Against the cooling problem of engine heat exchangers

the flow and heat transfer characteristics of hydrogen in vertical and U-shaped tubes at supercritical pressures are studied. The influence of pressure and mass flow rate on heat transfer of the pipeline is studied by numerical method

and the heat transfer law is obtained. The heat transfer mechanism of the elbow section is discussed in depth

and the effect of dimensionless force on heat transfer is analyzed. The results show that

the closer the pressure is to the quasi-critical or when the mass flow rate increases

the convective heat transfer coefficient will increase

resulting in heat transfer enhancement. The bend section of the U-shaped tube can enhance heat transfer effectively

reaching a peak near θ=90°. There is a buoyancy effect in the straight pipe section at the inlet

but when the pressure is higher than 2.0 MPa

the buoyancy effect can be ignored after the hydrogen flows through the elbow section due to the influence of density difference. The Dean vortex caused by the secondary flow is the main factor to enhance the heat transfer performance of the elbow section

and the influence on the inlet section is significantly weaker than that on the outlet section.