Fusion Reactor Divertor Subcooled Flow Boiling Critical Heat Flux Simulation Analysis

The fusion reactor divertor is subjected to extremely high heat load.When the heat load exceeds the critical heat flux?CHF?,there will be a phenomenon that departure from nuclear boiling?DNB,one of the forms of heat transfer deterioration?,resulting in a sudden drop in the heat transfer coefficient.The rapid increase in temperature eventually leads to damage to the divertor,which greatly threatens the operating life of the fusion device.The critical heat flux is an important thermal hydraulic parameter in the safety review of divertor.Therefore,studying the critical heat flux density is of great significance for the design and safe operation of the divertor cooling system.In this paper,water is used as the cooling medium,and the theory and model of critical heat flux heat transfer in subcooled flow boiling are analyzed.Under the condition of high mass flow rate and high heat load,the Euler multiphase flow model is combined with the critical heat flux and two by using Fluent software.The phase interaction model studied the CHF and pressure drop of a vertically upward unilaterally heated plain tube and inserted the twisted tube.?1?Effects of thermal hydraulic parameter on CHF in the subcooled flow boilingIn order to validate the accuracy of the used numerical model,the comparison between the critical heat flux of the numerical simulation and the experimental data was conducted in a cooling plain tube by using Fluent software.This section carried out the temperature distribution of the solid component in cooling tubes,the boling heat transfer regularities and the influences of mass flux and inlet subcooling on CHF.The results are as follows.There are two different heat transfer modes in different regions at the inside surface of the cooling tube.At the upper part of the inside surface of the tube,the nucleate subcooled boiling is the primary heat transfer mechanism.In the other side,along the lower parts of cooling tube inner wall,the heat transfer mode is the single-phase convection.It is indicated that the subcooled boiling region on the cross-sectional plane is enlarged with the increasing of the incident heat flux;The CHF increases by increasing the mass fluxes.The location of DNB for the tube with twisted tape inserts at G=9756 kg/m² s is 37.33%larger than that at G=9000 kg/m² s while104.76%larger than that at G=8000 kg/m² s at 30 MW/m²;The critical heat flux increases with increasing inlet subcooling.The location of DNB at?T_sub,in=157 K is85.63%larger than that at?T_sub,in=107 K while 91.19%larger than that at?T_sub,in=57 K when heat flux is 30 MW/m².?2?Effects of structure parameter on CHF in the subcooled flow boilingUnder the high mass flux and high heat flux,the effects of structure parameter?length-to-diameter ratio,twist ratio and tape width ratio?on CHF in the subcooled flow boiling.The results are as follows.Compared with the plain tube,it is demonstrated that tube with twisted tape inserts can delay the occurrence of DNB and the sharp rise of wall temperature.The decreasing the length-to-diameter ratios can delay the sharp rise of wall temperature and the occurrence of DNB.Moreover,the less the length-to-diameter ratios is,the more apparent the influence of the length-to-diameter ratios on delaying the sharp rise of wall temperature is.The location of DNB for the plain tube at L/D=21.4 is 69.86%larger than that at L/D=27.3 while165.91%larger than that at L/D=36 at 30 MW/m²;By decreasing the twisted ratio in tube with twisted tape inserts,the occurrence of the sharp rise of wall temperature and DNB can be delayed and the heat transfer performance can be enhanced.CHF can be strongly influenced by the lower twist ratio.The location of DNB for the tube with twisted tape inserts at y=6 is 27.88%larger than that at y=10 while 120.64%larger than that for the plain tube at 9756 kg/m² s;By increasing tape width ratios,the sharp rise of wall temperature and the occurrence of DNB can be delayed while the heat transfer is enhanced.The location of DNB for the tube with twisted tape inserts at w=0.43 is 36.04%larger than that at w=0.29 while 141.66%larger than that for the plain tube at 28 MW/m².?3?Parametric trends on pressure drop in subcooled flow boilingThe effects of structure parameter?length-to-diameter ratio,twist ratio and tape width ratio?and thermal hydraulic parameters?mass flux and inlet subcooling?on pressure drop in the subcooled flow boiling.The results are as follows.The pressure drop can increase with increasing the length-to-diameter ratios.The pressure drop at L/D=36 is 121.87%larger than that at L/D=27.3 while 221.76%larger than that at L/D=21.4 when heat flux is 30 MW/m²;Due to the flow blockage from the twisted tape on the cross section,the less the twist ratio becomes and the larger the pressure drop becomes.The pressure drop at y=2 is 19.75%larger than that at y=6 while21.89%larger than that at y=10 when heat flux is 30 MW/m²;The more the tape width ratio becomes,the larger the pressure drops become.The pressure drop at w=0.86 is 3.83%larger than that at w=0.43 while 10.80%larger than that at w=0.29when heat flux is 30 MW/m².The pressure drop between the inlet and outlet increases with increasing the mass flux.The pressure drop at G=12000 kg/m² s is 20.21%larger than that at G=9756 kg/m² s while 68.85%larger than that at G=8000 kg/m² s when heat flux is 30 MW/m²;The lower inlet subcooling can increase the pressure drops.The pressure drop at?T_sub,in=57 K is 18.02%larger than that at?T_sub,in=107 K while24.86%larger than that at?T_sub,in=157 K when heat flux is 30 MW/m².Figure[42]table[5]reference[60].