Application of heat pipe based refrigeration system for an electric train traction converter. An experimental study case

Refrigeration systems of railway traction inverters have experienced crucial progress recently. The use of assisted convection has been one of the most significant improvements, being heat pipe based heat sinks (HPHS) the main application. Due to the operating principle of a heat pipe, which lies in evaporation and condensation of a fluid, the HPHS is a very non-linear device. Several variables play a critical role and a simple theoretical analysis by itself does not provide enough information for an accurate model. As a result, in order to evaluate the performance of a HPHS for a generic traction converter, we have developed an experimentation process. It consists of aerodynamic tests in an airport and thermal tests in a self-designed wind tunnel. The objective of this method is the complete characterisation of the HPHS and thereby, the prediction of the behaviour of the refrigeration system for the real operation of a train. During the aerodynamic tests we have deduced the relationship between the air-flow through the HPHS and the train speed. Besides, we have analysed some extra phenomena, such as the double-cavity flow and the air-leakage of the system. The thermal study has allowed us to determine the thermal resistance network, working out the influence of the power losses of the inverter and the air velocity in the overall efficiency of the HPHS. In addition, we have examined transient response and the importance of natural convection. The paper summarizes both series of tests carried out with the system subject to study and presents the main results and conclusions.