Abstract

Experimental data for the performance of a novel ultracompact thermal energy storage (TES) heat exchanger, designed as a micro-channel finned-tube exchanger are presented. A salt hydrate phase change material (PCM), Lithium Nitrate Trihydrate (LiNO3·3H2O; Tsf = 30°C, hsf = 274 kJ/kg), was encased on the fin side with water as the heat-cooling fluid. The TES performance was characterized experimentally to establish: (a) average heat transfer rates and power density with 10 and 24 fins/inch heat exchanger designs, and (b) TES reliability under thermal cycling field conditions. With high average heat transfer coefficients (Upcm = 100–500 W/m2K), a substantially high power density is obtained (∼ 367 kW/m3 during freezing) primarily due to the reduction in the PCM encasement length scale (L < 3 mm). In the thermal cycling test, the TES was subjected to accelerated heating and cooling cycles under typical arid region conditions (diurnal variation between 42°C–25°C). Employing the self-seeding method to obviate subcooling, the TES was found to exhibit stable long-cycle operation with very high-power density. The results clearly establish that highly compact heat exchangers used as TES units are significantly superior and attractive alternatives to conventional ones.

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