Correlations for boiling heat transfer characteristics of high-velocity circular jet impingement on the nano-characteristic stagnation zone

The jet impingement boiling is the most effective heat transfer method among all the steady-state heat transfer forms. However, various researches on the jet impingement boiling still lack experimental data for heat transfer characteristics under high impact velocity and special heated surface topography. Due to this reason, the present experimental study investigates the heat transfer characteristics of high-velocity circular jet impingement boiling on the nano-characteristic surface of the stagnation zone with different surface wettability. The wettability of the copper surface is varied to hydrophilic or hydrophobic nano-characteristic surface by modifying surface topography and chemistry. The effects of impact velocity, subcooling and solid-liquid contact angle (CA) on the onset of nucleate boiling (ONB), nucleate boiling heat transfer coefficient (HTC) and critical heat flux (CHF) are studied experimentally. It is found that the effects of impact velocity, subcooling and CA on the ONB are respectively independent. Comprehensive effects of impact velocity and CA on the nucleate boiling HTC are also obtained. The proportion of nucleate boiling HTC after the ONB point gets more significant with increasing wall superheat. The HTC will increase with increasing impact velocity and CA. Some empirical correlations are proposed for predicting the effects of impact velocity, subcooling and CA on the jet boiling heat transfer characteristics. What's more, the method for predicting the wall superheat corresponding to the CHF is discussed. The comparison results indicate the predicted value agrees well with the experimental data.