Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
4
3
1997
Boiling Heat Transfer in the Miniature Axially-Grooved Rectangular Channel with Discrete Heat Sources
163-174
10.1615/JEnhHeatTransf.v4.i3.10
Dmitry
Khrustalev
Department of Mechanical Engineering, University of Connecticut, Storrs, Connecticut 06269, U.S.A.
Amir
Faghri
College of Engineering, Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Rd., Unit 3139, Storrs CT 06269-3139, USA; Department of Mechanical and Materials Engineering Wright State University Dayton, OH 45435
An axially-grooved copper-water miniature heat sink with external dimensions 2.6 × 7.7 × 40 mm has been tested in the horizontal orientation with heat fluxes on both side walls of up to 100 W/cm2. The wall temperature variations along the heat sink, effective local heat transfer coefficients, and important information on the critical heat flux are presented. This heat sink provides a nearly uniform surface temperature, a low thermal resistance and operates with a significantly smaller pressure drop and larger heated length compared to single-phase heat sinks with microchannels. It can be used in two-phase thermal control systems applied to cooling of electronic components.
Enhanced Boiling Heat Transfer in Porous Layers with Application to Electronic Component Cooling
175-186
10.1615/JEnhHeatTransf.v4.i3.20
N. D.
Konstantinou
Institute of Physical Chemistry, NCSR Demokritos, 15310 Aghia Paraskevi, Greece
Athanasios K.
Stubos
Environmental Research Laboratory, Institute of Nuclear Technology and Radiation Protection, NCSR Demokritos, 15310 Aghia Paraskevi
J. C.
Statharas
Environmental Research Laboratory, Institute of Nuclear Technology and Radiation Protection, NCSR Demokritos, 15310 Aghia Paraskevi, Greece
Nikolaos K.
Kanellopoulos
Institute of Physical Chemistry, NCSR Demokritos, 15310 Aghia Paraskevi, Greece
A. Ch.
Papaioannou
Department of Chemical Engineering, National Technical University of Athens, 15780 Zografos, Greece
The present contribution deals with a continuous approach to modeling steady state evaporative heat transfer and vapor/liquid counterfiow in porous media, in an attempt o identify the mechanisms responsible for the observed heat transfer enhancement during boiling of liquid coolants in porous layers. A 1-D computer code is developed solving the mass, momentum and energy conservation equations for a bottom and/or volumetrically heated, capillary porous medium. The limitations of such a macroscopic study are recognized and relate mainly to its inability to provide an insight of the micromechanics aspects at the pore level. Nevertheless, the macroscopic calculations are employed to highlight the effects of the relevant parameters (fluid properties, medium permeability and porosity, thermal conductivity of solid matrix, layer thickness) and identify the relative significance of the different mechanisms (capillarity, counter-flow, phase change). A simplified analytical approach is taken to describe the steady state thermohydraulic behaviour of a liquid saturated porous medium. This offers a fast, approximate method for predicting the limiting dryout heat flux in the porous layer. Qualitative agreement is obtained when the theoretical reproduction of the experimental boiling curves is attempted. Based on the understanding gained, investigations are underway to suggest geometric and thermal modifications of the system which may contribute to a significant increase of the heat flux removed in the case of electronic components cooling.
Enhanced Heat Transfer Characteristics of Single-Phase Flows in a Plate Heat Exchanger with Mixed Chevron Plates
187-201
10.1615/JEnhHeatTransf.v4.i3.30
Arun
Muley
Department of Mechanical, Industrial and Nuclear Engineering University of Cincinnati, Cincinnati, OH 45221-0072
Raj M.
Manglik
Thermal-Fluids and Thermal Processing Laboratory, Mechanical and Materials Engineering, University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45220, USA
The enhanced thermal-hydraulic performance of single-phase flows in a plate heat exchanger with mixed chevron plates is investigated experimentally. The mixed arrangement consists of plates with chevron angle β = 30° and 60°, alternatingly stacked in a single-pass, U-type, counterflow configuration. Vegetable oil (130 < Pr < 220) and water (2.4 < Pr < 4.5) are used as test fluids, with flow rates in the laminar, transition, and turbulent flow regimes (2 < Re < 6000). Results for isothermal friction factor and heat transfer under cooling conditions, along with respective correlations for laminar (2 < Re < 400) and fully developed turbulent (Re ≥ 1000) flows are presented; transition is observed to set in when Re ∼ 500. The heat transfer data are obtained from controlled experiments, employing an extension of the Wilson Plot technique. A comparison of the data with previously reported results and predictive equations for Nu and / highlights the latter’s lack of general applicability, and the need for a larger database. The relative impact of using mixed chevron plate arrangement is discussed, and their enhanced performance, in comparison with parallel-plate channels, is evaluated.
Enhancement of Subcooled Flow Boiling Heat Transfer on Cylinders Using Interfere Sleeves
203-215
10.1615/JEnhHeatTransf.v4.i3.40
S. Madhusudana
Rao
Department of Chemical Engineering Indian Institute of Technology, Madras, Chennai 600 036, India
Arcot R
Balakrishnan
Dept. of Chemical Engineering, Indian Institute of Technology, Madras, Chennai - 600 036, India; School of Mechanical Engineering, SASTRA Deemed University, India
This paper describes a experimental study of sub cooled flow boiling of water on a horizontal stainless steel tube with an interference sleeve (a sleeve with perforations). The flow of water is in the annular section between the sleeve surface and a outer glass tube. Six sleeves were used with different hole geometries (hole diameters and the pitch of holes) and the clearance between the sleeve and the boiling tube. Results show that sleeves with larger values of clearances and pitch needed lower temperature driving forces for a given heat flux, but with the disadvantage of an early transition to film boiling. However, interference sleeves with hole diameters of 1 mm and those with a combination of 1 mm and 2 mm holes on alternate rows required high heat fluxes for transition to film boiling. The level of inlet sub-cooling showed a marked effect of the two phase heat transfer coefficient. A sub-cooling of 20 K gave heat transfer coefficients that were two to three times lower than that obtained with a sub-cooling of 5 K. An increase in the inlet mass velocity of the liquid showed a significant increase in the wall superheat accompanied by a greatly increased heat flux required for transition to film boiling. A correlation has been proposed for the two phase heat transfer coefficient and the importance of the parameters in the correlation is discussed in terms of the physics of the process.
Tube and Fin Geometry Alternatives for the Design of Absorption-Heat-Pump Heat Exchangers
217-235
10.1615/JEnhHeatTransf.v4.i3.50
Srinivas
Garimella
Sustainable Thermal Systems Laboratory, The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
J. W.
Coleman
Department of Mechanical and Aeronautical Engineering Western Michigan University, Kalamazoo, MI 49008
A.
Wicht
Universität-GH-Paderborn Fachbereich Verfahrenstechnik Paderborn, Germany
The present study investigates the possibility of using highly compact, flat-tube/multilouver fin heat exchangers as replacements for conventional round-tube hydronic fluid-to-air heat exchangers used in space-conditioning applications. The advantages of these novel heat exchangers such as smaller frontal obstruction to air flow compared to round tubes (drag and fan power reduction), larger heat transfer coefficients due to the interrupted multilouver fins, and larger surface areas per unit volume can benefit absorption space-conditioning systems.
A comparison of the performance of this new geometry versus conventional round-tube heat exchangers was performed through the quantification of the decrease in heat exchanger mass for equivalent heat duties. Within the limitations of the available heat transfer and friction factor correlations, round-tube heat exchangers with flat, wavy, louvered and annular fins, and flat-tube heat exchangers with multilouver fins were designed to meet typical absorption cycle design conditions. The effect of design variables such as parallel/serpentine flow arrangements of tubes, fin densities, core depth, and other parameters on heat transfer performance and tube- and air-side pressure drops was investigated. It was shown that flat-tube heat exchangers can transfer equivalent heat duties while meeting pressure drop constraints with a significant reduction in the overall mass and size.