Semnan University PressJournal of Heat and Mass Transfer Research2345-508X5220181001Analytical solution of pressure driven gas flow and heat transfer in micro-Couette using the Burnett equations8794270210.22075/jhmtr.2017.1775.1131ENAhmadReza Rahmatiuniversity of KashanF. Najatiuniversity of KashanJournal Article20161229In 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.http://jhmtr.journals.semnan.ac.ir/article_2702_56d450929f2143ab16e918bf2972a49a.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X5220181001Energy and Exergy Analysis of a Diesel Engine Running with Biodiesel Fuel95104270510.22075/jhmtr.2017.11293.1160ENReza BahooshDepartment of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, IranMohammad Sedeh GhahfarokhiDepartment of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, IranMohamadreza SaffarianDepartment of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.0000-0003-0326-0505Journal Article20170509Availability 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.http://jhmtr.journals.semnan.ac.ir/article_2705_80890b8a55515778cad0db60a07757f7.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X5220181001Physico-Acoustic Study on Thermal Conductivity of Silver Nanofluid105110288310.22075/jhmtr.2018.12036.1175ENGaneswar NathDepartment of Physics
BurlaJournal Article20170803Low 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.http://jhmtr.journals.semnan.ac.ir/article_2883_4b3b0cdca2cfa3cd4ba0a67687b093bc.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X5220181001Numerical Study of Spherical Vapor Layer Growth Due to Contact of a Hot Object and Water111120288410.22075/jhmtr.2018.12775.1192ENAli JahangiriFaculty of Mechanical &amp; Energy Engineering, Shahid Beheshti University, A.C., Tehran, IranJournal Article20171019Vapor 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.<br />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.http://jhmtr.journals.semnan.ac.ir/article_2884_1614101748d41debb2aefd30d56853bb.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X5220181001Constructul design of tree-shaped conductive pathways for cooling a heat generating volume121128299010.22075/jhmtr.2018.10481.1144ENmohammad-reza nattajDepartment of mechanical engineering, Qom university of technology, Qom, Iranmahdi sahebiDepartment of mechanical engineering, Qom University of Technology, Qom, IranJournal Article20170205Constructal 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.http://jhmtr.journals.semnan.ac.ir/article_2990_c42c6892078389a5469168dc63eea806.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X5220181001Mixed Convection Heat Transfer of Water-Alumina Nanofluid in an Inclined and Baffled C-Shaped Enclosure129138299610.22075/jhmtr.2018.13390.1196ENMorteza BayarehMechanical Engineering, Shahrekord University, Shahrekord, IranAmin KianfarDepartment of Mechanical Engineering, Lamerd Branch, Islamic Azad University, Lamerd, IranAbbas KasaeipoorcDepartment of Mechanical Engineering, Faculty of Engineering, University of Isfahan, Isfahan 81746-73441, Iran.Journal Article20171217In this paper, mixed convection heat transfer of alumina-water nanofluid in an inclined and baffled c-shape 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 finite-difference 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.http://jhmtr.journals.semnan.ac.ir/article_2996_2ec4ecf28443968f7738cdb91b55f8ef.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X5220181001Effect of opening diffuser and return vent location on air quality, thermal comfort and energy saving in desk displacement ventilation (DDV) system139148302010.22075/jhmtr.2018.12784.1193ENAmir Mohammad JadidiSemnan UniversityBahram RahmatiStudent of BSC, Semnan University, Semnan, IranAli HeidarianBSC Student, Semnan University, Semnan, IranJournal Article20171022Recently, 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.http://jhmtr.journals.semnan.ac.ir/article_3020_94ebb2271758b8e810ff1c99114ffac8.pdf