Correlation of heat pipe heat transport limits with vapor pressure

Correlations are developed for the sonic limit, entrainment limit, and boiling limit of heat pipes as simple power law functions of the pressure of the heat pipe vapor. The correlations agree very well with calculations using actual heat transport limit equations for lithium, sodium, water, ammonia, and (for the sonic limit) Freon 11. Since the operational vapor pressure for most heat pipe fluids lies within the range of 1 to 100 psia, the correlations permit the heat transport capabilities of widely divergent fluids to be readily compared. The correlations may be manipulated further to minimize the spread in heat transport limits for various fluids at a given vapor pressure, raising the possibility of a single equation for each limit which is valid for all fluids.