“How can we have a completely passive thermal cooling mechanism?”
Thermal cooling is often required in many cases. But sometimes an active cooling solution may not be appropriate. So how can we have truly passive cooling? Well, what if we were to have a pipe with a working fluid, and have it constructed such that the heat source will heat up the medium to evaporation, which then moves along the pipe until it cools down and condensates, turning back into its original form and repeating the process? These are known as Heat Pipes and are an interesting application of passive cooling.
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