Lesson 11 - Jacketed Vessels SAQ
This lesson allows you to test yourself on the material covered in the Jacketed Vessel lesson and determine the level to which you have met the learning outcomes.
Suggested Response - Q4
** List two reasons why the heat transfer rate of a jacketed vessel would exceed its design performance.
Response
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Heat transfer surfaces will scale and/or foul up over time. Fouling adds resistance to heat transfer, in turn lowering the overall heat transfer coefficient and hence reducing the heat transfer rate. Fouling/scale can be removed by cleaning the heat transfer surface, but realistically, this can only be done with limited frequency. When sizing a jacketed vessel, the heat transfer area of the jacket must be sized for the ‘worst case’ scenario, e.g. when fouling/scale is at its maximum (just before cleaning). Therefore, a new vessel with no fouling/scaling will not have this added resistance to heat transfer, and will thus exceed its performance specification.
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Heat transfer in jacketed vessels is unsteady, which means that the heat transfer rate changes over time. When sizing a jacketed vessel, the heat transfer area of the jacket must be sized for the ‘worst case’ scenario, e.g. the point where heat transfer rate is at its maximum. Therefore, any operating point where the heat transfer rate is not at this maximum, the heat transfer surface area will be more than is actually required. This means that the heat transfer rate will be better than actually required.