Condenser Temperature Effect on the Transient Behavior of a Pulsating Heat Pipe

A Pulsating Heat Pipe filled up with distilled water has been designed and tested at different condenser wall temperatures and heat power inputs. The device consists in a copper tube (internal and external diameters of 3.18 and 4.76 mm), bended into a planar serpentine with five U-turns in the heated zone. The tube is closed in a loop, evacuated and partially filled with pure water, with a filling ratio of 50%. The heating section is equipped by means of two heating elements able to dissipate up to 350W as total. A cold plate, directly connected to a thermal bath, keeping the condenser at a constant temperature in the range of 10 °C up to 60 °C, permits to perform tests at different condenser temperature levels. The temperature evolutions recorded both at the condenser and at the evaporator zone allow to evaluate the overall PHP thermal performance for all the configurations tested. The experimental results show different temperature superheats at different heat fluxes as the condenser temperatures and the input powers are changed. Based on experimental data, a theoretical analysis of the heat transfer mechanisms for the dynamic behavior of the PHP has been made. The most relevant equations of boiling and evaporation have been compared with the experimental results. Based on Roshenow equation, a simplified conductive model is proposed, which is compared with experimental data. It is found that the model is in good agreement with the experimental results, especially after the full activation.