Mompei Shirato

The Terzaghi-Voigt combined model for constant-pressure consolidation of filter cakes and homogeneous semi-solid materials

Abstract Theories of constant-pressure consolidation are reexamined in detail. A Voigt model for constant-pressure consolidation is solved and the time factors which govern a secondary consolidation process are obtained. It is found that three kinds of retardation times exist in the solution of the Terzaghi-Voigt combined model; the first factor, Θ 1 , is due to liquid flow resistance of the Terzaghi element; the second, Θ 2 , is due to liquid flow resistance of the Voigt element; and the third, Θ 3 , is due to creep deformation of the particulate bed. One can derive the conventional solutions of the Terzaghi-Voigt combined model for constant-pressure consolidation under the normal assumption that both Θ 1 and Θ 2 are much less than Θ 3 .

Experimental analysis of flux decline mechanism of batch ultrafiltration (filtration characteristics of gel layer)

Abstract In order to make the so-called membrane fouling phenomena during ultrafiltration clearer, it is Important to visualise, by any means, the characteristics of the gel layer formed on the membrane surface. Unstirred dead-end ultrafiltration experiments were conducted under constant pressure, by using a newly-designed batchwise filter which had a sudden change in its filtration area. The variation in gel cake thickness with time, was determined on the basis of experimental measurements and then the overall characteristic values, such as the average specific filtration resistance, average porosity and the ratio of wet to dry cake mass were calculated on the basis of experimentally determined gel cake thickness. It has become evident that the relationship between filtration characteristics and operating conditions can be thoroughly analysed on the same basis as the conventional cake filtration theories or concept.

DELIQUORING BY EXPRESSION -PART 1 CONSTANT-PRESSURE EXPRESSION

Abstract The basic analitical method for so-called expression operation, the separation of liquid from solid-liquid systems by compression, are presented in view of the flow through compressible porous media. It has become evident that the expression mechanism consists of two flow phenomena. These types of phenomena can be analyzed by consideration of the flow mechanism through compressible porous beds, first by the filtration theory and second by the so-called consolidation theory. A simplified equation is also presented. It is shown that the simplified equation is well applicable to industrial expression problems even when the creep effects of matarials to be expressed are appreciable

PRESS DEWATERING OF BROWN COAL : PART 2 -BATCH AND CONTINUOUS-SCREW OPERATIONS-

ABSTRACT The brown coal is wet-ground and expressed in a batch constant-pressure or constant-rate operation and in a continuous screw-press operation. It is found that 90% of the moisture of the as-mined coal can be removed under the pressure of about 100 ma. Batch operations under a constant-pressure or a con-stant-rate can be analyzed well by using the Terzaghi-Voigt model and constant-pressure analysis. In a continuous screw-press operation, the resistance of the filter medium, the feed concentration and the die resistance affect the screw performance. The volumetric discharge rate under the open discharge condition can be expressed well by a lubrication theory. With discharge restricted by a screw-type die, the slip factor decreases with increase in die resistance.

DELIQUORING BY EXPRESSION - PART 2 VARIABLE-PRESSURE EXPRESSION

ABSTRACT Expression processes under variable-pressure condition are analyzed in view of the flow through compressible porous media. It has been demonstrated that the expression mechanism of slurry consists of two flow phenomena and these types of phenomena can be analyzed first by filtration theory and second by the so-called consolidation theory. By assuming that the continuous screw expression process con- sists of a succession of batch processes, the basic equations ex- pressing the relationship between the dehydration rate, the feed rate, and the expression pressure distribution are derived.

In search of professional excellence

Mompei Shirato, President of the Filtration Society Japan Association shares his thoughts on striving for technical excellence, in the latest of his columns.

Society column: Roundup

From this months issue our new society roundup column will allow filtration societies around the world to update readers on their developments – as well as allow us to offer truly global and up-to-date perspectives on filtration. In the inaugural column, we hear from Mompei Shirato, president of the Filtration Society Japan Association

Velocity Distribution in Filter Chamber of a Rotating-Disk Dynamic Filter without Permeation.

To analyze the flow pattern in the filter chamber of a dynamic filter with a rotating disk, the velocity of Newtonian liquid flow without permeation was measured by use of a fiber-optic laser velocimeter. The effects of the rotational speed of the disk and chamber dimensions on the flow pattern can be evaluated in terms of the ratio K of the tangential velocities of the core and the rotating disk. New empirical equations for K-value are presented and successfully correlate our data compared with the former equations.

Effects of film flow on gravitational drainage of highly viscous fluids.

A method is presented for calculating the drained liquid volume in gravitational drainage by applying an empirical correction, which takes into account the effects of liquid viscosity on film flow, to the authors prior equations for the dewatering of granular beds. It was shown that the dehydration rate of highly viscous Newtonian liquid is strongly affected by the existence of filmwise liquid flow when the modified capillary number is larger than 2.5.The predicted results agreed well with the experimental results for packed beds of glass beads and calcium carbonate particles of diameter 1641875 μm, under conditions where the liquid viscosity ranges from 0.001 to 0.76 Pa · s.

Collection efficiency of granular bed filters with dust loads.

粉じん負荷を伴う粒子充てん層フィルタの捕集効率の簡便な推定法を得るために, 前報の繊維充てん層フィルタの解析で提案したさえぎりモデルに基づき, 充てん層内の流れを表す桑原・Happelのセルモデルを適用した単一球あたりの捕集効率の推定式を提案した.エアロゾル粒子は濾過過程が進行するにつれて充てん粒子表面上に堆積し, この堆積粒子によるさえぎり効果が捕集効率上昇の支配的機構であると仮定して, 単一球捕集効率の増加分を表した.また, 捕集粒子層の平均充てん率を考慮するため, 補正係数Kの実験式をさえぎりパラメータNRの関数として求め, NR0.4Kの値が流入粉じん負荷量にはよらないことを実験的に示した.