Visualisation and Heat Transfer Performance of Mini-Channel Flat Heat Pipe with a Binary Mixture

To unravel the intricacies of two-phase gas-liquid flow characteristics and heat transfer behavior, an array mini-channel gravity plate heat pipe (AMGPHP) is proposed in this work, which allows for observing the internal changes in the state of the working fluids. The flow patterns such as pool flow, columnar flow, and slug flow, are experimentally explored and analyzed in detail. It is found that the optimal volume fill ratio is 20% by utilizing start-up time and thermal resistance as performance evaluation metrics. With this fill ratio, a medium optimization strategy by blending ethanol within R141b is proposed and evaluated. In comparison to pure working fluids, the heat transfer performance of AMGFHP in the binary fluid has been significantly augmented due to temperature and concentration shifts resulting from disparate boiling points. Under the 10% volume fraction ethanol blending condition, the equivalent thermal conductivity of the heat pipe is dramatically elevated, with a value of 3110 W/(m·°C), along with the reduction of the minimum start-up power to 4 W. In general, applying such a medium to heat pipes has considerable potential in practical applications.