A Multi-Node Lumped Parameter Model Including Gravity and Real Gas Effects for Steady and Transient Analysis of Heat Pipes

This work presents a multi-node lumped parameter model able to predict the steady and transient behavior of capillary heat pipes, taking into account the effects of gravity (orientation angle) and the real gas effects in the vapor modeling. The model was validated against experimental results acquired by Leonardo S.p.A., which were obtained by simulating the behavior of a heat pipe embedded in a chassis cover, subject to seven cycles of transient thermal loading. After the validation, the analysis is focused on the model accuracy when using the ideal and real gas assumptions, using different working fluids (water, ammonia, acetone, HFC134a). The results showed that when using water or ammonia as working fluid, the error in modeling the vapor as an ideal instead of as real gas is negligible, both for the vapor temperatures and pressures predictions. On the contrary, when using acetone or HFC134a as working fluid, modeling the vapor as a real gas leads to a significant increase in the accuracy of the vapor pressure predictions.