The increase of heat transfer area is beneficial to the increase of heat transfer load, but when the heat transfer area increases to a certain extent, the Reynolds number decreases, which may change from turbulent flow to laminar flow. This will reduce the heat transfer coefficient, but on the contrary, reduce the heat load. This effect is sometimes worse than that of using the original area for heat transfer. The opposite is true, so it is most appropriate to achieve a balanced and suitable heat transfer area.