Pressure fluctuation data were obtained from an air-fluidized sand bed (-48 + 65 Tyler mesh) with openended cylindrical packing. The tests were made in a 5-inch diameter column, and with packings made from steel wire cloth 4-, 6-, or 14-mesh per inch and '/? X '/2, "4 X 3/4, and 1 X 1 inch in size. These data were analyzed to yield r.m.s. values, the probability density, and the normalized power spectral density functions. The r.m.s. values of the pressure fluctuations were lower for the packed fluidized beds than for the same bed fluidized with no packing. For each packing, a maximum was observed on a plot of r.m.s. vs. flow rate or bed expansion. When no packing was used, r.m.s. values increased continuously with gas flow or bed expansion; the distributions were Gaussian at low flow rates, and skewed at high flow rates. The probability distributions of the differential pressure fluctuations were Gaussian for a fluidized bed containing packings over the whole flow range tested. The normalized power spectral density functions were similar for the packed and unpacked fluidized beds, though peak frequencies showed some dependence on packing dimensions. PRESSURE drop fluctu,ations in aggregative fluidized beds have been studied as a basis for defining an index of fluidized bed quality (Fiocco, 1964;Shuster and Kisliak, 1952;Sutherland, 1964). In these studies. strip chart recordings of the pressure changes \vere analyzed in various ways to give peak counts, line-cut counts, average fluctuation, etc. These data are of limited value because of the arbitrary way in which the recordings Lvere analyzed. In the present study, the pressure data were analyzed b;; a current spectral technique, which provides a more detailed examination of the data.The source of the pressure fluctuation is not yet fully understood. In gas-solid fluidized beds, the pressure drop fluctuations correspond directly to the bubble flow, though the pressure drops are really a consequence of changes in gas flow through the dense phase. Reuter (1963Reuter ( , 1966 has reported that the axial pressure gradient in the dense phase near the bubble is larger than in the undisturbed regions of the bed, \vhile the gradient inside the bubble is nil. Though Reuter's kvork provides a partial explanation for the pressure fluctuation in fluidized beds, the data are not yet sufficient for a complete interpretation of a fluctuating pressure signal.In this paper. preliminary experiments are first reported on the correlation of pressure fluctuations \vith bed height fluctuations, and then on the pressure change \vhich occurs when a single artificial bubble ]passes through a bed. Finally, data are given on the effect of screen packing on pressure fluctuations in a fluidized sand bed.Various packings, such as spheres, solid cylinders, Raschig rings, Berl saddles, and screen rings. have been used to improve fluidization. Data have been reported on the effect of packings on gas mixing (Chen and Osberg, 1967;Gabor and Mecham, 1964); solid mixing (Gabor, , 1965(Gabor, , 19...
