Begell House Inc.
Heat Transfer Research
HTR
1064-2285
43
8
2012
HEAT TRANSFER ENHANCEMENT IN MICROCHANNELS BY UTILIZING THE Al2O3−WATER NANOFLUID
695-707
Shuangling
Dong
Beijing University of Chemical Technology
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
Junhong
Zhang
Naval University of Engineering, Wuhan 430033, Hubei, China
Heat transfer enhancement by utilizing nanofluids in a microchannel flow is investigated for specific flow regimes and boundary conditions. Accompanied with the slip velocity and jump temperature boundary conditions, the governing mass, momentum, and energy equations for a
nanofluid flow inside a microchannel have been discretized using the characteristic finite element method. The above equations are improved and solved taking into account the particle dispersion and anomalous diffusion due to the particle random motion. Based on theoretical models and experimental correlations, the thermal conductivity and viscosity coefficients required for simulation were used. Based upon numerical simulations, the effects of Reynolds number and the volume fraction of nanoparticles on heat transfer from the channel walls are presented. Simulated results shows reasonably good agreement with the previous numerical and experimental data. An obvious increase in the averaged Nusselt number is found for the nanofluid. The results provide insight into the statement that nanoparticles can increase the rate of heat transfer in microchannels.
EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER IN A NOVEL HEAT SINK BY MEANS OF ALUMINA NANOFLUIDS
709-720
Hootan
Zirakzadeh
Department of Mechanical Engineering, University of Tehran, Tehran, Iran
Alireza
Mashayekh
Department of Mechanical Engineering, University of Tehran, Tehran, Iran
Hossein Noori
Bidgoli
Department of Mechanical Engineering, Islamic Azad University of Kashan, Kashan, Iran
Mehdi
Ashjaee
Department of Mechanical Engineering, University of Tehran, Tehran, Iran
In this paper, heat transfer characteristics of a miniature heat sink cooled by Al2O3−water nanofluids were investigated experimentally. Based on plate fin heat sinks, a new type of plate pin-finnned
heat sink is developed which is composed of a plate fin heat sink and columnar pins between the plate fins. The heat sink was fabricated from aluminum and insulated by plexiglass cover plates and consisted of five pin-finned rectangular channels with a length of 42 mm. The volume fraction of the Al2O3−water nanofluid particles was in the range from 0.5 to 2%. Mixtures were prepared without a dispersion agent. Tests were performed while supplying a 180 W/cm2 heat flux to the bottom of heat sink. Experimental results showed that dispersion of Al2O3 nanoparticles in water increased significantly the overall heat transfer coefficient, while the thermal resistance of heat sink decreased. Also, the plate pin-finned heat sink showed an increase in the heat transfer coefficient up to 20% in comparison with the conventional plate fin
heat sink.
FINITE ELEMENT FREQUENCY-DOMAIN DIFFUSION APPROXIMATION OF TRANSIENT RADIATIVE TRANSPORT IN PLANAR GRADED INDEX MEDIA
721-731
Lijun
Liu
School of Civil Engineering, Northeast Petroleum University Daqing 163318, People's Republic of China
Xiaoyan
Liu
School of Civil Engineering, Northeast Petroleum University, Daqing 163318, People's Republic of China
The diffusion approximation equation in a frequency domain is presented for analyzing laser pulse transport in graded index planar media, and a finite element method is developed to obtain the solutions. The amplitude and phase of the hemispherical reflectance and the transmittance in
the frequency domain are investigated. The effect of the optical depth and single scattering albedo of the media on the precision of the diffusion approximation are analyzed as compared to the results obtained on the basis of the radiative transfer equation. The results show that the diffusion approximation has a poor accuracy in the case where the radiative intensity is most unevenly
distributed. The phase predicted by the finite element method based on the diffusion approximation is greatly influenced by the wave shape of the incident pulse.
EFFECTS OF DISSIPATIVE HEATING AND THERMAL DIFFUSION ON THE PERISTALTIC FLOW OF A POWER-LAW FLUID IN A NONUNIFORM INCLINED TUBE
733-748
Obaid Ullah
Mehmood
Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia; Department of Mathematics, COMSATS Institute of Information Technology, Wah Cantt. 47040, Pakistan
Norzieha
Mustapha
Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
Sharidan
Shafie
Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia
81310 UTM Johor Bahru, Johor, Malaysia
Constantin
Fetecau
Academy of Romanian Scientists, Bucharest 050094, Romania; Department of Mathematics, Technical University of Iasi 700050, Romania
The paper describes the study of the combined effects of heat and mass transfer on the peristaltic flow of a power-law fluid in a nonuniform inclined tube. The effects of dissipative heating and thermal diffusion are taken into account. The governing equations have been linearized by employing the long wavelength and small Reynolds number approximation. Exact solutions for the stream function, axial pressure gradient, axial velocity, temperature, and concentration have been derived. The effects of
various interesting parameters are presented graphically. A comparative study on the temperature and concentration for a viscous, shear thinning and shear thickening fluid has been made. Comparisons with published results for limiting cases showed good agreement.
THE EFFECT OF AIR GAP THICKNESS ON HEAT TRANSFER IN FIREFIGHTERS' PROTECTIVE CLOTHING UNDER CONDITIONS OF SHORT EXPOSURE TO HEAT
749-765
Song
He
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, P. R. China
Dongmei
Huang
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, P. R. China
Zhengkun
Qi
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, P. R. China
Hui
Yang
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, P. R. China
Yin
Hu
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, P. R. China
Heping
Zhang
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, P. R. China
In this paper, the mechanism of heat transfer through the air gap between the layers of the fire protective clothing (FPC) and human skin under conditions of relatively short exposure to heat is studied. In the experiments, the thickness of the air gap varied from 0 mm to 10 mm with a
step of 1 mm. The temperature on the simulated skin increased with the air gap until the thickness
reached 7 mm. During a further increase from 8 mm to 10 mm, the temperature remained the same, and a little change could be observed. Corresponding to the experimental results, the Rayleigh number exceeded a value of 103 when the air-gap thickness was larger than 7 mm, and the convective heat transfer in the air gap cannot be ignored.
A JET IMPINGEMENT/CHANNEL RECEIVER FOR COOLING DENSELY PACKED PHOTOVOLTAIC CELLS UNDER A PARABOLOIDAL DISH SOLAR CONCENTRATOR
767-778
Jie
Ji
Department of Thermal Science and Energy Engineering, University of Science and Technology of China,
Hefei 230027, China
Wang
Yunfeng
Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Jinzhai Road 96#, Hefei City, Anhui Province People's Republic of China
Tin-Tai
Chow
Division of Building Science & Technology, City University of Hong Kong,Tat Chee Avenue, Kowloon, Hong Kong SAR, People's Republic of China
Haifei
Chen
Department of Thermal Science and Energy Engineering, University of Science Technology of China, Jinzhai Road 96#, Hefei City, Anhui Province, People's Republic of China
Gang
Pei
Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei, 230027, China
A new hybrid cooling scheme is proposed for cooling densely packed photovoltaic cells under a paraboloidal dish concentrator. The scheme integrates the cooling effects of a microchannel flow and jet impingement. A numerical model has been developed and experiment was conducted to verify the computational approach. The simulation results are found to be in good agreement
with the experimental results. Further numerical predictions were then performed, and the key parameters have been identified over a range of coolant flow rates. These include heat efficiency, average temperature, and temperature difference over the radiance receiver plate. It is also shown that the new cooling scheme has the desirable working performance and is of good application
potential for the cooling of photovoltaic cells exposed to a high heat flux.
EFFECTS OF SLIP FACTORS ON THE UNSTEADY STAGNATION POINT FLOW AND HEAT TRANSFER TOWARDS A STRETCHING SHEET: AN ANALYTICAL STUDY
779-794
Najeeb Alam
Khan
Department of Mathematics, University of Karachi, Karachi 75270, Pakistan
Muhammad
Jamil
Department of Mathematics, NED University of Engineering and Technology, Karachi-75270, Pakistan
Nadeem Alam
Khan
Department of Mathematical Sciences, University of Karachi, Karachi 75270, Pakistan
This paper aims at presenting an analytical solution to the problem of unsteady stagnation-point flow and heat transfer towards a stretching sheet. The homotopy analysis method (HAM) is employed to compute the solution of the system of nonlinear equations governing the problem. The
slip contributions, which appeared in the solution as expected, tend to zero when the parameters λ and δ tend to zero. Finally, the influence of the material, slip, and the unsteadiness parameters of the fluid motion, as well as a comparison with the numerical solution are also discussed with the aid of graphical illustrations.
INDEX
795-801