Pressure drop prediction models

1. Pressure drop prediction models • Wilson et al. (2003) • Considered parameters • Single-phase pressure gradients (liquid-only) • Martinelli parameter Horizontal condensing in flattened round smooth, axial, and helical microfin tubes. Heat and Mass Transfer Laboratory

2. Pressure drop prediction models • Wilson et al. (2003) 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. The liquid only formulation treats all refrigerant mass flow as if it is in the liquid phase. Heat and Mass Transfer Laboratory

3. 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 3

4. Pressure drop prediction models Sensitivity of the parameters: • Wilson et al. (2003) Heat and Mass Transfer Laboratory 4

5. 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

6. Heat transfer prediction models Applicability range: If range is respected, compute liquid-only transfer coefficient: • Shah (1979) Heat and Mass Transfer Laboratory 6

7. 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 7

8. 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 8

9. Heat transfer prediction models Calculate the modified Soliman Froude number: • Dobson and Chato (1998) Heat and Mass Transfer Laboratory 9

10. Heat transfer prediction models With: • Dobson and Chato (1998) Heat and Mass Transfer Laboratory 10

11. 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 11