Operation analysis, response and performance evaluation of a pulsating heat pipe for low temperature heat recovery

Abstract

In the present work, a series of tests were designed and conducted aiming at investigating the thermal response and performance of a pulsating heat pipe operating with graphene-water ethylene glycol nano-suspension. The heat pipe was tested at various applied heat values between 10 and 100 W, concentrations of 0.1 g/l to 2 g/l of graphene nanoplatelets dispersed in water-ethylene glycol, different filling ratios, and condenser temperatures. Thermal conductivity and viscosity of the nano-suspensions were experimentally measured at various concentrations. A response surface methodology model was developed to optimize the thermal performance of the heat pipe by minimizing the thermal resistance of the system. Results showed that the thermal resistance value decreases by increasing the concentration of the graphene nanoplatelets and also by increasing the heat load to the evaporator. Likewise, filling ratio and temperature of the condenser were found to have a complementary effect on the optimization of the performance of the heat pipe such that the minimum thermal resistance value of 0.36 K/W was obtained at 85 W and condenser temperature of 23 °C, filling ratio of 0.35 and concentration of 2 g/l. It was identified that the presence of the graphene nanoplatelets contributes to the promotion of heat transfer mechanisms due to the intensification in micro-scale phenomena such as Brownian motion and thermophoresis effect. Using nonlinear regression analysis, a correlation was developed to predict the thermal resistance value of the system with an accuracy of <8.7%.