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Research Papers

Computational Fluid Dynamics and Optimization of Flow and Heat Transfer in Coiled Tube-in-Tube Heat Exchangers Under Turbulent Flow Conditions

[+] Author and Article Information
Wael I. A. Aly

Department of Refrigeration
and Air Conditioning Technology,
Faculty of Industrial Education,
Helwan University,
Cairo 11282, Egypt
e-mail: aly_wael@helwan.edu.eg,
aly_wael@yahoo.com

1Corresponding author.

Manuscript received April 7, 2013; final manuscript received November 25, 2013; published online January 31, 2014. Assoc. Editor: Arun Muley.

J. Thermal Sci. Eng. Appl 6(3), 031001 (Jan 31, 2014) (10 pages) Paper No: TSEA-13-1084; doi: 10.1115/1.4026120 History: Received April 07, 2013; Revised November 25, 2013

The present computational fluid dynamics (CFD) study was performed to investigate the 3D turbulent flow and heat transfer of coiled tube-in-tube heat exchangers (CTITHEs). The realizable k-ε model with enhanced wall treatment was used to simulate the turbulent flow and heat transfer in the heat exchangers. Temperature dependent thermophysical properties of water were used and heat exchangers are analyzed considering conjugate heat transfer from hot fluid in the inner-coiled tube to cold fluid in the annulus region. After simulations, Taguchi method was used for finding the optimum condition for some design parameters in the range of coil diameter from 0.18 to 0.3 m, tube and annulus flow rates from 2 to 4 and 10 to 20 LPM, respectively. Results show that the Gnielinski correlation used extensively for predicting Nusselt number for turbulent flow in ducts can be used to predict Nusselt number for both inner-coiled tube and annular coiled tube using the friction factor correlation for helical tubes of Mishra and Gupta. Contribution ratio obtained by Taguchi method shows that annulus side flow rate, tube side flow rate, coil diameter, and flow configuration are the most important design parameters in coiled tube-in-tube heat exchangers, respectively.

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References

Figures

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Fig. 1

Schematic diagram and coordinate system of the tube-in-tube heat exchanger

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Fig. 2

Grid system for tube-in-tube heat exchanger

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Fig. 3

Grid density versus Nu and f

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Fig. 4

Developments of velocity and temperature fields for Coil B, Dni = 3200 and Dno = 3700 [((a) φ = 15 deg; (b) φ = 30 deg; (c) φ = 60 deg; (d) φ = 90 deg; (e) φ = 120 deg; (f) φ = 180 deg; (g) φ = 270 deg; (h) φ = 360 deg; (i) φ = 720 deg]). (a) Velocity fields for inner tube of the CTITHE; (b) velocity fields for outer tube of the CTITHE; (c) temperature fields for inner tube of the tube-in-tube heat exchanger; and (d) temperature fields for outer tube of the CTITHE.

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Fig. 5

Friction factor versus (a) inner Dean number and (b) outer Dean number.

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Fig. 6

Nusselt number versus (a) inner Dean number and (b) outer Dean number.

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Fig. 7

Nusselt number computed by CFD against that predicted by (a) Ginelinski correlation and (b) Pethukov correlation using computed values of f.

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Fig. 8

Nusselt number computed by CFD against that predicted by by (a) Ginelinski correlation using the values of f given by the Mishra and Gupta's correlation and (b) Pethukov correlation using the values of f given by the Ito's correlation.

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