Heat-triggered two-phase flow maldistribution in a micromachined cryogenic cooler

•Liquid nitrogen maldistribution results in temperature irregularities along microcoolers.•Flow maldistribution in microcoolers is mainly caused by the non-uniform heat load.•Flow maldistribution can be tuned during the cool-down process and operation at 100 K.•Flow maldistribution deteriorates heat exchanger efficiency and microcooler performance. Counter flow heat exchangers (CFHXs) are essential elements of micromachined Joule–Thomson (JT) cryogenic coolers. The performance of CFHXs has a crucial influence on the overall behavior of JT microcoolers. Flow maldistribution, especially those with phase change, can adversely affect the performance of JT microcoolers. However, the underlying mechanisms of flow maldistribution for two-phase flow in JT microcoolers remain unexplored. Here we report the heat triggered switching of two-phase flow maldistribution in the heat exchanger of JT microcoolers by both microscopic observations and temperature measurements. A measure against flow maldistribution is proposed.