Journal of Heat and Mass Transfer Research(JHMTR)Journal of Heat and Mass Transfer Research(JHMTR)
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Feed provided by Journal of Heat and Mass Transfer Research(JHMTR). Click to visit.New Achievements in Fe3O4 Nanofluid Fully Developed Forced Convection Heat Transfer under the ...
http://jhmtr.journals.semnan.ac.ir/article_486_364.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.Fri, 31 Mar 2017 19:30:00 +0100Experimental study of free convective heat transfer in a direction-sensitive open cavity
http://jhmtr.journals.semnan.ac.ir/article_506_364.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.Fri, 31 Mar 2017 19:30:00 +0100Analysis of heat transfer in the pyrolysis of differently shaped biomass particles subjected to ...
http://jhmtr.journals.semnan.ac.ir/article_2357_364.html
The conversion and utilization of biomass as an alternative source of energy have been subjects of interest in various countries, but technical barriers to the technology and design of conversion plants have considerably impeded the development and use of alternative power sources. Theoretical studies on the conversion process enhance our understanding of the thermochemical conversion of solid fuels. Carrying out such research necessitates the development of thermal and kinetic models of pyrolysis, on which the conversion process integrally depends. Another requirement is to analytically solve the aforementioned models to derive valuable insight into the actual process of biomass conversion. Accordingly, this study used Laplace and Hankel transforms to obtain analytical solutions to heat transfer models of rectangular, cylindrical, and spherical biomass particles. Pyrolysis kinetic models were also analytically solved using the Laplace transform. The study then investigated the effects of particle shape, particle size, isothermal and non-isothermal heating conditions, and convective and radiative heat transfer (calculated using a modified Biot number) on the pyrolysis of a biomass particle. This work is expected to substantially contribute to the design of pyrolysis reactors/units and the optimal design of biomass gasifiers.Fri, 31 Mar 2017 19:30:00 +0100Numerical simulation of transient natural gas flow in pipelines using high order DG-ADER scheme
http://jhmtr.journals.semnan.ac.ir/article_497_364.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.Fri, 31 Mar 2017 19:30:00 +0100Heat Transfer under Double Turbulent Pulsating Jets Impinging on a Flat Surface
http://jhmtr.journals.semnan.ac.ir/article_2352_364.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.Fri, 31 Mar 2017 19:30:00 +0100Temperature proﬁle of a power-law ﬂuid over a moving wall with arbitrary injection/suction ...
http://jhmtr.journals.semnan.ac.ir/article_519_364.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, 31 Mar 2017 19:30:00 +0100Analysis of Gasketed-plate Heat Exchanger Performance Using Nanofluid
http://jhmtr.journals.semnan.ac.ir/article_2331_364.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.Fri, 31 Mar 2017 19:30:00 +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 +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 +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 +0100A Numerical Investigation of Heat Transfer and Pressure Drop in a Novel Cylindrical Heat Sink ...
http://jhmtr.journals.semnan.ac.ir/article_2580_0.html
Heat transfer and fluid flow characteristics in a novel cylindrical heat sink with helical minchannels for laminar flow with temperature-dependent fluid properties is investigated numerically in this study. A finite volume method (FVM) is employed for solution of governing equations. The effects of helical angle, channel aspect ratio and Reynolds number, considered as main parameters in this study and the overall performance of helical minchannels heat sink were analyzed by the thermal performance factor and augmentation entropy generation number. The obtained results show that decreasing in channel helix angle and increasing in channel aspect ratio and Reynolds number, enhance the average heat transfer coefficient and grow up the pressure drop. By using of thermal performance factor and entropy generation minimization method, it is found that the aspect ratio of 1.2 has best performance in all helix angles and when the helix angle decreases, the performance increases, especially in low aspect ratios.Tue, 11 Jul 2017 19:30:00 +0100Fluid flow and heat transfer characteristics in a curved rectangular duct using Al2O3-water ...
http://jhmtr.journals.semnan.ac.ir/article_2606_0.html
In the present research, the laminar forced convective heat transfer and fluid flow characteristics for Al2O3-water nanofluid flowing in different bend (i.e., 180o and 90o) pipes have been investigated numerically in a three-dimensional computational domain using the finite volume technique. The effects of different pertinent parameters, such as the Reynolds number of the duct, volume fraction of the nanoparticle, the diameter of the nanoparticle, aspect ratio of the duct and the duct bend angle on the hydrodynamic and thermal characteristics of the flow has been presented. It is observed that the heat transfer is augmented by replacing conventional fluid by Al2O3-water nanofluid. The nanoparticle volume fraction is found to be an important parameter to increase the heat transfer in the bend pipe. It is also observed that the thermo-hydraulic characteristics of the flow changes with the duct aspect ratio, and the heat transfer rate is improved with aspect ratio. The heat transfer with a 180o bend pipe is obtained to be higher than a 90o bend pipe at a particular value of volume fraction and Reynolds number. Moreover, the present computed Nusselt number for 180o bend pipe of rectangular cross-section has been validated with the existing literature. validated with the existing literature.Fri, 21 Jul 2017 19:30:00 +0100Heat And Mass Transfer Effects On MHD Natural Convective Flow Past A Vertical Porous Plate ...
http://jhmtr.journals.semnan.ac.ir/article_2633_0.html
The aim of this investigation is to study the effect of hall current on an unsteady natural convective flow of a viscous, incompressible, electrically conducting optically thick radiating fluid past a vertical porous plate in the presence of a uniform transverse magnetic field. The Rosseland diffusion approximation is used to describe the radiative heat flux in the energy equation. Analytical and numerical solutions of the coupled governing partial differential equations for the fluid velocity, fluid temperature and fluid concentration profiles are obtained by perturbation and finite element techniques respectively. The effects of the various dimensionless engineering parameters viz., Grashof number for heat and mass transfer, Magnetic field parameter, Prandtl number, Schmidt number, Thermal radiation parameter and Hall parameter entering into the problem on the primary and secondary velocities, temperature and concentration profiles throughout the boundary layer are investigated through graphs. The expressions of skin-friction, Nusselt number and Sherwood number are derived and represented through tabular form. The results reveal that the flow field and the temperature distribution are greatly influenced by thermal radiation parameter. Furthermore, the limiting cases are obtained and are found to be in good agreement with the previously published results.Sat, 02 Sep 2017 19:30:00 +0100CFD Simulation of Flow Pattern and Performance for A Conventional and A Dual-Cone Gas-Particle ...
http://jhmtr.journals.semnan.ac.ir/article_2649_0.html
One of the main concern of researchers is the separation of suspended particles in a fluid. Therefore, In the current study, the effect of the conical section structure on the flow pattern of the Stairmand cyclone has been investigated numerically by simulating a single-cone and a dual cone cyclone. A turbulent model is used for the incompressible gas-particle flow inside the cyclone while particles movements have been studied via Eulerian-Lagrangian approach. Despite simplicity in the geometry of a cyclone, the inside two-phase flow is very complicated yet anisotropic, so the Reynolds Stress Model has been applied. The numerical results have been compared to those of experimental ones. In order to track the calcium carbonate particles, drag and gravity forces have been considered in the Lagrangian model. According to the results, adding a second cone section at the bottom of the cyclone leads to an increase in tangential velocity and expands the Rankine vortex region. Moreover, an increasing trend has been seen in the descending flow. Increasing in the number of conical section raise the pressure drop for all velocities. In comparison with a typical cyclone, a dual-cone cyclone has a higher efficiency originated in smaller end part which limits the particles motion and increases the collecting performance.Sun, 17 Sep 2017 19:30:00 +0100Numerical study of Non-Fourier conduction with Variable Thermal Conductivity using Lattice ...
http://jhmtr.journals.semnan.ac.ir/article_2697_0.html
Abstract: In the present work, implementation of the lattice Boltzmann method (LBM) is considered for the analysis of non-Fourier heat conduction in 2-D geometry with temperature-dependent thermal conductivity. Evolution of the wave like temperature distributions in the medium is obtained. Also temperature distribution along some parts in the plate, for both having heat generation and having constant thermal conductivity, is obtained and compared with each other. The LBM results are validated against those available in the literature. Results of the LBM are in excellent agreement with those reported in the literature. In addition, the temperature contours at four different times from the first to achieve steady state condition have been analyzed. Results show that, duo to increase thermal conductivity with rising of temperature and so high ability of material for transferring of heat energy, temperature gradient decreases compared with the state that plate has constant thermal conductivity. Keywords: Non-Fourier conduction, lattice Boltzmann method, variable thermal conductivity, constant thermal conductivity, heat generationTue, 03 Oct 2017 20:30:00 +0100Analytical solution of pressure driven gas flow and heat transfer in micro-Couette using the ...
http://jhmtr.journals.semnan.ac.ir/article_2702_0.html
In the current work, an incompressible thermal flow in a micro-Couette in the presence of a pressure gradient is investigated utilizing the analytical solution of the Burnett equations with first-order and second-order slip boundary conditions, for the first time. The lower plate of this micro-Couette is stationary while the upper plate moves with a constant velocity. Both non-dimensional axial velocity and temperature profiles were obtained using two types of the slip boundary conditions and compared in transition flow regime (0.1≤ Kn ≤10). The results show that the effect of the rarefaction is considerable on both velocity and temperature profiles in this regime. Because of the presence of pressure gradient in direction of the flow, both the non-dimensional velocity and temperature profiles are obtained parabolically and become flatter as the Knudsen number increases. Besides, both Poiseuille number and Nusselt number were obtained using analytical solution. The obtained results show that the Poiseuille number and Nusselt number decrease with increasing the Knudsen number. It should be noted that at the absence of an axial pressure gradient, velocity profile is obtained linearly and show a good agreement with the other works in literature.Wed, 11 Oct 2017 20:30:00 +0100Effect of Magnetic Reynolds Number Variation on Magnetic Field Distribution of Electrically ...
http://jhmtr.journals.semnan.ac.ir/article_2703_0.html
In this study the effect of magnetic Reynolds number variation on magnetic distribution of natural convection heat transfer in an enclosure is numerically investigated. The geometry is a two dimensional enclosure which the left wall is hot, the right wall is cold and the top and bottom walls are adiabatic. Fluid is molten sodium with Pr=0.01 and natural convection heat transfer for Rayleigh number, Ra=105 , and magnetic Reynolds numbers 10-1, 10-3 and 10-5 are considered and the governing equations including continuum, momentum, energy and magnetic induction are solved together concurrent. The numerical method finite volume and simpler algorithm for coupling the velocity and pressure is used. The results show for high magnetic Reynolds number the non-dimensional magnetic field in X and Y directions approximately are constant because diffusion of magnetic Reynolds number is more than advection but as magnetic Reynolds number increases the magnetic field in enclosure is not equal to applied magnetic field and is not constant and deviation from one is increased so that for Rem=10-1 the non-dimensional magnetic field in X direction from 0.09 to 6.6 and in Y direction from -1.164 to 4.05 changes.Wed, 11 Oct 2017 20:30:00 +0100Energy and Exergy Analysis of a Diesel Engine Running with Biodiesel Fuel
http://jhmtr.journals.semnan.ac.ir/article_2705_0.html
Availability analysis is performed as an effective way to study of energy conversion for systems to identify the inefficiency. In this paper, a Single-zone model has been used in order to study the energy performance parameters and heat release rates. The governing equation of availability analysis is applied in this model; in addition, the possibility of using biodiesel that obtained from sunflower oil in diesel engine is investigated by mathematical simulation. Moreover, the different exergy parts of pure diesel fuel and pure biodiesel are compared in any crank angle. Results indicate that, by running considered diesel engine with biodiesel fuel, energy and exergy efficiencies would decrease about 2.72 and 2.61 percent respectively. As a result, work exergy and heat transfer exergy decreases and exhaust gases exergy and irreversibility increases. Consequently, when biodiesel is replaced by diesel fuel, CO amount is decreased and CO2 and NOx formation would be increased because of its molecular structure has more percentage of oxygen.Fri, 20 Oct 2017 20:30:00 +0100Two Dimensional Simulation of Mass Transfer and Nano-Particle Deposition of Cigarette Smoke in ...
http://jhmtr.journals.semnan.ac.ir/article_2710_0.html
Studies indicate that being exposed to cigarette smoke increases the chance of developing lung cancer. Understanding the deposition of carcinogenic particles present in human airway is necessary to understand the development of specific histologic type cancers. In this paper, the mass transfer and deposition of cigarette smoke inside the human airway are investigated by the finite element method. The mass transfer and depositions of four critical cigarette smoke: 1, 3-butadiene, acrolein, acetaldehyde and carbon monoxide (CO), in a total human airway model from mouth to generation B3 under inhalation conditions have been simulated. In this study, concentration distribution in inhalation is evaluated. The model developed for the vapor deposition with volumetric flow rates of 30 and 80 L/min. To this end, we reconstructed a two-dimension model of human airway from the mouth to generation B3 and used the low-Reynolds-number (LRN) k–ω turbulence equation to simulate the mass transfers and deposition fraction.Sat, 28 Oct 2017 20:30:00 +0100Three-dimensional numerical simulation of temperature and flow fields in a Czochralski growth ...
http://jhmtr.journals.semnan.ac.ir/article_2751_0.html
For a Czochralski growth of Ge crystal, the flow and temperature fields have been studied numerically using the three-dimensional finite volume method (FLUENT package). The configuration applied in a real Czochralski crystal growth lab including a graphite crucible, heat shield, resistance heater, thermal insulation including two gas ducts in the bottom and chamber including two gas outlets. We have considered two cases for calculations, which are configuration containing (a) only gas and (b) melt and gas, related to initial stages of the growth process (seeding process). It has been assumed that the growth system is in steady state, fluids (melt and gas) are incompressible Newtonian fluids and the flow is laminar. It was shown that the thermal field in the growth setup is completely three-dimensional. Especially, the temperature field at the melt free surface has not a uniform radial distribution due to the three-dimensional orientation of Argon flow above it.Tue, 19 Dec 2017 20:30:00 +0100Physico-Acoustic Study on Thermal Conductivity of Silver Nanofluid
http://jhmtr.journals.semnan.ac.ir/article_2883_0.html
Low transmission of heat is one of the major problems for heat exchanger fluids in many industrial and scientific applications. This includes cooling of the engines, high power transformers to heat exchangers in solar hot water panels or in refrigeration systems. In order to meet these problems in thermal industries, nanofluids can have a significant role as excellent heat exchanger materials for thermal applications. Silver nanofluids can be used abundantly for thermal applications due to their low cost and high thermal conductivity. The present paper describes the green synthesis of silver nanoparticles from AgNO3 powder using some plant product like tannic acid. The silver nanoparticles are characterized by XRD, UV-visible spectrophotometer, TEM. The silver nanofluids of different concentrations are prepared using water as base fluid. The ultrasonic velocity is calculated for different concentration at room temperature. Acoustical parameters like compressibility, intermolecular free length and acoustic impedance are calculated using ultrasonic velocity, density and viscosity and the results are discussed in terms of intermolecular interactions between the nanoparticles and base fluid. The variation of ultrasonic velocity and other calculated acoustic parameters are used to analyse in amplification of heat conductivity of silver nanofluids.Thu, 08 Feb 2018 20:30:00 +0100Numerical Study of Spherical Vapor Layer Growth Due to Contact of a Hot Object and Water
http://jhmtr.journals.semnan.ac.ir/article_2884_0.html
Vapor film formation and growth due to contact of a hot body and other liquids arises in some industrial applications including nuclear fuel rods, foundry and production of paper.The possibility of a steam explosion remains in most of these cases which may result in injuries and financial damage. Since this phenomenon is important, this study deals vapor layer forming, growth and its internal pressure are investigated. A mathematical model of a molten spherical droplet immersed in water is developed, and results of the numerical solution are discussed. The effects of changing various characteristics (e.g. hot body size, temperature, and hydrostatic effects, as well as temperature of bulk fluid) are investigated. These parameters impact the vapor layer size, vapor internal pressure, and the saturated temperature at the interface between vapor & liquid phases. Finally, conclusions indicate that internal vapor pressure jump, being up to several times larger than that of the initial condition. These pressure pulses and related vapor layer thickness variations could cause thermal fragmentation of the droplet which in turn results in strong pressure shock build-up due to small pieces of the droplet in contact with the water, which could then escalate to become a propagating large scale vapor explosion. The vapor explosions could be hazardous and endanger the system safety.Thu, 15 Feb 2018 20:30:00 +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 +0100