A loop heat pipe (LHP), which is a two-phase heat transfer device, was studied experimentally and theoretically. The steady-state operating characteristics of a LHP when it is operated at adverse (the condenser is below the evaporator) and zero elevations (the evaporator and the condenser are at the same level) had been studied intensively in the past. However, study of a LHP when it is operated at positive elevation (the condenser is above the evaporator) is still lacking. This paper presents detailed theoretical analysis of the steady-state behavior of a LHP operated at positive elevation. The present analysis agrees with experimental results, and is confirmed by flow visualization images. Testing was performed for a wide range of heat loads (20 W-600 W) at three positive elevations: 25.4mm, 76.2mm, and 127mm. Flow visualization images were taken by neutron radiography when the LHP was operated at 102mm positive elevation.

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