Influencing factors of convective heat transfer film coefficient a: 1. Fluid flow pattern and convection 2. Physical properties of the fluid itself (thermal conductivity, specific heat capacity, density, expansion coefficient, etc.) 3. Whether there is a phase change in the heat transfer process 4. Heat transfer Temperature 5. Equipment structure (shape, arrangement and size of wall surface) Distillation basis: gas-liquid two-phase with the same or similar composition are in contact with each other for mass transfer and heat exchange, multiple partial gasification and multiple partial condensation occur, light The components are enriched in the gas phase, the heavy components are enriched in the liquid phase, the N molar heavy components in the gas phase are condensed and exothermic, and the N molar light components in the liquid phase are vaporized and endothermic. The rectification tower provides this operation. place. Fluid flow pattern: 1. Features of stagnation (laminar flow): ① Because the flow velocity is very slow, the fluid flows layer by layer. ② The fluid particle moves only in the axial direction and hardly moves in the radial direction. ③ The trajectory of particle motion is parabolic and the tip is sharp. ④Vmax = 2V average V average, = 1 / 2Vmax. 2. Turbulent flow characteristics: ① Due to the fast velocity, the fluid is no longer a layer-by-layer movement, but a chaotic movement, and the interface between layers disappears. ② Fluid particles move not only in the axial direction but also in the radial direction. ③ The trajectory of the mass particle is distributed in a parabola, and the tip is relatively smooth. ④V average = 0.8Vmax.