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Heat transfer, pressure drop and flow patterns during flow boiling of R407C in a horizontal microfin tube

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Abstract

The heat transfer, pressure drop and flow patterns during flow boiling of R407C in a horizontal microfin tube have been investigated. The microfin tube is made of copper with a total fin number of 55 and a helix angle of 15°. The fin height is 0.24 mm and the inner tube diameter at fin root is 8.95 mm. The test tube is 1 m long. It is heated electrically. The experiments have been performed at saturation temperatures between −30°C and +10°C. The mass flux was varied between 25 and 300 kg/m2/s, the heat flux from 20,000 W/m2 down to 1,000 W/m2. The vapour quality was kept constant at 0.1, 0.3, 0.5, 0.7 at the inlet and 0.8, 1.0 at the outlet, respectively. The measured heat transfer coefficient is compared with the correlations of Cavallini et al., Shah as well as Zhang et al. Cavallini’s correlation contains seven experimental constants. After fitting these constants to our measured values, the correlation achieves good agreement. The measured pressure drop is compared to the correlations of Pierre, Kuo and Wang as well as Müller-Steinhagen and Heck. The best agreement is achieved with the correlation of Kuo and Wang. Almost all values are calculated within an accuracy of ±30%. The flow regimes were observed. It is shown, that changes in the flow regime affect the heat transfer coefficient significantly.

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Abbreviations

A,B,C,F,S,U,V,Z:

Dimensionless constants (–)

Bo:

Boiling number (–)

Bon:

Bond number (–)

Co:

Convection number (–)

cp :

Specific heat capacity (J/kg/K)

dH :

Hydraulic diameter (m)

di :

Diameter from fin tip to fin tip (m)

dK :

Diameter at fin root (m)

d0 :

Reference diameter (m)

FC :

Mixture correction factor (–)

Emf :

Enhancement factor for microfin tubes (–)

ERB :

Convection enhancement factor (–)

Fr:

Froude number (–)

g:

Gravitational acceleration (m/s2)

G:

Mass flux (kg/m2/s)

G0 :

Reference mass flux (kg/m2/s)

Kf :

Pierre’s Boiling number (–)

L:

Length of test section (m)

M:

Molar mass (kg/kmol)

n:

Number of fins (–)

N:

Dimensionless number (–)

p:

Pressure (Pa)

pr :

Reduced pressure (–)

Pr:

Prandtl number (–)

q, \( \dot{q} \) :

Heat flux (W/m2)

Re:

Reynolds number (–)

Rx:

Geometry amplification factor (–)

t:

Fin height (m)

v:

Specific volume (m3/kg)

w:

Velocity (m/s)

x:

Mass-specific vapour quality (–)

Xtt :

Martinelli parameter (–)

z:

Coordinate parallel to the test section (m)

α:

Heat transfer coefficient (W/m2/K)

β:

Helix angle of fins (°)

γ:

Apex angle of fins (°)

ΔhV :

Specific enthalpy of vaporization (J/kg)

Δp:

Pressure drop (Pa)

ΔTglide :

Temperature glide (K)

η:

Dynamic viscosity (Pa s)

λ:

Thermal conductivity (W/m/K)

ξ:

Friction factor (–)

ρ:

Density (kg/m3)

σ:

Surface tension (N/m)

Φ:

Two-phase multiplier (–)

cal:

Calculated

cv:

Convective

exp:

Experimental

I:

Inlet

l:

Liquid

m:

Mean

nb:

Nucleate boiling

O:

Outlet

plane:

Measurement plane

pure:

Pure refrigerant

S:

Saturation

v:

Vapour

References

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Acknowledgments

This work was supported by the German Bundesministerium für Wirtschaft (BMWi) through the Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF). The project was accompanied by a working party of the Forschungsrat Kältetechnik e.V. (FKT), Frankfurt a. M., Germany. The final report [3] is available at FKT e.V.

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Authors and Affiliations

  1. Institute of Thermodynamics and Thermal Engineering, University of Stuttgart, Stuttgart, Germany

    P. Rollmann & K. Spindler

  2. Technical University of Dresden, Dresden, Germany

    H. Müller-Steinhagen

Authors
  1. P. Rollmann
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  2. K. Spindler
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  3. H. Müller-Steinhagen
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Correspondence to P. Rollmann.

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Dedicated to Prof. Dr.-Ing. Dr.-Ing. E.h. mult. Franz Mayinger on the occasion of his 80th birthday.

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Rollmann, P., Spindler, K. & Müller-Steinhagen, H. Heat transfer, pressure drop and flow patterns during flow boiling of R407C in a horizontal microfin tube. Heat Mass Transfer 47, 951–961 (2011). https://doi.org/10.1007/s00231-011-0857-x

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