Extended surface heat transfer in fluidized beds
TL;DR: In this article, a critical review of the effects of some important fluidization and fin geometry parameters on the bed-to-tube surface heat transfer is presented, and significant features of finned tube heat transfer are discussed and areas requiring further attention are suggested.
Abstract: The emerging technology of fluidized bed combustion of coal and recognition of the fluidized bed heat exchanger as a heat transfer device with great potential have regenerated interest in the heat transfer process between a gas fluidized bed and immersed tubes with extended surfaces or fins. In the present work, a critical review of the effects of some important fluidization and fin geometry parameters on the bed-to-tube-surface heat transfer is presented. The significant features of finned tube heat transfer are discussed and areas requiring further attention are suggested.
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TL;DR: In this paper, the authors measured the heat transfer coefficient between an electrically heated single horizontal tube and air-solid fluidized beds of glass beads, dolomite, sand, silicon carbide and alumina particles.
93 citations
TL;DR: In this article, the relationship between boiler tubes and the fluidized bed is empirically developed on the basis of the observed data with limited attention to the mechanisms of the heat transfer process.
Abstract: Publisher Summary Bed–to–surface heat transfer can be calculated with good reliability, if particle-residence times and their population near the surface are known The mechanism of heat transfer between boiler tubes and the fluidized bed is very complicated because of the many fluidized-bed variables and the variations in heat-transfer tube design Correlations are empirically developed on the basis of the observed data with limited attention to the mechanisms of the heat-transfer process This chapter reviews the design application of local as well as total heat-transfer coefficients for horizontal and slanted tubes, and for vertical tubes Single tubes and tube banks in different orientations to the bed are also considered The fundamental mechanisms of wall–to–bed heat transfer are reviewed and the criteria for evaluation of correlations for full-scale application are examined Particle movement is a complex function of the particle and gas properties, fluidization velocity, gas distributor, and geometry of the bed This approach generally gives the designer a good degree of assurance, requires a judicious choice of a representative system as well as the expense of pilot scale development The consideration must be given to the unsteady-state conduction component, the radiation component, and the gas convective component in boiler design
75 citations
TL;DR: In this paper, the authors present a review of the major mechanisms of heat transfer in coal combustion, focusing on two main schools of thought: (a) the principal resistance to heat transfer is a fluid film, and the moving fluidized particles scour the film to reduce the resistance of the heat transfer; and (b) heat is absorbed by the fluidised particles and the rate of heat transferred depends on the rates of heat absorption.
35 citations
TL;DR: In this paper, a generalized correlation for heat transfer coefficient between a horizontal tube bundle and a gas-solid fluidized bed is proposed, based on the experimental data for heat transferred coefficient between electrically heated horizontal tube bundles (12.7 and 28.6 mm diam.) and square fluidized beds (30.5 × 30.5 cm).
20 citations
TL;DR: In this paper, the authors compared the heat transfer coefficient of rough and smooth tubes and showed that the ratio of pitch (P/sub f/) to the average particle diameter (d/sub p/), where p is the distance between the two corresponding points on consecutive threads or knurls, strongly depends on the ratio between the pitch ratio and the particle diameter.
Abstract: Experimental results of the total heat transfer coefficient between 127 mm dia copper tubes with four different rough surfaces and glass beads of three different sizes as taken in a 0305 m x 0305 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 (P/sub f/) to the average particle diameter (d/sub p/), where P/sub f/ is the distance between the two corresponding points on consecutive threads or knurls By the proper choice of (P/sub f//d/sub p/) ratio, the maximum total heat transfer coefficient for V-thread tubes (h/sub w/fb) 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 (P/sub f//d/sub p/) less than 095, 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 (P/sub f//d) is explained on the basis of the combined effect of contact geometry between the solid particles and the heatmore » 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« less
20 citations