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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: [email protected]
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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
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