Numerical Investigation On Heat Transfer Of Supercritical Water In Core Channel With Grid Spacer

Supercritical water cooled reactor(SCWR)is a supercritical power generation technology using nuclear energy.It is efficient,economical and safe.The SCWR medium flows through the core channel of the fuel rod to transport nuclear fission heat.The channel structure is complex,and the existence of the grid spacer changes the flow and heat transfer in the core channel.Because of the limitation of technology,the test is difficult and the flow field in the channel cannot be observed very well.Therefore,numerical study on the flow and heat transfer in the core becomes an effective method.Numerical research on smooth channel based on SCWR core triangle channel test was carried out firstly in this paper.The influence of different thermal parameters on the heat transfer,the influence of the solid heat conduction and entropy production change of flow and heat transfer process within the smooth channel were analyzed.And it established a channel geometric model based on channel with grid spacer test,verified turbulence model,checked grid independence validation and analyzed the characteristics of heat transfer with or not grid spacer.Finally,the influence of different types of spacer grids on the flow field and heat transfer in the core channel were analyzed.And the compare analysis were made by changing the structural parameters of different type of grid spacer.The analysis of smooth channel shows that the influence of pressure is mainly reflected in the pseudo critical zone.With the increase of pressure,the peak value of heat transfer coefficient decreases gradually.The enhancement of mass velocity can effectively enhance heat transfer.The inner wall temperature rises gradually with the heat flux increasing.The inner wall temperature is higher and the heat transfer coefficient is smaller when fluid-solid coupling is adopted.The mainstream of entropy production decreases firstly and then rises gradually with the increase of enthalpy.The heat transfer enhancement phenomenon happens when the entropy production is at the minimum.The fluid-solid coupling calculation model is built up about channel with grid spacer and the SSG turbulence model can be better used to study the characteristics of heat transfer of supercritical water.The numerical study on the flow field and heat transfer in the core channel with different types of grid spacer shows that cross section of the mainstream speed is greatly increased,the wall temperature decreases rapidly,and the heat transfer coefficient increases rapidly when through the standard grid spacer.The velocity of the radial turbulence kinetic energy in the lower reaches of the channel has the largest change,and the pressure in the center of the channel is reduced.Because the existence of flow blockage discs at the end of the grid spacer,the flow velocity is not uniform and the turbulence kinetic energy significantly increased in the center of the channel.The temperature of the wall at the end of the spacer is reduced rapidly.A plurality of vortices of varying speeds are formed on the cross section,the secondary flow distribution is extremely irregular.Due to the effect of the split-vanes on the flow field,the maximum velocity of the secondary flow is distributed at the heating wall,and the secondary flow in the channel forms a large flow around the wall,and the effects of turbulence is enhanced.The flow field in the whole channel is disturbed,which promotes the heat transfer between the fluid and the wall.By analyzing the influence of different grid spacer structure parameters on the flow heat transfer,it is found that at the grid spacer,with the thickness of the end face of the grid strap increasing,the wall temperature is lower,and the pressure drop is larger.At the end of the grid spacer,with the diameter of the flow blockage discs increases,the wall temperature drops sharply.The increase of the pressure in the upstream of the grid spacer is obvious.The cross section of began to weaken heat transfer is closer to the end of the grid spacer with the angle between the split-vanes and the axial gets larger.Different types of grid spacer in the body and its downstream appeare heat transfer enhancement area,the existence of grid spacer makes the regional wall temperature much smaller than without grid spacer.Regardless of which structure of the grid spacer,the total pressure drop along the axial direction is greater than without grid spacer.Pressure drop of grid spacer with the type of flow blockage discs is slightly larger than that of grid spacer with the type of split-vanes.Because the structure characteristics of flow strengthen at the end of the grid spacer is different,the latter structure is more linear and the structural resistance is relatively smaller.The support of the national natural science foundation of China(NO.51406026)and the plan of innovative talents in universities of Henan Province(NO.2012HASTIT018)is gratefully acknowledged.