Study Of The Non-azeotropic Mixed Working Medium In The Pulsating Heat Pipe's Start-up And Running Characteristics

PHP has been proved to be good at thermal conductivity.With reasonable process and design of heat pipe of u-model structure, PHP could satisfy more efficient appliance in small space. Because of the influence of high temperature booting and limitation of heat conduct, some products will have probles in the application. But the study of no- azeotropy mix-up could solve these problems, so the mix-up working substance is necessary.This paper uses different proportion of water and HFE-7100 as working mediums to make a visual performance testing in plate-type PHP. By observing the phenomenon of variations in working substance of different proportion at start-up and stable phase and analyzing the thermal conductivity of test data in different working condition when PHP start and operate stably, and here are some test conclusions below:(1) Visual experiment.There are different flow patterns in working substance of PHP, including bubble flow, plug flow and mixed airflow; When HFE-7100 is added, it's easier to form circulated flow than others in low heating power;In stable operating phase when a certain propotion of HFE-7100 is added, density of gas-liquid distribution becomes denser and vibration amplitude and frequency becomes larger; in increasing heating power change or change under the condition of water mixed with HFE-7100 proportion, PHP working substance inside one-way circulation flow direction change would happen.(2) Start-up phaseThere are different types in the plate-type PHP. If the heating power is over high, the pipe will become stably transitional and when it refers to modest heating power, the PHP is temperature-mutational operating type.At the low heating power, the relatively lower proportion of HFE-7100 helps the booting and if the proportion is very low even to zero,plate-type PHP won't boot; When the heating power is enough, proper proportion of HFE-7100 will diminish booting time and the temperature of booting point is low; When the heating power is too high, it's nearly no discriminative booting comparing pure working substance with working substance mixed with HFE-7100.(3) Stable operation phaseHFE-7100 boots rapidly and operates steadily and has a good operating result;When the heating power is enough, proper proportion of HFE-7100 will make working medium shock relatively violently and the working medium could form a single-way circulation, which is good for the heating conduct of PHP; When the heating power is too high, the proportion of latent heat transfers will increase because of bigger rate of containing gas and that would deteriorate the effect of heating conduct of PHP. Comparing with HFE-7100, the water with latent heat of vaporization in high heating power shows more stable performances.(4) Numerical simulationBy using the VOF model, this paper has tried a variety of simulations and found that all the working medium changings started with gas-liquid interface; Under different working conditions, there exsites different flow pattens including the formation of a stable bubbles and do one-way circulation flow pattern, reciprocating oscillation flow pattern in adiabatic section, direct gasification circulation flow pattern in one direction with no bubble and so on.