Employing multi-passing on the tube side of a shell-and-tube exchanger for a fixed heat load and mass flow rate is done because it__________________?
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Answer: C. Increases the overall heat transfer coefficient
Explanation
Multi-passing on the tube side forces fluid through fewer tubes at a time, increasing flow velocity. Higher fluid velocity increases the Reynolds number, enhancing turbulent mixing and convective heat transfer. Improved convective heat transfer coefficient raises the overall thermal performance of the heat exchanger. Tube-side multi-passing uses partition plates in channel heads to direct fluid back and forth across tubes. Convective heat transfer coefficients in turbulent pipe flow scale with velocity raised to a fractional power. Pressure drop increases significantly when fluid velocity is raised through multi-pass tube arrangements.
Designers use multi-pass tube configurations to achieve required fluid velocities when flow rates are low. Balancing heat transfer coefficient enhancement against allowable tube-side pressure drop is a key design task. Shell-and-tube exchangers in chemical plants often feature two, four, or six tube passes for optimal operation. Multi-passing actually increases tube-side pressure drop due to higher velocities and directional header turns. Outlet temperatures are determined by overall heat duty and mass flow rates rather than pass configuration alone. Stating none of these is incorrect because multi-passing directly increases the overall heat transfer coefficient.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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