Influence of Nucleate Boiling on the Design of Automotive Cooling Systems

With higher power ratings in automotive cooling systems the correct calculation of the heat transfer coefficient when nucleate boiling is occurring has become important. In accounting for the enhanced cooling that nucleate boiling provides, analysts can achieve two goals: more accurate metal temperature prediction at local hot spots; and an assessment of the probability that catastrophic film boiling will occur. Two correlations examined: the classic Chen correlation and the more recent Liu and Winterton correlation. The method of extending the correlations to mixtures is explained. Predictions are presented for the 50:50 mixture of water and ethylene glycol, and compared with literature data. The method of incorporating these correlations into engine CAE analysis is explained and demonstrated. The paper also considers the effect of nucleate boiling on vapor production, leading to vapor blanketing and the critical heat flux. A method of estimating critical heat flux for the mixture is described.