Selection of shell and tube heat exchangers

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1.3 Selection of shell and tube heat exchangers 1.3.1 Process conditions (1) Temperature The outlet temperature of the cooling water should not be higher than 60°C to avoid serious scaling. The temperature difference at the high temperature end should not be less than 20°C, and the temperature difference at the low temperature end should not be less than 5°C. (2) The pressure drop increases the process flow rate, which can increase the heat transfer coefficient and make the heat exchanger compact. However, increasing the flow rate will affect the pressure drop of the heat exchanger, aggravating abrasion and vibration damage. The increase in pressure drop increases power consumption, and there is usually an allowable pressure drop range. (3) Logistics arrangement ① In order to save the insulation layer and reduce the thickness of the shell, high-temperature logistics generally go through the tube side. Sometimes, for the cooling of materials, high-temperature logistics can also go through the shell side. ②The higher pressure material flows through the pipeline. ③The flow with higher viscosity goes through the shell side, and a higher heat transfer coefficient can be obtained in the shell side. ④Process streams that have specific requirements for pressure drop should be routed through the tube side because the calculation errors of the heat transfer coefficient and pressure drop in the tube side are small. ⑤Logistics with strong corrosiveness should go through the pipe route. ⑥Dirty and easily scaled materials should go through the shell side to facilitate cleaning and scale control. If a shell side is necessary, a square tube arrangement should be used, and a detachable (floating head, stuffing function, U-tube) heat exchanger should be used. ⑦Streams with a small flow rate should go to the shell side, which can easily cause the logistics to form a turbulent flow state, thereby increasing the heat transfer coefficient. ⑧Streams with a small heat transfer film coefficient (such as gas) should go to the shell side to easily increase the heat transfer film coefficient.