Closed-type pneumatic temperature control of a pressure-controlled loop heat pipe with a mechanically driven gas pressure controller

Abstract

Precise and rapid temperature controls without overshooting or undershooting are of prime importance in numerous industrial and scientific applications. The recently-suggested pneumatic temperature control technique with a pressure-controlled loop heat pipe (PCLHP) was considered to be a fit-for-purpose method achieving those required features despite its open nature caused by use of an open-type commercial gas pressure controller. In this work, a closed-type pneumatic temperature control method was established based on the PCLHP equipped with a mechanically driven gas pressure controller (MDGPC). The MDGPC comprised a variable-volume bellows chamber and a linear actuator, and gas pressure control was realized by varying the axial dimension of the bellows chamber. The MDGPC attained a pressure control stability and resolution of approximately 1 Pa and 10 Pa, respectively. Rapid and stable recovery from sudden external pressure disturbances was demonstrated, and stepwise pressure changes of ±5 kPa were successfully achieved with a stability of approximately 1 Pa without any instabilities. With the MDGPC, pneumatic temperature control of the PCLHP was realized in a closed manner; the stability of the pneumatically controlled temperature was approximately 0.01 °C, which is comparable to the stability obtained with a commercial open-type gas pressure controller. Temperature steps of approximately 0.8 °C were generated via pressure steps of ±2.5 kPa, and the change in temperature was accurately predicted with a thermodynamic relationship. Wide-range and stable temperature changes were also attained under gradual pressure changes generated by the MDGPC. Overall, closed-type pneumatic temperature control of the PCLHP was successfully realized with the MDGPC.