The coolant-side model we currently use assumes free convection, which is not true in a lot of cases where the wall temperature is above the boiling point of the coolant. There are some correlations to roughly model nucleate boiling, given in the Wikipedia article above.
https://en.wikipedia.org/wiki/Nucleate_boiling#Boiling_heat_transfer_correlations
The coolant-side model we currently use assumes free convection, which is not true in a lot of cases where the wall temperature is above the boiling point of the coolant. There are some correlations to roughly model nucleate boiling, given in the Wikipedia article above.