Boiling is an extensive heat transfer mechanism which allows cooling of high heat flux components such as electronic circuits etc. In those components the gaps between the heating sources are usually small and aprediction of the incipient boiling is not sufficiently accurate in the available models.
In the present work an experimental research of heat transfer between two isothermal vertical parallel plates was conducted in an enclosure. The experiments were performed in various gap sizes,δ, between 0.7 – 5 mm, and various heat fluxes, with water at an atmospheric pressure. The results in relatively large gaps for the single-phase heat transfer show a good agreement with common correlations such as Macgregor et al. 1969:
(1) 0.42·(Gr·pr)^0.25·pr^0.012·(L/δ)^-0.3
In small gap sizes (Raδ<2000), modified conduction was observed, in contrast to the common behavior of pure conduction. The incipience of boiling was detected visually between the plates and also by a slope change of the heat flux vs. ΔT(superheat) curve of the heated plate. Preliminary analysis of the incipient point results was done and it was observed that the heat flux in the two-phase zone increases at the same superheat as the gap size decreases. This behavior also influences the incipient boiling heat flux and superheat in the same manner.
