%A LU Guoqiang, HAN Jitian, KONG Lingjian, CHEN Changnian, HU Guiqiu, CHEN Jun, LI Jiangfei %T Effect of mass flux on onset of nucleate flow boiling of R134a and tube wall temperature characteristics %0 Journal Article %D 2016 %J Journal of Shandong University(Engineering Science) %R 10.6040/j.issn.1672-3961.0.2015.288 %P 117-122 %V 46 %N 3 %U {http://gxbwk.njournal.sdu.edu.cn/CN/abstract/article_1456.shtml} %8 2016-06-30 %X In order to obtain the characteristics of onset of nucleate flow boiling(ONB)and tube wall temperature distributions in helically-coiled tube, an experiment was conducted with the working medium R134a. The ONB was determined by observing the wall temperature changes when the heat flux was increased gradually. Analysis of the experimental results was performed to reveal the related mechanism. The results indicated that the heat flux of ONB increased with increase in the mass flux of R134a, however, the mass flux, centrifugal and gravity forces had different influences on the bubble behavior of detaching and reattaching in some cases, resulting in different trends in some positions measured in the experiment. In single-phase, the wall temperatures in the selected points decreased with increase in the mass flux of R134a; under flow boiling conditions, the increase in the mass flux only resulted in a slight change in the tube wall temperatures. The experimental results can provide a reference for the reliable design and safe operation of helically-coiled tube heat exchangers.