Enhanced Pool Boiling Heat Transfer by Porous Structure Surface
Date Issued
2007
Date
2007
Author(s)
Yeh, Ching-Ting
DOI
zh-TW
Abstract
On the tendency of higher and higher power density devices in modern technology, the need for more effective heat exchangers have motivated the development of enhanced surfaces. Therefore, the central purpose in presented research is to enhance boiling heat transfer capacity by utilizing two pore size distributions of a biporous surface structure. This surface is sintered from the mixture of dendritic copper powders and the pore former, Na2CO3, which formed the larger pores in the matrix. By changing the volumetric ratio of pore former, it’s able to alter the porosity and the numbers of larger pores in the porous media. At high heat flux, the larger pores provide venting passages for bubbles generated inside the structure and reduce the liquid-vapor counterflow resistance adjacent to the surface, while the smaller pores continue to function as liquid supply routes.
The experiments were conducted with the 3-cm diameter test surfaces, horizontally oriented, and submerged in saturated R-134a, at an absolute pressure of 5.5 bar. At low heat flux, the results show that the heat transfer coefficients of mono and biporous surfaces are up to 120 and 70 kW/m2K, respectively. The heat transfer enhancement ratios are 9~11 and 4~8 compared to a smooth surface. At high heat flux, due to the larger pores in the porous structure, the biporous surface really prolongs the critical heat flux to 869 kW/m2, which is about 2.2 and 1.3 times over a smooth and monoporous surface, respectively.
Future research is needed to optimize the mixture of the pore former and cooper powders, which can result in substantial further enhancement.
Subjects
熱傳
池沸騰
雙孔徑毛細結構表面
熱傳增強表面
Heat transfer
Pool boiling
Biporous surface
Enhanced surface
Type
thesis
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