Tube side flow rate of a shell and tube heat exchanger during phase change
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When designing a heat exchanger, the recommended flow rates for the tube side are 0.5–3 for liquids and 5–30 for gases. So what flow rate should be used in cases where there is phase change? Taking an external circulation evaporator with atmospheric pressure water vaporization as an example, for 100 L of water with a vaporization rate of 10%, the volume of the steam at the outlet is 16 m3; thus, the volume difference between the inlet and outlet is 160 times. When calculating the flow rate in the tube side, is it more appropriate to use the values related to the gas phase or those related to the liquid phase?
For this, I usually choose 15 for the gas-phase inlet and 0.5 for the liquid-phase outlet
It must be in the gas phase! Is it necessary to control the flow rate of the liquid inside the tubes? Is a high flow rate useful? So you should consider the outlet flow rate first! At normal pressure, 15–25 is fine; going slower is beneficial!