Session: 11-02 Severe accident mitigation phenomena

Paper Number: 134969

134969 - Experimental Study of Rectangular Channel Heat Transfer With Buoyancy-Aided Flow Under Asymmetrically Heating 

Abstract: 

Mixed convection in vertical channels is widely used as a common heat transfer method in various engineering facilities. Especially after the Fukushima nuclear accident, the demand for non-energetic safety systems with natural convection circulation of air has been increasing. In this context, the HPR1000 passive containment cooling system (PCS) outer heat exchanger tank air cooling channel can be used as a case study for mixed convection. The PCS system of the HPR1000 can guarantee the safety of the reactor for 72 hours after the accident. However, if the reactor accident remains uncontrolled after 72 hours and the water in the heat exchanger tank evaporates, the reactor will be in danger again. Therefore, to extend the effective operation time of the PCS, it is necessary to make use of the convective heat transfer of air so that the heat exchange capacity of the heat exchange tank can be further improved.

Mixed convection can be classified as buoyancy-aided flow or buoyancy-opposed flow based on the buoyancy effect of forced convection in the same or opposite direction and natural convection. In contrast to forced convection, the phenomenon of "heat transfer deterioration" is frequently seen in buoyancy-aided flow. The fact that heat transfer gradually weakens with increasing buoyancy force in the case of modest buoyancy force and gradually strengthens with increasing buoyancy force is indicative of this phenomenon.

Many nuclear power facilities use natural air circulation as part of their non-energetic safety mechanisms to remove heat. Both forced and spontaneous convection are frequently involved in the flow during this cooling process in vertical channels. The flow is referred to as buoyancy-aided flow when the directions of forced convection and natural convection coincide. The mixed convection heat transfer coefficient phenomenon is lower than the forced convection heat transfer coefficient, and this type of flow will be in a specific buoyancy range. The supercritical fluid and water as the working medium, four-sided test-mode heating, asymmetric heating, and air as the work material of the experimental research are the main topics of current research on buoyancy-aided flow. Thus, the investigation of mixed convection under buoyancy-aided conditions is presented in this study, along with a comparison of the experimental findings with the current correlations and an analysis of the causes of the differences. Lastly, a modified Buoyancy number with an average deviation of ±20% is offered as a new correlation. This will serve as a point of reference for the relevant mixed convection heat transfer calculation.

Keywords: Asymmetrically heating; Mixed convection; Buoyancy-aided flow; Rectangular channel

Presenting Author: Zhongning Sun Heilongjiang Provincial Key Laboratory of Nuclear Power System & Equipment, Harbin Engineering University

Presenting Author Biography: I am a PhD student from the Harbin Engineering University. My research interests include experimental and numerical studies of convection and heat transfer in rectangular channel.

Authors:

Yongan Ji Harbin Engineering University
Zehua Guo Heilongjiang Provincial Key Laboratory of Nuclear Power System & Equipment, Harbin Engineering University
Ming Ding Heilongjiang Provincial Key Laboratory of Nuclear Power System & Equipment, Harbin Engineering University
Zhongning Sun Heilongjiang Provincial Key Laboratory of Nuclear Power System & Equipment, Harbin Engineering University