Journal of Heat and Mass Transfer Research(JHMTR)
Journal of Heat and Mass Transfer Research(JHMTR)
http://jhmtr.journals.semnan.ac.ir/
Tue, 18 Dec 2018 21:02:43 +0100
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Journal of Heat and Mass Transfer Research(JHMTR)
http://jhmtr.journals.semnan.ac.ir/
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Using the Lattice Boltzmann Method for the numerical study of nonfourier conduction with ...
http://jhmtr.journals.semnan.ac.ir/article_2697_408.html
The lattice Boltzmann method (LBM) was used to analyze twodimensional (2D) nonFourier heat conduction with temperaturedependent thermal conductivity. To this end, the evolution of wavelike temperature distributions in a 2D plate was obtained. The temperature distributions along certain parts of the plate, which was subjected to heat generation and constant thermal conductivity conditions, were also derived and compared. The LBM results are in good agreement with those reported in other works. Additionally, the temperature contours at four different times in which steady state conditions can be achieved were analyzed. The results showed that thermal conductivity increased with rising temperature. Given the material’s considerable effectiveness in transferring heat energy under heat generation conditions, the temperature gradient of the plate decreased to a level lower than that observed under constant thermal conductivity.
Keywords: NonFourier conduction, lattice Boltzmann method, variable thermal conductivity, constant thermal conductivity, heat generation
Mon, 30 Apr 2018 19:30:00 +0100

A numerical investigation of heat transfer and pressure drop in a novel cylindrical heat sink ...
http://jhmtr.journals.semnan.ac.ir/article_2580_408.html
This study numerically investigated heat transfer and fluid flow characteristics in a novel cylindrical heat sink with helical minichannels for the laminar flow of fluid with temperaturedependent properties. A finite volume method was employed to obtain the solution of governing equations. The effects of helical angle, channel aspect ratio, and Reynolds number, which were regarded as main parameters, were determined. The overall performance of the heat sink was also analyzed on the basis of the thermal performance factor and the augmentation entropy generation number. Results showed that a decrease in the channel helix angle and an increase in the channel aspect ratio and Reynolds number enhance the average heat transfer coefficient and pressure drop in the heat sink. The thermal performance factor and entropy generation minimization method revealed that an aspect ratio of 1.2 enables the best heat sink performance at all helix angles. When the helix angle decreases, performance increases, especially at low aspect ratios.
Mon, 30 Apr 2018 19:30:00 +0100

Computational fluid dynamics simulation of the flow patterns and performance of conventional ...
http://jhmtr.journals.semnan.ac.ir/article_2649_408.html
One of the main concerns of researchers is the separation of suspended particles in a fluid. Accordingly, the current study numerically investigated the effects of a conical section on the flow pattern of a Stairmand cyclone by simulating singlecone and dualcone cyclones. A turbulence model was used to analyze incompressible gasparticle flow in the cyclone models, and the Eulerian–Lagrangian approach was employed to examine particle movement. Despite the simplicity of cyclone geometry, internal twophase flow in such devices is very complicated and anisotropic. This flow was therefore analyzed using a Reynolds stress model. The numerical results were then compared with those of experimental studies. To track calcium carbonate particles, drag and gravity forces were considered in the Lagrangian model. The findings indicated that adding a second conical section at the bottom of the cyclones increases tangential velocity and expands the Rankine vortex region. Moreover, an increasing trend of descending flow occurs. Increasing the number of conical sections elevates pressure drop at all velocities. Finally, the dualcone cyclone has higher efficiency than the typical cyclone because the smaller end of the former limits particle motion and increases collection performance.
Mon, 30 Apr 2018 19:30:00 +0100

Numerical study of a combined convection flow in a cavity filled with nanofluid considering ...
http://jhmtr.journals.semnan.ac.ir/article_428_408.html
The present paper focuses on problem of mixed convection fluid flow and heat transfer of Al2O3water nanofluid with temperature and nanoparticles concentration dependent thermal conductivity and effective viscosity inside Liddriven 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 results show that at all solid volume fraction the average Nusselt number has inverse relationship with nanoparticles diameter. Also the results have clearly indicated that with increasing slope of the cavity to 90 degree, heat transfer continuously decreases at all studied Richardson numbers© 2017 Published by Semnan University Press. All rights reserved.
Mon, 30 Apr 2018 19:30:00 +0100

Characterization of unsteady doublediffusive mixed convection flow with soret and dufour ...
http://jhmtr.journals.semnan.ac.ir/article_2261_408.html
The present study considers the numerical examination of an unsteady thermosolutal mixed convection when the extra mass and heat diffusions, called as Soret and Dufour effects, were not neglected. The numerical simulations were performed in a liddriven cavity, where the horizontal walls were kept in constant temperatures and concentrations. The vertical walls were well insulated. A finite volume method based on SIMPLE algorithm was utilized to solve the coupled governing equations. Numerical simulations are performed for wide 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 thermosolutal system are also analyzed.
Results demonstrate that Soret and Dufour effects insignificantly influence the fluid flow and transport phenomena when flow is affected to some extent 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.
Mon, 30 Apr 2018 19:30:00 +0100

Threedimensional numerical simulation of temperature and flow fields in a Czochralski growth ...
http://jhmtr.journals.semnan.ac.ir/article_2751_408.html
For a Czochralski growth of Ge crystal, thermal fields have been analysed numerically using the threedimensional finite volume method (FLUENT package). The arrangement used in a real Czochralski crystal growth lab included a graphite crucible, heat shield, heating device, thermal insulation 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 are incompressible Newtonian fluids and the flow is laminar. It was shown that the thermal field in the growth setup is completely threedimensional. Especially, the temperature field at the melt free surface has not a uniform radial distribution due to the threedimensional orientation of Argon flow above it.
Mon, 30 Apr 2018 19:30:00 +0100

Twodimensional Simulation of Mass Transfer and NanoParticle Deposition of Cigarette Smoke in ...
http://jhmtr.journals.semnan.ac.ir/article_2710_408.html
The chance of developing lung cancer is increased through being exposed to cigarette smoke illustrated by studies. It is vital to understand the development of particular histologictype cancers regarding the deposition of carcinogenic particles, which are present in human airway. In this paper, the mass transfer and deposition of cigarette smoke, inside the human airway, are investigated applying the finite element method. The mass transfer and depositions of four types of critical cigarette smoke, namely 1, 3butadiene, acrolein, acetaldehyde and carbon monoxide (CO), in a complete humanairway model (from mouth to B3 generation), under inhalation conditions, have been simulated. In this study, concentration distribution in inhalation is evaluated. The vapour deposition was modelled with 30 and 80 L.min1 volumetric flow rates. Therefore, a twodimensional model of human airway from the mouth to generation B3 was reconstructed. Then, for simulating the mass transfers and deposition fraction, the lowReynoldsnumber (LRN) k–ω turbulence equation was used.
Mon, 30 Apr 2018 19:30:00 +0100

Spectral quasilinearization 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 quasilinearization 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 nonnewtonian 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 quasilinearization methods(SQLM) seeks to linearised the original system of PDEs using the NewtonRaphson 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 +0100

Analytical solution of pressure driven gas flow and heat transfer in microCouette using the ...
http://jhmtr.journals.semnan.ac.ir/article_2702_0.html
In the current work, an incompressible thermal flow in a microCouette in the presence of a pressure gradient is investigated utilizing the analytical solution of the Burnett equations with firstorder and secondorder slip boundary conditions, for the first time. The lower plate of this microCouette is stationary while the upper plate moves with a constant velocity. Both nondimensional 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 nondimensional 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 +0100

Energy 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 Singlezone 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 +0100

PhysicoAcoustic 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, UVvisible 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 +0100

Numerical 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 buildup 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 +0100

Performance Investigation of Two Modified TwoStage TransCritical Carbon Dioxide Refrigeration ...
http://jhmtr.journals.semnan.ac.ir/article_2894_0.html
In the present work, the performances of two new twostage multi intercooler 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 intercooler 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 gascooler pressure, evaporator temperature and gascooler temperature on the cycle performance have been analysed. The obtained results show that if the cooling flow for second intercooler 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

Constructul design of treeshaped conductive pathways for cooling a heat generating volume
http://jhmtr.journals.semnan.ac.ir/article_2990_0.html
Constructal design is used to study heat removal from a square heated body with a tree shaped high thermal conductivity pathways which are embedded in the body. The objective is to minimize the defined maximum dimensionless temperature difference for the body. The thermal conductivity of the body is low, and there is a uniform heat generation on it. The volume of the body is fixed. The amount of high conductivity material for building the pathways are also fixed, but their length and diameter are variable. The effect of parameters such as the angle among the pathways, number of pathways, thermal conductivity coefficient, dimensionless area fraction and different length ratios are investigated. The results show that by optimizing the angle among the pathways, the operation of them improves up to %12. By increasing the number of blades, dimensionless temperature difference decreases, but the best heat removal achieves when the pathways place along the direction of the diagonal of the square body, because, as the simulations show, the maximum temperature in the body occurs at the corners of the square.
Tue, 15 May 2018 19:30:00 +0100

Mixed Convection Heat Transfer of WaterAlumina Nanofluid in an Inclined and Baffled CShaped ...
http://jhmtr.journals.semnan.ac.ir/article_2996_0.html
In this paper, mixed convection heat transfer of aluminawater nanofluid in an inclined and baffled cshape enclosure is studied. It is assumed that the flow is laminar and steady. There is no energy production, energy storage and viscous heat dissipation. Also, the nanofluid is considered as a continuous, Newtonian and incompressible fluid. Governing equations are discretised by finitedifference method and solved by SIMPLE algorithm simultaneously. Reynolds number (10 < Re < 1000), rotation angle of enclosure ( < α < ), length of baffle (0.1 < Bf < 0.4), Richardson number (0.1 < Ri < 100) are changed. In addition, volume percent of nanoparticles are changed in the range of 0 < φ < 0.06. The results show that the Nusselt number increases with increase of Reynolds number. Adding nanoparticles always results in cooling enclosure. At high Reynolds number, increase of nanoparticles has less effect on the heat transfer rate. Furthermore, heat transfer increases with the Richardson number, the enclosure angle and the length of baffle.
Thu, 24 May 2018 19:30:00 +0100

Effect of opening diffuser and return vent location on air quality, thermal comfort and energy ...
http://jhmtr.journals.semnan.ac.ir/article_3020_0.html
Recently, many investigations have been performed on return vent height; showing that the height of 1.3 m from the floor is the best height for this vent. In this article, the effect of distance between opening diffuser and return vent was investigated on air quality, thermal comfort and energy saving. The results showed, by increasing the distance between opening and return vent up to 5 m, the return vent could be placed near the floor at height of 0.6 m without any unacceptable result in indices. Therefore in this case, energy saving of 15.8% could be achieved rather than 8%, 10.9% and 15.2% in other cases. But, the air quality was lower than other cases. The case which brought better air quality and more thermal comfort with acceptable energy saving of 15.2%, was when the opening and return vent were relocated at maximum distance between them (5 meters) and return vent was placed at the suggested height of 1.3 m from the floor, which was the optimum case in this research.
Wed, 20 Jun 2018 19:30:00 +0100

Influence of inclined Lorentz forces on entropy generation analysis for viscoelastic fluid over ...
http://jhmtr.journals.semnan.ac.ir/article_3084_0.html
In the present work, the entropy generation analysis for viscoelastic fluid flow including inclined magnetic field and nonlinear thermal radiation aspects with the heat source and sink over a stretching sheet was investigated analytically. The boundary layer governing partial differential equations are transformed by appropriate similarity transformations to nonlinear coupled ordinary differential equations. These equations are solved by applying Kummer's function and used to compute the entropy generation. Influences of various pertinent parameters on velocity, temperature and entropy generation were discussed in detail and illustrated graphically. Based on the results, it was revealed that the presence of radiation and heat source parameters reduced the entropy production and at the same time aligned magnetic field, Reynolds number, the dimensionless group parameter, Hartmann number, Prandtl number and viscoelastic parameters are produces more entropy. It is also found that the presence of inclined magnetic field and thermal radiation enhances the heat transfer rate. The wall temperature gradient was also calculated and compared with some previous publications, which show outstanding agreement.
Wed, 01 Aug 2018 19:30:00 +0100

Numerical study of flow and heat transfer characteristics of CuO/H2O nanofluid within a mini tube
http://jhmtr.journals.semnan.ac.ir/article_3091_0.html
Nanofluids are a new heat transfer fluids, which improve thermal performance and reduce the size of systems. In this study, the numerical domain as a threedimensional 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 twophase mixture model. The results showed 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 plateletshaped nanoparticles have the highest reduction in friction factor. Also, as new formulas, we suggested two correlations to calculate the Nusselt number of nanofluids according to the effect of nanoparticle shape in the laminar and turbulent flow regimes.
Thu, 09 Aug 2018 19:30:00 +0100

Investigating Tubes Material Selection on Thermal Stress in Shell Side Inlet Zone of a Vertical ...
http://jhmtr.journals.semnan.ac.ir/article_3100_0.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 commonly heat exchangers used in industries. One of the most common failures in these exchangers in the industry is tube failure at the junction of the tube to tubesheet. When the shell side and tube side fluid with temperature difference, flow in the heat exchangers, 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 is tried to make changes that reduce the effect of thermal stress in the failure. For this purpose, temperature distribution, thermal stress distribution and its effects on failure are investigated by changing the material. To perform the required analysis, three dimensional model of inlet zone of the shell side is created and steady state temperature distribution is obtained and the stress caused by temperature gradient is analyzed. Because of interference between fluid and structure in this study the indirect coupled field analysis is used. In this way the thermal analysis results are converted to indirect couple structural analysis as loading. Among the analyzed materials, the lowest rate of stress is for copper tubes. However, steel tubes have the best safety factor for thermal stress.
Fri, 17 Aug 2018 19:30:00 +0100

Investigation on Turbulent Nanofluid Flow in Helical Tube in Tube Heat Exchangers
http://jhmtr.journals.semnan.ac.ir/article_3101_0.html
The thermal characteristics of turbulent nanofluid flow in a helical tube in tube heat exchanger (HTTHE) are assessed numerically through computational fluid dynamics (CFD) simulation. The turbulent flow and heat transfer of two nanofluids (SiO2, Al2O3) and base fluid with respect to swirl dominated flow is simulated through the RNG model. It is concluded that at 1 % volume concentration of SiO2 nanoﬂuid and Al2O3 nanoﬂuid the heat transfer coefficient of both the nanofluids is 8.6 % and 8.2 % greater than the basefluid in annulus tube side, respectively, while this value is 4.3 % and 1.5 % in inner tube side. The findings of both the turbulent models: realizable kepsion (kε) and renormalisation group (RNG) kepsilon are compared. The temperature distribution contours show that realizable and RNG kε models, together with the swirl dominated flow are of more uniform temperature distribution. The proper prediction of twolayer theory leads to having a uniform temperature distribution and proper dimensionless wall distance (Y+). 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.
Fri, 17 Aug 2018 19:30:00 +0100

Numerical Investigation of Roofing Materials Effect on Solar Heat Gain in Different External ...
http://jhmtr.journals.semnan.ac.ir/article_3155_0.html
In this study, thermal performance of three kinds of roofs with different heat capacity and thermal conductivity under different external conditions is investigated by a numerical method. For this purpose, the combined solar radiation, conduction and convection heat transfer were calculated implicitly using a onedimensional finite difference method. Different high and low solar radiation conditions in two common climates in the Middle East including hothumid and hotdry are considered. The effect of roofing materials is investigated in terms of their thermal storage and overall heat transfer coefficient. Also, the time lags and decrement factors are evaluated to compare roofs performance. The numerical model has been validated using EnergyPlus. The results show 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 the total load of roof 1 to roofs 2 and 3 are about 12 percent lower than the ratio of overall heat transfer coefficients. Also, the solar radiation intensity had considerable effects on time lags. Finally, the external conditions have no significant effect on the decrement factor.
Fri, 07 Sep 2018 19:30:00 +0100

Mixed 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 basefluid. 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 +0100

Experimental 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 twostep 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 +0100

Rapid mixing of Newtonian and nonNewtonian fluids in a threedimensional micromixer using ...
http://jhmtr.journals.semnan.ac.ir/article_3504_0.html
The mixing of Newtonian and nonNewtonian fluids in a magnetic micromixer is studied numerically using 〖Fe〗_3 O_4 ferrofluid. The mixing process is performed in a threedimensional steadystate micromixer. A magnetic source is mounted at the entrance of the microchannel to oscillate the magnetic particles. The effects of electric current, inlet velocity, size of magnetic particles and nonNewtonian fluid are examined on the mixing efficiency. It is demonstrated that the mixing efficiency increases 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 lead to the mixing efficiency of 10% and 83%, respectively. Also, the results demonstrates that the effect of the size of magnetic particles is not considerable in comparison with the electric field In addition, the present results reveal that the mixing efficiency of a nonNewtonian fluid (blood) is smaller than that of Newtonian one.
Tue, 11 Dec 2018 20:30:00 +0100