HT7'ppt Exchanger Effectiveness

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HT7.pptExchanger Effectiveness
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Components of Course What Stage are We Up To?

• Types of exchangers, revision of OHTCs, fouling
  factors.
• Heat exchanger selection.
• Thermal performance analysis (NTUs) for co-
  counter-current exchangers.
• Multi-pass exchangers (ST).
• Condensation boiling.
• Radiation.

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Outcomes This Lecture

• Know difference between stream and exchanger
  effectiveness.

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Exchanger Effectiveness

• Find stream with minimum heat capacity rate.
• This tells us which stream has the greatest
  temperature change.

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Exchanger Effectiveness (continued)
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Exchanger Effectiveness (continued)

• The stream with the greatest temperature change
  will limit the duty of the exchanger (i.e. adding
  more length will not give more heat transfer)
• Effectiveness of a heat exchanger (definition)
• Q/ Qmax
• where Q UADTlm (mCp)hDTh
  (mCp)cDTc
• and Qmax (mCp)min DTmax
• (set DTmax Th in Tc in )

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Conclusions

• Stream effectiveness method may be used for both
  performance design problems easiest to use.
• Exchanger effectiveness concept is useful for
  appreciating effect of exchanger extensiveness
  (need to find minimum stream).
• Charts can be used to implement effectiveness
  method.