HEAT TRANSFER

• Condenser


  Device used to condense a vapor into a liquid

  
• Types of Condenser


  • Direct contact condenser
  • Shell & tube condenser

  
• Direct Contact Condenser


  1. Spray condenser

  2. Baffled Column

  3. Packed Column

  4. Jet condenser

  5. Sparge pipe

  
• Shell & Tube Condenser

  • Wider baffle spacing, lB=DS
  • 4 configurations possible: Horizontal with condensation in shell/tubes, Vertical with condensation in shell/tubes

  
• Main functions of baffles in shell & tube condensers

  
• Condensation mechanism


  Film-wise and drop-wise condensation

  
• Commercial condensers use film-wise condensation

  
• Condenser Heat Transfer Equations

  1. Condensation outside horizontal tubes

  2. Condensation inside and outside vertical tubes

  3. Flooding in vertical tubes

  4. Condensation inside horizontal tubes

  5. Condensation of steam

  6. Mean temperature difference

  7. Desuperheating and sub-cooling

  8. Condensation of mixtures

  9. Pressure drop

  
• Condensation outside horizontal tubes follows Nusselt model

  
• Condensation inside and outside vertical tubes follows Nusselt model for Re > 30
• Flooding in vertical tubes should not occur if a certain condition is satisfied
• Condensation inside horizontal tubes follows Stratified flow or Annular Flow models

  
• For condensation of steam, initial assumption value of h = 8000 W/m2°C
• Mean temperature difference


  For non-isothermal process with small temperature change, can use logarithmic mean temperature difference
• Desuperheating and sub-cooling


  Necessary to divide temperature profile into sections and determine mean temperature difference and heat transfer coefficient separately for each section

  
• Condensation of Mixtures


  • Condensation is not isothermal, different dew points
  • Transfer of sensible heat from condensate
  • Physical properties vary
  • Rate of condensation governed by rate of diffusion and heat transfer

  
• Differential vs Integral condensation

  Differential: liquid separates from vapor it condensed from

  Integral: liquid remains in equilibrium with uncondensed vapor
• Pressure drop in condenser is difficult to predict due to two-phase flow
• Pressure drop is calculated using average vapor flow-rate in shell/tubes