Thermosiphon, thermosyphon, compact storage, air conditioner, heat pump
The Roving Comforter (RoCo) is an innovative personal thermal management technology currently being developed at the University of Maryland as part of Advanced Research Projects Agency â€“ Energy (ARPA-e) project. Among several system configurations of RoCo, the paper focuses on a miniature battery-powered vapor compression cycle (VCC) system fitted on an autonomous robotic platform. The heat rejected from the condenser during its operation is stored in a compact phase change material (PCM) based heat storage device. The PCM can store only a limited amount of heat until it melts completely. The PCM heat exchanger needs to be designed so that it captures the heat generated during the VCC operation and then gets frozen with minimal energy usage during the non-operation mode. A thermosiphon mechanism is envisioned for this recharging of PCM material during the non-operation mode. It operates through the same refrigerant circuit by bypassing certain components like the compressor. Thus the circuit operates as a VCC during the day and as thermosiphon during the night. The VCC needs to have a high coefficient of performance (COP) while the thermosiphon needs to reject heat at highest possible rate. Hence transient modeling of thermosiphon is desired. The prototype developed has a COP of 2.85 and needs roughly 8 hours to recharge the thermosiphon. These trends have been captured on a transient model for the VCC operation while the development of thermosiphon modeling is being carried out. Comparison of modeling results with the experimental data have been provided to estimate the error in the model. Several cases of RoCo thermosiphon are then simulated using the model for the optimum design fulfilling requirements for both VCC and thermosiphon.