Lumped parameter model of sintered heat pipe: Transient numerical analysis and validation

This paper describes a lumped parameter numerical model which is able to simulate the transient as well as the steady-state operation of a sintered heat pipe. The main objective of the work is to build a simple, engineering-approach simulation tool to define the HP characteristics of small HPs, which are now in the market with doubtful specifications. The code has been validated by comparisons with numerical and experimental results readily available from the open literature and an extensive numerical simulation campaign has been carried out in order to characterize the thermal-hydraulic behavior of mini heat pipes. This analysis focuses particularly on the effects of wick thickness, porosity, grain structure and void fraction level in the evaporator on thermal performance and working limits. Mini HPs with different dimensions (8, 5 and 3 mm outer diameter, 1 mm wall thickness, sintered copper wick, water as filling fluid) have been considered. It was found that there is an optimum wick thickness which minimizes the thermal resistance with no remarkable grain radius effect, while, as expected, the grain size affects the evaporator wick dryness.