Abstract:

ESDU 79012 is one of a group of five on heat pipe performance. It provides information from which the thermal resistance of the pipe can be estimated and the overall rate of heat transfer predicted. That overall heat transfer rate must then be compared with various calculated limits that must not be exceeded. They are the circulation limit that defines the maximum pressure difference that the wick can support, the vapour pressure (or viscous) limit which constrains the pressure drop in the vapour duct, the sonic limit for vapour sonic flow, and the entrainment limit above which the vapour will tear liquid droplets off the wick. A comprehensive practical worked example shows how a calculation flowchart is applied in design. ESDU 79013 gives wick properties, ESDU 81038 treats two-phase closed thermosyphons, ESDU 80013 introduces the use of heat pipes and includes practical design information, and ESDU 80017 gives properties of fluids relevant to heat pipe operation at temperatures of 210 to 570 K.