Abstract

The purpose of this work is to present an analytical model to predict the Geyser Boiling limit for high temperature two-phase thermosyphons. By this limit, it is understood the minimum heat flux required to the thermosyphon to work in the ideal operation regime. The Geyser Boiling phenomenon is characterized by a nucleate pool boiling instability that occurs in the evaporator mainly at low heat fluxes, resulting in abrupt synchronized temperature and pressure oscillations, in both the evaporator and condenser, not recommended in most actual applications. A new dimensionless “bubble release number”, which represents the wall superheat necessary to generate a bubble at given diameter and temperature operation conditions, is proposed. It is observed experimentally that thermosyphons operate in ideal regime, surpassing the Geyser Boiling, when the bubble release number is less than 0.01, value taken as the Geyser Boiling limit. Therefore, the minimum heat transfer rate necessary to operate high temperature thermosyphons in de ideal regime is given by the Geyser Boiling limit. The modeling presented in this paper can be used as an engineering tool to design high performance, safe operation systems, involving high temperature two-phase thermosyphons that operate outside the Geyser Boiling regime.