Heat transfer rate, heat transfer residence time? !
Thread Content
Today a colleague asked me a question about cooling. I suggested adding a heat exchanger, but he asked whether the heat could be removed in such a short time I thought about it the other way around, and it’s true. In many gas heat exchange processes, the gas flow velocity is very high, resulting in a very short residence time within the heat exchanger. Heat exchange also takes time. In fact, the overall heat transfer coefficient K already includes the concept of time. For that definite amount of heat, how short is the shortest time required for it to be transferred?
The number of tubes or shells in the heat exchanger can be changed to increase the residence time. You can refer to the design of heat exchangers to make an estimate.
The overall heat transfer coefficient K includes the time parameter. Residence time is not the key to heat transfer.
Consider increasing the number of tubes or shells in the heat exchanger to increase the residence time； Increase the flow diameter of the heat exchanger, reduce the fluid velocity, and prolong the residence time.
Then the heat transfer coefficient doesn’t decrease? !
There is no concept of residence time for heat exchangers. The heat transfer coefficient is related to flow rate, structure, and size, and these have been taken into account.
The unit of the heat transfer coefficient is W/m2K; watts represent the energy transferred per unit of time. When calculating the K value, flow velocity is taken into account, and time is already included in the calculation
What should be the appropriate heat exchange time for a normal shell-and-tube heat exchanger?