FLOW REGIME RECOGNITION IN TWO-PHASE THERMOSYPHON LOOPS USING PRESSURE PULSE ANALYSES

Abstract

The nuclear industry finds application for natural circulation in the form of passive heat removal systems used under accident conditions as well as for the removal of parasitic heat loss during normal operation. A high temperature gas-cooled reactor containment cooling system for instance can take the form of a series of closed-loop two-phase natural circulation thermosyphon type heat pipes. In this paper a means of remotely predicting the flow patterns in the two-phase regions of a closed loop heat pipe is proposed. The process involves the measurement of the working fluid pressure response in the single-phase flow region where safe access to the loop is possible from a nuclear radiation hazard point-of-view. The pressure signal is then decomposed and a frequency spectrum generated in order to find a characteristic frequency for each of the flow phenomenon observed. To establish the validity of the analytical method a 2.2 m high rectangular loop was built using 25 mm diameter copper pipe. Experiments were performed and a comparison of the frequency spectrums shows the ability of the proposed analytical method to correctly identify the presence of different flow patterns. It is thus provisionally concluded that the procedure as outlined in this paper can be used to remotely characterising the flow pattern associated with the different flow regimes in a closed loop two-phase thermosyphon-type heat pipe.