THREE-DIMENSIONAL NUMERICAL STUDY OF CIRCULAR-FIN TUBE HEAT EXCHANGER FOR UAV

摘要

The proton exchange membrane fuel cell (PEMFC) has been regarded as promising alternative power sources for unmanned aerial vehicle (UAV). The temperature of PEMFC stack should be maintained an optimal range around 60~80℃ to prevent stack membrane damages at high temperature or low efficiency of stack at low temperature. Therefore, thermal management is crucial to maximize the performance of the PEMFC. Generally, the thermal management system (TMS) of PEMFC is composed of heat exchanger (HEX), fan, and pump. In this work, since the weight of UAV is one of the main factors to affect the UAV flight, the fan is eliminated. That means only the air flowing through the UAV is used to cool down the stack coolant water. Therefore a design optimization of HEX is important to get the best performance of PEMFC for UAV. The three dimensional numerical modeling has been developed by using the commercial code of STAR-CCM+~®. In this simulation, the UAV body, circular-fin tube HEX, and duct are considered. Since the cruise velocity of the UAV is 40km/h, the air velocity at the duct inlet is set to be 40km/h. Heat exchanger is located at the top of the UAV, and the coolant water from the pump is flowing through the header and divided several tubes to increase the surface area of heat rejection rate or decrease the pressure drop. The mass flow rate of air flowing into each fin of HEX is determined by fluid analysis. In order to validate this model, the simulation results are compared with the experimental data, which is obtained at various coolant inlet temperatures, and coolant flow rates. And the parametric study of HEX model was conducted with various UAV velocities and air temperatures. One reference data point is selected to tune several unknown parameters in the model, and once established, the same parameter values are used for all other conditions. The simulation results are in good agreement with the experimental data. This model can be helpful to develop the optimal design of heat exchanger for UAV.