Experimental and mechanical research on CHF characteristics during combined/bottom quenching in narrow rectangular channel

Abstract

Critical heat flux (CHF) phenomenon plays an important role during quenching phase when loss of coolant accident (LOCA) occurs in plate-type fuel reactor core. Heat transfer capability can be greatly enhanced with larger CHF value so that the cladding integrity can be maintained during quenching process. However, the related research on transient CHF during quenching process in narrow rectangular channel is extremely limited in literature, not to speak of combined quenching. Considered that quenching CHF mechanism may be totally different from that during heating process, experimental and mechanical researches were conducted comprehensively on CHF behavior during combined/bottom quenching in this article.Conclusion can be obtained that during combined quenching, bottom injection portion plays a dominant role because major portion of top injection may be expelled due to counter current flow limitation (CCFL) in narrow rectangular channel. Besides, boundary conditions such as injection methods, inlet subcooling, pressure and heating power have strong effect on CHF behavior. Based on previous visualization results, mechanism of quenching CHF can be attributed to dryout of liquid sublayer beneath coalesced bubble, and the proposed CHF model matches well with experimental data (RMS error 22.24%). The relevant findings are important for safety operation of plate-type fuel reactor and also can be applied in other industrial scenes where quenching phenomenon are encountered.