Journal of Heat and Mass Transfer ResearchJournal of Heat and Mass Transfer Research
https://jhmtr.semnan.ac.ir/
Mon, 24 Feb 2020 14:43:39 +0100FeedCreatorJournal of Heat and Mass Transfer Research
https://jhmtr.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 ...
https://jhmtr.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 Two-Stage Trans-Critical Carbon Dioxide Refrigeration Cycles ...
https://jhmtr.semnan.ac.ir/article_2894_453.html
In the present work, the performances of improved two-stage multi inter-cooler trans- critical carbon dioxide (CO2) refrigeration cycles with ejector and internal heat exchanger have been examined. In the new improved cycles, an internal heat exchanger is append to the cycles. Also, second inter-cooler in improved cycles, cooled with the refrigeration of the cycle, so that in first cycle it is a branch of saturated vapour flow from separator and in second cycle it is a branch of supersaturated steam from internal heat exchanger as well. Results are validated against those available in the literature. Comparisons of the results indicate that there is an excellent agreement between them. The influences of important operational parameters in the cycle performance such as pressure of gas-cooler, temperature of evaporator and temperature of gas-cooler on the performance of cycle have been analysed. The obtained results present that if the cooling flow for second inter-cooler supply from saturated vapour from separator, maximum coefficient of performance can be improved 25% in comparison with the conventional cycle at the considered specific states for operation.Mon, 30 Sep 2019 20:30:00 +0100Mixed convection study in a ventilated square cavity using nanofluids
https://jhmtr.semnan.ac.ir/article_3485_453.html
This work indicates a numerical study on the laminar heat transfer mixed convection in a square cavity with two openings (an inlet and an outlet) on vertical walls through which nanofluid flows. Two flow directions are examined: i) ascending flow which enters the bottom opening and exits the upper opening; ii) descending flow which enters the upper opening and exits the bottom opening. The ascending flow contributes to buoyancy forces while for the descending flow, the opposite takes place. The intention is to cool a 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 103 to 105. It is noteworthy to mention that in some cases, the fluid is stuck inside the cavity which weakens the heat transfer. The nanoparticles increase the heat transfer of 4% for the ascending primary flow inside the cavity.Mon, 30 Sep 2019 20:30:00 +0100Experimental Investigation of the Alumina/Paraffin Thermal Conductivity Nanofluids with a New ...
https://jhmtr.semnan.ac.ir/article_3489_453.html
Liquid paraffin as a coolant fluid can be applied in electronic devices as a result 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 article, the influence of the nanoparticles on the thermal conductivity of base material was assessed. Temperature (20-50°C) and volume fractions (0-3%) effect on the thermal conductivity of paraffin/alumina nanofluids have been considered. Nanofluid samples were prepared applying the two-step method. The thermal conductivity was measured by a KD2 pro instrument. The results indicated the thermal conductivity augments smoothly with an increase in volume fraction of nanoparticles as well as temperature. Moreover, it observed that for nanofluids with more volume-fraction the temperature affection is more remarkable. 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 nanofluid accurately.Mon, 30 Sep 2019 20:30:00 +0100Numerical Study of turbulent free convection of liquid metal with constant and variable ...
https://jhmtr.semnan.ac.ir/article_3624_453.html
In this research, turbulent MHD convection of liquid metal with constant and variable properties is investigated numerically. The finite volume method is applied to model the fluid flow and natural convection heat transfer in a square cavity. The fluid flow and heat transfer were simulated 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 slope near the hot wall is more than the cold wall. For both cases, the temperature gradient near the hot and cold walls 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. However,in the case variable properties as it was expected the temperature profile doesn’t pass one point and the slope of temperature profile at high Hartmann numbers near the hot and cold walls is partly different. Furthermore, it is indicated that for the case constant properties the Nusselt number is less than the case variable properties.Mon, 30 Sep 2019 20:30:00 +01003D Simulation of the Effects of the Plasma Actuator on the Unsteady, Turbulent and Developing ...
https://jhmtr.semnan.ac.ir/article_3628_453.html
The objective of current paper is 3D simulation of turbulent, developing flow and unsteady within a circular duct in presence of the body force vector persuaded by Dielectric barrier discharge (DBD) plasma actuator inside the surface of geometry for the first time. This article aims at investigating of applying 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.Subesequently, to examine the effect of the presence of the plasma actuator a numerical study is carried out on a 3D flow. The physics of the problem is determined by three phenomena of increasing the flow cross-sectional, developing flow and simultaneous flow in both radial and tangential directions, especially the pressure gradients. As a result of the geometry of the problem, the actuators are arranged differently and the electrodes are arranged in radial direction. The results indicate that plasma actuator delay the separation point.Mon, 30 Sep 2019 20:30:00 +0100GDL construction effects on distribution of reactants and electrical current density in PEMFC
https://jhmtr.semnan.ac.ir/article_3770_453.html
In this article, 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 contemplated as a random generated circular porous media. Lattice Boltzmann method is applied to inquire 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 that by increasing the diameter of the carbon fibers in the gas diffusion layer within constant porosity facilitates both the flow of oxygen and the vapor species inside the GDL, while affecting the produced electrical current on the surface of the catalyst layer.Mon, 30 Sep 2019 20:30:00 +0100Heat and mass transfer of nanofluid over a linear stretching surface with Viscous dissipation effect
https://jhmtr.semnan.ac.ir/article_3858_453.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.
The main objective of this paper is to extend the numerical investigation of boundary-layer flow of steady state, two-dimensional flow of nanofluid over a stretching surface with the impact of viscous dissipation. The ordinary differential equations are obtained by applying similarity transformation on partial differential equations. Then, the system is solved by applying the shooting techniques together with Adams-Bashforth Moulton Method. Software Fortran is used to compute the numerical results and the resulting values are indicated through graphs and tables.Mon, 30 Sep 2019 20:30:00 +0100Radiation and Chemical Reaction Effects on Unsteady Coupled Heat and Mass Transfer by Free ...
https://jhmtr.semnan.ac.ir/article_3951_0.html
A numerical solution is presented for unsteady coupled heat and mass transfer by natural convection from a vertical plate embedded in a uniform porous medium in the presence of thermal radiation and chemical reaction effects. The governing equations for this problem were developed and non-dimensionalized and the resulting equations were then solved numerically by an explicit finite-difference scheme. The Roseland approximation is used to describe the radiative heat flux in the energy equation. The solutions at each time step have been found to reach the steady state solution properly. The numerical results are presented in the graphical form to show the effects of material parameters including the thermal buoyancy, the solutal buoyancy, Reynolds number, the inverse thermal radiation parameter, the permeability parameter, Prandtl number, Schmidt number and the chemical reaction parameter on the skin-friction coefficient, the Nusselt number, the Sherwood number, the velocity profiles, the temperature profiles and the concentration profiles in the boundary layer.Mon, 22 Jul 2019 19:30:00 +0100Analytical Solutions for Spatially Variable Transport-Dispersion of Non-Conservative Pollutants
https://jhmtr.semnan.ac.ir/article_3952_453.html
Analytical solutions have been obtained for both conservative and non-conservative forms of one-dimensional transport and transport-dispersion equations applicable for pollution as a result of a non-conservative pollutant-disposal in an open channel with linear spatially varying transport velocity and nonlinear spatially varying dispersion coefficient on account of a steady unpolluted lateral inflow in accordance to the channel. A logarithmic transformation in the space variable has been applied in order to derive a general solution of the transport equation for spatially variable initial pollutant distribution and upstream time-dependent pollutant concentration. The logarithmic transformation reduces both conservative and non-conservative forms of transport-dispersion equation to a form with constant coefficients that is solvable by analytical methods. An analysis of these solutions indicates that only the solution of a conservative form of the governing equation yields appropriate results that are conceptually acceptable in a real physical situation. The solution lends to analyze the damping effect of such transport on the pollutant with an initial Gaussian profile, in contrast with that of the initial quasi-Gaussian profile available in the literature. It is noteworthy to mention that the solution of conservative form of the transport equation implies that mass of the non-conservative pollutant in the channel decreases with an increase in time, and finally reaches to a constant value that is a ratio of product of the transport velocity coefficient and upstream concentration to the coefficient of decay of the pollutant.Mon, 30 Sep 2019 20:30:00 +0100Heat Transfer Studies of Supercritical Water Flows in an Upward Vertical Tube
https://jhmtr.semnan.ac.ir/article_3985_0.html
A study of heat transfer characteristics at supercritical pressure fluid flowing in a uniformly heated vertical tube has been carried out. In order to reduce the thermal emissions and to increase the thermal efficiency, supercritical boilers were developed at various sizes. Above supercritical pressure, the distinction of liquid and gas phases disappears. This eliminates the problem of critical heat flux and dry out phenomenon which occurs in subcritical pressure. However, the study of heat transfer behavior above supercritical pressure is indeed necessary since heat transfer deterioration occurs at high heat flux to mass flux ratio. In the present work, numerical simulation has been carried out to study the effect of various parameters such as heat flux to mass flux ratio, diameter and pressure that causes heat transfer deterioration. Shear Stress Transport k-ω model has been used for all the computations. It is observed that the metal temperature predicted by numerical simulation is more accurate than the empirical correlations available in the literature. A Visual Basic Program has also been developed to assess the empirical correlations in the context of predicting metal temperature under 5280 different operating conditions. Tube sizes of 10, 15 & 20 mm inner diameter with 4 m length, pressure between 225 and 280 bar and heat flux to mass flux ratio between 0.27 and 0.67 has been chosen to study the effect of diameter, pressure and heat flux respectively.Mon, 23 Sep 2019 20:30:00 +0100Heat transfer correlation for two-phase flow in a mixing tank
https://jhmtr.semnan.ac.ir/article_4228_0.html
Mixing tanks equipped with mechanical stirrer are widely used in chemical and petrochemical industries because of variety of industrial process requirements. In this study, helical single blade mixer was designed using catia software and then mixing of fluid and solid particles, in a tank with this agitator was studied by OpenFOAM software. For velocity distribution in the mixing tank, continuity, momentum equations, boundary conditions and coding were performed using C++ language scripts in the software. The results of velocity distributions in three directions coordinates were showed that the efficiency of helical blade mainly was related to axial and tangential flows. The radial flow has less important role in mixing operation. Also, solid particles concentration distribution were calculated in the fluid phase and it was shown that the particles were distributed homogeneously in the tank. In addition, temperature distribution was obtained using continuity, momentum and energy equations as well as utilizing necessary code and boundary conditions in the software. Then, a correlation for Nusselt number as a function of Re, Pr and Vi was obtained by using temperature profile and dimensional analysis. The results achieved are in good agreement with literature.Fri, 31 Jan 2020 20:30:00 +0100The effect of SiO2 nanoparticle on the performance of photovoltaic thermal system: Experimental ...
https://jhmtr.semnan.ac.ir/article_4229_0.html
The low conversion efficiency of solar cells produces large amounts of thermal energy to the cells, and with an increase in the temperature of solar cells, their electrical efficiency decreases. Therefore, a hybrid photovoltaic thermal system improves the overall efficiency of the system by adding thermal equipment to the solar cell and removing excessive heat from these cells. In this paper, we study the effect of SiO2/water nanofluids on thermal and electrical efficiency of domestic photovoltaic thermal systems (DPVT) theoretically and experimentally. In the theoretical part, based on the control-volume finite-difference approach, an explicit dynamic model was developed for a single-glazed flat-plate water-heating photovoltaic thermal collector with closed loop cooling system with withdrawing urban water from the storage tank. The model accuracy was verified in comparison with the measured experimental data. Experimental results show that by increasing concentrations of nanofluid, the thermal and electrical performance has improved and overall efficiency decreased by increasing the diameter of the nanoparticles. The overall efficiency of the DPVT for 0 and 3 weight percent of SiO2/ water nanofluids with a diameter of 11-14 nanometers increased to 5.4% and 7.76% compared to base fluid, respectively.Fri, 31 Jan 2020 20:30:00 +0100Numerical analysis of gas flows in a microchannel using the Cascaded Lattice Boltzmann Method ...
https://jhmtr.semnan.ac.ir/article_4230_0.html
Abstract. In this paper, a Cascaded Lattice Boltzmann Method with second order slip boundary conditions is developed to study gas flows in a microchannel in the slip and transition flow regimes with a wide range of Knudsen numbers. For the first time the effect of wall confinement is considered on the effective mean free path of the gas molecules using a function with nonconstant Bosanquet parameter instead of the constant one. The constant-force driven and pressure-driven gas flows in a long microchannel are simulated under different conditions. The results of the velocity profile, pressure distribution, and mass flow rate are in good agreement with the benchmark solutions and experimental data reported in the literature. The Knudsen minimum phenomenon is also well captured by the present model. The proposed Cascaded Lattice Boltzmann Method shows a clear improvement in predicting the flow behaviors of microchannel gas flows for the previous classic and Cascaded Lattice Boltzmann MethodFri, 31 Jan 2020 20:30:00 +0100EFFECT OF VISCOUS DISSIPATION ON STEADY NATURAL CONVECTION HEAT AND MASS TRANSFER FLOW THROUGH ...
https://jhmtr.semnan.ac.ir/article_4260_0.html
In this study, effects of viscous dissipation and variable physical properties on steady natural convection heat and mass transfer flow through a vertical channel were investigated. The variability in viscosity and thermal conductivity are considered linear function of temperature. The governing equations are transformed into a set of coupled nonlinear ordinary differential equations and solved using Differential Transformation Method (DTM). Results obtained were compared with exact solution when some of the flow conditions were relaxed and results from DTM show an excellent agreement with the exact solution which was obtained analytically. The influence of the flow parameters on fluid temperature, concentration and velocity are presented graphically and discussed for variations of the governing parameters. From the course of investigation, it was found that increasing viscous dissipation causes fluid temperature, velocity as well as the skin friction on the surface of both channels to increase. However, increasing the fluid viscosity retards the fluid motion and causes fluid temperature to decrease.Sun, 23 Feb 2020 20:30:00 +0100Heat transfer enhancement in a spiral plate heat exchanger model using continuous rods
https://jhmtr.semnan.ac.ir/article_4261_0.html
This study presents an innovative and simple way to increase the rate of heat transfer in a spiral plate heat exchanger model. Several circular cross-section rods, as continuous vortex generators, have been inserted within the spiral plate heat exchanger in the cross-stream plane. The vortex generators are located at various azimuth angles of α=30◦, 60◦, 90◦, and 120◦ with non-dimensional diameters of d/H=0.3, 0.4, and 0.5. Computations have been carried out numerically by means of the finite volume approach under different Dean numbers (De) ranging from 500 to 1500 in the laminar regime. The flow physics within the advanced spiral heat exchanger model has been discussed using several velocity and temperature contours. It was found that by inserting the continuous vortex generators in the cross-stream plane of a spiral plate heat exchanger, the unsteady flow develops within the channel in which the rate of unsteadiness is proportional to d/H and De directly and to azimuth angle inversely. The maximum heat transfer enhancement with respect to the conventional spiral plate heat exchanger (without continuous vortex generators) is found to be 341% for α=30◦, d/H=0.5, and De=1500. Additionally, values of pressure drop penalty and thermal-hydraulic performance have been determined accordingly.Sun, 23 Feb 2020 20:30:00 +0100