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Heat transfer characteristics at an axial tube in a circulating fluidised bed riser.

Author(s) : KOLAR A. K., SUNDARESAN R.

Summary

Experimental surface-average heat transfer coefficients of a vertical tube located at various positions along the axis of a Circulating Fluidized Bed riser (CFB) are presented. Experiments were carried out on the tube in a 100 × 100 mm cross-section and 5.5 m tall CFB cold unit using silica sand of mean particle size 363 m as the bed material. The copper tube was 9.6 mm OD and 0.6 m high placed in the core of the riser with hot water flowing through it. The tube was located axially at distances of 0.97, 1.62, 3.0 and 4.0 m from the distributor plate. The fluidising air velocity and solid circulation flux were varied in the range of 4.5-7.3 m/s and 21-72 kg/m2.s respectively. The measured average heat transfer coefficient varied in the range of 58-101 W/m2.K and showed a decreasing trend from the riser bottom to the riser exit. At a given location, increasing the fluidising velocity resulted in reduced heat transfer coefficient while increasing the solid circulation flux enhanced it. At a given average suspension density, the local dynamics of gas and solids adjacent to the tube surface affected the heat transfer. Gas convective contribution was found to be substantial at high gas velocities especially at higher tube locations. Using the experimental data for the axial tube, two empirical heat transfer correlations were developed in terms of the important design and operating parameters including a non-dimensional height parameter. Comparisons were made with literature available under similar but not identical operating parameters.

Details

  • Original title: Heat transfer characteristics at an axial tube in a circulating fluidised bed riser.
  • Record ID : 2004-2700
  • Languages: English
  • Publication date: 2002/07
  • Source: Source: Int. J. therm. Sci./Proc. ExHFT-5, Thessaloniki
    vol. 41; n. 7; 673-681; fig.; tabl.; 11 ref.

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