V. A. Borodulya

Heat transfer between a surface and a fluidized bed: consideration of pressure and temperature effects

Abstract A two-zone model of heat transfer between a fluidized bed and an immersed surface ( J. Engng Phys . 56(5), 767–773 (1989)) is used to correctly take into account the effect of the fluidized gas pressure and of the surface and bed temperatures on the overall heat transfer coefficient considered as the sum of conductive ( h cond ), convective ( h conv ) and radiative ( h r ) components. The quantity h cond represents the effect of contact thermal conductivity of solid particles and also their convection near the heat transfer surface, h r takes account of the effect of the bed non-isothermicity near the surface on its effective emissivity. Based on the model used, correlations are obtained for computing the overall heat transfer coefficient. Comparison with the literature data shows that these correlations are valid over a wide range of experimental conditions: 0.1 ⩽ d ⩽ 6.0 mm ; 0.1 ⩽ p ⩽ 10.0 MPa , 293 ⩽ T ∞ ⩽ 1713 K ; 293 ⩽ T w ⩽ 1373 K .

Horizontal particle mixing in a free fluidized bed

Horizontal particle diffusion in free fluidized beds is investigated experimentally.

External heat transfer in polydispersed fluidized beds at elevated temperatures

The authors present results of a theoretical and experimental study of heat transfer in polydispersed fluidized beds of coarse particles at temperatures up to 1273 K.

Heat transfer between a surface and an infiltrated bed of solid particles

Abstract A two-zone model of heat transfer between a surface and an infiltrated disperse bed of solid particles that takes into account the thermal conductivities of wall gas layer and bed particles and the gasdriven convective heat transfer is suggested. Equations obtained on its basis make it possible to describe the laws governing external heat transfer over a wide range of superficial gas velocities (fixed, fluidized and compressed beds). Consideration is given to special cases of heat transfer in developed fluidized and gasblown fixed beds. The results are presented in the form of simple computational relations. Their validity is checked experimentally and against data available in the literature (including experiments at high temperatures and pressures).

Heat transfer in fluidized beds

We propose a simplified model of external heat transfer in a fluidized bed. We compare calculated and experimental data, and recommend a computational procedure in polydisperse beds.

Axial solids mixing in a circulating fluidized bed

A phenomenological model of axial solids mixing in a circulating fluidized bed is formulated. The model allows for main specific features of the process: ascending motion of particles in the core zone and their descending motion in the annular zone (inner circulation of solids); substantial changes of particle concentration, sizes of core and annular zones over the bed height; net circulation of solids and the effect of the bottom bed on the process. The validity of initial postulates is confirmed by comparison of calculated and experimental curves of mixing.

Two-phase theory of fluidization

The effect of the circulational motion of particles on the form of the gas distribution between phases is taken into account.

Burning of solid biofuels in a cyclone-bed furnace chamber

Burning of solid biofuels (wood chips, milled peat, crushed peat bricks) in a cyclone-bed furnace of an air-heater boiler with power of 16.5 kW is investigated experimentally. It is established that the radial temperature distribution in a burning chamber is characterized by considerable nonisothermicity, which somewhat decreases as the amount of small fractions in the fuel increases. The influence of the air excess coefficient on the CO and NO concentrations in exhaust flue gases is shown. The dependence of the NO concentration on the air excess coefficient has the extremum in the studied range of experimental conditions. The comparison of established concentrations of CO and NO with regulations shows that when burning the wood fuel and peat brick according to the cyclone-bed technology, the air excess at the furnace output can be lowered to 1.07 (depending on the boiler aggregate power) simultaneously attaining the limiting CO concen tration, which makes it possible to increase the boiler efficiency compared with efficiency of boilers with bed furnaces (air excess coefficient of 1.3–1.6) by 2–4%.

Expansion of coarse-grained fluidized beds impeded by horizontal tube arrays

Experimental data on the expansion of fluidized beds with immersed arrays of horizontal tubes are obtained and generalized.

Velocity of Complete Fluidization of a Polydisperse Mixture of Various Fuels

Using the principle of hydrodynamic equivalence, the procedure of calculating a velocity of complete fluidization of different-density polydisperse granular materials has been developed with account for changes in their initial size distribution. It is shown that coarse particles in composition of polydisperse mixtures can be fluidized when the velocity u cf is substantially smaller than their minimum fluidization velocity (u mf)max.