Determination of charged pressure of working fluid and its effect on the operation of a miniature CLHP

In this paper, a miniature cryogenic loop heat pipe (CLHP) with nitrogen as the working fluid was designed, and the principle and calculation method to determine the charged pressure of working fluid were proposed and experimentally validated. Meanwhile, the effect of reduced charged pressure of working fluid on the operation of the CLHP such as the supercritical startup, matching characteristics of heat loads applied to the primary and secondary evaporators and heat transport capacity was experimentally investigated. Experimental results reveal that with an appropriate charged pressure of working fluid, the CLHP can reliably realize the supercritical startup, the primary evaporator can operate independently when the heat load applied to the primary evaporator is larger than a certain threshold value, and it achieves a heat transport capacity of 12 W. The effect of reduced charged pressure of working fluid on the supercritical startup and heat transport capacity of the CLHP is not salient. However, it has significant effect on the matching characteristics of heat loads applied to the primary and secondary evaporators, and the secondary evaporator must be kept in operation to assist the normal operation of the primary evaporator even though the heat load applied to the primary evaporator is comparatively large.