Condensation and Boiling Heat Transfer

# Condensation and Boiling Heat Transfer

## Condensation and Boiling Heat Transfer

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1. Condensation and BoilingHeat Transfer • boiling, condensation : high heat transfer rates • understand the processes to design the appropriate heat-transfer equipment Source: Vishwas V. Wadekar, HTFS, Aspen Technology J.P. Holman

2. Condensation Heat Transfer

3. Modes of condensation • Dropwise/filmwise condensation • Direct/Indirect/homogeneous condensation

4. Modes of condensation In vertical flat plate, Tw < Tsat : condensate will form at surface. • Dropwise condensation: liquid does not wet the surface, droplets are formed. • Filmwise condensation: liquid wets the surface, smooth film is formed. The surface is blanked by the film, which grows in thickness as it moves down the plate.

5. Filmwise Condensation

6. Dropwise Condensation

7. Homogeneous Condensation

8. Direct Contact Condensation

9. Condensation • In the remaining lecture we now focus on indirect contact filmwise condensation

10. General approach to condensation

11. General approach to condensation

12. Condensation on Flat Plate

13. Nusselt Analysis - Assumptions

14. Mass flow of condensate Heat transfer at wall

15. Heat transfer coefficient

16. In term of Nusselt number For vertical plates and cylinders and fluids with Pr > 0.5 and cT/hfg ≤ 1.0

17. For non-linear temperature profile For laminar film condensation on horizontal tubes

18. To determine flow (laminar or turbulence) use Renolds number Critical Re is 1800 For Vertical plate of unit depth, P = 1 For Vertical tube, P = d

19. Using 20 % safety factor in design problems For inclined surfaces

20. Condensation number (Co)

21. For condensation of refrigerants at low vapor velocities inside horizontal tubes For higher flow rates

22. A vertical square plate, 30 by 30 cm, is exposed to steam at atmospheric pressure. The plate temperature is 98C. Calculate the heat transfer and the mass of steam condensed per hour. Example 1

23. Example 2 • One hundred tubes of 1.27 cm diameter are arranged in a square array and exposed to atmospheric steam. Calculate the mass of steam condensed per unit length of tubes for a tube wall temperature of 98C. (use condensate properties from Ex.1)