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The selection of fluid flow velocity in plate heat exchangers has a significant impact on heat transfer efficiency, energy consumption, and operating costs. Increasing the flow rate of the fluid in a plate heat exchanger can improve heat transfer efficiency and reduce equipment costs, but it also increases operating expenses; therefore, the choice of flow rate should be determined by considering various factors. Many problems were encountered during the selection process that affects the flow rate. But there is a theory regarding flow rate; let’s learn about it through the following information. 1. According to relevant information, the heat exchange area is proportional to the 0.6–0.9 power of the velocity. Power consumption, on the other hand, is proportional to the cube of the speed. It can be seen that low flow rates help save energy and reduce operating costs. However, too low a flow rate will lead to a significant decrease in the heat transfer coefficient, an increase in the heat exchange area, and higher initial investment costs. 2. Theoretically, a plate heat exchanger should have an appropriate flow rate, at which both the initial investment and operating costs of the equipment are low. Practice has shown that a water flow rate of 0.2~0.6 m/s is generally optimal. For centralized heating systems using hot water, the allowable pressure drop in the external network for the heat exchange station is generally 30–50 kPa. Therefore, in the calculation of plate heat exchangers, the flow velocity of the heat transfer fluid on the primary side should be kept within the range of 0.2 to 0.6 m/s. The fluid flow velocity in the aforementioned plate heat exchangers is merely a theoretical value; when making a choice, users should consider their actual operating conditions and not select such exchangers blindly, to avoid adverse effects on the heat exchange system.