Towards a numerical simulation of a closed loop pulsating heat pipe in different gravity levels

A Closed Loop Pulsating Heat Pipe (CLPHP) is a new concept of wickless heat pipe, which represents a promising and a flexible solution for moderately high heat flux applications. Numerous are the attempts to simulate the complex behaviour of a CLPHP and in particular one model was already successfully implemented by two of the authors (Mameli and Marengo). However, none of the existing models is able to well represent the effects of various gravity levels, and therefore a novel lumped parameter numerical model for the transient thermo-hydraulic simulation of a CLPHP has been developed. It consists of a two-phase separated flow model applicable to a confined operating regime, meaning that capillary slug flow is assumed a priori. A complete set of balance ordinary differential equations (mass, momentum and energy) accounts for thermal and fluid-dynamic phenomena. The suppression of the common assumption of saturated vapor plugs and the consequent implantation of heterogeneous phase changes represent the principal novelties with respect to the previous codes. The numerical tool is here used to simulate the thermal-hydraulic behavior of a planar CLPHP made of a copper tube (I.D./O.D. 1.1mm/2.0mm) and partially filled with FC-72 in modified gravity conditions (1g, 2g and 10g). This simulated configuration has already been tested experimentally both on ground (normal gravity) and on the ESA-ESTEC Large Diameter Centrifuge which allows reaching accelerations up to 20g. First comparisons with these operating conditions are provided.