Saturated Flow Boiling Heat Transfer In A Vertical Narrow Rectangular Channel

Saturated flow boiling in a narrow channel has the characteristics of high heat transfer coefficient and low temperature difference of heat transfer, therefore, narrow channels are suitable for being manufactured into compact heat transfer components with high heat transfer performance. This new technology of heat transfer enhancement with no source is widely applied to various fields such as microelectronic heat sink, cryogenic industry, air-conditioning, chemical industry and aeronautic & astronautic industry, etc.As to the. investigation of saturated flow boiling heat transfer in a narrow rectangular channel, reports are focused on experimental research with low latent heat work substance, at home and abroad, but reports on theoretical investigation are relatively small.A model of vapor-liquid two-phase cocurrent separated flow, for the first time, is established for saturated flow boiling heat transfer in a vertical narrow rectangular channel in this paper. The model equations have been numerically solved, the comparison of the heat transfer coefficient predicted by the model with a reported experimental correlation shows that this model can predict well, and the following results are obtained:(1) heat conduction in liquid film is the predominant mechanism of boiling heat transfer in vapor-liquid separated flow region in a vertical narrow rectangular channel;(2) when dryness fraction is kept constant, liquid film thickness increases with inlet pressure increasing, and decreases with channel space decreasing or mass flux increasing, but the decreasing trend becomes slowly with dryness fraction increasing;(3) the effect of the relative change of the channel space on liquid film is higher than that of mass flux;(4) when the channel space is kept constant, slip ratio increases with mass flux increasing, but decreases with liquid phase Reynolds number increasing; when mass flux is kept constant and the channel space is kept increasing, the decreasing trend of slip ratio with liquid phase Reynolds number increasing becomes slowly;(5) the ratio of frictional pressure gradient to total pressure gradient increases with dryness fraction increasing or mass flux increasing, and the increasing trend becomes slowly with dryness fraction increasing, the ratio increases with the channelspace decreasing and decreases with inlet pressure increasing;(6) the effect of interfacial evaporation term can be neglected when the heat flux is low and the work substance's latent heat is high.Saturated flow boiling heat transfer of water in a vertical narrow rectangular channel has been investigated experimentally. The comparison of primary experiment results with a reported correlation suitable for conventional pipes shows that the heat transfer augmentation factor is 1.25 ~ 2.0.Based on the results of the theoretical model in this paper, the skeleton of a semi-empirical correlation is established for boiling heat transfer in vapor-liquid separated flow region in a vertical narrow rectangular channel.