Next step toward the miniaturisation of space cryocoolers
PhD thesis under the supervision of:
- Frédéric AYELA - LEGI
- Damien COLOMBET - LEGI
- Nicolas LUCHIER - SBT/INAC, CEA Grenoble
- Manuel MEDRANO MUNOZ - SBT/INAC, CEA Grenoble
Abstract
This research is done in the framework of miniaturisation of pulse tube cryocoolers studies and especially to gain a better understanding of the mass flow and heat transfert in the regenerator, which is a crucial component of these type of cryocoolers. In this work we present a numerical and experimental study of the Darcy Weisbach friction factor and Nusselt number for a continuous and steady flow at moderate Reynolds number O(1−100) in a micro-machined regenerators. The influence of porosity from 40 to 80 % and of geometry parameters are studied. Well-controlled microstructures represent convoluted channels of 10, 20 or 40 μm width and 100−150 or 300 μm depth generated by rhombic- or sinusoidal-shaped columns. The channels are etched in Silicon wafers using DRIE MEMS technology. The thermometers are integrated inside the regenerator’s micro-structure to measure the temperature evolution. The efficiency of the regenerators is estimated using two different approaches : the first, as a ratio of pressure drop losses and heat transfer efficiency (NPH/NTU) ; the second, as a volumetric heat transfer density coefficient proposed by Bejan.