The transfer of heat is accomplished by evaporating off of one liquid surface at the hot side and condensing the vapor produced at another liquid surface at the cold side. The advantages of CPL s are that they require no power to operate and they can transfer heat over distances as large as 30 or more feet. Their reliance upon evaporation and condensation to transfer heat makes them much more economical in terms of weight than conventional heat transfer systems. The disadvantage of CPL s is that they have proven to be unreliable in space operations and the explanation for this reliability problem has been elusive. A generalized diagram of this type of device is shown in figure 1.
Capillary action drives the recondensed liquid back to the evaporator side.
The premise for the CHT research is based upon previous internal pressure measurements of CPL devices when unexpected system failure has been observed. In virtually all cases, substantial pressure oscillations have been observed. Previous research by Hallinan and Allen has shown that these pressure oscillations can be attributed to unstable evaporator menisci. Short-duration rapid evaporative flux increases have been observed. This rapidly evaporating liquid gives rise to significant vapor recoil stresses on the menisci present in the evaporator which causes the liquid to recede from the heated zone.