Squeezing mechanism

The basic mechanism of foam degradation in porous medium is film coalescence. It depends on film thickness and capillary pressure. In the process of advancement the film thickness changes considerably thickens in the narrow parts (pore throats) and thins in the wider parts (pore bodies). Visual observations of such a stretching-squeezing mechanism are reported by Huh et al. [178]. Therefore, the film thickness would depend on the liquid/gas ratio, the rate of movement and the ratio of pore-body to pore-throat. When the critical capillary (disjoining) pressure is reached, the film will rupture. 

The results were consistent with the positive squeezing mechanism when the temperature was increased and maintained at 40°C, nearly constant release pattern was observed. No significantly sustained, but rapidly decreased release was observed on the temperature change to 25°C. The thermosensitive release profile... 

The squeezing mechanism is observed in T-mixers at Cfl<0.02 when the interfacial forces dominate the shearing forces [40, 54] (Figure 9.8). Pohorecki and Kula [55] proposed an equation to estimate the bubble size for switching mechanism in a Y-mixer at lQ[Pg.220]

Recovery of sorbed heavy oil from carbon materials was carried out either by filtering under suction (about 5 to 7 kPa pressure), washing with solvents, centrifuging at 3800 rpm, or by squeezing mechanically. The recovered sorbent was repeatedly subjected to sorption of the heavy oil. To determine its cycling performance, this cycle of sorption and recovery (desorption) was repeated up... 

Mechanical Squeezing of Cakes. Mechanical squeesing of the cake in the so-called variable chamber filters has been used relatively recendy to lower moisture content of the final cake. This is appHcable only to cakes that are compressible. Many filters are available in which some form of mechanical expression of the cake is used either to foUow a conventional filtration process or to replace it. 

Dryers. A drying operation (see Drying agents) needs to be viewed as both a separation and a heat-exchange step. When it is seen as a separation, the obvious perspective is to cut down the required work. This is accompHshed by mechanically squeezing out the water. The objective is to cut the moisture in the feed to the thermal operation to less than 10%. In terms of hardware, this requires centrifuges and filters, and may involve mechanical expression or a compressed air blow. In terms of process, it means big crystals. 

Belt Presses Belt presses were fiiUy described in the section on filtration. The description here is intended to cover only the parts and designs that apply expression pressure by a mechanism in adchtion to the normal compression obtained from tensioning the belts and pulling them over rollers of smaller and smaller diameters. The tension on the belt produces a squeezing pressure on the filter cake proportional to the diameter of the rollers. Normally, that static pressure is calculated as P = 2T/D, where P is the pressure (psi), T is the tension on the belts (Ib/hnear in), and D is the roller diameter. This calculation results in values about one-half as great as the measured values because it ignores pressure created by drive torque and some other forces [Laros, Advances in Filtration and Separation Technology, 7 (System Approach to Separation and Filtration Process Equipment), pp. 505-510 (1993)]. 

Diffusion in the bulk of a crystal can occur by two mechanisms. The first is interstitial diffusion. Atoms in all crystals have spaces, or interstices, between them, and small atoms dissolved in the crystal can diffuse around by squeezing between atoms, jumping - when they have enough energy - from one interstice to another (Fig. 18.6). Carbon, a small atom, diffuses through steel in this way in fact C, O, N, B and H diffuse interstitially in most crystals. These small atoms diffuse very quickly. This is reflected in their exceptionally small values of Q/RTm, seen in the last column of Table 18.1. 

The transducer most commonly used to obtain vibration measurements is an accelerometer. It incorporates piezoelectric (i.e., pressure-sensitive) films to convert mechanical energy into electrical signals. The device generally incorporates a weight suspended between two piezoelectric films. The weight moves in response to vibration and squeezes the piezoelectric films, which sends an electrical signal each time the weight squeezes it. 

Generally, a variety of mechanical deformation processes cause the nonuniform deformation that results in the formation of residual stresses. This nonhomogeneous deformation in a material is produced by the material s parameters, largely its process parameters such as the tool geometry and frictional characteristics. For example, the rolling of a strip can be accomplished by using relatively cold squeeze rolls. In the rolling process, parameters with a small roll diameter and little reduction produce deformation penetration that is shallow and close to the surface, whereas the interior of the strip remains almost undeformed. After the removal of the deformation forces and a complete... 

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