Heat transfer correlation for intermittent spray impingement: A dynamic approach

The work presented here investigates a new approach in the development of heat transfer empirical correlations for intermittent spray impingement, based on simultaneous measurements of the spray droplets characteristics and the surface thermal behavior. Conventionally, heat transfer correlations for spray impingement do not consider the temporal variations of droplets characteristics. However, in applications using intermittent sprays (internal combustion engines, cryogen spray cooling or microprocessor thermal management), the spray transient behavior suggests that heat transfer predictions may be improved using a dynamic approach. Additionally, the impact of multiple consecutive injections on a heated surface implies a certain degree of interaction, depending on the frequency of their intermittency. If the time between consecutive injections is shorten, the result is the formation of a liquid film which mitigates phase-change and privileges a single-phase heat transfer over a two-phase. This suggests that heat transfer correlations for spray impingement should take the spray unsteadiness and the multiple injections interaction degree into account. The dynamic approach here suggested presupposes the identification of systematic periods characterizing the spray dynamic behavior and, once identified, the development of a heat transfer correlation for each period. The analysis ends with a comparison between the dynamic heat transfer correlation with a correlation obtained using the conventional approach and a significant improvement in heat transfer predictions is achieved if the spray dynamic nature is considered.