| The emergence of heat transfer devices with high heat flux stimulates the development of research on the flow boiling in micro/mini-channel,there are already some achievements can be applied.Surface modification as a passive strengthening heat transfer method,has the advantages of stong operation and high reliability and is paid more and more attention by the researchers,the study of resistance characteristics is one of the most important contents.A micro/mini-channel flow boiling experiment platform was established,rectangular channels with wall contact angles of 0°,62°,158°,cross section size of 1mm×2mm were prepared by EDM,chemical etching and surface fluorination,and the flow boiling experiment of refrigerant R141 b was undertaken.The effects of wall wettability on the flow boiling resistance and its fluction in micro/mini-channels were investigated,the main contents of this paper were as follows:Study on two-phase friction pressure drop of micro/mini-channels with different wettability.By comparing the two-phase friction pressure drop and the pressure curve along the channel of three micro/mini-channels with different wettability,it was found that for the single-phase flow region,the single-phase friction pressure drop due to the existence of the wall slip is minimal of the micro/mini-channel with poor wettability(contact angle of 158°);but two-phase friction pressure drop because of the bigger bubble departure diameter and smaller departure frequency was maximum,approximately,it was 1.3 times of the fine wetting micro/mini-channel(contact angle of 0°).Considering the effect of wall wettability on the two-phase friction pressure drop,the surface energy of the micro-channel wall was introduced and the new empirical correlation was fitted,the average absolute deviation of the correlation and experimental values was only 11.6%.Study on the total pressure drop fluctuation of micro/mini-channels with different wettability.By comparing the power spectral density function(PSD)and Hurst exponent of the total pressure drop signal of micro/mini-channels with different wettability was analyzed.it was found that the PSD curve of the micro/mini-channel with poor wettability is the largest,and the area formed by the PSD curve of micro/mini-channel with the horizontal axis(frequency axis)was maximum,which indicated that the micro/mini-channel with poor wettability has more energy and more pressure fluctuation.The Hurst exponent of the micro/mini-channel with poor wettability was larger than that of the other two micro/mini-channels,indicating that the pressure fluctuation was more pronounced,the main reason was that the micro/mini-channel with poor wettability produced more bubbles and was the bigger bubble departure diameter. |
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