Experimental research on flow boiling characteristics of micro pin-fin arrays with different hydrophobic coatings

Experimental investigations have been conducted on flow and thermal performance of coolant flow boiling in diamond micro arrays with different contact angles (90 degrees, 120 degrees and 150 degrees). Working fluid circulating under mass flow rates in the scope of 21.54-962.75 kg/(m2.s). Images captured by high-speed camera with 500fps showed the coolant flow pattern in these micro pin-fin arrays. Comparative experiments of thermal performance of four micro pin-fins were performed at inlet temperature of 30 degrees C. The flow patterns of flow boiling could be divided into four states: film boiling state, transition state, nucleate boiling state and single-phase state. The pressure drop of hydrophobic surface is 90% lower than that of bare copper surface as the mass flow rate is 215 kg/(m2.s) The flow resistance is reduced after being covered with hydrophobic coatings. With the increase of contact angles, the micro arrays' thermal characteristics becomes deteriorated rapidly. The flow and thermal performance of diamond micro arrays is better than other three shapes, as the structure of diamond pin-fins plays a significant role in separation and migration of vapor film and bubbles. When the mass flow rate reaches 448 kg/ (m2.s), the heat transfer coefficient of diamond is 76% higher than that of triangle.