DROPWISE CONDENSATION ON HYDROPHOBIC MICROPOROUS POWDER AND THE TRANSITION TO INTRAPOWDER DROPLET REMOVAL
To improve condensation heat transfer technologies, various coating techniques have been used to generate rough hydrophobic surfaces. Condensation on micro-textured hydrophobic surfaces can demonstrate variable heat transfer enhancement compared to smooth hydrophobic surfaces. This is primarily directed towards the improvement in efficiency of condensers for direct dry cooling power plants. Here we investigate the use of a thiol-based self-assembled monolayer deposited on variably-sized microporous copper powder wick monolayers. A custom condensation chamber was fabricated to demonstrate the effect of enhanced dropwise condensation. Although rough hydrophobic surfaces have shown advantageous droplet growth dynamics, precise heat transfer measurements are underdeveloped at high heat flux. At consistent operating conditions, we experimentally demonstrated a 23% improvement in the local condensation heat transfer coefficient for a 4µm hydrophobic microporous copper powder surface compared to a smooth hydrophobic copper surface. This improvement is attributed to the reduction in contact angle hysteresis as evidenced by the decrease in departing droplet size. For larger powder sizes, surface flooding inhibited thermal performance due to larger departing droplet sizes and a decreased conduction pathway. With microporous powder sizes greater than 119µm, a transition of dropwise condensation to intrapowder droplet removal is evident. The use of enhanced two-phase thermal management technologies for high heat flux applications can benefit from the specific design of textured hydrophobic surfaces.