Study On Flow Characteristics Of Small Natural Circulation Loop

The passive residual heat removal system is very important for the heat removal of reactors under stable operation or accident conditions.Its main principle is the phenomenon of natural circulation,and the study of natural circulation flow and heat transfer process is the key to the research of passive residual heat removal systems.At present,research on natural circulation circuits focuses on large-sized circuits,which have geometric parameters in the order of decimeters and meters,while there is relatively little research on small-sized circuits with geometric parameters in the order of millimeters.Conducting in-depth research on the flow and heat transfer characteristics of small natural circulation circuits can provide reference and selection for the heat dissipation of micro thermal components or electronic components.In this paper,CFD(computational fluid dynamics)method is used to study the natural circulation process.Use SOLID WORKS and ANSYS ICEM software to perform geometric modeling and mesh partitioning of the circuit;Using FLUENT software to perform numerical simulation calculations on the loop model,the flow and heat transfer laws of the natural circulation loop with small geometric parameters are calculated,providing data reference for theoretical analysis.This article first conducts numerical simulations on existing natural circulation experimental circuits to verify the feasibility of small-scale circuits;After that,small loops with the same length diameter ratio and different pipe diameters are numerically simulated to obtain the temperature and velocity distribution of each loop under different power.Through analysis,an effective method for optimizing the small-scale natural circulation circuit model is obtained.The results show that the steady-state flow rate of a single-phase natural circulation circuit is directly proportional to the 1/(m+1)th power of the heating power;For small natural circulation circuits,the magnitude of the eigenvalue m will decrease with the increase of pipe diameter.