Abstract
The study investigates the boiling heat transfer and two-phase flow phenomena in a micro-evaporator with local heating for the diverging microchannels only. The micro-evaporator with a dimension of 2cm 2cm is composed of V-shaped micro diffusers for the entrance region to provide uniform flow distribution and parallel diverging channels with diverging angle of 0.55 degrees and 2/3 of the total length. In order to provide uniform mixture of methanol vapor, water vapor and oxygen to the reformer, the present study mixes the 50% hydrogen peroxide and methanol as the working fluid in the micro-evaporator. In the experiment, we compared the boiling heat transfer phenomenon of methanol and three mixtures of 50% hydrogen peroxide and methanol with volume ratio(C) of 1/2, 1/3, 1/4 with three flow rate, 0.18ml/min, 0.36ml/min, and 0.54ml/min. The experimental results indicate that the addition of hydrogen peroxide can significantly enhance boiling heat transfer as well as the critical heat flux. In the case of C=1/2 and flow rate of 0.54ml/min, the critical heat flux is 196.3 kW/m2. With the increase of the flow rate, critical heat flux, heat transfer coefficient and heat transfer efficiency are promoted. The addition of hydrogen peroxide may also result in severe two phase flow boiling instability, i.e., pressure drop and wall temperature oscillations occurs: this is most severe for the case of C=1/2 and flow rate of 0.36ml/min. Based on the results of this study, the mixture with C=1/3 showing the best heat transfer coefficient may be the optimized working fluid for a micro-evaporator to serve the purpose of this study. Key words: Hydrogen Peroxide、Evaporator、Microchannel、Two-Phase Flow、Reformed Methanol Fuel Cell