Study Of Flow Boiling Heat Transfer Characteristics Inside Micro-channels With R134a

With the miniaturization of electronic devices, the study about the application of micro-scale heat transfer equipment become more widely, and micro-channel flow boiling heat transfer mechanism has been paid more attention. Study on the boiling heat transfer characteristics in micro-channels is carried out in the paper using numerical simulation method, which can provide theoretical guidance for application of R134a inside micro channels.In this dissertation, numerical simulation for gas-liquid phase change inside micro channel is studied. Three-dimensional rectangular channel is designed, and the effect of dimensions of the channel, the mass flow rate, wall heat flux on the distributions of bulk temperature, volume fraction and heat transfer coefficient etc are analyzed. The influence of dimensionless numbers such as Ja、Re and Bo on the boiling heat transfer characteristics are studied too. The influence of wall heat flux and mass flow rate on the nucleation site density are analyzed. The main work and conclusions are as follows:1. Among three channels(2mmxlmm,2mmx2mm,2mmx3mm), in the condition of same heat flux and same inlet mass flow rate, the flow temperature in channel of 2mm×1mm reaches saturation temperature more quickly. The onset of saturation temperature moves downstream with increasing of cross section. Among the three channels, when the mean temperature of the R134a flow close to the saturation temperature, the liquid change into vapor, and mean temperature increase slightly and more than the saturation temperature, the section fraction increase quickly, the mean temperature of the flow become decrease to saturation temperature at last.2. Among the three channels, the liquid inside channel of 2mm×1mm changed to vapor earliest, the onset of the vapor become retarded with increasing the cross section.3. The dissertation focused on the effect of Ja,Bo and Re number on the boiling heat transfer characteristics. Due to the dominant function of the evaporation heat transfer, the Reynolds number affect slightly the mean heat transfer coefficient.the heat transfer coefficient (h) and the Ja number increase with increasing of wall heat flux(q). The heat transfer coefficient increased with increasing of Bo for the three channels, indicating that the heat transfer effect has been enhanced and the nucleate boiling plays a dominant role in the boiling flow.4.The dissertation carried out study of relationship among the nucleation site density, mass flow rate and the wall heat flux. Within the scope of this article, the nucleation site density decreases slightly with increase of mass flow rate, and increases with increasing of the heat flux(q).