Experimental Analysis of Heat and Mass Transfer in Small Dimension, Two Phase Loop Thermosyphons

This paper analyzes the thermofluiddynamics of compact twophase loops with natural circulation which are mainly ruled by the heat input supplied to the evaporator. The objective is to understand if in small two-phase thermosyphons the heat transfer performances are only due to the heat transfer in the evaporator section rather than the fluiddynamic characteristics of the entire loop. The results of the experimental analysis are obtained with water and FC72 and with two different types of loop thermosyphons. The first, type A, is characterized by the evaporator internal diameter much larger than the bubble diameter, while in the second, type B, evaporator and connecting pipes have diameters 4–5 times larger than the bubble diameter. For both thermosyphons capillary forces are not involved in the heat and mass transfer. For the type A thermosyphon the performances are mainly influenced only by the heat transfer regime in the evaporator section, and in type B thermosyphons, the performances are influenced by the fluiddynamic characteristics of the whole loop, and mainly by the mass flow rate.