LAMINAR AIR FLOW FREE CONVECTIVE HEAT TRANSFER INSIDE A VERTICAL CIRCULAR PIPE WITH DIFFERENT INLET CONFIGURATIONS

Abstract

Free convection heat transfer has been experimentally investigated for laminar air flow in a vertical circular pipe by using the boundary condition of constant wall heat flux in the ranges of RaL from 1.1 109 to 4.7 109. The experimental setup was designed for determining the effect of different configurations placed at the inlet of a vertical heated pipe, on the surface temperature, the local and average heat transfer coefficients. The apparatus was made with an electrically heated aluminum pipe with length of 900 mm and inside diameter 30 mm. The inlet configurations included two circular pipes having the same diameter as the heated pipe but with lengths of 600 mm, 1200 mm, sharp- edge and bell-mouth. It was found that the surface temperature along the pipe surface for same heat flux would be higher values for inlet condition with length of 1200 mm and would be lower values for bell-mouth inlet condition. The results show that the local Nusselt number Nux and average Nusselt number values would be higher for bell-mouth inlet condition and lower values for 1200 mm inlet condition. For all inlet configurations, the results reveal that the Nusselt number increases as the heat flux increases. Empirical correlations have been proposed in a form of Log versus Log for each case investigated and a general correlation for all cases has been obtained which reveals the effect of inlet conditions existence on the free convection heat transfer process in a vertical circular pipe.

Keywords

Dates

  • Submission Date2006-05-14
  • Revision Date2006-10-20
  • Acceptance Date2006-10-25

DOI Reference

10.2298/TSCI0701043M

References

  1. Incropera F.P. and DeWitt D. P., Fundamentals of Heat and Mass Transfer, 5th edition, John Wiley & Sons Inc., New York, USA, 2003.
  2. Meric R.A., An Analytical Study of Natural Convection in a Vertical Open Tube, Int. J. Heat and Mass Transfer, Vol.20 (1977), pp.429-431.
  3. Barrow R.D., Heat Transfer by Free Convection in Open Ended Vertical Duct, Int. Heat Transfer Conference, 5th Proc., Vol.3, Tokyo (1974), Paper No.NC2.5, pp.59-63.
  4. Kokugan T. and Kinoshita T., Natural Convection Flow Rate in a Heated Vertical Tube , Journal of the Chemical Engineering of Japanese, Vol. 8 (1975), No.6, pp.445-450.
  5. Hess C.F. and Miller, C.W., Natural Convection in a Vertical Cylinder Subject to Constant Heat Flux, Int. J. Heat and Mass Transfer, Vol.22 (1979), No.3, pp.421- 430.
  6. Shigeo K. and Adrian B., Experimental Study of Natural Convection in a Horizontal Cylinder with Different End Temperatures, Int. J. of Heat and Mass Transfer, Vol. 23 (1980), Issue 8, pp.1117-1126.
  7. Shenoy A. V., Natural Convection Effects on Heat Transfer to Power-Law Fluids Flowing under Turbulent Conditions in Vertical Pipes, Int. Communications in Heat and Mass Transfer, Vol.11 (1984), Issue 5, pp.467-476.
  8. Chang C. J., Lin T. F. and Yan W. M., Natural Convection Flows in a Vertical Open Tube Resulting from Combined Buoyancy Effects of Thermal and Mass Diffusion, Int. J. of Heat and Mass Transfer, Vol. 29 (1986), Issue 10, pp.1543 -1552.
  9. Al-Arabi M., Khamis M. and Abd-ul-Aziz, Heat Transfer by Natural Convection from the inside Surface of a Uniformly Heated Vertical Tube, Int. J.Heat and Mass Transfer, Vol.34 (1991), No.4/5, pp.1019-1025.
  10. Abd-el-Malek B. M. and Nagwa A.B., Group Method Analysis of Steady Free-Convective Laminar Boundary-Layer Flow on a Nonisothermal Vertical Circular Cylinder, Journal of Computational and Applied Mathematics,Vol.36 (1991), Issue 2, pp.227-238.
  11. Fukusako S. and Takahashi M., Free Convection Heat Transfer of Air-Water Layers in a Horizontal Cooled Circular Tube, Int. J. of Heat and Mass Transfer, Vol. 34 (1991), Issue 3, pp.693-702.
  12. Yan W. M. and Lin T. F., Theoretical and Experimental Study of Natural Convection Pipe Flows at High Rayleigh Number, Int. J. of Heat and Mass Transfer, Vol.34 (1991), Issue 1, pp. 291-303.
  13. Vinokurov V. F., Volkov S. V., Martynenko O. G., Khramtsov P. P. and Shikh I. A., Some Aspects of Free-Convective Heat Transfer in Eddy Flow through a Horizontal Tube, Int. J. of Heat and Mass Transfer, Vol.36 (1993), Issue 18, pp. 4487- 4491.
  14. Yissu W., Laminar Natural Convection in Vertical Tubes with One End Open to a Large Reservoir, Int. J .of Heat Transfer, Vol.56-06 (1995), Section: B, pp.3411.
  15. Kuan-Tzong L., Fully Developed Laminar Natural Convection Heat and Mass Transfer in Partially Heated Vertical Pipe, Int.Communications in Heat and Mass Transfer, Vol.27 (2000), Issue 7, pp.995-1001.
  16. Wojciech T. K., Natural Convection Heat Transfer around Horizontal Tube in Vertical Slot, Int. J. of Heat and Mass Transfer, Vol.43 (2000), Issue 3, pp. 447- 455.
  17. He Y. L., Tao W. Q., Qu Z. G. and Chen Z. Q., Steady Natural Convection in a Vertical Cylindrical Envelope with Adiabatic Lateral Wall, Int. J. of Heat and Mass Transfer, Vol.47 (2004), Issues 14-16, pp.3131-3144.
  18. Moawed M., Experimental Investigation of Natural Convection from Vertical and Horizontal Helicoidal Pipes in HVAC Applications, Energy Conversion and Management, Vol.46 (2005), Issues 18-19, pp.2996-3013.
  19. Holman J.P., Experimental Methods for Engineers, 7th edition, McGraw-Hill International Inc, New York, USA, 2001.
  20. McAdams W.H., Heat Transmission, 3rd edition, McGraw Hill- Company, New York, USA, 1954 (quoted from Holman J.P., Heat Transfer, 8th edition, McGraw-Hill International Inc.,New York, USA, 1997, chapter 7).
Volume 11, Issue 1, Pages43 -63