COND4.ppt Calculation Procedure for Assessing Multi-Component Effects

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COND4.pptCalculation Procedure for Assessing
Multi-Component Effects
(Chapter in Outline Notes Condensation Heat
Transfer )
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Basic Problem

• Why is this calculation necessary anyway?
• Isnt a temperature change of 0.2oC small enough
  to ignore?
• How small is a small temperature change of
  0.2oC?
• How much does this affect the effective
  condensation heat-transfer coefficient?

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Key equation
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To calculate the term hsv (Single-Phase,
Standard Forced Convection Analysis)

• Need to know
• mass flowrate of vapour (mv) (but which one,
  because it decreases through condenser?)
• number (Nt) diameter (di) of tubes
• vapour viscosity (?V or ?G), specific heat
  capacity (CPV), thermal conductivity (kV or ?V or
  kG or ?G)

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(No Transcript)
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qsv/qt
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• CPV from before
• ?T is temperature change in vapour to liquid
  condensation (0.2oC here) if mV is the total
  vapour flowrate
• ?Q is total heat duty (condensation plus vapour
  cooling)

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Which Vapour Flowrate?Total Flowrate is
Reasonable Start if ?T is Small

• We could cut up the condenser into sections with
  different vapour flowrates (mV) in each (1
  section at inlet, full vapour flowrate next
  section, lower vapour flowrate, etc)
• As mV is decreased, qsv/qt decreases, so does
  hsv, so

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Conclusions

• Have reviewed
• calculation of single-phase (gas) heat-transfer
  coefficient
• vapour cooling / total heat duty