Experimental Investigation Of Pool Boiling Heat Transfer Characteristics On Micro-square Column With Porous Medium Surface

Boiling heat transfer has advantages of occupying small space and good heat transfer performance,is an efficient heat dissipation method and is widely used in different fields.The surface morphology and structure of the heat transfer surface have a crucial influence on the boiling heat transfer performance.This paper focuses on the influence of the surface of the micro-square column with porous medium structure on the pool boiling heat transfer performance,done experiments and made analysis,provided strong bases for the further improvement of pool boiling heat transfer.Firstly,a visualized pool boiling experiment system based on experimental requirements was designed and built.The principle and test method of equipment,the process of data collection,data processing and error analysis are introduced.Then,according to the experimental prediction,the smooth surface,the uniform copper foam surface and the micro-square column with porous media surface were designed.And the manufacture process of the micro-square column with porous media surface includes the selection of soldering lugs,the welding of foam copper and the Wire cutting of micro-square column surface.The pool boiling heat transfer performance of the smooth surface,the uniform foamed copper surface,micro-square column with porous medium structure was tested by using the deionized water as working fluid.Combined with the characteristics of surface structure,in-depth analysis of different structural surface heat transfer performance,dynamic changes of bubble,pool boiling enhancement mechanism.The main contents and research results of this paper are summarized as follows:?1?Analyzed the boiling heat transfer characteristics of the micro-square column with porous media surface and compared with the uniform copper foam and the smooth surface.It is found that the heat flux and heat transfer coefficient of the most micro-square column with porous medium surface were higher than the uniform copper foam and the smooth surface at the same wall superheat.In the range of experiments,the maximum heat flux of the micro-square column with porous medium surface is 3.31×10⁶W.m^-2,which is 2.87 times of the uniform copper foam surface(2.17×10⁶W.m^-2)and 1.52 times of the smooth surface(1.15×10⁶W.m^-2)respectively;the maximum of heat transfer coefficient of the micro-square column with porous medium surface is 1.43×10⁵W.m^-2.K^-1,which is 2.47 times of the uniform copper foam surface(0.58×10⁵W.m^-2.K^-1)and 2.8 times of the smooth surface(0.51×10⁵W.m^-2.K^-1).At low wall superheat,a higher heat flux is achieved and the heat exchange efficiency is significantly improved.The h3.2w0.6 surface has the best heat transfer performance.In addition,with the height of the micro-column increasing,the column spacing of optimal heat transfer efficiency surface decreases.?2?At the same wall superheat conditions,with the increase of the column spacing and the height of the microcolumn,the bubble departure diameter slightly increases,but the change is not obvious.The bubble departure diameter increases,with the increase of wall superheat.In the measured data,the maximum and minimum diameter of the micro-square column with porous medium surface are2.38mm and 0.56,respectively;which are smaller than the smooth surface?2.24mm-2.64mm?and larger than the uniform copper foam surface?0.58mm-1.06mm?.?3?With the wall superheat increasing,the bubble departure frequency and nucleation site increase.And the onset of nucleate boiling of uniform copper foam surface and micro-square column with porous medium surface is at lower wall superheat than smooth surface.With the increase of column spacing,the bubble departure frequency and nucleation site on the micro-square column with porous medium surface decrease.?4?The enhancement mechanism of the boiling heat transfer performance of micro-square column with porous medium under low,medium and high heat flux was analyzed.The surface of the micro-column increases the heat transfer area,the bubbles move and separate from the inter-column space,reduces the bubble departure resistance,the copper foam increases the nucleation site,enhances the liquid replenishment capability,so the heat transfer efficiency is enhanced.