COMBINED EFFECTS OF CHANNEL DEPTH AND SUBCOOLING ON POOL BOILING HEAT TRANSFER FROM VERTICALLY ORIENTATED SURFACES

An experimental investigation has been carried out to study the effect of liquid subcooling and channel geometry on pool boiling heat transfer characteristics of vertically orientated surfaces. Plane and structured surfaces, covered by a vertically orientated array of open microchannels, with an area of 10×10 mm² were used as test surfaces. Deionized water was used as the working fluid. The channel width and fin thickness were fixed at 780 µm and 200 µm respectively. The channel depth was varied from 200 µm to 800 µm. Experiments were performed for saturated and liquid subcooling of 5 °C, 10 °C, and 15 °C at atmospheric pressure. The bubble dynamics during pool boiling was captured using a high-speed camera. The effect of surface micro-structure and liquid subcooling on heat transfer mechanisms has been discussed. In comparison with the plane surface, all the microchannel structured surfaces were found effective for boiling heat transfer. It was observed that deeper channels show better heat transfer performance as compared to shallower channels for all liquid subcoolings. The liquid subcooling decreases the bubble coalescence and crowding near the boiling surface, improves the liquid supply to boiling surface. Modifying the heating surface to the microchannel structured surface affects the heat transfer performance with more nucleation site density, and separate vapor-removal and liquid-supply pathways. These enhancements show that combined use of liquid subcooling and deep microchannel structured surface can be effective solution for thermal stability of high heat flux cooling applications.