Evaporative heat transfer at the evaporative section of a grooved heat pipe

Abstract

Evaporative heat and mass transfer phenomena in the vicinity of the liquid meniscus edge in the evaporator of a groove heat pipe is investigated theoretically and experimentally. A theoretical model for simulating the phenomena is proposed, which consists of macro- and microregions. The former represents the part of the liquid meniscus region where conventional heat and mass transfer take place, whereas the latter is a narrow meniscus edge region close and contacted to the solid wall where transport phenomenon is affected by the intermolecular forces or disjoining pressure. The numerical results obtained for ammonia as a working fluid indicate that a large heat flux on the order of megawatt per square meters is transported in the narrow microregion, and accordingly more than one-third of the total heat energy supplied from outer surface is transported through the microregion that is less than one-hundredth of the total meniscus area. An optical measurement was conducted at the meniscus edge to confirm the existence of the thin nonevaporative liquid film and to identify its thickness on the order of several tens of nanometers. These magnitudes of nonevaporative film thickness can be explained by the proposed theory.