How is the length of the heat exchange tube determined for condensation in low-pressure steam pipes?
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I need to design a shell-and-tube heat exchanger for the condensation of low-pressure steam; the steam pressure is 34 kPa and the flow rate is 42.8 t/h. Condensation takes place inside the horizontal tubes, and I know the heat exchange area as well as the diameter of the heat exchange tubes. Question: How should the length of the heat exchange tubes or the number of tubes be determined? Is it based on the steam inlet velocity or something else?
The heat exchanger is selected based on the heat exchange area as well as pressure and temperature conditions. First, a standard model with a similar area is chosen, followed by calculations for the heat exchanger to determine whether the actual pressure drop and actual heat transfer coefficient meet the required standards. The percentage difference between the actual heat transfer coefficient and the specified value should be between 110% and 120%; this allows for the determination of the actual specifications and length of the heat exchange tubes. The calculation involves a complex iterative process; textbooks on chemical engineering principles provide the relevant calculation methods, or calculations can be carried out using books dedicated to the selection of heat exchange equipment.