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
Wilson et al. (2003)
Knowing the single-phase pressure gradient, the two-phase pressure grandient is:
with
Single-phase friction factors are calculated using the Churchill correlation (1977):
Heat and Mass Transfer Laboratory 3

4. Pressure drop prediction models
Wilson et al. (2003)
Sensitivity of the parameters:
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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
Large database from 21 sources
Widely used general purpose empirical correlation
R11, R12, R22, R113, ethanol, methanol
Heat and Mass Transfer Laboratory

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

7. Heat transfer prediction models
Shah (1979)
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.
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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
Fluid properties effect not very significant
No significant effect of diameter reduction
Heat and Mass Transfer Laboratory 8

9. Heat transfer prediction models
Dobson and Chato (1998)
Calculate the modified Soliman Froude number:
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10. Heat transfer prediction models
Dobson and Chato (1998)
With:
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11. Heat transfer prediction models
Dobson and Chato (1998)
For Frso > 20, the annular flow correlation proposed is
And the resulting heat transfer coefficient is:
Heat and Mass Transfer Laboratory 11