Experimental study on spray heat transfer enhancement by micro-structured surface with nanoencapsulated phase change material slurry (NPCMS)

Abstract

Spray cooling is receiving increased attention due to the highly efficient and uniform heat transfer. However, previous investigations seldomly focused on its enhancement with the combination of phase change materials (PCMs) and micro-finned surface. Herein, in this article, we enhance the spray cooling with NPCMS and micro fins to improve the heat capacity of coolant, heat transfer area and nucleate sites of contact boiling. Results show that two peaks of heat transfer coefficient are observed in sequence as heatflux increases, separately derived from latent heat absorption of melting of core PCM and nucleate boiling of carrying fluid. Compared to the smooth surface, the convective heat transfer coefficients under three cubic fin heights (0.2 mm, 0.3 mm and 0.4 mm) are improved maximally by 22.3 %, 17.6 % and 11.8 % in phase change of NPCMS, while the maximum improvements of 45.8 %, 39.8 % and 39.8 % are obtained in the nucleate boiling. The staggered arrangement of cylinder fins can induce stronger capillary force, which is responsible for the best enhancement of nucleate boiling. Also, the shortest survival time of droplet on the staggered cylinder fins are observed, confirming that capillary force is the reason of increasing heatflux and lifting Leidenfrost point of boiling.