What is the reason for the high return water temperature in the primary network of the heat exchange station?
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There are two plate heat exchangers in the heat exchange station. The supply and return temperatures of the primary network are 55~45°C, with a total flow rate of 55 m3/h for this network. The temperature of the secondary network is 39~33°C; there is no flow meter on this network. Two water pumps are in operation, each with a rated flow rate of 65 m3/h. They operate at around 40 Hz, resulting in a total flow rate of approximately 90 m3/h. The temperature in the primary network cannot be reduced, and the temperature supply in the secondary network cannot be increased. What could be the reason? Thank you~
The heat exchanger does not have sufficient capacity; it’s a problem stemming from the initial design of the heat exchanger. It’s likely that costs were saved by not hiring a qualified designer.
Hello, may I ask what is causing the insufficient heat exchange capacity? If the heat exchange area is reduced, do I need to add more plates? Is it because the heat exchange area is larger, resulting in a lower flow velocity inside the plate exchanger? Should it be the plate exchanger manufacturer who makes the adjustments, or the designer?
It depends on the flow channel structure of your heat exchanger; generally, the principle is: 1. When the cross-sectional area of the flow channel remains constant (i.e., the linear velocity remains unchanged), the area is increased ； 2. It is estimated to be difficult to reduce the flow channel cross-sectional area while keeping the area constant in order to increase the linear velocity.
I don’t quite understand what the poster means by a primary network and a secondary network. In my understanding, the temperature on the hot side should be between 55–45°C, while it should be between 39–33°C on the cold side. There are several possible reasons for this: 1. The plate heat exchanger has been in use for a long time, resulting in dirt buildup (the manufacturer can be contacted to clean it). 2. The heat exchanger may not be capable of transferring enough heat. 3. Changes in the operating conditions on the hot or cold side may also lead to insufficient heat transfer. The poster only mentioned that the temperature in the primary network doesn’t drop, and the temperature in the secondary network doesn’t rise; it’s difficult to determine the cause. Some detailed data could be provided for reference, so that we can discuss this together
This post was last edited by Huda Ma on 2017-1-16 at 11:40. Yes, the operating conditions do not meet the design specifications. The plate exchanger is of counter-current type, with 28 flow channels per pass and a heat transfer area of 19 m2. Bore diameter DN65/DN100.
The plate exchanger is of counter-current type, with 28 flow channels per pass and a heat transfer area of 19 m2. Bore diameter DN65/DN100. I think if the flow rate on the hot side can’t be increased, then by increasing the area, the flow velocity between the plates decreases, and the K value becomes smaller. I tried running only one heat exchanger to increase the flow rate, but it didn’t work; the flow rate in Network 1 decreased, and the temperature in Network 2 dropped quickly to 2.5°C.
I did the calculations; 19 m2 should be sufficient. I’m not sure why it wouldn’t work