Thermal-hydraulics and two-phase flow in capillary pumped loops

This investigation of Capillary Pumped Loops (CPL) with various geometries, component and working fluid charge level variations established steady-state circulation between the heat exchangers and was shown to have operation between natural circulation (i.e. circulation generated by elevation head only), forced convection from capillary action, and thermal contraction due to condensation and subcooling. The motivation behind this parametric study was to investigate the effect on the operational characteristics of the CPL for miniaturization of transport lines, packaging of the system, and off-design point operation in ground based applications. At less than optimal charge levels, a quasi-steady state circulation occurred between the capillary evaporator and the condenser with two-phase flow regime of slug-annular oscillation developing in the horizontal condensate return section and rising Taylor bubbles moving upward to the condenser exit. These quasi-steady state circulation phenomena occurred with the possible combination of back conduction from the capillary evaporator and a cavitation like phenomena due to the large subcooling of the condenser and/or the contraction in the horizontal condensate return section.;Through the use of single-phase mass flow measurement techniques and two-phase flow characteristic determination such as void fraction measurements and flow regime identification via high speed imaging, a more complete view of circulation in the CPL under terrestrial conditions has been accomplished.