Performance of a flat-plate micro heat pipe at different filling ratios and working fluids

An experiment was carried out to study the effect of liquid filling ratio, inclination angle, and type of working fluid on the performance of a novel flat-plate micro heat pipe (FPMHP). The FPMHP is developed based on a multiport micro/minichannel flat tube, capable of the advantages such as the simple manufacturing process, flexible structure, good isothermal performance and heat transport with a long distance. Results shows that a filling ratio has a significant effect on thermal performance, and a FPMHP with a filling ratio of 20% has the best performance. The temperature distribution along the adiabatic section showed nearly no difference between two measuring points, indicating that the FPMHP is able to employed as a high-efficiency heat transfer equipment of phase change. FPMHP performance was improved remarkably when the inclination angle increased from 0° to 20° due to the effect of gravitational and buoyancy force, but the performance difference was negligible when the inclination angle increased from 20° to 90°. For different working fluids, the higher transmission factor, the better working fluids thermal performance. Thus, the FPMHP using methanol has the best performance, with a minimum thermal resistance of 0.18 K/W and a maximum thermal conductivity of 8539 W/mK, respectively.