Effects of local flow on the heat transfer characteristics of a cowled,finned system

Abstract

Experimental studies of the local flow and heat transfer characteristics within the finned region of a cowled, annularly finned cylinder are presented. The temperature and local heat fluxes across fin surfaces were measured using thermocouples and Micro-foil™ heat flux sensors. Areas of maximum heat transfer coefficients greater than 60 W/m²K were observed in the forward fin tip and base regions. A local minimum of 12 W/m²K was found in the mid-fin regions behind the finned cylinder. The local flow characteristics with in the finned region were measured using laser Doppler anemometry at an inlet Reynolds number of 4 × 10⁵. Areas of high turbulence intensity and shifting high-velocity zones were found. Correlation between the heat transfer and flow characteristics confirm the existence of boundary layer development, forward edge separation, and root and tip vortices. The application of the cowl system on a finned cylinder leads to a heat transfer enhancement of greater than 29 per cent. Localized fluctuations of the heat flux on the fin surface are also discussed.

Keywords

cowl finned cylinder local heat transfer and flow characteristics

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References

Davis

K. R.

The use of barrel heater/cooler systems on barrel extruders. Report 1746, University of Wales Cardiff, 1993.

Neal

S. B.H.C.

Hitchcock

J. A.

A study of the heat transfer processes in the banks of finned tubes in cross flow, using a large scale model technique. In Proceedings of the Third International Heat Transfer Conference, Chicago, Illinois, 1966, vol. 3, pp. 290–298.

Jacobi

A. M.

Local heat transfer behaviour and its impact on a single-row, annularly finned tube heat exchanger. Trans. ASME, J. Heat Transfer, February 1993, 115, 66–74.

Lin

Griffiths

A. J.

Local flow characteristics and its effect on cowled finned systems. Proc. Instn Mech. Engrs, Part E, Journal of Process Mechanical Engineering, 211 (E2), 95–108.

Incropera

F. P.

De Witt

D. P.

Fundamentals of Heat and Mass Transfer, 1990, Ch. 6 (John Wiley, New York).

Lemmon

A. W.

Colburn

J. R.

Nottage

H. B.

Heat transfer from a baffled-finned cylinder to air. Trans. ASME, November 1945, 601–612.

Kruckels

Kottke

Investigation of the local heat transfer on finned tubes and modelling. Chemie-Ing-Technik, 1970, 42, 355–362.

Legkiy

V. M.

Pavlenko

V. P.

Makarov

A. S.

Zhehidov

Y. S.

Investigation of local heat transfer in a tube with annular fins in transverse air flow. Heat Transfer: Soviet Res., 1974, 6 (6), 101–107.

Sparrow

E. M.

Chastain

S. R.

Effect of angle of attack on the heat transfer coefficient for an annular fin. Int. J. Heat and Mass Transfer, 1986, 29 (8), 1185–1191.

10.

Sung

H. J.

Yang

J. S.

Park

T. S.

Local convective mass transfer on circular cylinder with transverse annular fins in crossflow. Int. J. Heat Mass Transfer, 1996, 39 (5), 1093–1101.

11.

Geidt

W. H.

Investigation of variation of point unit heat transfer coefficient around a cylinder normal to an air stream. Trans. ASME, May 1949, 375–381.

12.

Drain

L. E.

The Laser Doppler Technique, 1980, Chs 2 and 6 (John Wiley, New York).

13.

Lin

Characterisation of local flow within cowled finned systems. PhD thesis, University of Wales Cardiff, 1996.

14.

Ower

Pankhurst

R. C.

The Measurement of Air Flow, 1977, Ch. VI (Pergamon, Oxford).

15.

Bates

C. J.

The use of laser Doppler anemometry for the study of water flow pipes. PhD thesis, University of Wales College of Cardiff, 1977.

16.

Long

C. A.

Calibration technique for thermopile heat-flux gauges. In Proceedings of the Fifth International Exhibition and Congress for

Sensor and Systems Technology, 1991.

17.

Rogers

G. F.C.

Mayhew

Y. R.

Thermodynamic and Transport Properties of Fluids, 4th edition, 1993 (Blackwell, Oxford).

18.

Ozisik

M. N.

Basic Heat Transfer, 1977, Ch. 9 (McGraw-Hill, New York).

19.

White

F. M.

Heat and Mass Transfer, 1988, Ch. 6 (Addison-Wesley, Reading, Massachusetts).