Critical heat flux of boiling heat transfer in a moderate narrow space

Boiling heat transfer process is analyzed in a moderate narrow space consisted of two horizontal plates. The main difference between this process and the conventional unconfined pool boiling is the liquid supply mechanism which is absolutely prevented by the growth of coalescence bubble along with the heated surface in the narrow space. As a result, the macrolayer becomes thinner due to the evaporation of the individual bubbles within the macrolayer during the period of bubble coalescence, with or without dryout that depends on both the gap size of narrow space and the size of heated surface. For a specified size of the heated surface, the initial thickness of the liquid layer has a critical value which approaches a constant while the space height is larger than a critical value. The individual bubble behaviors and the heat transfer can be considered as the same as that in the unconfined pool boiling, if the space gap is large. However, the individual bubbles do not generate in the last period of the bubble coalescence and a lower maximum heat flux will be resulted if the space gap is reduced. In such a case, the macrolayer is dryout.