Dynamic characteristics of heat transfer coefficient have been investigated in a pressurized bubble column (0.152 m, i.d. and 2.0 m in height) by adopting the chaos theory. Effects of gas velocity (0–0.12 m/s), pressure (0.1–0.6 MPa) and liquid viscosity (1.0–38.0 mPa s) on the immersed heater-to-column heat transfer characteristics have been examined. The temperature difference fluctuations between the immersed heater and the column content proper have been analyzed by means of attractor trajectories and correlation dimension to characterize the dynamic heat transfer behavior. The immersed heater-to-column heat transfer coefficient has increased with increasing gas velocity or pressure, but it has decreased with increasing liquid viscosity. It has been found that the attractor trajectories and correlation dimension are effective tools to describe the dynamic heat transfer behavior in the pressurized bubble columns with viscous liquid medium. The correlation dimension of the temperature fluctuations and the range of heat-transfer coefficient fluctuations have decreased with increasing pressure, but they have increased with increasing gas velocity or liquid viscosity. The heat transfer coefficient, correlation dimension of temperature difference fluctuations or the range of fluctuations of heat transfer coefficient, have been well correlated with operating variables.

Dynamic characteristics of heat transfer coefficient in pressurized bubble columns with viscous liquid medium

Characteristics of heat transfer and hydrodynamics have been investigated in two- and three-phase inverse fluidized beds whose diameters are 0.152 and 2.5 m in height. Effects of gas and liquid velocities and particle density (polyethylene and polypropylene) on the immersed heater-to-bed heat-transfer coefficient, individual phase holdup, and minimum liquid fluidization velocity have been determined. It has been found that the minimum liquid fluidization velocity decreases with increasing gas velocity in the inverse fluidized beds. The gas and liquid holdups increase with an increase in the gas or liquid velocity in the beds. The heat-transfer coefficient in two-and three-phase inverse fluidized beds of relatively high density particles (polyethylene) has been higher than that in the beds of relatively low density particles (polypropylene). The heat-transfer coefficient increases with increasing gas velocity; however, it exhibits a maximum value with increasing liquid velocity in liquid-solid as well as three-phase inverse fluidized beds. The liquid velocity at which the h value attains its maximum value decreases with increasing particle density or gas velocity. The immersed heater-to-bed heat-transfer coefficient has been well correlated in terms of dimensionless groups as Nu 1 =0.001(Pr)(Re 1 ) 1.282 , Nu 2 =0.084(Pr)-(Re 2 ) 0.944 , and Nu 3 =0.050(Pr)(Re 3 ) 0.810 .

Heat transfer and hydrodynamics in two- and three-phase inverse fluidized beds

Flow regime identification in a three-phase bubble column based on statistical, Hurst, Hilbert–Huang transform and Shannon entropy analysis

Molecular simulations have been performed on adsorption equilibria and diffusivities of pure and mixed-gases of ethanol/water in micropores of an NaA zeolite crystal by using the μVT-ensemble orientational-bias Monte Carlo and the NVT-ensemble equilibrium molecular dynamics techniques. The temperature and the total pressure were set at 378 K and 0.1 MPa respectively for comparison with the data of vapor permeation of a corresponding system. Adsorption equilibrium selectivity of water to ethanol was found to increase with an increasing ethanol composition in the gas phase, which was qualitatively in agreement with the experimental permselectivity, though the latter was three orders of magnitude higher than the first. The diffusivity of water in the zeolite was found to be in the region of 3.9–7.9 × 10–10 m2/s while the ethanol molecules were confined in the α-cage and did not go through the window during a simulation period of 3 ns, which indicated that the diffusivity of ethanol might be much smaller than that of water. Therefore, it is concluded that the high permselectivity of water through an NaA zeolite membrane is ascribed to the cooperation of two factors: the high adsorption selectivity and the high diffusivity of water. It is also noted that the selective adsorption of water may be important for preventing the blockage by ethanol molecules at the entrance and inside of the membrane.

Molecular Simulation Study on Adsorption and Diffusion Behavior of Ethanol/Water Molecules in NaA Zeolite Crystal

Non-uniform flow behavior of fluidized solid particles in three-phase fluidized beds has been analyzed by adopting the stochastic method. More specifically, pressure fluctuation signals from three-phase fluidized beds (0.152 m ID x 2.5 m in height) have been analyzed by resorting to fractal and spectral analysis. Effects of gas flow rate (0.01-0.07 m/s), liquid flow rate (0.06-0.18 m/s) and particle size (0.001-0.006 m) on the characteristics of the Hurst exponent, spectral exponent and Shannon entropy of pressure fluctuations have been investigated. The Hurst exponent and spectral exponent of pressure fluctuations attained their local maxima with the variation of liquid flow rate. The Shannon entropy of pressure fluctuation data, however, attained its local minima with the variation of liquid flow rate. The flow transition of fluidized solid particles was detected conveniently by means of the variations of the Hurst exponent, spectral exponent and Shannon entropy of pressure fluctuations in the beds. The flow behavior resulting from multiphase contact in three-phase fluidized beds appeared to be persistent and can be characterized as a higher order deterministic chaos.

Particle flow behavior in three-phase fluidized beds

Pressure fluctuations in a three phase bubble column reactor operating at relatively low pressure (92 KPa) have been analyzed by adopting the spectral and fractal analyses to get the engineering informations for the on-line control and fault diagnosis of the reactors. The mean value, standard deviation, skewness and kurtosis of the pressure fluctuations have been obtained. The local fractal dimension has been determined from the Pox diagram obtained by means of the rescaled range analysis of the pressure fluctuations based on the fractional Brownian motion. The local fractal dimension of pressure fluctuations has increased and thus the pressure fluctuation signals have become less persistent and irregular, with increases in the gas flow rate reaction temperature, particle size and solid content in the slurry phase. The local fractal dimension has been well correlated in terms of the operating variables.

Fractal analysis of pressure fluctuations in a three phase bubble column reactor operating at low pressure

Comminution characteristics of diatomaceous earth have been investigated in a vertical type jet mill of pilot plant scale; the diameter of the chamber of mill is 26.3 cm. Fluidization of the particles in the chamber has been proposed to enhance the comminution efficiency of the jet mill by promoting the effective contacting of powders with compressed air as well as the chamber wall. Effects of the pressures or densities of pulverizing-air and fluidizing-air and comminution time on the mean size of the particles and the rate of comminution have been examined. The statistical analysis of pressure fluctuations in the chamber of the mill has been utilized to predict the characteristics of the vertical-type jet mill taking advantage of the fluidization technique. The particle size and comminution rate have been correlated with the operating variables, respectively.

Sang Do Kim

Papers

Fractal analysis of pressure fluctuations in a three phase bubble column reactor operating at low pressure

Effective comminution of diatomaceous earth in a vertical type jet mill