Heat and Mass Transfer (HEAT MASS TRANSFER)

Publications in this journal

• Article: On Flow Structure, Heat Transfer and Pressure Drop in Varying Aspect Ratio Two-Pass Rectangular Channel with Ribs at 45°

  W. Siddique, I.V. Shevchuk, L. El-Gabry, N.B. Hushmandi, T.H. Fransson
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  ABSTRACT: To increase the thermal efficiency of gas turbines, inlet temperature of gas is increased. This results in the requirement of cooling of gas turbine blades and vanes. Internal cooling of gas turbine blades and vanes is one of several options. Two-pass channels are provided with ribs to enhance heat transfer at the expense of an increased pressure drop. The space in the blade is limited and requires channels with small aspect ratios. Numerical simulations have been performed to investigate heat transfer, flow field and pressure loss in a two-pass channel equipped with 45 degree ribs with aspect ratio (Win/H) equal to 1:3 in the inlet pass and 1:1 in the outlet pass with both connected together with a 180 degree bend. The results are compared with a higher aspect ratio channel (Win/H = 1:2, inlet pass). In the ribbed channel, a decrease in pressure drop was observed with a decrease in the aspect ratio of the channel. The smaller aspect ratio channel not only allows using more cooling channels in the blade, but also results in more heat transfer enhancement. The divider-to-tip wall distance (Wel) has influence on the pressure drop, as well as on the heat transfer enhancement at the bend and outlet pass. Heat transfer decreases with decrease in aspect ratio of the inlet pass of the two-pass channel. With increase in divider-to-tip wall distance, heat transfer tries to attain a constant value.
  Heat and Mass Transfer 02/2013; 49(5):679–694.
• Article: A numerical and experimental study of natural convective heat transfer from an inclined isothermal square cylinder with an exposed top surface

  Abdulrahim Kalendar and PH Oosthuizen
  Heat and Mass Transfer 01/2013;
• Article: A numerical investigation of new film cooling hole configuration at the leading edge of asymmetrical turbine blade: part A

  benabed mustapha
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  ABSTRACT: The focus of the first part of this numerical study is to investigate the effects of two new configurations: (1) slot with cylindrical end and (2) slot with median cylindrical hole, generated by the combination between two film cooling configurations: cylindrical hole and uniform slot. Computational results are presented for a row of coolant injection holes on each side of an asymmetrical turbine blade model near the leading edge. For each configuration, three values of the radius are taken: R = 0.4, R = 0.8 and R = 1.2. The six cases simulations, thus obtained, are conducted for the same density ratio of 1.0 and the same inlet plenum pressure. A new parameter, Rc, is defined to measure the rate of blade coverage by the film cooling. Results show that, at the pressure side; for the two new configurations, the six studied cases exceed the case baseline in cooling effectiveness term with the best result obtained for R = 0.8 (case 2). For the suction side, only configurations with R = 0.4 (cases 1 and 4) provide an increase of film effectiveness compared to the case baseline. The following configuration: Cases 1 or 4 at the suction side and case 2 at the pressure side, gets the best thermal protection because of their higher coverage and strong cooling effectiveness.
  Heat and Mass Transfer 12/2012;
• Article: Numerical study of fractal characteristics of heat transfer interface in two-dimensional thermal planer jets

  Nan Gui, Zhongli Ji, Jinsen Gao
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  ABSTRACT: A numerical study of fractal characteristics of heat transfer interface in incompressible two-dimensional thermal planar jets is conducted. The fractal characteristics of heat transfer interface are investigated under three typical Prandtl numbers and two-types of inflow velocity profiles. The results show that heat transfer interface is fractal, and the fractal dimension decreases as the Prandtl number increases. It is caused mainly by the non-negligible effect of rapider development of thermal diffusion than momentum diffusion, which could produce finer structures in lower Pr flows. Moreover, this trend is enhanced by the increased inflow momentum thickness of the jets, as a thicker inflow boundary layer could initiate more space for heat transfer development.
  Heat and Mass Transfer 08/2012; 49:21-30.
• Article: The effects of casting speed on steel continuous casting process

  Mohammad Sadat, Ali Honarvar Gheysari, Saeid Sadat
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  ABSTRACT: A three dimensional simulation of molten steel flow, heat transfer and solidification in mold and “secondary cooling zone” of Continuous Casting machine was performed with consideration of standard k−ε model. For this purpose, computational fluid dynamics software, FLUENT was utilized. From the simulation standpoint, the main distinction between this work and preceding ones is that, the phase change process (solidification) and flow (turbulent in mold section and laminar in secondary cooling zone) have been coupled and solved jointly instead of dividing it into “transient heat conduction” and “steady fluid flow” that can lead to more realistic simulation. Determining the appropriate boundary conditions in secondary cooling zone is very complicated because of various forms of heat transfer involved, including natural and forced convection and simultaneous radiation heat transfer. The main objective of this work is to have better understanding of heat transfer and solidification in the continuous casting process. Also, effects of casting speed on heat flux and shell thickness and role of radiation in total heat transfer is discussed.
  Heat and Mass Transfer 05/2012; 47(12):1601-1609.
• Article: Peristaltic flow of a nanofluid in a non-uniform tube

  Noreen Sher Akbar, S. Nadeem, T. Hayat, Awatif A. Hendi
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  ABSTRACT: The present analysis discusses the peristaltic flow of a nanofluid in a diverging tube. This is the first article on the peristaltic flow in nanofluids. The governing equations for nanofluid are modelled in cylindrical coordinates system. The flow is investigated in a wave frame of reference moving with velocity of the wave c. Temperature and nanoparticle equations are coupled so Homotopy perturbation method is used to calculate the solutions of temperature and nanoparticle equations, while exact solutions have been calculated for velocity profile and pressure gradient. The solution depends on Brownian motion number N b , thermophoresis number N t , local temperature Grashof number B r and local nanoparticle Grashof number G r . The effects of various emerging parameters are investigated for five different peristaltic waves. It is observed that the pressure rise decreases with the increase in thermophoresis number N t . Increase in the Brownian motion parameter N b and the thermophoresis parameter N t temperature profile increases. Streamlines have been plotted at the end of the article.
  Heat and Mass Transfer 05/2012; 48(3):451-459.
• Article: Parametric studies and correlations for combined conduction-mixed convection–radiation from a non-identically and discretely heated vertical plate

  G. Ganesh Kumar, C. Gururaja Rao
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  ABSTRACT: The present paper reports the parametric studies and correlations for the problem of combined conduction-mixed convection–radiation from a non-identically and discretely heated vertical plate. Three discrete heat sources of non-identical heights but with identical volumetric rate of heat generation are assumed to be flush-mounted in a thin vertical plate. The longest and the shortest heaters are provided at the leading and trailing edges of the plate, while the remaining heater is located centrally. The governing fluid flow and heat transfer equations are considered in their full strength without the boundary layer approximations and are solved using the finite volume method. A computer code is written to solve the problem and various parametric studies have been performed. The relative roles of free convection, forced convection and radiation in various fluid flow and heat transfer results have been elucidated. In conclusion, based on a large set of data generated from the code, correlations for maximum non-dimensional plate temperature, average non-dimensional plate temperature and mean friction coefficient have been evolved.
  Heat and Mass Transfer 05/2012; 48(3):505-517.
• Article: A modified heat transfer correlation for two-phase flow

  Mahesh J. Vaze, Jyotirmay Banerjee
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  ABSTRACT: Experimental investigations for two-phase flow under constant heat flux condition are carried out by varying the mass flow rate of gas and liquid phases. A modified correlation for Nusselt number is developed based on the experimental measurements involving superficial gas and liquid Reynolds number, fluid properties and Lockhart-Martinelli parameter. The accuracy of this correlation for all two-phase flow regimes is validated with the recent correlation proposed by Kim and Ghajar.
  Heat and Mass Transfer 05/2012; 47(9):1159-1170.
• Article: Dynamic heat and moisture transfer in bulky PAN nanofiber mats

  Sedigheh Borhani, Seyed Gholamreza Etemad, Seyed Abdolkarim Hosseini Ravandi
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  ABSTRACT: In this study a non-conventional electrospinning technique was designed for the production of high bulky polyacrylonitrile (PAN) nanofiber mats. Optimum nanofiber mats are achieved with 15wt.% solution of PAN in dimethylformamide. Such mats result in a bulk porosity which is as high as 99.9 and a density as low as 0.84×10−3g/cm3. The effect of the porosity of nanofiber mats on the air permeability and coupled heat and moisture transfer of fibers was investigated. Based on the results, high bulky nanofiber mats possess high heat and moisture transfer. Experimental data reveal that upon a slight decrease in the bulk porosity, air permeability and heat transfer decrease noticeably, while moisture transfer variation is low.
  Heat and Mass Transfer 05/2012; 47(7):807-811.
• Article: Temperature fields induced by direct contact condensation of steam in a cross-flow in a channel

  N. Clerx, L. G. M. van Deurzen, A. Pecenko, R. Liew, C. W. M. van der Geld, J. G. M. Kuerten
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  ABSTRACT: The temperature fields in the center plane of a channel with a square cross-section have been measured. Steam injected at relatively low mass fluxes through a small hole in one of the walls of the channel condensed intermittently in a small area close to the inlet. The upstream temperature of the liquid cross-flow, T L , the momentum ratio, J, and the Prandtl number proved to be important for the single-phase temperature field induced in the jet further away from the steam inlet. Jet centerlines of velocity and temperature are measured and positions are compared. Different locations for J<100 and low T L are explained from dependencies on Reynolds and Prandtl numbers. Next to the jet centerline a second high-temperature zone was found to occur, close to the wall and downstream of the steam inlet. The importance of capillary forces is investigated with the aid of 3D CFD computations.
  Heat and Mass Transfer 05/2012; 47(8):981-990.
• Article: Experimental investigation on condensation heat transfer and pressure drop of R134a in a plate heat exchanger

  Z.-Y. Shi, J.-P. Chen, V. Grabenstein, S. Kabelac
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  ABSTRACT: Condensation heat transfer of R134a in a vertical plate heat exchanger was investigated experimentally. The local heat transfer coefficients are determined by means of the measured local wall temperatures. A differential energy balance model is developed for data evaluation. It is found that the correlation proposed by Shah using Ψ and Z factors is suitable for condensation in plate heat exchangers and is adopted to fit the measured data.
  Heat and Mass Transfer 05/2012; 46(10):1177-1185.
• Article: Experimental investigation of the start-up phase during direct chill and low frequency electromagnetic casting of 6063 aluminum alloy processes

  Xiangjie Wang, Haitao Zhang, Zhihao Zhao, Qingfeng Zhu, Gaosong Wang, Huixue Jiang, Jianzhong Cui
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  ABSTRACT: On the basis of conventional hot-top casting and Casting, Refining and Electromagnetic process, a lower frequency electromagnetic field was applied during the conventional hot-top casting process. Nine thermocouples (type K) were introduced into the metal to study the temperature profile in the ingot during the start-up phase of casting process. The experimental results show that under the effect of the low frequency electromagnetic filed, the heat transfer is changed greatly and the film boiling disappears, which could restrain the formation of fine subsurface cracks; the sump is shallow, and the macrostructure of the ingot butt is fine during the start-up phase of direct chill casting process.
  Heat and Mass Transfer 05/2012; 46(6):657-664.
• Article: An experimental investigation on interior thermal conditions and human body temperatures during cooling period in automobile

  M. Kilic, O. Kaynakli
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  ABSTRACT: Determining the thermal conditions in an automobile and their effects on the driver is an important issue from both thermal comfort and driving safety points of view. Especially in hot summer season, the interior thermal conditions in automobile change rapidly when the air conditioning unit runs. In this study, standard air conditioning system is switched in an automobile parked in the sun and then the interior thermal conditions of the automobile are determined in detail during the 1-h cooling period. During the period, relative humidity, air velocity, air and surface temperature measurements are taken at numerous locations in the automobile. Moreover, in order to evaluate the effects of transient interior thermal conditions on the occupant, the skin temperatures of human body are measured at nine points. In addition to this, the thermal sensation of the human subject is also questioned during the cooling period. Subjective thermal comfort data is recorded using a questionnaire. The series of tests are conducted on two different automobiles, and the experimental results for both automobiles are presented and scrutinized.
  Heat and Mass Transfer 05/2012; 47(4):407-418.