Issues regarding the temperature difference of the cooling water return flow in heat exchangers
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May I ask whether, for heat exchangers, it is better to have a lower temperature difference in the cooling water return flow, or rather a larger temperature difference between the inlet and outlet of the return flow? What impact does this have on the design of the heat exchanger? Thank you
Regarding this issue, it is necessary to consider heat load and heat transfer rate. In industrial heat exchangers, the amount of heat exchanged between the cold and hot fluids per unit time is determined by the heat exchange requirements specified by the process, and this is referred to as the heat load of the heat exchanger. The heat load of a heat exchanger refers to its capacity for heat exchange; the requirement imposed on heat exchangers in production processes is that the heat transfer rate must be equal to or slightly greater than the heat load.
It is a comparison of the cost of heat exchangers and the operating costs of utility systems, taking corrosion and scaling into account
The outlet temperature of the cooling water should not exceed 60°C to avoid severe 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. When heat exchange occurs between the two process streams, the temperature difference at the lower-temperature end should not be less than 20°C. Typically, the cooling water inlet temperature is set at 30°C, and the outlet temperature at 40°C℃
For normal cooling (with both the hot and cold media being liquids), the temperature difference is 8–10°C.