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Allocation principle: In shell-and-tube heat exchangers with fluid heat transfer without phase change, the flow channels for the cold and hot fluids can be selected according to the following principle. 01 Materials that are dirty or prone to forming deposits should flow through the side that is easy to clean. For straight tube bundles, it is generally advisable to have the flow take place inside the tubes; this makes it easier to control the fluid velocity. Additionally, a higher fluid velocity is allowed inside the tubes, which can also help reduce scaling ； When the tube bundle can be removed for cleaning, it can also be processed outside the tubes. 02 Corrosive fluids should be passed through pipes to prevent both the tube bundle and the shell from being corroded. 03 Materials with very high (or very low) temperatures should be conveyed through pipes in order to reduce heat (or cold) loss, as this also helps to decrease the need for special metals and thus lowers the cost of heat exchangers ； However, it is advisable for the fluid to be cooled to flow in the shell side, to facilitate heat dissipation. 04 Materials under high pressure should be used in the tube side, so as to avoid the shell from bearing pressure and thereby reduce costs. 05 Fluids that allow for very low pressure drops should be used in the tube side; when the pressure drop is the same, a higher heat transfer coefficient can be achieved in the tube side. 06 Steam should flow in the shell side, as it is cleaner there, the heat transfer coefficient has less dependence on flow velocity, and it is also easier to remove the condensate. 07 Fluids with high viscosity are generally suitable for use in the shell side, as turbulence can be achieved at lower flow rates. If turbulence cannot be achieved in the shell side, it is advisable to use the tube side, as the calculated heat transfer coefficient for the tube side is more accurate. 08 Fluids with low flow rates should be used in the shell side, as turbulence can be achieved at lower flow velocities, allowing for the most economical design. 09 In cases where there is a large temperature difference between the two fluids, for heat exchangers with rigid structures, it is advisable to circulate the fluid with a higher heat transfer coefficient in the shell side in order to reduce thermal stress. 10 Fluids that require an increased flow rate to boost their heat transfer coefficient should be used in the tube side, as the cross-sectional area inside the tubes is smaller and multi-tube arrangements can be easily implemented.