Journal of Heat and Mass Transfer Research(JHMTR)Journal of Heat and Mass Transfer Research(JHMTR)
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(JHMTR). Click to visit.Instabilities of Thin Viscous Liquid Film Flowing down a Uniformly Heated Inclined Plane
http://jhmtr.journals.semnan.ac.ir/article_345_78.html
Instabilities of a thin viscous film flowing down a uniformly heated plane are investigated in this study. The heating generates a surface tension gradient that induces thermocapillary stresses on the free surface. Thus, the film is not only influenced by gravity and mean surface tension but also the thermocapillary force is acting on the free surface. Moreover, the heat transfer at the free surface plays a crucial role in the evolution of the film. The main objective of this study is to scrutinize the impact of Biot number Bi which describes heat transfer at the free surface on instability mechanism. Using the long wave expansion method, a generalized non-linear evolution equation of Benney type, including the above mentioned effects, is derived for the development of the free surface. A normal mode approach and the method of multiple scales are used to obtain the linear and weakly nonlinear stability solution for the film flow. The linear stability analysis of the evolution equation shows that the Biot number plays a double role; for Bi < 1 it gives destabilizing effect but for Bi > 1 it produces stabilization. At Bi = 1, the instability is maximum. The weakly nonlinear study reveals that the impact of Marangoni number Mr is very strong on the bifurcation scenario even for its slight variation. This behaviour of the Biot number is the consequence of the fact that the interfacialtemperature is held close to the plane temperature for Bi > 1, thus weakening the Marangoni eﬀect. The weakly nonlinearstudy reveals that the impact of Marangoni number Mr is very strong on the bifurcation scenario even for its slight variation.Fri, 30 Sep 2016 20:30:00 +0100Numerical Study of Entropy Generation for Natural Convection in Cylindrical Cavities
http://jhmtr.journals.semnan.ac.ir/article_347_78.html
In this paper, an enhanced computational code was developed using finite-volume method for solving the incompressible natural convection flow within the cylindrical cavities. Grids were generated by an easy method with a view to computer program providing. An explicit integration algorithm was applied to find the steady state condition. Also instead of the conventional algorithms of SIMPLE, SIMPLEM and SIMPLEC, an artificial compressibility technique is applied for coupling the continuity to the momentum equations. The entropy generation, which is a representation of the irreversibility and efficiency loss in engineering heat transfer processes, has been analyzed in detail. The discretization of the diffusion terms were very simplified using the enhanced scheme similar to the flux averaging in the convective term. Additionally an analysis of the entropy generation in a cylindrical enclosure was performed. In order to show the validation of this study, the code was reproduced to solve similar problem of cited paper. Finally, the solutions were extended for the new cases.Fri, 30 Sep 2016 20:30:00 +0100Flow field and heat transfer in a channel with a permeable wall filled with Al2O3-Cu/water ...
http://jhmtr.journals.semnan.ac.ir/article_447_78.html
In this study, flow field and heat transfer of Al2O3-Cu/water micropolar hybrid nanofluid is investigated in a permeable channel using the least square method. The channel is encountered to chemical reaction, and a constant magnetic field is also applied. The bottom wall is hot and coolant fluid is injected into the channel from the top wall. The effects of different parameters such as the Reynolds number, the Hartmann number, microrotation factor and nanoparticles concentration on flow field and heat transfer are examined. The results show that with increasing the Hartmann number and the Reynolds number, the Nusselt and Sherwood numbers increase. Furthermore, when the hybrid nanofluid is applied rather than pure nanofluid, the heat transfer coefficient will increase significantly. It is also observed that in the case of generative chemical reaction, the fluid concentration is more than the case of destructive chemical reaction. Moreover, the Nusselt number and Sherwood number when the micropolar model is used, is less than when it is not considered.Fri, 30 Sep 2016 20:30:00 +0100A Comparative Solution of Natural Convection in an Open Cavity using Different Boundary ...
http://jhmtr.journals.semnan.ac.ir/article_363_78.html
A Lattice Boltzmann method is applied to demonstrate the comparison results of simulating natural convection in an open end cavity using different hydrodynamic and thermal boundary conditions. The Prandtl number in the present simulation is 0.71, Rayleigh numbers are 104,105 and 106 and viscosities are selected 0.02 and 0.05. On-Grid bounce-back method with first-order accuracy and non-slip method with second-order accuracy are employed for implementation of hydrodynamic boundary conditions. Moreover, two different thermal boundary conditions (with first and second order of accuracy) are also presented for thermal modelling. The results showed that first and second order boundary conditions (thermal/hydrodynamic) are the same for a two-dimensional, single phase, convective heat transfer problem including geometry with straight walls. The obtained results for different hydrodynamic and thermal boundary conditions are useful for the researchers in the field of lattice Boltzmann method in order to implement accurate condition on the boundaries, in different physics.Fri, 30 Sep 2016 20:30:00 +0100Development of a phase change model for volume-of-fluid method in OpenFOAM
http://jhmtr.journals.semnan.ac.ir/article_467_78.html
In this present study, volume of fluid method in OpenFOAM open source CFD package will be extended to consider phase change phenomena with modified model due to condensation and boiling processes. This model is suitable for the case in which both unsaturated phase and saturated phase are present and for beginning boiling and condensation process needn't initial interface. Both phases (liquid-vapor) are incompressible and immiscible. Interface between two phases is tracked with color function volume of fluid (CF-VOF) method. Surface Tension is taken into consideration by Continuous Surface Force (CSF) model. Pressure-Velocity coupling will be solved with PISO algorithm in the collocated grid. The accuracy of this phase-change model is verified by two evaporation problems (a one-dimensional Stefan problem and a two-dimensional film boiling problem) and two condensation problem (a one-dimensional Stefan problem and Filmwise condensation). The simulation results of this model show good agreement with the classical analytical or numerical results, proving its accuracy and feasibility.Fri, 30 Sep 2016 20:30:00 +0100A study of a Stefan problem governed with space–time fractional derivatives
http://jhmtr.journals.semnan.ac.ir/article_384_78.html
This paper presents a fractional mathematical model of a one-dimensional phase-change problem (Stefan problem) with a variable latent-heat (a power function of position). This model includes space–time fractional derivatives in the Caputo sense and time-dependent surface-heat flux. An approximate solution of this model is obtained by using the optimal homotopy asymptotic method to find the solutions of temperature distribution in the domain 0 ≤x≤s(t) and interface’s tracking or location. The results thus obtained are compared with existing exact solutions for the case of the integer order derivative at some particular values of the governing parameters. The dependency of movement of the interface on certain parameters is also studied.Fri, 30 Sep 2016 20:30:00 +0100Analytical and Numerical Studies on Hydromagnetic Flow of Boungiorno Model Nanofluid over a ...
http://jhmtr.journals.semnan.ac.ir/article_362_78.html
MHD boundary layer flow of two phase model nanofluid over a vertical plate is investigated both analytically and numerically. A system of governing nonlinear partial differential equations is converted into a set of nonlinear ordinary differential equations by suitable similarity transformations and then solved analytically using homotopy analysis method and numerically by the fourth order Runge-Kutta method along with shooting iteration technique. The effects of magnetic parameter, Prandtl number, Lewis number, buoyancy-ratio parameter, Brownian motion parameter and thermophoresis parameter on the velocity profile, temperature profile and concentration profile of the nanofluid are discussed graphically. The values of reduced local Nusselt number and reduced local sherwood number are tabulated and discussed. It is noted that the Brownian motion and thermophoresis parameters enhance the velocity distribution and the temperature distribution, but it suppress the concentration distribution. Furthermore, comparisons have been made with bench mark solutions for a special case and obtained a very good agreement..Fri, 30 Sep 2016 20:30:00 +0100Spectral 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 +0100Numerical investigation of combined convection flow in a cavity subjected to a nanofluid with ...
http://jhmtr.journals.semnan.ac.ir/article_428_0.html
The present paper focuses on problem of mixed convection fluid flow and heat transfer of Al2O3-water nanofluid with temperature and nanoparticles concentration dependent thermal conductivity and effective viscosity inside Lid-driven cavity having a hot rectangular obstacle. The governing equations are discretized using the finite volume method while the SIMPLER algorithm is employed to couple velocity and pressure fields. Using the developed code, the effects of cavity inclination angle, diameter and solid volume fraction of the Al2O3 nanoparticles on the flow and thermal fields and heat transfer inside the cavity are studied. The obtained results show that the average Nusselt number for all range of solid volume fraction decreases with increase in diameter of nanoparticles. Also the results have clearly indicated that With increasing slope of the cavity to 90 degree, heat transfer continuously decreases at all studied Richardson numbersSun, 19 Jun 2016 19:30:00 +0100New Achievements in Fe3O4 Nanofluid Fully Developed Forced Convection Heat Transfer under the ...
http://jhmtr.journals.semnan.ac.ir/article_486_0.html
Fe3O4 nanofluid fully developed forced convection inside a copper tube is empirically investigated under the effect of a magnetic field. All of the investigations are performed under laminar flow regime (670≤Re≤1700) and thermal boundary conditions of the tube with uniform thermal flux. The tube is under the effect of a magnetic field in certain points. This research aims to study the effect of various parameters, namely use of nanofluid, nanoparticles volume percent, Reynolds number of the flow, constant magnetic field, and alternating magnetic field with various frequencies on flow behavior. To validate the experiment set-up, distilled water is utilized as working fluid. The results are compared with Shah’s equation and acceptable agreements are achieved. The results suggest that owing to complex convectional flows developed in the fluid as a result of Fe3O4 nanoparticles-magnetic field interaction, increased alternating frequency of the magnetic field and increased volume fraction lead to increase heat transfer to maximum value 4.62. As Reynolds number increases, the rate of the said increase is reduced and reached to 0.29. At a constant Reynolds number, increased frequency of the alternating magnetic field results in an increased local heat transfer coefficient. However, this increase is unproportional to increase in frequency. In high frequencies, increased frequency leads to a slight increase in the heat transfer coefficient.Tue, 01 Nov 2016 20:30:00 +0100Numerical simulation of transient natural gas flow in pipelines using high order DG-ADER scheme
http://jhmtr.journals.semnan.ac.ir/article_497_0.html
To increase the numerical accuracy in solving engineering problems, either conventional methods on a fine grid or methods with a high order of accuracy on a coarse grid can be used. In the present research, the second approach is utilized and the arbitrary high order Discontinues Galerkin Arbitrary DERivative (DG-ADER) method is applied to analyze the transient isothermal flow of natural gas through pipelines. The problem is investigated one dimensionally and the effect of friction force between the pipe wall and fluid flow is considered as a source term on the right-hand side of the momentum equation. Therefore, the governing equations have a hyperbolic nature. Two real problems with available field data are simulated using this method. The results show that using DG-ADER method, high accurate results can be obtained even on a coarse grid. Furthermore, the conventional small-amplitude oscillations of DG-ADER scheme do not appear in the transient natural gas flow problems, due to the smoothness of flow field properties.Thu, 24 Nov 2016 20:30:00 +0100Experimental study of free convective heat transfer in a direction-sensitive open cavity
http://jhmtr.journals.semnan.ac.ir/article_506_0.html
The aim of the present study was to propose a panel being sensitive to the direction of heat transfer. For this purpose, a vertical rectangular cavity with prescribed dimensions was prepared and filled with water as the working fluid. A vertical mid-plane solid partition was installed within the cavity. Two relatively wide openings were created at the top and bottom of the partition and they were so equipped to operate as a pair of one-way flow controllers. The cavity was then fixed between two thick aluminum blocks by which, the contact surfaces of the cavity were maintained at almost constant but different temperatures. Heat transfer rate through the cavity was evaluated for the same temperature difference applied in the two opposed directions. Based on the results, heat transfer rate in one direction was about 30% higher than that of the reverse direction. The difference in the heat transfer rate was obviously due to the individual flow patterns developed within the modified cavity. As a result, the proposed cavity is capable of restricting heat transfer rate in one direction compared to the other, when applying the same temperature difference across the cavity.Thu, 22 Dec 2016 20:30:00 +0100Temperature proﬁle of a power-law ﬂuid over a moving wall with arbitrary injection/suction ...
http://jhmtr.journals.semnan.ac.ir/article_519_0.html
The heat transfer for a non-Newtonian power-law fluid over a moving surface is investigated by applying a uniform suction/injection velocity proﬁle. The ﬂow is inﬂuenced by internal heat generation/absorption. The energy equation is solved at constant surface temperature condition. The Merk-Chao series is applied to obtain a set of ODEs instead of a complicated PDE. The converted ordinary differential equations are solved numerically, adopting the fourth order Runge–Kutta method coupled with the shooting technique. The effects of the fluid type, suction/injection and heat source/sink parameters on heat-transfer are discussed. It is observed that thermal boundary layers for pseudo plastic fluids are thicker than that of the dilatants. There exists a direct relation between dimensionless temperature and the injection parameter or the heat generation parameter rise. Injection of a ﬂuid to the surface generates more flow penetration into the fluid, which causes an increase in the thermal boundary layer and the temperature.Fri, 13 Jan 2017 20:30:00 +0100Characterization of Unsteady Thermo-Solutal Mixed Convection Flow with Soret and Dufour Effects ...
http://jhmtr.journals.semnan.ac.ir/article_2261_0.html
The present study considers the numerical examination of an unsteady thermo-solutal mixed convection in the presence of extra mass and heat diffusions, Soret and Dufour effects. The study is carried out in a lid-driven square enclosure where the vertical walls are heated and concentrated uniformly and the horizontal walls are well insulated. The governing equations are solved numerically on a staggered grid using a finite volume method based on SIMPLE algorithm. Numerical solutions are produced for representative combinations of Soret and Duofour coefficients and are given by streamlines, isotherms, isoconcentrations, fluid velocities, average Nusselt and Sherwood numbers. The influences of pertinent parameters on the various heat transfer modes, i.e. convective and conductive modes, as well as the total kinematic energy of the studied thermo-solutal system are also analyzed. Results show that Soret and Dufour effects insignificantly influence the fluid flow and transport phenomena when flow is dominated by the forced convection. It is also achieved that the extra heat diffusion, Dufour effect, affects heat transfer by creating thermal eddies especially when flow is dominated by the natural convection. Besides, the conductive mode of heat transfer is attenuated by Dufour coefficient.Tue, 31 Jan 2017 20:30:00 +0100Analysis of Gasketed-plate Heat Exchanger Performance Using Nanofluid
http://jhmtr.journals.semnan.ac.ir/article_2331_0.html
A heat exchanger using nanofluid needs to operate at optimum mass concentration level to get the maximum heat transfer performance. A numerical analysis is performed on the heat transfer and pressure drop of water-based γ-Al2O3 nanofluid gasketed-plate heat exchanger to specify its optimum conditions. Cold water will be heated by γ-Al2O3/water nanofluid. The results showed that optimal volume concentration of γ-Al2O3/water nanofluid based on a maximum performance index is about 0.016. The heat transfer rate at the optimal concentration of nanofluid is approximately 12.3% higher than that of pure water (base fluid), while pumping power is increased by 1.15%. With regard to 1% enhancement in heat transfer rate with increasing ϕ values from ϕ=0.016 to ϕ=0.028 (optimum volume concentration for maximum heat transfer rate) and the pumping power required for nanofluid, the optimum concentration for maximum performance index is selected as the best level of particle volume fraction for γ-Al2O3/water nanofluid in this research.Sat, 04 Mar 2017 20:30:00 +0100Heat Transfer under Double Turbulent Pulsating Jets Impinging on a Flat Surface
http://jhmtr.journals.semnan.ac.ir/article_2352_0.html
In this study, the numerical analysis of turbulent flow and heat transfer of double pulsating impinging jets on a flat surface has been investigated. The unsteady two-dimensional numerical solution for two similar and dissimilar jets was performed using the RNG k-ε model. The results showed that the RNG k-ε model has more satisfactory predictions of the Nusselt number distribution. Comparisons show that for two identical jets with constant frequency and amplitude, increasing Reynolds number leads to the considerable increase of time-averaged Nusselt number. Also, with increasing oscillation amplitude, the averaged Nusselt number of surface increased. The results show that increasing the phase difference angle of pulsating jets leads to the increase of mixing between jets, which consequences the increase of Nusselt number in this zone. It should be mentioned that for two jets by equal frequency and phase angle, increasing oscillating amplitude of one jet leads to an asymmetric distribution of the Nusselt number. In this case, the averaged Nusselt number between two jets increased. Furthermore, the array of double jets with different oscillating type (intermittent and sinusoidal) leads to the increase of averaged Nusselt number considerably in the stagnation region between the jets.Sat, 08 Apr 2017 19:30:00 +0100Heat Transfer Analysis in Pyrolysis of Different Shapes Biomass Particles Subjected to ...
http://jhmtr.journals.semnan.ac.ir/article_2357_0.html
The conversion and utilization of biomass as an alternative source of energy has been a subject of interest in various countries. However, the technical barriers in the technology and in the design of the conversion plant have been one of the major challenges impeding the development and the utilization of the alternative energy. In the conversion process, Pyrolysis plays an integral role. The theoretical studies of this process enhance better understanding of the thermochemical conversion of the solid fuels. In order to carry out such studies, the development of thermal and kinetic models of the pyrolysis process is required and such are needed to be solved analytically in order to gain better insight of the actual process. Therefore, in this study, Laplace transform and Hankel transform are used to present analytical solutions to the heat transfer models of rectangular, cylindrical and spherical particle shapes. Also, the pyrolysis kinetic models were solved analytical using Laplace transform. The study is used to investigate the effects of particle shape, particle size, isothermal and non-isothermal heating conditions, convective and radiative heat transfer (through the use of a modified Biot number) on the pyrolysis of a biomass particle. This work is of great importance in the design of some pyrolysis reactors/units and in the optimal design of the biomass gasifiers.Sat, 15 Apr 2017 19:30:00 +0100Thermo-Economic Analysis of Applying Cooling System Using Fog on GE-F5 Gas Turbines (Case Study)
http://jhmtr.journals.semnan.ac.ir/article_2455_0.html
Presently, nearly 26,000 MW gas power plant and nearly 16,000 MW of combined cycle has been installed in the country. But their power output in summer reduces to a minimum, where most demand is required, compared to the winter season. The main reason for that is gas turbine dependence on the ambient air temperature. Since most of our country has warm and dry climates, cooling down the input air to the compressor by means of water evaporation is the simplest method.In this paper, attempts have been made to investigate the thermos-dynamical and economical behavior of fog system on four units of GE-F5 applied in Shahid Zanbagh power plant. The results show that application of this method, causes increase in mass flow rate of the air input and reduces consuming work of compressor, where power production increases by 2.64 MW and the required water for each unit is equal to 0.761 kg/s, also the payback time for this system was calculated to be less than 3 years.Thu, 18 May 2017 19:30:00 +0100Effect of baffle oientation on shell tube heat exchanger performance
http://jhmtr.journals.semnan.ac.ir/article_2526_0.html
In this paper, fluid flow and heat transfer in the laboratory (small size) shell tube heat exchanger are analysed by computational fluid dynamic software. In this type of shell tube heat exchanger baffles with different angles of rotation: 00 (horizontal segmental baffle), 150 (from horizontal), 300, 450, 600, 750, 900 (vertical segmental baffle) is used. Effect of baffle orientation on shell tube heat exchanger performance is investigated. The flow domain is meshed by three-dimensional tetrahedral elements. The obtained result has a good agreement with the analytical method (Bell method) and experimental data in the literature. By comparing the pressure drop, heat transfer and heat transfer versus pressure drop (Q/ P) at same flow rate, the shell tube heat exchanger with orientation of (900) have better performance than other angles of baffle orientation. decrease pressure drop 26%, 4.1%, 17.6%, 24.42%, 14% rather than 150, 300, 450 ,600,750 ,00 angle of orientation respectively. That show have better performance than other angles of baffle orientation. So by reducing pressure drop with maintaining heat transfer rate, the operating cost reducing that can be best choice among other models.Tue, 13 Jun 2017 19:30:00 +0100Unsteady Boundary Layer Flow of a Casson Fluid Past a Wedge With Wall Slip Velocity
http://jhmtr.journals.semnan.ac.ir/article_2527_0.html
In this paper an analysis is presented to understand the effect of non–Newtonian rheology, velocity slip at the boundary, thermal radiation, heat absorption/generation and first order chemical reaction on unsteady MHD mixed convective heat and mass transfer of Casson fluid past a wedge in the presence of a transverse magnetic field with variable electrical conductivity. The partial differential equations governing the flow with the pertinent boundary conditions are solved numerically. The computational results are presented graphically for different values of the non-dimensional parameters occurred in the analysis. The results for particular cases are compared with the published results available in literature and are found to be in excellent agreement. Present analysis indicates that the Casson parameter representing the non-Newtonian rheology has an increasing influence on velocity and temperature. The point of flow separation is found for negative values of wedge angle parameter. The radiation parameter enhances the rate of heat transfer. The mass transfer rate is reduced with chemical reaction parameter and Schmidt’s number.Fri, 16 Jun 2017 19:30:00 +0100