To ensure the accuracy and time of CFD numerical computation, the appropriate quality and quantity of grids are very important. In this Radotinib（IY-5511) study, four three-dimensional meshes are generated by using ANSYS ICEM to investigate the effects of grid numbers on numerical results. They are mesh-1 (NX = 25, NY = 20, NZ = 100), mesh-2 (NX = 40, NY = 30, NZ = 150), mesh-3 (NX = 70, NY = 50, NZ = 200) and mesh-4 (NX = 90, NY = 65, NZ = 220). In order to accurately capture the thermal–hydraulic characteristics, the grid densities near the tube walls of all meshes are sufficiently high, as shown in Fig. 4. Table 1 lists the average Nusselt number Nu‾ and Fanning friction factor f‾ under laminar flow (Re = 100) of water in the flat tube shown in Fig. 1 when the inlet temperature is shoot 293 K.equation(10)Nu‾=1L∫0Lh(x)Dhkdxequation(11)f‾=ρDhΔP2LG2where h(x) = q″/(Tw(x) − Tb(x)) is the local heat transfer coefficient. ΔP and G are the pressure drop and mass velocity, respectively.