Effect of h-BN coating on nucleate boiling heat transfer performance in pool boiling

We report a simple and efficient surface modulation method for enhancing boiling heat transfer performance using a commercial spray can of boron nitride (h-BN). The surface was prepared by successive spraying, drying, and annealing, resulting in a thin coating of film composed of closely packed h-BN particles. We controlled the thickness of the coating by varying the number of repetitions of the spraying and drying steps, and evaluated the effects on boiling performance. We observed a trade-off between the boiling heat transfer coefficient (HTC) and the critical heat flux (CHF) as the thickness varied. We obtained the largest improvement from the thinnest b-BN coating, at 8 μm, which yielded an HTC enhancement of 160% compared with the uncoated silicon surface. We obtained a similar improvement to the CHF. Meanwhile, the surface coated with the thickest layer, 27 μm of h-BN, exhibited the largest CHF enhancement, 70%, but the worst HTC performance, increasing the HTC of the silicon wafer only by 9%. We attributed the enhancement in the HTC performance to the higher nucleate site density on the h-BN coated surface. However, the thermal properties of the surface were worse than those of uncoated silicon, leading to degradation in the HTC with increasing thickness.