in single-row, two-row modes are studied, and the heat transfer and pressure drop through these fins are checked. Also, the surface and volume analysis of the rigid and porous fins is also provided. In addition, the effect of diameter and material of the balls on the temperature distribution and heat transfer coefficient is examined in two cases of constant flux and constant temperature at the base. The results show that the steel fin has a different heat transfer behavior compared to other fins; the suitable material for the constant pressure and constant flux are copper and aluminum, respectively. Also, it is found that utilization of this type of connection decrease the volume of the fin about 39% of and increase the surface are about 37%.Tue, 30 Apr 2019 19:30:00 +0100Numerical Study of turbulent free convection of liquid metal with constant and variable ...
http://jhmtr.journals.semnan.ac.ir/article_3624_0.html
In the present study, turbulent MHD convection of liquid metal with constant and variable properties is investigated numerically. The finite volume method is used to simulate the fluid flow and natural convection heat transfer in a square cavity. The fluid flow and heat transfer were calculated and compared for two cases constant and variable properties. It is observed that for the case variable properties in high Hartmann numbers (Ha) the temperature gradient near the hot wall is more than the cold wall. For both cases the temperature gradient near the hot and cold walls and also the slope of temperature profile is high. By applying magnetic field and increasing the Ha the temperature slope reduces so at Ha=800 the profile is linear. In the case constant properties the slope of temperature profile near the vertical walls is the same and the temperature profiles pass from one point at the center of the cavity. But in the case variable properties as it was expected the temperature profile doesn’t pass one point and the slope of lines at high Hartmann numbers near the hot and cold walls are partly different. Also it is observed that for the case constant properties the Nusselt number is less than the case variable properties.Thu, 31 Jan 2019 20:30:00 +01003D Simulation of the Effects of the Plasma Actuator on the Unsteady, Turbulent and Developing ...
http://jhmtr.journals.semnan.ac.ir/article_3628_0.html
The purpose of this paper is 3D simulation of unsteady, turbulent and developing flow within a circular duct in presence of the body force vector induced by Dielectric barrier discharge (DBD) plasma actuator. This study aims at investigating of using plasma actuator to control separation with special arrangement of electrodes. For this reason, the plasma actuator is modeled in OpenFOAM software and the results are validated. Then, a computational study is carried out on a 3D flow to examine the effect of the presence of the plasma actuator. Three phenomena of increasing the flow cross-sectional, developing flow and simultaneous flow in both tangential and radial directions determine the physics of the problem, especially the pressure gradients. Due to the geometry of the problem, the actuators are arranged differently and for the first time the electrodes are radially arranged. The results show that presence of a plasma actuator delay the separation point.Mon, 04 Feb 2019 20:30:00 +0100GDL construction Effects on distribution of reactants and electrical current density in PEMFC
http://jhmtr.journals.semnan.ac.ir/article_3770_0.html
A two dimensional pore scale model of polymeric fuel cell, which is promising of a clean and renewable energy production, is presented here. Let reactive gases behave as an ideal gas; inhomogeneous anisotropic structure of the gas diffusion layer, is considered as a random generated circular porous media. Lattice Boltzmann method is used to study the fluid flow and mass transfer within the cathode microstructure. All parts of the cathode have the same temperature and the electrochemical reaction on the surface of the catalyst layer enters the solution as a boundary condition. Effects of the gas diffusion layer structure (carbon fibers diameters changes) on the flow of reactive gases, molar fraction of various oxygen species, and water vapor within the various parts of the gas diffusion layer as well as the electrical current density are investigated. The results indicate increasing the diameter of the carbon fibers of the gas diffusion layer of a constant porosity facilitates both the flow of oxygen and vapor species inside the GDL while affecting the electrical current produced on the surface of the catalyst layer as well. Effects of increasing the carbon fiber diameter on the electrical current density are greater in a GDL with less porosity.Tue, 23 Apr 2019 19:30:00 +0100Heat and Mass transfer of a nanofluid over a linear stretching sheet with viscous dissipation effect
http://jhmtr.journals.semnan.ac.ir/article_3858_0.html
Boundary Layer Flow past a stretching surface with constant wall temperature, of a nanofluid is studied for heat transfer characteristics. The system of partial differential equations describing such a flow is subjected to similarity transformations gives rise to a boundary value problem involving a system of ordinary differential equations. This system is solved by a shooting method. Effect of the non-dimensional parameters on temperature and concentration profiles are displayed graphically for different values of the parameters, namely, Brownian motion parameter, Lewis number, Prandtl number and thermophoresis parameter. The reduced Nusselt number and the reduced Sherwood number are also shown in a tabular form.Boundary Layer Flow past a stretching surface with constant wall temperature, of a nanofluid is studied for heat transfer characteristics. The system of partial differential equations describing such a flow is subjected to similarity transformations gives rise to a boundary value problem involving a system of ordinary differential equations. This system is solved by a shooting method. Effect of the non-dimensional parameters on temperature and concentration profiles are displayed graphically for different values of the parameters, namely, Brownian motion parameter, Lewis number, Prandtl number and thermophoresis parameter. The reduced Nusselt number and the reduced Sherwood number are also shown in a tabular form.Sun, 02 Jun 2019 19:30:00 +0100