非共沸不互溶混合工质脉动热管启动特性分析

针对低加热功率下脉动热管难启动的问题，本文提出一种用于脉动热管相变传热的非共沸不互溶混合工质（HFE-7100和水），其中低沸点工质潜热小、比热容低、密度大，高沸点工质潜热大、比热容高、密度低。选取水为高沸点工质， HFE-7100为低沸点工质，并将两者按照4∶1、2∶1、1∶1、1∶2、1∶4比例混合，实验研究了不同混合比例工质在不同充灌率和不同加热功率下的启动特性。结果表明：相对于水，HFE-7100的低汽化潜热值和高(dp/dT)_sat值等特点能够加快蒸发段气泡的形成，加速脉动热管的启动；相对于纯工质脉动热管，非共沸不互溶混合工质相当于缩短了脉动热管的有效长度，加快系统启动；在低加热功率下，纯工质脉动热管无法启动，但混合工质脉动热管能够正常启动，且混合比例为2∶1、1∶1和1∶2时启动较快；在高加热功率下，混合比例2∶1启动最快。同时，对于非共沸不互溶混合工质脉动热管，充灌率为30%时启动效果最好。

Analysis of start-up characteristics of pulsating heat pipe with zeotropic immiscible mixtures

Based on the difficulty of starting pulsating heat pipes (PHP) at low heating power, a zeotropic immiscible mixture was proposed. The low boiling point working fluid has low latent heat, low specific heat and high density, while the high boiling point working fluid has high latent heat, high specific heat and low density. Water was chosen as high boiling point working fluid and HFE-7100 as low boiling point working fluid. The two working fluids were mixed in proportion of 4∶1, 2∶1, 1∶1, 1∶2 and 1∶4, respectively. The start-up characteristics of different mixing ratio refrigerants at different filling rates and heating powers were studied experimentally. The results showed that compared with water, the low latent heat of vaporization and high (dp/dT)_sat of HFE-7100 could accelerate the formation of bubbles in evaporation section and the start-up of PHP. Compared with pure working fluid, zeotropic immiscible mixtures were equivalent to shortening the effective length of PHP and speeding up system start-up. Under low heating power, pure working fluid PHP cannot start, but mixture PHP could start normally, and the starting speed was faster when the mixing ratio was 2∶1, 1∶1 and 1∶2. Under the high heating power, the starting speed was the fastest when the mixing ratio was 2∶1. At the same time, the start-up effect of PHP with zeotropic immiscible mixtures was the best when the filling rate was 30%.