Begell House Inc.
Heat Transfer Research
HTR
1064-2285
48
5
2017
EXPERIMENTAL STUDY OF CONDENSATION OF HUMID AIR IN LAMINAR FLOW IN A VERTICAL CHANNEL
379-390
V. Murali
Krishna
Department of Mechanical Engineering, B.V. Raju Institute of Technology, Narsapur, Medak (Dist)-502313, India
V. Dharma
Rao
Department of Mechanical Engineering, G.V.P. College of Engineering, Visakhapatnam, India
An experimental study is presented for the problem of laminar film condensation of a vapor from a vapor-gas mixture in laminar flow in a vertical parallel plate channel. The flowing gas-vapor mixture contains a noncondensable gas of high concentration. An example of this case is the flow of humid air, in which air is present in high concentration. Vapor condenses at the dew point corresponding to the mass fraction of vapor in the gas-vapor mixture and total pressure. The rate of condensation is controlled by the diffusion of vapor through the noncondensable gas. The test rig is instrumented to obtain all data necessary to estimate the end condensate Reynolds number and average condensation heat transfer coefficient, and to measure the gas-vapor mixture temperature along the length of the channel. The condensation Reynolds numbers at the exit of the channel and average condensation heat transfer coefficient estimated from the experimental data are compared with the results obtained from theoretical model of Dharma Rao et al. (2009). The experimentally measured local temperatures of the gas-vapor mixture are compared with the theoretical results obtained for identical values of system parameters. The agreement between the experimental and theoretical results is found to be good.
NATURAL CONVECTION IN A RECTANGULAR ENCLOSURE WITH AN ARRAY OF DISCRETE HEAT SOURCES
391-399
S.
Saravanan
UGC-DRS Center for Fluid Dynamics, Department of Mathematics, Bharathiar University, Coimbatore 641 046, Tamil Nadu, India
V. P. M. Senthil
Nayaki
Department of Mathematics, Bharathiar University, Coimbatore 641 046, Tamil Nadu, India
P.
Kandaswamy
Department of Mathematics, Bharathiar University, Coimbatore 641 046, Tamil Nadu, India
A study of natural convection from a 3 × 3 array of isoflux discrete heat sources mounted on one of the vertical walls in a three-dimensional rectangular enclosure is made. Two different boundary conditions are considered, one in which the two side walls are cooled and the other in which the top and bottom walls are cooled. Numerical solutions are obtained using a finite volume method. Flow and heat transfer characteristics are investigated as a function of Rayleigh number (Ra), aspect ratio (A), and Prandtl number (Pr). The results show that the heat transfer rate increases with Ra. It also increases against A in the range 1-3, however, attains a maximum at around A = 3 and decreases beyond that. The entire enclosure above the bottom heaters is found to be more thermally active when the top and bottom walls are kept cold. However, an effective cooling is possible only in the case of side cold walls.
OPTIMIZATION OF HEAT TRANSFER THROUGH ANNULAR FINS WITH A THERMODEPENDENT THERMAL CONDUCTIVITY AND HEAT TRANSFER COEFFICIENT
401-417
Youb Khaled
Benkahla
Faculté de Génie Mécanique et de Génie des Procédés, Université des Sciences et de la Technologie Houari Boumediene USTHB, B.P. 32, El-Alia Bab-Ezzouar, 16111 Algiers, Algeria
A numerical investigation based on the finite volume method is undertaken in order to study heat transfer through an annular fin of different cross sections (rectangular, triangular, hyperbolic, and parabolic). The validation of the computing code is confirmed by comparing the present results with those obtained from analytical and numerical solutions found in the literature. The first part of the study consists of examining the fin's geometrical parameters effect, i.e., the reduced length R and the characteristic parameter mf on its efficiency. The emphasis is put thereafter on the effect of the thermal dependence of the fin's thermal conductivity, then that of the heat transfer coefficient, and, finally, the simultaneous variation of both of them. An optimization of the fin's dimensions in the case of thermodependent properties is then undertaken. When considering only the fin's efficiency in cases of constant and thermodependent properties, it appears that the annular fin of rectangular cross section has a significant efficiency in comparison with the three other geometrical forms but when optimizing the fin's dimensions, the concave parabolic fin seems to be more efficient and, thus, heat transfer is more enhanced.
UPGRADING THE THERMAL PERFORMANCE OF PARALLEL AND CROSS-FLOW CONCENTRIC TUBE HEAT EXCHANGERS USING MgO NANOFLUID
419-434
Adnan
Sözen
Gazi University, Technology Faculty, Energy Systems Engineering, 06500, Ankara, Turkey
Halil Ibrahim
Variyenli
Gazi University, Technology Faculty, Energy Systems Engineering, 06500, Ankara, Turkey
M. Bahadir
Özdemir
Gazi University, Department of Energy Systems Engineering, Technology Faculty, Teknikokullar,
06503 Ankara , Turkey
Metin
Gürü
Gazi University, Engineering Faculty, Chemical Engineering, 06500, Ankara, Turkey
The aim of this study is to investigate the effects of MgO nanofluid on the thermal performance of parallel and cross-flow concentric tube heat exchangers. A parallel (PFCTHE) or a cross-flow (CFCTHE) concentric tube heat exchanger was selected in these experiments, and its thermal performance was improved with the fluid. The MgO nanofluid/water and water/water hot/cold running fluids were used for monitoring the differences in the performance of the heat exchangers. The Triton X-110 surface active agent was added to the fluid to prepare 2% (wt.) concentration of the MgO nanofluid. The heat exchanger is of double-pipe type with the hot water flowing through the central tube while the cooling water flows through the annular space. A double-pipe heat exchanger with concurrent or countercurrent flow was utilized along with all auxillary equipment and instrumentation for the determination of the surface and overall heat transfer coefficients during turbulent flow. When the MgO nanofluid was used as the running fluid, an improvement of 33.4% and 20.4% was recorded for the efficiency of the PFCTHE and CFCTHE, respectively.
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF VORTEX PROMOTER EFFECTS ON HEAT TRANSFER FROM HEATED ELECTRONIC COMPONENTS IN A RECTANGULAR CHANNEL WITH AN IMPINGING JET
435-463
Mustafa
Kilic
Adana Science and Technology University, Department of Mechanical Engineering, Department of Mechanical Engineering, Dep. of Mechanical Engineering, Yesiloba Yerleskesi Yesiloba Mah. Ogretmenler Bulvarı 46278 Sokak No:3 01180 Seyhan / ADANA
Tamer
Calisir
Gazi University
Senol
Baskaya
Department of Mechanical Engineering, Gazi University, Eti Mah. Yukselis Sok. 5, 06570 Ankara, Turkey
Thermal control of electronic components is a continuously emerging problem as power loads keep increasing. In this study effects of vortex promoter on cooling 18 flash-mounted electronic components, which have constant heat fluxes, inside a rectangular channel, consisting of one open and three blocked sides were investigated experimentally and numerically by using a single jet flow. Copper blocks were used as electronic components. Flow velocities at the inlet to the channel were measured by using a Laser Doppler Anemometer (LDA) system. Temperature measurements were performed by using thermocouples. In order to improve heat transfer from electronic components, effects of vortex promoter parameters (length, location, number, and angular position) on heat transfer were investigated for a Reynolds number of Re = 8000, heat flux q" = 1000 W/m2, and the ratio of the jet-to-plate distance to hydraulic diameter of a nozzle H/Dh = 6. The local and mean Nu numbers were determined as a function of the ratio of distance between vortex promoter and jet inlet to hydraulic diameter of jet inlet (N/Dh) in the range 0.55-5.0, the ratio of vortex promoter's length to channel height (K/H) in the range 0.5-0.9, the ratio of the distance between two vortex promoters to channel height (W/H) in the range 0.5-1.5, and the angle of vortex promoter θ in the range (-5°-(+45°). The low-Reynolds number k-ε turbulence model was used in numerical investigations. The heat transfer rate for N/Dh = 0.7-5.0 improved when the vortex promoter approached the jet entrance. It was observed that heat transfer is sensitive to the location, length, and angular position of the vortex promoter.
FORCED CONVECTION HEAT TRANSFER OF NON-NEWTONIAN CROSS FLUID IN A SQUARE CAVITY
465-476
Jinhu
Zhao
School of Mathematics and Statistics, Fuyang Normal College, Fuyang 236037, Anhui, China
Liancun
Zheng
School of Mathematics and Physics, University of Science and Technology Beĳing, Beĳing 100083,
China
Xinxin
Zhang
School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China; Beijing Key Laboratory of Energy Saving and Emission Reduction for Metallurgical Industry, University of Science and Technology Beijing, Beijing 100083, China
A numerical research is presented for forced convection heat transfer of non-Newtonian fluid in a square cavity, which finds wide domestic and industrial applications. The Cross viscosity model is introduced in characterizing the constitutive relation of the fluid, as it cannot only be used to describe the power-law rheological behavior at high shear rate, but also be a good description of Newtonian rheological behavior near zero shear stress. The coupled equations are solved numerically using the finite-volume method. With fixed inlet and outlet, a total of 112 cases are performed with different Reynolds numbers, power-law coefficients, and indices. The results indicate that the dimensionless vertical velocity at the outlet decreases markedly and the fluid viscosity increases with augmentation of these parameters. Moreover, other effects of involved parameters on the transport characteristics of velocity and temperature fields are analyzed.