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

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

12. Condensation on Flat Plate

13. Nusselt Analysis - Assumptions

15. Mass flow of condensate Heat transfer at wall

16. Amount of condensate added between x and x+dx Thus

17. Heat transfer coefficient

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

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

20. 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

21. Relate mass flow with total heat transfer and heat transfer coefficient

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

23. Condensation number (Co)

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

25. Example 1 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.

26. 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)