Experimental investigation into the feasibility of using a variable conductance heat pipe for controlled heat release from a phase-change material thermal store

Abstract

Traditional heat storage uses large water tanks, with wide operating temperature differentials that restrict their use with heat pumps and Stirling engine DCHP systems. In contrast, the system developed under the 'THERMAC' project uses phase change materials (PCMs) for thermal storage to reduce system size, with a self-regulating, variable conductance heat pipe (VCHP) to control heat output. The VCHP is a heat pipe whose condenser is linked to a reservoir of non-condensable gas -in this case argon. Small temperature gradients expand or contract the argon along the condenser, so that it acts as a thermal switch by controlling the active length of the condenser.The study was successful in its main objective of demonstrating the basic technical feasibility of (i) Erythritol PCM as a means of heat storage (ii) over-coming the PCM's low thermal conductivity by using fins on the VCHP, and, (iii) a VCHP as a means of controlling the thermal output of the PCM storage system, thereby increasing their overall efficiency.Recommendations are made for further development of the 'THERMAC' concept.

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“…There are various types of VCHPs: simple gas, VCHP using nanofluid, loop type, integrated with reservoir, pulsating with ferrofluid, VCHP with an inert gas 238 . Law et al 239 investigated the possibility of VCHP to handle the heat released from a thermal store that contains Erythritol as a phase change material and reported encouraging results. Vehicle thermal management was explored by Leriche et al 240 using VCHP.…”

“…The liquid is transferred owing to the pressure difference between the evaporator and condenser. However, the liquid return in RHP depends on the centrifugal force 236‐290 . There are two types of RHPs; axial RHP and radial RHP.…”