Wall Temperature Fluctuation Under Flow Pulsation in a Vertical Tube

Abstract

Flow boiling has been receiving lots of attention and researches because it is commonly encountered in nuclear reactors and stream generators. Experimental studies on heat transfer in a circular tube with constant wall heat flux were carried out in laminar flow regime. The experiments were under steady and pulsating conditions and performed over a range of <500 Re <2000 and under atmospheric pressure. The wall temperature near inlet (T w1 ) was investigated. The experiment results show that in a pulsation period, the wall temperature fluctuates periodically and has a sharp drop when the inlet pressure fluctuates intensely. The rise time of T w1 accounts for 80–85% of one pulsation period. The experiment results demonstrate that the pulsating period and amplitude have a strong influence on this phenomenon. The pulsating period and amplitude influence the shape of the wall temperature curve. Only when the fluid in the wave trough starts boiling, the phenomenon of sharp drop of wall temperature occurs, and a small wave trough appears in the rising of the wall temperature if the boiling time is long. Furthermore, the flow regime transition induced by buoyancy or the intense fluctuation of inlet pressure could be the reasons for a sharp drop of wall temperature.