Onset of nucleate boiling in minichannels

Subcooled flow boiling of R-134a in vertical channels of small diameter

“…The wall superheat needed to initiate boiling, DT sat,ONB , was found to be considerably higher for the same given values of heat and mass flux. The same trend for boiling incipience in microchannels is reported by Hapke et al (2000); and Ghiaasiaan and Chedester (2002). This increase is related by the latter, to the gaining importance of the thermocapillary force in microchannels, which would suppress the microbubbles that tend to form on the wall cavities.…”

Onset of Nucleate Boiling in Mini and Microchannels: A Brief Review

“…Although the result of comparison is not always reported, ΔT W and q W at ONB are usually higher than those predicted by conventional correlations (Hapke et al, 2000;Kennedy et al, 2000;Martín-Callizo et al, 2007;Qi et al, 2007) with a certain number of exceptions (Inasaka et al, 1989;Liu et al, 2005). Even if the nucleation site density is constant, the total number of nucleation sites should be smaller in a microchannel because of its small surface area.…”

“…In mini and microchannels, several investigators reported that the wall superheats needed for boiling incipience can noticeably be higher than those predicted by the conventional correlations (Hapke et al, 2000;Kennedy et al, 2000;Martín-Callizo et al, 2007;Qi et al, 2007). Since the presence of bubbles alters the characteristics of the pressure loss and heat transfer as in the conventional-sized channels, accurate prediction of ONB is of importance in the design of the heat exchangers or the heat sinks using microchannels.…”

Flow Patterns and Heat Transfer for Flow Boiling in Small to Micro Diameter Tubes

“…In the low quality region, the heat transfer coefficient was observed to decrease with quality up to approximately x = 0.25 and then became almost constant with further increase in quality. Hapke et al (2000) investigated boiling in a 1.5 mm internal diameter tube and reported that the onset of boiling occurred at higher liquid superheat than required for conventional tubes. Peng and Wang (1993) and Peng et al (1998), based on their observations of boiling in microchannels of hydraulic diameter 200 -600 m, argued that nucleation can hardly be seen in microchannels.…”