Number of heat transfer units of plate heat exchanger
The plate heat exchanger is a kind of heat exchange device. During the startup process, the heat exchange effect will be used continuously. This is due to its heat transfer unit, which will also require us to change the plate. The heat transfer unit of the heat exchanger is effectively calculated.
(1) Introducing a dimensionless parameter NTU in the heat transfer unit number method, called the number of heat transfer units, which indicates the heat transfer capacity of the heat exchanger relative to the fluid heat capacity flow(the dimensionless "heat transfer capacity" of the heat exchanger).
(2) For the plate heat exchanger, KA/MC=△t/△tm, △t/△tm is called the temperature difference ratio. The process on the right side of the above formula is expressed by NTUp, and the condition of the left heat exchange equipment expressed by NTUE.NTUp is the ratio of the change of fluid temperature to the average temperature difference. It indicates the value of the temperature change of several degrees of fluid caused by the change of Δtm at 1 °C. When Δtm is large, NTUp is small; when Δtm is small, it becomes larger.
(3) In the process of NTUp becoming larger, the temperature change of Δtm is larger, and when NTUp is smaller, the temperature change of Δtm is smaller. The optimal design calculation of the plate heat exchanger is to determine the model, process and heat transfer area reasonably under the condition of known temperature difference ratio NTUE, so that NTUp is equal to NTUE.