Abstract
Direct contact condensation (DCC) as a complex thermal-hydraulic phenomenon has been performed a great deal of research under forced flow conditions. It is an interesting challenge to study the phenomenon in a natural circulation system (NCS). In this paper, the flow behaviors along with DCC phenomena were experimentally investigated by visualization method in a NCS at low pressure. Moreover, the influence of initial parameters including heat flux, inlet temperature and resistance of the heated section on the NCS was analyzed in detail. The experimental results revealed that two types of DCC phenomena were found in the NCS. When Type I DCC occurs, the interface wave will be formed due to the hydraulic jump caused the reverse flow of subcooled water. Interface wave easily contributes to occurring Type II DCC due to the Kelvin-Helmholtz instability. In addition, the NCS tends to be more unstable with the increase in the heat flux or the inlet resistance. The influence of inlet temperature on the flow rate should comprehensively consider the changes of outlet parameters and subcooled degree of the steam and the subcooled water.
Highlights
Direct contact condensation (DCC) is a common and important thermal-hydraulic phenomenon where the saturated steam is condensed on a subcooled water interface
It can appear in Light Water Rectors (LWRs) during a postulated Loss of Coolant Accident (LOCA) (Park et al, 2009) or some passive natural circulation safety systems in Floating Nuclear Power Plants (FNPPs) (Sun et al, 2020)
Once the steam is entrapped by the subcooled water and forms a steam slug, the condensation induced water hammer (CIWH) may occur due to rapid condensation of the steam (Urban and Schlüter, 2014; Datta et al, 2016)
Summary
Direct contact condensation (DCC) is a common and important thermal-hydraulic phenomenon where the saturated steam is condensed on a subcooled water interface It can appear in Light Water Rectors (LWRs) during a postulated Loss of Coolant Accident (LOCA) (Park et al, 2009) or some passive natural circulation safety systems in Floating Nuclear Power Plants (FNPPs) (Sun et al, 2020). The pressure surge caused by CIWH can Abbreviations: CIWH, condensation induced water hammer; DCC, direct contact condensation; FNPP, floating nuclear power plant; HTC, heat transfer coefficient; LOCA, loss of coolant accident; LWR, light water reactor; NCS, natural circulation system; NMR, novel modular reactor; NPP, nuclear power plants; PCCS, passive containment cooling system; TC, thermocouple. Flow instability may occur if the DCC phenomenon occurs in an NCS (Sun et al, 2020)
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