Feasibility of a double-shell-pass heat exchanger?
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A heat exchanger in which wastewater flows through the tube side; the temperature drops from 72 to 52 degrees, with a flow rate of 175 m3/h. The fluid contains solid particles as impurities, and the flow velocity inside the tubes needs to be maintained above 1 m/s. The shell side carries an ethylene glycol solution at temperatures ranging from 49 to 69 degrees. The diameter of the shell is limited to DN600, while there is no limit on the length of the equipment. The current approach uses a double-pass system to ensure the flow rate; is it reasonable to further divide the shell side into two separate shell passes? According to HTRI simulations, the feedback indicates that the heat leakage at the shell-side partition is excessive; therefore, a double-shell-and-tube design is not recommended? I don’t know how to develop a plan now; could you give some guidance?
No one has come to guide me yet; I have to pull through on my own – don’t sink
Many such heat exchangers have been built; as you said, the purpose is to increase the flow rate in the shell side and enhance heat transfer.
You have temperature cross-over here; a double-shell arrangement with pure counterflow is used to avoid this issue. As for the leakage issue you mentioned, it might be due to the fact that no gaps or seals have been installed, but that’s not the main point. The key is the purpose for which you choose a double-pass design: 1. To increase the flow rate and enhance heat transfer; 2. To achieve pure counterflow, thereby increasing the heat transfer coefficient and reducing the size of the equipment.
When checking the process parameters, the average temperature difference between the cold and hot fluids is only 3 degrees, while the temperature difference of the cold fluid at the inlet and outlet of the shell side is 20 degrees. The temperature difference of the cold fluid on either side of the partition in the shell side is even greater than that between the cold and hot fluids. Could there be a problem with this?
No photos, no drawings, shall we take a look?
The interwall heat transfer in the design of the partitions is not taken into account (as far as I’ve seen); this aspect should have a minimal impact on the overall system, but that is still relative to normal equipment under standard operating conditions. It seems that someone has conducted similar research, and there are papers you can download and take a look at.