Heat transfer characteristics in a condenser of closed two‐phase thermosyphon: Effect of entrainment on heat transfer deterioration

Condensation heat transfer in a closed two‐phase thermosyphon is experimentally examined using two different types of test section. Test Section 1 is a straight‐pipe‐type thermosyphon, whereas Test Section 2 has a large‐diameter evaporator compared with a condenser to minimize entrainment at the evaporator. Condensation heat transfer in Test Section 1 shows much lower heat transfer coefficients than those estimated by a Nusselt theory. This low condensation heat transfer occurs due to a working fluid entrainment. It is confirmed from a result of Test Section 2 that the condensation heat transfer is similar to the values predicted by the Nusselt theory as far as the effect of the working fluid entrainment is negligible and flooding does not occur. A new correlation for the heat transfer coefficient considering the effect of entrainment is proposed.