Molecular dynamics study of wettability and pitch effects on maximum critical heat flux in evaporation and pool boiling heat transfer

Molecular dynamics simulations were employed to investigate the effects of wettability (contact angle) and pitch on nanoscale evaporation and pool boiling heat transfer of a liquid argon thin film on a horizontal copper substrate topped with cubic nano-pillars. The liquid-solid potential was incrementally altered to vary the contact angle between hydrophilic (similar to 0 degrees) and hydrophobic (similar to 127 degrees),and the pitch (distance between nano-pillars) was varied between 21.7 and 106.6 angstrom to observe the resultant effect on boiling heat transfer enhancement. For each contact angle, the superheat was gradually increased to initiate nucleate boiling and eventually pass the critical heat flux (CHF) into the film boiling regime. The CHF increases with pitch, and tends to decrease substantially with increasing contact angle. A maximum overall heat flux of 1.59. 10(8) W/m(2) occurs at the largest pitch investigated (106.6 angstrom), and as the contact angle increases the superheat required to reach the CHF condition also increases. Finally, in certain cases of small pitch and large contact angle, the liquid film was seen to transition to a Cassie-Baxter state, which greatly hindered heat transfer.