Heat Transfer And Flow Characteristics Study On Supercirtical Water In Subchannnel With Square Distribution Of Reactor

Today, the world is facing a severe energy crisis and climate change, and energy hasbecome one of the important factors that affect human development. Especially in China,duing to the use of fossil fuels, a wide range of persistent fog and haze weather appears inrecent years, so making the adjustment of energy structure is imminent. Because nuclearpower does not cause pollution to the atmosphere, so developing nuclear power has becominga key policy of China’s energy construction. The fourth-generation nuclear power technologyis the development direction of nuclear power technology in the future. Supercriticalwater-cooled reactor (SCWR) is one of the six new fourth-generation reactors, and it has highenergy efficiency, simply system, compact structure and good economy. Based on thefoundation of existing nuclear reactors and supercritical thermal powers, SCWR is one of anew generation of nuclear power technology research and development in our country. Insupercritical water cooled reactor, the flow and heat transfer characteristics andthermal-hydraulic characteristics in core rod bundle channel play a vital role in the safety andeconomic operation of the entire system. The regularity laws of flow and heat transfercharacteristics on the core channel must be studied and solved in development of SCWRtechnology.The study subject of this paper was the sub-channel with square distribution, which wasformed that the diameter D of fuel rods was8mm and the pitch-to-diameter ratio P/D was1.2.Within the range of pressure from23to28MPa, inner wall heat flux from200to1000kW/m2, and mass velocity from700to1300kg/(m2s), the effect of pressure, inner wall heatflux and mass velocity on the inner wall temperature distribution, heat transfer, frictionalpressure drop, and secondary flow characteristics were analyzed. The experimental data,numerical simulation results and correlations were also preformed compared analyses. The heat transfer characteristics of supercritical pressure water flowing in sub-channelwith square distribution of SCWR were investigated by experiment and numerical simulation.The investigation results show that the heat transfer coefficient reaches a peak at the vicinityof pseudo-critical termperature.The enhancement of heat transfer is obvious. The inner walltemperature increases and heat transfer coefficient peak decreases as pressure and heat fluxincrease, but inner wall temperature decreases and heat transfer coefficient peak increases asmass velocity increase. All of pressure, heat flux and mass velocity have a significant impacton heat transfer coefficient in the large specific heat region, but have a little effect in the lowenthalpy region and the high enthalpy region which far away from the large specific heatregion. The specific heat and Prandtl number of supercritical pressure water reach peaks, anddensity, drnamic viscosity and thermal conductivity of supercritical pressure water sharpdecrease in the vicinity of pseudo-critical termperature region. This causes that the inner walltemperature increases gently as the water bulk enthalpy increases, and the heat transfercoefficient reaches a peak. Because the density sharply reduces at the vicinity ofpseudo-critical termperature, it can produce a small density fluid layer similar bubble. Thislayer hinders heat transfer between fluid and tube wall. The smaller of heat flux and massvelocity ratio (q/G), the more obvious heat transfer enhancement.The frictional pressure drop characteristics of supercritical pressure water flowing insub-channel with square distribution of SCWR were investigated experimentally. The resultsshow that mass velocity has a bigger influence on frictional pressure drop than pressure andheat flux. The increase of mass velocity makes the frictional pressure drop increaseconsiderably. The thermodynamic state of supercritical water is liquid in the low enthalpyregion but is gas in the high enthalpy region. This leads to the effect of mass velocity on thefriction pressure drop in the high enthalpy region has a more significant influence than in thelow enthalpy region. In the low enthalpy region, the influence of pressure and heat fluxincrease on the frictional pressure drop is not obvious; but in the high enthalpy region, thefrictional pressure drop decreases as pressure and heat flux increase.The secondary flow characteristics of supercritical pressure water flowing in sub-channelwith square distribution of SCWR were investigated by numerical simulation. The resultsshow that the pressure has a little influence on the structure and intensity of the secondaryflow, and heat flux and mass velocity have a vital effect on the structure and intensity of thesecondary flow. When the heat flux and mass velocity ratio (q/G) is small,8secondary flowvortexes are formd in sub-channel with square distrubition. Every1/8area has a vortex, everytwo adjacent vortexes flow symmetry. When the heat flux and mass velocity ratio (q/G) islarge,16secondary flow vortexes are formd in sub-channel with square distrubition. Every1/8area has two vortexes, and they rotate in opposite directions. The increase of heat flux and the decrease of mass velocity can make the ratio of the largest secondary flow velocity andthe mainstream velocity reduce. Under the different condition of pressure, heat flux and massvelocity, the secondary flow velocity is much smaller than the mainstream velocity, and theratio of the largest secondary flow velocity and the mainstream velocity is less than0.4%.Compared experimental data with numerical simulation results in sub-channel withsquare distribution of SCWR in this paper, and the heat transfer coefficient of experiment andnumerical simulation were also compared with correlations. The analysis researches show thatthe inner wall temperature trends along with water enthalpy well, and the value of the innerwall temperature much closes between experiment and numerical simulation. The heattransfer coefficient trends along with water enthalpy well, but the value of heat transfercoefficient has a certain deviation between experiment and numerical simulation. Themaximum deviation rate of inner wall temperature is6.2%, which is mainly caused by solvingthe one-dimensional steady-state heat conduction problem of sub-channel with squaredistribution. The deviation rate of experiment and numerical simulation heat transfercoefficient is large, which mainly caused by highly calculated inner wall temperature inexperiment. The heat transfer coefficients of numerical simulation can be conformed thecorrelations well overall, and conform the Petukhov k.(1983) correlation best well. The heattransfer coefficients of the experiment is small than the three correlations.