【Q&A】July 2, 2017

①Unclean and scaling-prone fluids should be routed in the tube side, as cleaning inside the tubes is more convenient； ②Corrosive fluids should be passed through the tube side to prevent both the tube bundle and the shell from being corroded simultaneously ； ③Fluids with high pressure should flow in the tube side to prevent the shell from being subjected to pressure ； ④Saturated steam should flow in the shell side, as the heat transfer coefficient for steam condensation is independent of flow velocity, and the condensate can be easily removed ； ⑤If the temperature difference between the two fluids is large, when using a fixed-tube-sheet heat exchanger, it is advisable to arrange the fluid with a higher heat transfer coefficient in the shell side in order to reduce thermal stress.

Tube side: relatively low temperature and pressure; shell side: relatively clean and high temperature

The selection principle is: in terms of heat transfer efficiency, the material to be heated or cooled should flow through the tube side. However, considering that the tube side is easier to clean than the shell side, materials prone to scaling are generally chosen for the tube side.

Generally, materials that are heated or cooled should be placed in the tube side, but since the tube side is easier to clean than the shell side, materials prone to scaling are given priority to be placed in the tube side.

Principles for selecting the tube side and shell side in heat exchangers: (1) Fluids that are dirty or prone to scaling should be routed on the tube side, as cleaning inside the tubes is easier; (2) Toxic fluids should be placed on the tube side to reduce the risk of leaks; (3) Fluids with high pressure should be on the tube side to avoid stress being applied to the shell as well; (4) Corrosive fluids should be on the tube side to prevent both the tube bundle and the shell from being corroded, and it also facilitates cleaning and maintenance; (5) The fluid to be cooled should be on the shell side, as this aids heat dissipation and improves the cooling effect; (6) When there is a large temperature difference between the two fluids, the fluid with a higher coefficient of thermal expansion should be on the shell side, thereby reducing the temperature difference between the tube walls and the shell walls; (7) Fluids with low flow rates or high viscosity should be on the shell side, as baffle plates can help achieve turbulence at low Reynolds numbers (Re>100), or multiple tube rows can be used inside the tubes; (8) Saturated steam should be routed on the shell side, as this facilitates the removal of condensate and non-condensable gases, and the steam remains clean and does not cause contamination. In practice, it is often not possible to take all of these principles into account simultaneously, as they may conflict with each other. In such cases, it is necessary to consider the actual situation and focus on the most important factors as the basis for making a decision.