scholarly journals Flow Boiling of Low-Pressure Water in Microchannels of Large Aspect Ratio

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2689
Author(s):  
Liang Chen ◽  
Xingchen Li ◽  
Runfeng Xiao ◽  
Kunpeng Lv ◽  
Xue Yang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Power Electronics ◽  
Thermal Management ◽  
High Power ◽  
Flow Boiling ◽  
Width Ratio ◽  
Bubble Behavior ◽  
Uniform Wall Temperature ◽  
Pressure Water ◽  
Uniform Wall

Flow boiling heat transfer in microchannels can provide a high cooling rate, while maintaining a uniform wall temperature, which has been extensively studied as an attractive solution for the thermal management of high-power electronics. The depth-to-width ratio of the microchannel is an important parameter, which not only determines the heat transfer area but also has dominant effect on the heat transfer mechanisms. In the present study, numerical simulations based on the volume of fraction models are performed on the flow boiling in very deep microchannels. The effects of the depth-to-width ratio on the heat transfer coefficient and pressure drop are discussed. The bubble behavior and heat transfer characteristics are analyzed to explain the mechanism of heat transfer enhancement. The results show the very deep microchannels can effectively enhance the heat transfer, lower the temperature rise and show promising applications in the thermal management of high-power electronics.

Simulations of Metal Foam Cooling of High-Power Electronics Using the Equivalent Thermal Conductivity

2003 ◽  
Author(s):  
Nihad Dukhan ◽  
Pable D. Quinones
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Power Electronics ◽  
Thermal Management ◽  
High Power ◽  
Metal Foam ◽  
Maximum Temperature ◽  
Transfer Model ◽  
Aluminum Foams ◽  
Equivalent Thermal Conductivity

A one-dimensional heat transfer model for open-cell metal foam is presented. The model includes both the conduction and the convection in the ligaments and in the pores of the foam. It uses the typical foam parameters provided by the manufacturers. Three aluminum foams having different relative surface areas, relative densities, ligament diameters, and number of pores per inch are analyzed and an effective thermal conductivity is determined. The heat transfer increases with the number of pores per inch. The resulting improvement in heat transfer can be as high as 57 percent over solid aluminum. The model is general enough such that it can handle other types of foam and geometries. For simulations using packages for thermal management, the foam can be modeled as a solid having an equivalent conductivity with an effective convection heat transfer on its outer surfaces. This eliminates the need to model the microscopic flow and heat transfer in and around the pores. It also allows quick feasibility studies and comparisons of different arrangements using aluminum foams for thermal management systems of high-power electronics. A few such simulations are presented in this work. The simulations show a big promise for using the foam in place of the traditional heat sinks for cooling high-power electronics: they reduce the cooling system’s weight substantially and reduce the maximum temperature significantly.

Second Order Slip Flow Effects on Heat Transfer Performance of Microchannels

2009 ◽  
Author(s):  
Cem Dolu ◽  
Lu¨tfullah Kuddusi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Flow Model ◽  
Slip Flow ◽  
Second Order ◽  
Flow Models ◽  
Uniform Wall Temperature ◽  
Uniform Wall ◽  
Slip Flow Regime ◽  
Flow Effects

First and second order slip flow models in rectangular microchannels heated at constant and uniform wall temperature are studied. The velocity and temperature profiles for hydrodynamically and thermally developed incompressible slip flow regime available in literature are used. The average nondimensional slip velocity and temperature jump are found by using first and second order slip flow models. The average Nusselt number is also derived by using both first and second order slip flow models. The effects of Knudsen number, aspect ratio and second order slip flow model on the heat transfer characteristics of microchannel are explored.

Numerical Study of Circular Tube inserted Arc Belt on Fluid Flow and Heat Transfer under Laminar Flow

2013 ◽  
Vol 561 ◽  
pp. 460-465
Author(s):  
Dong Hui Zhang ◽  
Jiao Gao
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Laminar Flow ◽  
Wall Temperature ◽  
Circular Tube ◽  
Numerical Study ◽  
Resistance Coefficient ◽  
Uniform Wall Temperature ◽  
Flow And Heat Transfer ◽  
Uniform Wall

The objective of this paper is to study the characteristic of a circular tube with a built-in arc belt on fluid flow and heat transfer in uniform wall temperature flows. Numerical simulations for hydrodynamically laminar flow was direct ran at Re between 600 and 1800. Preliminary results on velocity and temperature statistics for uniform wall temperature show that, arc belt can swirl the pipe fluid, so that the fluid at the center of the tube and the fluid of the boundary layer of the wall can mix fully, and plays the role of enhanced heat transfer, but also significantly increases the resistance of the fluid and makes the resistance coefficient of the enhanced tube greater than smooth tube. The combination property PEC is all above 1.5.

Heat Transfer in Cylindrical Pipes With Fully Established Turbulent Flow and Exposed to a Uniform Temperature Environment

1966 ◽  
Vol 88 (3) ◽  
pp. 305-311 ◽  
Author(s):  
J. W. Goresh
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Heat Equation ◽  
Jacobi Polynomials ◽  
Heat Losses ◽  
Uniform Temperature ◽  
Uniform Wall Temperature ◽  
Temperature Problem ◽  
Temperature Environment ◽  
Uniform Wall

The problem considered is that of determining the heat losses from a gas flowing turbulently in a poorly insulated pipe where the heat lost from the outer surface is by free convection and radiation. The approach employed in solving the heat equation is analogous to that first introduced by Latzko for the solution of the uniform wall temperature problem. Later, in 1957, Fettis obtained a solution to the same problem in terms of Jacobi polynomials. A method for coupling the inner convection with the environment is given in the later portion of the paper. The results obtained for a numerical case are also presented.

Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part I—Laminar Flows

1993 ◽  
Vol 115 (4) ◽  
pp. 881-889 ◽  
Author(s):  
R. M. Manglik ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Swirl Flow ◽  
Laminar Flows ◽  
Low Flow ◽  
Published Data ◽  
Twisted Tape ◽  
Flow Rates ◽  
Uniform Wall Temperature ◽  
Uniform Wall

Laminar flow correlations for f and Num are developed based on experimental data for water and ethylene glycol, with tape inserts of three different twist ratios. The uniform wall temperature condition is considered, which typifies practical heat exchangers in the chemical and process industry. These and other available data are analyzed to devise flow regime maps that characterize twisted-tape effects in terms of the dominant enhancement mechanisms. Depending upon flow rates and tape geometry, the enhancement in heat transfer is due to the tube partitioning and flow blockage, longer flow path, and secondary fluid circulation; fin effects are found to be negligible in snug- to loose-fitting tapes. The onset of swirl flow and its intensity is determined by a swirl parameter, Sw=Resw/y, that defines the interaction between viscous, convective inertia, and centrifugal forces. Buoyancy-driven free convection that comes into play at low flow rates with large y and ΔTw is shown to scale as Gr/Sw2≫ 1. These parameters, along with numerical baseline solutions for laminar flows with y = ∞, are incorporated into correlations for f and Num by matching the appropriate asymptotic behavior. The correlations describe the experimental data within ±10 to 15 percent, and their generalized applicability is verified by the comparison of predictions with previously published data.

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