Some Ideas on Thermosyphoning in a Heat Transport Loop

Abstract

Analysis of the experimental results from RD- 14M natural circulation tests have provided considerable insights into the conditions under which thermosyphoning can be an effective heat transport mechanism for the heat source. This paper focuses on the following aspects of heat transport under thermosyphoning conditions: a. transition from forced circulation to thermosyphoning, and b. transition from thermosyphoningto other natural circulation modes. From analysis of transition-from-forced-circulation-to-thermosyphoning RD-14M experiments(i.e., R-series tests), the transition period following the tripping of the primary heat transport pumps to the time when steady thermosyphoning conditions are established in the loop can be divided into three time phases: a pump rundown phase, a flow-power adjustment phase, and a phase during which a thermosyphoning density driving head is established. A physically reasonable criterion for the onset of local temperature excursions in the transition period is proposed, From analysis of transition-from-thermosyphoning-to-other-natural-circulation-mode RD-14M experiments (i. e., T-series tests), departure from two-phase thermosyphoning is characterized by the onset of flow reversals in some of the heated sections. A physically reasonable criterion for the onset of flow reversal in the heated sections has previously been proposed. It is shown that this criterion can be used to classify RD-14M T-series tests into three categories: tests with flow reversals under relatively steady conditions, tests with flow reversals under highly oscillatory conditions, and tests with hybrid flow reversals. A detailed discussion of the first and second categories of T-series tests is presented. Experimental observations and results are explained in terms of this flow reversal criterion.