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Condensation in mini- and microchannels

Condensation in mini- and microchannels. Hussein Dhanani Sebastian Schmidt Christian Metzger Assistant: Marcel Christians-Lupi Teacher: Prof. J.R Thome. 20 December 2007. Structure. Introduction to condensation in microchannels Pressure drop Prediction models Friedel (1979;1980)

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Condensation in mini- and microchannels

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  1. Condensation in mini- and microchannels Hussein Dhanani Sebastian Schmidt Christian Metzger Assistant: Marcel Christians-Lupi Teacher: Prof. J.R Thome 20 December 2007 Heat and Mass Transfer Laboratory

  2. Structure • Introduction to condensation in microchannels • Pressure drop • Prediction models • Friedel (1979;1980) • Chen (2001) • Cavallini (2001;2002) • Wilson (2003) • Garimella (2005) • Graph analysis Heat and Mass Transfer Laboratory

  3. Structure • Heat transfer • Prediction models • Shah (1979) • Dobson & Chato (1998) • Cavallini (2002) • Bandhauer (2005) • Graph analysis • Questions Heat and Mass Transfer Laboratory

  4. Introduction • Condensation inside horizontal microchannels • Automotive air-conditioning, petrochemical industry • Reduce use of ozone-killing fluids • Increase heat transfer coefficient and pressure drop • Surface tension + Viscosity>>> gravitational forces Heat and Mass Transfer Laboratory 4

  5. Pressure drop • Common parameters used by several correlations • Liquid Reynolds number • Vapor Reynolds number • Liquid-only Reynolds number • Vapor-only Reynolds number Heat and Mass Transfer Laboratory

  6. Pressure drop • Common parameters used by several correlations • Single-phase friction factor (smooth tube) • Single-phase pressure gradients Heat and Mass Transfer Laboratory

  7. Pressure drop prediction models • Friedel (1979;1980) • Considered Parameters • Liquid only single-phase pressure gradient • Liquid only and vapor only friction factor • Fluid and geometric properties • Range / applicability • D > 1 mm • Adiabatic • μl/μv < 1000 Heat and Mass Transfer Laboratory

  8. Pressure drop prediction models • Friedel (1979;1980) Heat and Mass Transfer Laboratory

  9. Pressure drop prediction models • Chen et al. (2001) • Modification of the Friedel correlation by adding two-phase multiplier • Considered Parameters • Two-phase pressure gradient by Friedel • We, Bo, Rev, Relo • Range / applicability • 3.17 < D < 9 mm for R-410A • 5°C < Tsat < 15°C • 50 < G < 600 kg/m2s Heat and Mass Transfer Laboratory

  10. Pressure drop prediction models • Chen et al. (2001) Heat and Mass Transfer Laboratory

  11. Pressure drop prediction models • Cavallini et al. (2002) • Modification of the Friedel correlaction for annular flow. • Considered Parameters • Liquid only single-phase pressure gradient • Liquid only and vapor only friction factor • Fluid and geometric properties • Range / applicability • D = 8 mm for R-134a , R-410a and others • 30°C < Tsat < 50°C • 100 < G < 750kg/m2s Heat and Mass Transfer Laboratory

  12. Pressure drop prediction models • Cavallini et al. (2002) Friedel Heat and Mass Transfer Laboratory

  13. Pressure drop prediction models • Cavallini et al. (2002) Heat and Mass Transfer Laboratory

  14. Pressure drop prediction models • Wilson et al. (2003) • Considered parameters • Single-phase pressure gradients (liquid-only) • Martinelli parameter • Range / applicabilty • Flattened round smooth, axial, and helical microfin tubes. • 1.84 < D < 7.79 mm for R-134a, R-410A • Tsat = 35°C • 75 < G < 400 kg/m2s Heat and Mass Transfer Laboratory 14

  15. Pressure drop prediction models Model uses liquid-only two-phase multiplier of Jung and Radermacher (1989): Xtt is the Martinelli dimensionless parameter for turbulent flow in the gas and liquid phases. Insert formulation • Wilson et al. (2003) Heat and Mass Transfer Laboratory 15

  16. Pressure drop prediction models Knowing the single-phase pressure gradient, the two-phase pressure grandient is: with Single-phase friction factors are calculated using the Churchill correlation (1977): • Wilson et al. (2003) Heat and Mass Transfer Laboratory 16

  17. Pressure drop prediction models • Garimella et al. (2005) • Considered parameters • Single-phase pressure gradients • Martinelli parameter • Surface tension parameter • Fluid and geometric properties • Range / applicabilty • 0.5 < D < 4.91 mm for R-134a • Tsat ~ 52°C • 150 < G < 750 kg/m2s Heat and Mass Transfer Laboratory 17

  18. Pressure drop prediction models Void fraction is calculated using the Baroczy (1965) correlation: Liquid and vapor Re values are given by: • Garimella et al. (2005) Heat and Mass Transfer Laboratory 18

  19. Pressure drop prediction models Liquid and vapor friction factors: Therefore, the single-phase pressure gradients are given and the Martinelli parameter is calculated: • Garimella et al. (2005) Heat and Mass Transfer Laboratory 19

  20. Pressure drop prediction models Liquid superficial velocity is given by: This velocity is used to evaluate the surface tension parameter: • Garimella et al. (2005) Heat and Mass Transfer Laboratory 20

  21. Pressure drop prediction models Interfacial friction factor: Laminar region: Turbulent region (Blasius): • Garimella et al. (2005) Heat and Mass Transfer Laboratory 21

  22. Pressure drop prediction models The pressure gradient is determined as follows: • Garimella et al. (2005) Heat and Mass Transfer Laboratory 22

  23. Pressure drop prediction models G = 400 kg/m2s G = 800 kg/m2s Tsat = 40°C , D = 1.4 mm • Graph analysis for R-134a Heat and Mass Transfer Laboratory 23

  24. Pressure drop prediction models G = 600 kg/m2s G = 1000 kg/m2s Tsat = 40°C , D = 1.4 mm • Graph analysis for R-410A Heat and Mass Transfer Laboratory 24

  25. Heat transfer • Common parameters used by several correlations • Prandtl number • Reduced pressure • Martinelli parameter Heat and Mass Transfer Laboratory 25

  26. Heat transfer prediction models • Shah (1979) • Considered parameters • Vapor Velocity • Liquid-only Reynolds number • Liquid Prandtl number • Reduced pressure • Fluid and geometric properties • Range / applicability • 7 < D < 40 mm • Various refrigerants • 11 < G < 211 kg/m2s • 21 < Tsat < 310°C Heat and Mass Transfer Laboratory 26

  27. Heat transfer prediction models Applicability range: If range is respected, compute liquid-only transfer coefficient: • Shah (1979) Heat and Mass Transfer Laboratory 27

  28. Heat transfer prediction models For heat transfer coefficient, apply multiplier: Widely used for design. Improvement needed for results near critical pressure and vapor quality from 0.85 to 1. • Shah (1979) Heat and Mass Transfer Laboratory 28

  29. Heat transfer prediction models • Dobson and Chato (1998) • Considered parameters • Liquid, vapor-only Reynolds number • Martinelli parameter • Zivi’s (1964) void fraction • Galileo number • Modified Soliman Froude number • Liquid Prandtl number • Range / applicability • D = 7.04 mm • 25 < G < 800 kg /m2s • 35 < Tsat < 60°C Heat and Mass Transfer Laboratory 29

  30. Heat transfer prediction models Calculate the modified Soliman Froude number: • Dobson and Chato (1998) Heat and Mass Transfer Laboratory 30

  31. Heat transfer prediction models With: • Dobson and Chato (1998) Heat and Mass Transfer Laboratory 31

  32. Heat transfer prediction models For Frso > 20, the annular flow correlation proposed is And the resulting heat transfer coefficient is: • Dobson and Chato (1998) Heat and Mass Transfer Laboratory 32

  33. Heat transfer prediction models • Cavallini et al. (2002) Applicable for annular regime only • Considered Parameters • Pressure drop • Dimensionless film thickness • Dimensionless temperature • Re, Pr • Fluid and geometric properties • Range / applicability • D = 8 mm • R134a and R410a • 100 < G < 750 kg/m2s • 30 < Tsat < 50°C Heat and Mass Transfer Laboratory 33

  34. Heat transfer prediction models • Calculation of the shear stress • Dimensionless film thickness Heat and Mass Transfer Laboratory 34

  35. Heat transfer prediction models • Heat transfer coefficient Heat and Mass Transfer Laboratory • Dimensionless temperature 35

  36. Heat transfer prediction models • Bandhauer et al. (2005) • Considered parameters • Pressure drop • Dimensionless film thickness • Turbulent dimensionless temperature • Pr • Fluid and geometric properties • Range / applicability • 0.4 < D < 4.9 mm • R134a • 150 < G < 750 kg/m2s Heat and Mass Transfer Laboratory 36

  37. Heat transfer prediction models Interfacial shear stress: Friction velocity is now calculated: • Bandhauer et al. (2005) Heat and Mass Transfer Laboratory 37

  38. Heat transfer prediction models Film thickness is directly calculated from void fraction: This thickness is used to obtain the dimensionless film thickness: • Bandhauer et al. (2005) Heat and Mass Transfer Laboratory 38

  39. Heat transfer prediction models Turbulent dimensionless temperature is given by: Therefore, the heat transfer coefficient is: • Bandhauer et al. (2005) Heat and Mass Transfer Laboratory 39

  40. Heat transfer G=175 kg/m2s G=400 kg/m2s D=2.75mm, Tsat=35°C Heat and Mass Transfer Laboratory • Graph analysis for R134a 40

  41. Heat transfer G=175 kg/m2s G=400 kg/m2s D=2.75mm, Tsat=35°C Heat and Mass Transfer Laboratory • Graph analysis for R410a 41

  42. Questions ?

  43. Thank you for your (hard) attention !

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