Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
15
4
2008
Study of Heat Transfer Characteristics of Copper-Water Nanofluid in a Differentially Heated Square Cavity with Different Viscosity Models
273-287
Apurba Kumar
Santra
Department of Power Engineering, Jadavpur University, Salt Lake Campus, Block − LB, Plot-8, Sector — III, Salt Lake, Kolkata — 700 098, India
Swarnendu
Sen
Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India
Niladri
Chakraborty
Department of Power Engineering, Jadavpur University, Salt Lake Campus, Block − LB, Plot-8, Sector — III, Salt Lake, Kolkata — 700 098, India
Effect of nanofluid (suspension of copper nanoparticles in water) has been studied as a cooling medium to simulate the behavior of heat transfer due to laminar natural convection in a differentially heated square cavity. The transport equations are solved numerically using the finite volume approach with the SIMPLER algorithm. The thermal conductivity of the nanofluid has been calculated from the model proposed by Patel et al. [2003, 2005]. The viscosity of the nanofluid has been calculated from the Brinkman [ 1952] model and also from experimental observations of Kwak and Kim [2005]. Study has been conducted for the Rayleigh number (Ra) from 104 to 107 while solid volume fraction (φ) of copper particles in water varied from 0% to 2%. For the first viscosity model, heat transfer increases with but it decreases for the second model. Also heat transfer increases with Ra. Correlations has been developed to obtain the average Nusselt number as a function of Ra and φ for both models. The copper nanoparticle diameter is 100 nm for all of our studies, which is constant.
Experimental Investigation and Modeling of Boiling Heat Transfer Hysteresis on Porous Surfaces
289-301
Tadeusz Michal
Wojcik
Kielce University of Technology, Al. Tysiaclecia P.P. 7, 25-314 Kielce, Poland
Mieczyslaw E.
Poniewski
Warsaw University of Technology, Plock Campus, ul. Jachowicza 2/4, 09-402 Plock, Poland
The paper presents the outcomes of experimental investigations and theoretical analysis of boiling heat transfer on surfaces covered with thin-layer porous structures. The results refer to metal, fibrous porous structures with heterogeneous pore-size distribution. The boiling curves were determined by both increasing and decreasing the heat flux. This procedure helped to reveal the hysteresis phenomena. A new model of type-II boiling heat transfer hysteresis is proposed. The data resulting from the visualization of vapor bubbles departing from the porous layer make it possible to develop the model with only one empirical constant. The results of numerical calculations demonstrated a satisfactory agreement with the observed experimental data.
Heat Transfer in a High Vertical Enclosure with Multiple Fins Attached to the Wall
303-312
Viktor I.
Terekhov
Kutateladze Institute of Thermophysics, Laboratory of Thermal and Gas Dynamics, Russian Academy of Sciences, Siberian Branch, 630090,1, Acad. Lavrent'ev Avenue, Novosibirsk, Russia; Novosibirsk State Technical University, K. Markx av., 20, Novosibirsk, 630073, Russia
Vladimir V.
Terekhov
Kutateladze Institute of Thermophysics SB RAS, Lavrentiev av., 1, Novosibirsk, 630090, Russia; Novosibirsk State University, Pirogov st., 2, Novosibirsk, 630090, Russia
The aim of the present work was to study numerically the flow and heat transfer in high-aspect-ratio, H/L = 40, vertical rectangular cavity. The vertical and horizontal walls were assumed isothermal and adiabatic, respectively. The main purpose was to examine the effect of sidewall ribbing (rib height and number of ribs) on the coefficient of heat transfer across the cavity. The number of ribs was 0 to 40, and the rib height was l/L = 0 − 0.75. Two types of ribs, perfectly conducting ribs and adiabatic ribs, were analyzed. The range of the Rayleigh number Ra = 103 − 105 included both the regime of thermal conduction and the multi-cell convection regime. Full two-dimensional Navier-Stokes equations in the "stream function-vorticity" variables were solved.
The calculations showed that, for all examined rib heights, the surface-average heat-transfer coefficient first increases, attains a maximum, and then decreases with increasing number of ribs. The most pronounced heat-transfer augmentation is observed for high ribs. No heat transfer suppression for perfectly conducting ribs was found; for adiabatic ribs, the heat-transfer rate decreases by 30% compared to its maximal value.
A Liquid Cooler Module with Carbon Foam for Electronics Cooling Applications
313-324
Yiding
Cao
Department of Mechanical and Materials Engineering, Florida International University,
Miami, Florida 33174
Rengasamy
Ponnappan
Universal Energy Systems, Inc., Dayton, OH 45432 USA
A liquid cooler module (LCM) employing high-thermal-conductivity, pitch-based carbon foam, which has effective conductivity of 150 W/m K and porosity of 90%, was studied. This study explores how this high-conductivity carbon foam could enhance liquid convection heat transfer due to the thermal dispersion effect. A three-dimensional numerical study of the carbon foam cooler was carried out. The numerical results indicate that with a heat flux of 100 W/cm2, the average temperature drop between the substrate and the liquid coolant remained below 20°C. Related experimental study was also conducted and the data were compared with the numerical results.
Experimental Investigation of Heat Transfer and Friction Factor Characteristics in a Circular Tube with Longitudinal Strip Inserts
325-333
L. Syam
Sundar
Center for Energy Studies, J.N.T.U. College of Engineering, J. N. T. University, Kukatpally, Andhra Pradesh (State), Hyderabad 500 085, India
K. V.
Sharma
Center for Energy Studies, J.N.T.U. College of Engineering, J. N. T. University, Kukatpally, Andhra Pradesh (State), Hyderabad 500 085, India
Longitudinal strip inserts are used as a heat transfer enhancement tool for both retrofit and new design of shell-and-tube heat exchangers. This paper discusses and reviews the characteristics and performance of full-length longitudinal strip inserts inside a circular tube experimentally. The strips considered for heat transfer behavior in a circular tube have been of rectangular and square cross sections with different aspect ratios (AR). The heat transfer test section was maintained constant wall heat flux (CWHF) boundary condition by supplying electricity. The Reynolds number of the fluid lies in between 4000 to 10,000. The friction factor and Nusselt number correlations have been developed. High heat transfer rates are obtained for the longitudinal strip insert of aspect ratio, AR = 1 and at the same time pressure drop is higher. The enhancement of heat transfer as compared to a conventional bare tube at the same Reynolds number based on the equivalent diameter was found to be about a factor of 22 at Re ≤ 10,000, while the friction factor rise was about a factor of 3.5 at Re ≤ 10,000. The following regression equation for the Nusselt number has been developed for longitudinal strip inserts:
Nu = 0.02278Re0.824 Pr0.412(AR + 1)−0.253(Di /l)0.055
Numerical Investigation of Laminar Forced Convection of Nanofluids through Circular Pipes
335-350
Mehrdad
Raisee
School of Mechanical Engineering, College of Engineering, University of Tehran, Center of
Excellence in Design and Optimization of Energy Systems (CEDOES), Tehran, Iran
Mostafa
Moghaddami
University of Tehran
This paper examines the effects of adding metallic nanoparticles γAl2O3 on the heat transfer enhancement of water flow through circular pipes either under constant wall temperature or uniform wall heat flux thermal boundary condition. Two nanofluid models are employed for simulations. The first model (simpler model) is developed by Maiga et al. [2004], while the second model, which considers the Brownian motion of nanoparticles, is proposed by Koo and Kleinstreuer [2004] based on experimental data of Das et al. [2003]. The numerical results are obtained using a 2D finite-volume code. The pressure field is obtained with the SIMPLE algorithm. Advective volume-face fluxes are approximated using the QUICK scheme. Comparisons of numerical results with experimental data of Zeinali et al. [2007] showed the simpler model underpredicts the heat transfer levels, whilst the second model, returns correct heat transfer levels. Moreover, the first model predicts a higher pressure drop than the second model. As expected, the addition of nanoparticles enhances the heat transfer. The lowest heat transfer enhancement is about 10% for φ = 1%, while the highest is around 30% for φ = 4%. It is also found that the use of nanofluids for heat transfer enhancement is more efficient at lower Reynolds numbers.
Prediction of Temperature Distribution of Spine Fins with an Arbitrary Profile
351-358
S. Ravi
Kumar
VCE, Hyderabad, India
G.
Ramamurthy
Department of Mechanical Engineering, MJCET, Hyderabad
Solutions to the problem of temperature distribution and heat transfer on arbitrary profiled fins can be found out by the general equation developed using Bessel's equations. The variation of temperature along the length of a fin for different profiles can be predicted by using the corresponding values of the fin parameter (N) in the equation. For the case of a fin with N = −1 and N = 0, the temperature difference between the surface of a fin and atmosphere is generated at different sections for various values of ε. These temperatures are compared with that of a cylindrical fin of identical dimensions on the graphs and the conclusions are drawn. From the analysis it is inferred that the parabolic profiled fin has a maximum heat transfer rate for the given weight of a fin material.
Indices to Volume 15
359-366