Effects of airborne hydrocarbon adsorption on pool boiling heat transfer

Abstract

During pool boiling, a significantly high heat flux leads to the transition from nucleate boiling to film boiling, where a vapor film forms over the boiling surface, drastically increasing thermal resistance. This transition at the critical heat flux (CHF) results in an abrupt increase in surface temperature and can lead to catastrophic failure of the boiler. However, reported CHF values vary greatly, even for smooth surfaces of the same material; for example, the CHF values on flat silicon and silicon dioxide surfaces vary across studies by up to 49% and 84%, respectively. Here, we address this discrepancy by accounting for hydrocarbon adsorption on boiling surface. Hydrocarbon adsorption on smooth boiling surfaces decreases surface wettability, hindering the ability to maintain liquid contact with the surface and, thus, lowering the pool boiling CHF. To investigate hydrocarbon adsorption kinetics under ambient conditions and the subsequent effect on CHF, we cleaned flat silicon dioxide samples with argon plasma to remove hydrocarbon contaminants and then exposed them to laboratory air for different periods of time before conducting pool boiling experiments. Pool boiling results along with x-ray photoelectron spectroscopy data showed that the amount of adsorbed hydrocarbon increased with exposure time in air, which resulted in a decrease in wettability and, accordingly, a decrease in CHF. This work has important implications for understanding the spread in CHF values reported in the literature and may serve as a guideline for the preparation of boiling surfaces to achieve consistent experimental results.