Heat pipesperformance of 2phase closed thermosiphons
Abstract
This Data Item is available as part of the ESDU Subseries on Heat Tranfer. Processes involved in a thermosiphon, whereby high rates of heat transfer can be obtained between surfaces that have only a small temperature difference between them, are described. Heat is transferred by means of evaporation and condensation, and gravity is used to return the liquid film to the evaporator as compared with capillarydriven designs which use a wick. The thermosiphons discussed have: (1) circular tubes of uniform cross section; (2) a single component working fluid and no noncondensable gas; (3) either no wick or a simple wick or insert in the evaporator wall; and (4) angles of inclination to the horizontal 5 to 90 degrees. The maximum overall rate of heat transfer depends on the overall temperature difference and the sum of the thermal resistances of the various solid, liquid, and vaporous media and interfaces involved. Methods are given for calculating each thermal resistance. Advice and expressions are also given for the limits of vapor pressure, sonic velocity in the vapor, dryout, boiling limit, and the countercurrent flow limit.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 July 1982
 Bibcode:
 1982STIN...8333090.
 Keywords:

 Heat Pipes;
 Heat Transfer;
 Thermal Resistance;
 Thermosiphons;
 Counterflow;
 Evaporators;
 Mathematical Models;
 Performance;
 Pressure Heads;
 Surface Roughness;
 Temperature Gradients;
 Turbulence Effects;
 Working Fluids;
 Fluid Mechanics and Heat Transfer