Effect of Surface Roughness on Heat Transfer from Horizontal Immersed Tubes in a Fluidized Bed

Abstract

Experimental results of the total heat transfer coefficient between 12.7 mm dia copper tubes with four different rough surfaces and glass beads of three different sizes as taken in a 0.305 m × 0.305 m square fluidized bed as a function of fluidizing velocity are reported. The comparison of results for the rough and technically smooth tubes suggests that the heat transfer coefficient strongly depends on the ratio of pitch (Pf) to the average particle diameter (dp), where Pf is the distance between the two corresponding points on consecutive threads or knurls. By the proper choice of (Pf/dp) ratio, the maximum total heat transfer coefficient for V-thread tubes (hwfb) can be increased by as much as 40 percent over the value for a smooth tube with the same outside diameter. However, for values of (Pf/dp) less than 0.95, the maximum heat transfer coefficient for the V-thread rough tubes is smaller than the smooth tube having the same outside diameter. The qualitative variation of the heat transfer coefficient for rough tubes with (Pf/dp) is explained on the basis of the combined effect of contact geometry between the solid particles and the heat transfer surface, and the solids renewal rate at the surface. The present findings are critically compared with somewhat similar investigations from the literature on the heat transfer from horizontal or vertical rough tubes and tubes with small fins.

Heat transfer between horizontal finned tubes and a gas-solid fluidized bed

“…Experiments are carried out in a square fluidized bed (0.305 X 0.305 m) which is described in earlier publications (Grewal and Saxena, 1979, 1981. The distributor plate consists of flat head bubble caps screwed into a 3.2-mm-thick steel plate with 6.4-mm-diameter holes at a 2%" center-to-center spacing arranged in a square array.…”

“…A number of investigations have been reported in the literature on the performance of transverse (Bartel and Genetti, 1973;Bark1 et al, 1971;Gelperin et al, 1972Gelperin et al, ,1974Genetti et al, 1971;Genetti and Kratovil, 1977;Grewal and Saxena, 1979;Krause and Peters, 1980;Natusch and Blenke, 1973;Petrie et al, 1968;Priebe and Genetti, 1977;Staub and Canada, 1978;Zabrodsky et al, 1980) and longitudinal (Natusch and Blenke, 1974) fiined horizontal tubes, transverse (Chen and Withers, 1975;Genetti et al, 1971Genetti et al, , 1980Vijayaraghavan and Sastri, 1975) and longitudinal (Vijayaraghavan and Sastri, 1975) finned vertical tubes, spiral finned tube (Genetti and Everly, 1978), and transverse and longitudinal V-groove vertical plates (Korolev and Syromyatnikov, 1975). All these efforts are summarized in Table I.…”

“…Further the heat-transfer rate from V-thread tubes increases with increase in pf/dp from 1 to 3 (Grewal and Saxena, 1979). The purpose of this paper is to further investigate the thermal performance of V-thread single tube and its tube bundles for pf/dp up to 30.…”

“…The heat-transfer rate from V-thread tubes is larger as compared to smooth tubes having diameters equal to fin tip diameter for pf/dp > 1 ( Grewal and Saxena, 1979).…”

Modeling the Heat Transfer Coefficient Between a Surface and Fixed and Fluidized Beds With Phase Change Material

“…Their results are comparable to studies utilizing small cylinders. A number of experimental and numerical investigations have been reported on the measurement of the heat transfer rate between a horizontal tube and fluidized beds [16][17][18][19][20][21][22][23][24][25].…”