Showing papers in "Journal of the Research Association of Powder Technology, Japan in 1977"

Mechanism of Adhesion due to Adsorbed Water Vapor an Powder Particles

Abstract: Adhesive forces generated at a contact point between spherical and plate specimens made of the same material due to water vapor adsorption on them were measured for four samples by using an electrobalance. The samples used here are commercial soda-lime glass bead, granulated urea and potassium halides, i.e. KCl and KBr. The values of the adhesive forces were collated with the amounts of adsorbed estimated from adsorption isotherms of water vapor on the above particle samples.The adhesive forces appeared at relative water vapor pressures of 0.25, 0.30, 0.30 and 0.17 for the glass bead, the granular urea, KCl and KBr, respectively. At this time, the thicknesses of adsorbed water layers were less than two layers for all the samples. Concerning the above results, this adhesive force can not be a binding-force due to a liquid bridge formed near the contact point. Therefore, the force which occurred in the early stage of a caking process is considered to be generated by the hydrogen bond induced between the two samples being attached with water layers. On the other hand, the force which increases considerably in high water vapor pressure range will be due to a liquid bridge between the two specimens. Moreover, it is concluded that the adsorbed water molecules less than 2 or 3 layers are influenced by surface properties of the solid, whereas the adsorbed more than 4 or 5 layers is no longer influenced from the solid surface. Thus, multi-layers of water molecules are thought to acquire an inherent property as the liquid water.

Power Requirement of Horizontal Ribbon Mixers

Abstract: Power requirement of solid mixers is influenced in a complicated manner by various factors, such as the operating conditions, the properties of the powders, the dimension of the mixers, and so on.In the present work, the relation between the torque of the horizontal mixers and those factors has been studied.The torque increases with increasing the charged ratio, f, the bulk density, ρa and the internal friction factor, μi of the powders, and the dimension of the mixer. On the other hand, the torque is not influenced by the rotating speed, N, in the range of 30≤N≤200r.p.m. The shear force has been found to be a dominant factor in the total power requirement of the mixer.The power data are well correlated with the experimental conditions by the relation Pgc=1.3μiρadf(φD02L)deNs de=[πL/4{2/P0(D02-(D0-2b0)2)+1/Pi(Di2-(Di-2bi)2)}]1/2 where D: diameter, L: length, b: width, Pi, 0: pitch, Ns: rotating speed, all in M. K. S. units, and suffices “0” and “i” refer to the outer and inner ribbon.

On the Bottom Pressure Distribution of Bulk Materials in the Cylindrical Vessel

Abstract: Though the vertical pressure of the bulk materials filled in the cylindrical vessel with a flat bottom has been reported by many investigators, there has been few detailed report of the vertical pressure distribution.In this paper, the size of cylindrical vessel, the filling method and the filling speed which affect the vertical pressure distribution are discussed.As the result, the following conclusion is obtained:1) In case of the peripheral feed, the curves of the vertical pressure distribution indicated by nondimension for each size of the vessel become roughly similarity, but that in case of the central feed becomes higher in the part closed to the wall than in the central part of a bed according to increase of the size of the vessel.2) The values of the vertical pressure in the part with closed to the wall agree nearly, independently of the filling method of materials, with the results obtained by the peripheral feed and the central feed respectively.3) The average pressure that obtained from the vertical pressure distribution measured differs greatly with the filling method of materials, in case of the peripheral feed with fine powder becomes higher pressure than that of the central feed, but granular materials becomes inversely.4) Though the average pressure of the peripheral feed with fine powder agrees nearly with the values, calculated using Janssen's theory, granular materials become less than about half.5) In case of the peripheral feed with fine powder, the vertical pressure in the central part of the vessel increases slightly according to increase of the filling speed, but that of granular materials is independently of the filling speed. In case of the central feed, the vertical pressure in the central part of the vessel filled increases slightly according to increase of the filling speed.

Stresses of Granular Materials in Vertical-Wall Section of Bunkers

Abstract: The initial stress exerted by bulk solids in the vertical-wall section of a bunker depends on the filling rate of solids. The flow stress is independent of the discharge rate of solids, The initial stress is ordinarily smaller than the flow stress. In the range of high filling rate of solids, however, the initial stress is similar to the flow stress. As a result, the upper bound of stresses can be established only and is estimated from the Janssen equation. In this case, the ratio of the horizontal to vertical stress, k, is represented by the equation k=(1-sin2φ)/(1+sin2φ) where φ is the frictional angle between solids and the vertical bunker walls. The stress ratio is therefore smaller than unity in the vertical-wall section of the bunker. The estimated stresses agree with the present data and early data of other sources. The wall coefficient of friction is the most important of the flow properties of bulk solids.

The Characteristics of a Fluidized Bed with Suspended Packings

Abstract: The vertical force acting on a single sphere was measured and the fluidizing conditions of the fluidized bed with suspended packings were studied.(1) The vertical force (F) acting on a single sphere which was hung in a fluidized bed was measured by a strain gage. At low gas velocity (near minimum fluidization), F was mainly determined by the apparent buoyancy and downward force arising from stagnant solids on the sphere. And with the increase in gas velocity, it was shown that this was gradually influenced by the drag force of moving solids.(2) The fluidizing conditions of the fluidized bed with suspended packings were studied by changing the diameter and density of the packings. It was found that the boundary of the packed fluidized bed (PFB) and suspended packing fluidized bed (SPFB) could be expressed by Wp/Ws=1 where Wp and Ws are the weight of suspended packings and fluidized particles, respectively. In SPFB, the left hand side in the preceding equation must be less than unity and the density of the packing should be less than the mean density of the bed. The pressure drop of SPFB(ΔP′) was accounted for by the following equation:ΔP′=ΔP(Wp/Ws+1) where ΔP is the pressure drop of a conventional fluidized bed (FB). And minimum fluidized velocity of SPFB(umf′) could be expressed experimentally by umf′=m(Vp/Vs)umf for Dp≥25.4mm. 0<(Vp/Vs)≤(Vp/Vs)* m is calculated by logm=log(1-ep)/(Vp/Vs) where Dp, Vp, Vs, (Vp/Vs)*, m, umf and ep are the diameter of suspended packing, volume of suspended packings, volume of fluidized particles, boundary value of PFB and SPFB, constant, minimum fluidized velocity of FB and void fraction of PFB, respectively. Also, It was observed experimentally that the bed expansion of SPFB was less than that of PFB.

Development of On-line Fineness Meter

Abstract: The on-line fineness meter is indispensable to design fully automatic cement grinding system and to save energy in the system. Several on-line fineness meters have been reported, but their prices, as well as durability and accuracy made their users hesitate to apply them. Bearing these points in mind, the authers have developed a new on-line fineness meter. It consists of a pilot air classifier, a balance with two belt conveyors functioning as the scale pan. These conveyors transport powder streams, i.e. classifier feed and coarse particles after classification. Through controling of the classifier cut-size, the ratio of flow rate of these two streams is kept constant automatically. As the result, the fineness of the sample can be indicated by the cut-point. From the test on a grinding system, following have been obtained:(1) accuracythe standard deviation of measured residue on 26μ: 0.6% (This corresponds to Blain specific surface area 30cm2/g)(2) indicial responsethe time constant: about 10min.

Power Requirement of Vertical Ribbon Mixer

Abstract: The effects of various operating conditions on the rotational torque of vertical ribbon mixers have been studied.The rotational torque, T[Kgm] of the mixers increases with increasing the height of powders bed, H[m], the bulk density, ρa[kg/m3] and the internal friction factor μi[-] of the powders, and the diameter of the ribbon, D0[m]. In the range of the rotating speed, N, of 30≤N≤100r.p.m., the torque remains almost constant and has a tendency to decrease as the ribbon width increases.The torque data are well correlated with the experimental conditions by the relation T=0.15ρa1.0μi0.7Rp1.2Rb-0.8H1.5D03.0, where, Rp [-] and Rb [-], respectively, are the ratios of the pitch and the width of the ribbon to the ribbon diameter.

On the Turbidity Currents between Inclined Parallel Planes

Abstract: The authors derived basic equations which express density current between parallel planes in a settling tank, where the phenomena are treated as two dimensional Problems.Nondimensional parameters which characterize the phenomena are given, and some applications of these equations are also investigated by numerical calculations after examining this mathematical model by experiments.

On the Design of a System for Particle Shape Analysis

Abstract: This paper has sought to outline the design of a particle shape analysis system. The discussion has exploited the assumption that shape, in this case the shape of powder particles, is assessed by the human observer using fuzzy sets. A three step system has been suggested in which the first step amounts to a clear example of decision making in a fuzzy environment. An attempt has been made to design the system by analoging certain features of the human perception of shape. A shape comparator is discussed and its design principles and an example of its construction is presented.The system will be further developed in particular:1. a detailed network comparator will be developed2. a study of the cost of shape assessment methods will be made.

Some Considerations on the Limit of Application of Alyavdin-Chujyo Equation

Abstract: The conditions of fine grinding with which Alyavdin-Chujyo's eqution holds been examined experimentally in this report. Ordinary ball mill grinding with a labratory scale batch mill (254mmφ×465mm length) and vibration ball milling with a batch mill (3000ml) were selected as the grinding methods.The results show that in ball milling the Alyavdin-Chujyo's equation can be applicable over wide grinding time and size range with few exceptions, but in vibration ball milling it is hardly applicable in any grinding conditions.The reasons of which are examined and disscussed, The theoretical consideration of the relation between Alyavdin-Chujyo's equation and size distribution equation, such as Rosin-Rammler's law, was tried, and it is found that, under the condition of Alyavdin-Chujyo's relation, the Rosin-Rammler size distribution law can hold.

Characteristics of Piezoelectric Microbalance for Dust Monitoring

Abstract: Mass concentration measurements of airborne suspended particulates have been made on the filtering method. On the otherhand, a light scattering method has been adopted in Japan for the routine monitoring. However, this method has a few defects. In the cases where the system of particulates changes or mist exists in the air, the mesured concentrations are effected and for accurate measurements the calibration procedure is required relating the filtering method.This paper describes on the characteristics of the dust monitor using a piezoelectric microbalance method, and shows its superiority over the light scattering method. The correcting method of mass sensitivity in this instrument, which is very important for practical use, has been developed applying water-soluble rhodamine. The collection efficiency of sample dusts (quartz powder, polystylene latex and lead fume) in this detector and the effects of relative humidity on measured concentrations are verified in this experiment.It is proposed that the instrument should be equipped with the humidity regulator for practrical measurement corresponding to the governmental environmental standard of suspended particulates.