A two-phase heat transfer device, a loop heat pipe (LHP), is studied analytically. It is noted that a LHP behaves differently when it is operated against gravity (adverse elevation) or at gravity assisted (positive elevation) conditions. Steady-state modeling of LHP operating characteristics at adverse or zero elevation was broadly studied in the past. This paper presents a steady-state model of a LHP when it is operated at positive elevation based on experimental results. The effects of elevation on the trend of steady-state operating temperature (SSOT) are then studied using the newly developed steady-state model. Experimental results agree with the model predictions at adverse (88.9mm), zero, and positive (88.9mm) elevations. This steady-state model is the only model known to have the capability to predict the operating characteristics at positive elevation. The model will help to design the LHPs utilized in terrestrial applications.

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