The effects of channel helight on floe boling of luqid nitrogen

摘要

The quest for high-power electronics operating in a cryogenic environment has given rise to the need for very effective cryogenic cooling of the electronic devies. Electronic chips are usually mounted on the circuit boards. Those boards are stacked one above or next to the others. For the electrnic engineers who design the electronic systems, how close the cricuit boards can be stacked together is very important. This paper presents an inestigation off effects of flow channel heights on flow boiling heat transfer with liquid nitrogen from small, discryete heat sources that simulate electronic chips. The experimental approatus is designed to allow visual observatioin of the phase-changephenomena of cryogen (liquid nitrogen) at the heat sources. Experiments with different flow channel heights have been conducted. it is noted that the channel height has little effect on the CHF until the channel heith is decreased to approximately 1.6 mm. The critical heat flux (CHF) and the heat transfer coefficient decreases significantly. There is no significant difference between the heat transfer conditions in flow channel hights of 6.35 mm and 3.18 mm, which inicates that distance between the multi-layer-stacked electronic boards should be larger than the multi-layer-stacked electornic boards should be larger than the cirtical heith (1.6 mm) in order to botian optimum cooling results. a model to describe the heat transfer mechanism near CHF was developed using the present results and those of prevous investigators. A correlation was established using this model and the experimental data. This correlation provides a good fit to the experimental data from various flow channel heights.