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Capillary-pumped two-phase fluid loops
Capillary-Pumped Loops (CPL) and Loop Heat Pipes (LHP) are capillary-pumped two-phase fluid loops which allow the transport of large amounts of heat over larger distances and provide also more flexibility during integration and ground testing compared to classical heat pipes.  
The main feature of these loops is the very high capillary pumping capability (typically one order of magnitude higher than those of classical heat pipes) allowing then the use of small diameter and very long fluid transport lines. The additional important feature is that these long fluid transport lines are wickless as opposed to heat pipes. Due to high available evaporator pumping capability, flexible lines (typically corrugated bellow structure covered by metallic overbraid) could also be inserted in the fluid transport lines. All these features provide consequently some structural flexibility not offered by the relatively rigid and monolithic heat pipe structures. Indeed, the heat pipe bending process is somewhat problematic due to the continuous capillary structure that has to be guaranteed in the bent sections. Moreover in capillary-pumped two-phase loops, the distance between the evaporating and condensing section are no longer limited to several metres but can reach typically one order of magnitude higher depending on the several system parameters.
Such new systems, of which the development was initiated by ESA in the mid 1980s, are currently baselined in combination with heat pipe networks for use in deployable radiators, for thermal control of large dissipation and bulky satellite payloads (e.g. laser-based instruments (laser communication terminal), on-board processors, etc) as well as for heat transport from remotely located equipment to the satellite radiators.
Last update: 27 March 2007

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