Semnan University PressJournal of Heat and Mass Transfer Research(JHMTR)2345-508X5220181001Using Burnett Equations to Derive an Analytical Solution to Pressure-Driven Gas Flow and Heat Transfer in Micro-Couette Flow8794365810.22075/jhmtr.2018.3658ENAhmad Reza RahmatiDepartment of Mechanical Engineering, University of Khashan, Kashan, IranFaezeh Nejati BarzokiDepartment of Mechanical Engineering, University of Khashan, Kashan, IranJournal Article20161229The aim of the present study is deriving an analytical solution to incompressible thermal flow in a micro-Couette geometry in the presence of a pressure gradient using Burnett equations with first- and second-order slip boundary conditions. The lower plate of the micro-Couette structure is stationary, whereas the upper plate moves at a constant velocity. Non-dimensional axial velocity and temperature profiles were obtained using the slip boundary conditions and were compared with the transition flow regime (0.1≤ <em>Kn</em> ≤10). The results showed that in this regime, rarefaction exerts a considerable effect on both the velocity and the temperature profiles. Because of the presence of the pressure gradient in the direction of the flow, the non-dimensional velocity and temperature profiles behave in a parabolic trend and flatten as the Knudsen number increases. The Poiseuille and Nusselt numbers, obtained using the derived analytical solution, decrease with increasing the Knudsen number. In the absence of an axial pressure gradient, the velocity profile behaves linearly and shows good agreement with the results of the previous works.http://jhmtr.journals.semnan.ac.ir/article_3658_a088782d4b0a8dbcce9d9cb666858440.pdfSemnan University PressJournal of Heat and Mass Transfer Research(JHMTR)2345-508X5220181001Energy and Exergy Analyses of a Diesel Engine Running on Biodiesel Fuel95104365910.22075/jhmtr.2018.3659ENReza BahooshDepartment of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran0000-0001-9609-052XMohammad Sedeh GhahfarokhiDepartment of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, IranMohammad Reza SaffarianDepartment of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran0000-0003-0326-0505Journal Article20170509Availability analysis is an effective approach to studying energy conversion in systems and identifying inefficiency. In the present study, a single-zone model was used to examine energy performance parameters and heat release rates. The governing equation of availability analysis was applied in the model, and the possibility of using biodiesel produced from sunflower oil as diesel engine was investigated via mathematical simulation. The different exergy components of pure diesel fuel and pure biodiesel were compared at different crank angles. Results indicated that combining the examined diesel engine with biodiesel fuel would decrease the energy and exergy efficiencies by about 2.72% and 2.61%, respectively. As a result, work exergy and heat transfer exergy decrease and exhaust gas exergy and irreversibility would increase. When biodiesel is replaced with diesel fuel, carbon monoxide decreases, carbon dioxide formation increases, and nitrogen oxide formation remains constant. However, considering the negligible decrease in the first- and second-law efficiencies of biodiesel fuel compared with the decrease in diesel fuel efficiencies, the former is regarded as a renewable fuel that produces less carbon monoxide. It can therefore serve as a substitute for diesel fuel.http://jhmtr.journals.semnan.ac.ir/article_3659_9bed2749a67802a13f54e8ddb4c74183.pdfSemnan University PressJournal of Heat and Mass Transfer Research(JHMTR)2345-508X5220181001Physico-Acoustic Study on Thermal Conductivity of Silver Nanofluid105110366010.22075/jhmtr.2018.3660ENGaneswar NathDepartment of Physics, Veer Surendra Sai University of Technology, Burla, Sambalpur- 768018, Odisha, IndiaJournal 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 tackle these problems in thermal industries, nanofluids could play 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 article describes the green synthesis of the 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 by means of water as the 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 the base fluid. The variation of ultrasonic velocity and other calculated acoustic parameters are used to analyze in amplification of heat conductivity of silver nanofluids.http://jhmtr.journals.semnan.ac.ir/article_3660_4910173579577b71dd08187f96967da1.pdfSemnan University PressJournal of Heat and Mass Transfer Research(JHMTR)2345-508X5220181001Numerical Study of Spherical Vapor Layer Growth Due to Contact of a Hot Object and Water111120366110.22075/jhmtr.2018.3661ENAli JahangiriFaculty of Mechanical & Energy Engineering, Shahid Beheshti University, Tehran, IranJournal Article20171019Vapor film formation and growth due to contact of a hot body and other liquids arise 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 could result in injuries and financial damage. Due to the importance of such phenomenon, this study deals with vapor layer forming, growth, and its internal pressure. A mathematical model of a molten spherical droplet immersed in water has been developed, and the 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 the temperature of bulk fluid) were investigated. These parameters affect the vapor layer size, vapor internal pressure, and the saturated temperature at the interface between vapor and liquid phases. Finally, conclusions indicate that the internal vapor pressure jumps, 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 threaten the system safety.http://jhmtr.journals.semnan.ac.ir/article_3661_71d29dd6c33eab3be1c9cbd1c6c12edb.pdfSemnan University PressJournal of Heat and Mass Transfer Research(JHMTR)2345-508X5220181001Constructal design of tree-shaped conductive pathways for cooling a heat generating volume121128366210.22075/jhmtr.2018.3662ENMohammad-Reza EbrahimnatajDepartment of Mechanical Engineering, Qom University of Technology (QUT), Qom, Iran.Mahdi SahebiDepartment of Mechanical Engineering, Qom University of Technology (QUT), Qom, Iran.Journal Article20170205Constructal design is used to study heat removal from a square heated body with a tree shaped high thermal conductivity pathways 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 would be achieved when the pathways place along the direction of the diagonal of the square body, since, as the simulations show, the maximum temperature in the body occurs at the corners of the square.http://jhmtr.journals.semnan.ac.ir/article_3662_5b8b8607c043fe5d19ab6287b295c96d.pdfSemnan University PressJournal of Heat and Mass Transfer Research(JHMTR)2345-508X5220181001Mixed Convection Heat Transfer of Water-Alumina Nanofluid in an Inclined and Baffled C-Shaped Enclosure129138366310.22075/jhmtr.2018.3663ENMorteza BayarehDepartment of Mechanical Engineering, Shahrekord University, Shahrekord, 88186- 34141, Iran.Mohammad Amin KianfarDepartment of Mechanical Engineering, Lamerd Branch, Islamic Azad University, Lamerd, Iran.Abbas KasaeipoorDepartment of Mechanical Engineering, Isfahan University, Isfahan, Iran.Journal Article20171217In this article, 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. Furthermore, the nanofluid is considered as a continuous, Newtonian and incompressible fluid. Governing equations are discretized by finite-difference method and solved by SIMPLE algorithm simultaneously. Reynolds number (10 < <em>Re</em> < 1000), rotation angle of enclosure ( < α < ), length of baffle (0.1 < Bf < 0.4), Richardson number (0.1 < <em>Ri</em> < 100) are changed. In addition, volume percent of nanoparticles are changed in the range of 0 < φ < 0.06. The results demonstrate that the Nusselt number increases with the Reynolds number. Adding nanoparticles always results in cooling enclosure. At high Reynolds number, increase of nanoparticles has less effect on the heat transfer rate than low ones. Finally, heat transfer increases with the Richardson number, the enclosure angle and the length of baffle.http://jhmtr.journals.semnan.ac.ir/article_3663_8e59e9de59a3a86e3d78308acff7971c.pdfSemnan University PressJournal of Heat and Mass Transfer Research(JHMTR)2345-508X5220181001Effect of opening diffuser and return vent location on air quality, thermal comfort and energy saving in desk displacement ventilation (DDV) system139148366410.22075/jhmtr.2018.3664ENAmir Mohammad JadidiMechanical Engineering Faculty, Semnan University, Semnan, Iran.Bahram RahmatiMechanical Engineering Faculty, Semnan University, Semnan, Iran.Ali HeidarianMechanical Engineering Faculty, Semnan University, Semnan, Iran.Journal Article20171022Many investigations have recently been performed on return vent height and indicate that having 1.3 m distance from the floor is the optimized height for it. In this article, the effect of distance between opening diffuser and return vent on air quality, thermal comfort and energy saving was investigated. According to the results, 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 consequence 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. However, the air quality was lower compared to the other cases. In the case having better air quality and more thermal comfort with acceptable energy saving of 15.2%, 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 found to be the optimum scenario.http://jhmtr.journals.semnan.ac.ir/article_3664_b53a42a37e9ed43647220bc02feb1484.pdf