The flow velocity inside the heat exchanger tubes is too high; increasing the diameter of the heat exchanger reduces this velocity, yet there is still an excessive amount of heat exchange surface area
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Heat exchange between 1.5 MPaG saturated steam and process gas, with the saturated steam flowing in the shell side and the process gas flowing in the tube side. Based on the process parameters, the heat exchanger size calculated using HTRI is φ400×2500, with a 13% margin in heat exchange area. The flow velocity in the shell side is 0.7 m/s (due to a low steam volume), while the flow velocity in the tube side is 187 m/s. By increasing the diameter of the heat exchanger, the flow velocity inside the tubes can be reduced to below 30 m/s; in this case, the heat exchanger diameter would be 1000, but the heat exchange area margin would be 500%. The flow rate is ensured, but the heat exchange surface is too large. How should this situation be handled? Is it necessary to change the design of the heat exchanger? (The simulation uses the BEM type)
Agree with what was said above: 1. A single-pass design can be used; process gases generally have requirements regarding pressure drop, so a single-pass design is often adopted. 2. The diameter of the heat exchange tubes can be increased, using tubes with diameters of φ38, φ45, or even φ57.
The larger the diameter of the heat exchange tubes, the fewer the number of tubes, and the smaller the total flow area.
Never jump to conclusions without thinking. The number of pipes is reduced, but the flow area per pipe has increased. The flow area obtained by multiplying the two is larger.
If that is the case, then it should be considered to try the opposite: having the process gas flow in the shell side and the steam flow in the tube side. Why must the process gas flow at less than 30 m/s?
It is recommended to try the approach suggested on the 7th floor: by having the process gas flow in the shell side, the flow velocity will **decrease**, and the heat transfer coefficient will increase as well, which is beneficial for heat transfer.
Is the default in HTRI a single-threaded model?
I thought there were generally only φ25 and 32 pipes. I’ve learned it!
Below 30 m/s is required by the HTRI tutorial, as the gas flow velocity in the tube side should generally not exceed 30 m/s. The process gas medium contains a high level of hydrogen, so the flow rate should not be too fast either.