Effect of Gravity on the Thermal Instability Of a Closed Loop Pulsating Heat Pipe

A multi-turn Closed Loop Pulsating Heat Pipe (CLPHP) made of copper (I.D. 1.1mm, O.D. 2mm), filled with FC-72 is experimentally investigated. The study focuses in particular on the combined effect of the inclination angle (gravity) and heat input level on the device stability and thermal performance. Results show that tilting has poor effect on the start-up heat input level while the CLPHP is more sensitive to the gravity head at high heat inputs. Furthermore the occurrence of multiple steady states, already detected in literature for the single loop configuration is observed also for the multi-turn CLPHP but only in the gravity assisted mode. The CLPHP in the horizontal position is less efficient, but it does not undergo any instability nor multiple working modes nor performance drops with respect to the heat input level until the maximum heat input level is reached.