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ETPFGM10

48th European Two-Phase Flow Group Meeting 2010

28th-30th June 2010, Brunel University, London, UK

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER IN

FLOW BOILING INSIDE A HELICALLY COILED SMALL

DIAMETER TUBE

A. M. El-Sayed, R. K. AL-Dadah1, S. M. Mahmoud, D.K. Aspinwall, S. L. Soo

School of Mechanical Engineering, University of Birmingham, Birmingham, B15 2TT.

Helical coils were originally developed for commercial liquefaction of air, but currently are

also used for boiling applications in petrochemical, cryogenic [1] and nuclear industries [2]. They

are suitable for boiling in the absence of gravity such as in space applications where the radial

acceleration imposed on the flow compensates the gravitational effect [1]. Additionally flow

boiling in micro channels is becoming increasingly important in many applications involving

devices used for cooling electronic processers and in compact refrigeration systems and heat

exchangers. Research activity relating to boiling heat transfer of refrigerants inside helically coiled

small diameter and micro tubes [3-4] which is relevant, is however limited. This paper initially

reviews previous research and presents experimental data for flow boiling of refrigerant R134a

inside helically coiled 4 mm diameter tubing.

Figure 1 shows a schematic of the test facility which comprises a compressor, water cooled

condenser, needle valve for controlling the refrigerant flow rate and water heated evaporator. The

evaporator incorporated a helically coiled tube (pitch of 7mm and coil diameter of 30mm) fitted

inside a cylindrical shell with an inside diameter of 50mm. Measurements of boiling pressure,refrigerant flow rate, refrigerant and water inlet/outlet temperatures and tube wall temperatures at

different positions on the coil, were all monitored.

Figure 2 shows the experimental average boiling heat transfer coefficients plotted against the

heat flux of the helically coiled tube compared to those predicted by the Chen correlation [5], for a

straight tube of the same diameter. The results showed that convective boiling was the dominant

mechanism for heat transfer with little dependency on heat flux and the heat transfer coefficients

varied with mass velocity (G). Furthermore, the coefficients for the coiled tube were higher than

those of straight tubes. Figure 3 shows good agreement between the experimental results and those

predicted using Schrock-Grossman and Guo correlations [6] for helically coiled tubes.

References

[1] Young, M. A. and K. J. Bell (1991). "Review of Two-phase flow and Heat Transfer

Phenomena in Helically Coiled Tubes." American Institute of Physics: 1214-1222.

[2] Nariai, H., Kobayashi, M., Matsuoka, T., Friction pressure drop and heat transfer coefficient of

two-phase flow in helically coiled tube once through steam generator for integrated type marine

water reactor.

[3] Vashisth, S., V. Kumar, et al. (2008) "A review on the potential applications of curved

geometries in process industry" Industrial Engineering Chemistry, 47, pp. 3291-3337.

1 Contact author: Tel: 0121-4143513, Email: r.k.al-dadah@bham.ac.uk

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[4] Naphon, P. and S. Wongwises (2006) "A review of flow and heat transfer characteristics in

curved tubes" Renewable and Sustainable Energy Reviews, 10, pp. 463490.

[5] Chen, J.C. (1966) A correlation for boiling heat transfer to saturated fluids in convective

flow, I & EC Process Design Develop, 5 (3), pp. 322329.

[6] Zhao, L., Guo, Guo, L., Bai, B., Hou, Y., Zhang, X., Convective boiling heat transfer and two

phase flow characteristics inside a small horizontal helically coiled tubing once-through steam

generator, International Journal of Heat and Mass Transfer, 46, pp. 4779-4788.

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Figure 2 Variation of heat transfer coefficient with mass velocity and heat flux.

Figure 3 Prediction of experimental results using Guo and Schrock-Grossman

correlations.

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1000 2000 3000 4000 5000

Experimental Heat Transfer Coefficient [W/m2.K]

Pre

dictedHeatTransferCoefficient

[W/m2.K

] Guo correlation [6]

Schrock-Grossman correlation [6]

+30%

-30%

0

500

1000

1500

2000

2500

3000

3500

4000

3000 4000 5000 6000 7000 8000

Heat Flux [W/m2]

HeatTransferCoefficient[W

/m2.K

]

G=60

G=54

Chen Correlation [5] (G=60 )

Chen Correlation [5] (G=54)

kg/m2.s

kg/m2.s