Particles foreign

Neumann and co-workers have used the term engulfrnent to describe what can happen when a foreign particle is overtaken by an advancing interface such as that between a freezing solid and its melt. This effect arises in floatation processes described in Section Xni-4A. Experiments studying engulfrnent have been useful to test semiempirical theories for interfacial tensions [25-27] and have been used to estimate the surface tension of cells [28] and the interfacial tension between ice and water [29]. 

Containers should be clear in order to allow detection of foreign particles. Outer coverings minimize irradiation. Plugs used as stoppers are selected with care to prevent flaking into the contents and possible component leaching into the product. 

As a part of the lubrication program, oil should be periodically tested. The testing requires drawing oil from the system for a laboratory analysis. The usual tests conducted to determine the condition of oils include viscosity, pH and neutralization number, precipitation, color and odor, and a check for foreign particles in the oil. The results should be reviewed and compared with new oil characteristics to determine the life characteristics of the oil. 

Extending the inteiwal between oil changes in automobiles and machinery is another way to conserve lubricants. Oil life is limited by depletion of oil additives, overheating, chemical contamination, and contamination of the oil by foreign particles. Using improved additives and filtering of particles, oil life can be considerably extended. 

A superheat exchanger is not needed for a centrifugal compressor system as far as gas condition is concerned. It may be a good unit as fer as other aspects of the process are involved. The centrifugal compressor requires only a suction knock-out drum to remove entrained liquid and foreign particles. 

The most common device installed in hydraulic systems to prevent foreign particles and contaminations from remaining in the system are referred to as hlters. They may be located in the reservoir, in the return line, in the pressure line, or in any other location in the system where the designer of the system decides they are needed to safeguard the system against impurities. 

After the tubing is cut, remove all burrs and sharp edges from the inside and outside of the tube with a deburring tool. Figure 40.29. Clean out the tubing. Make sure no foreign particles remain. 

In 1906, Einstein worked out a theory of the viscosity of a liquid which contains, in suspension, spherical particles which are large compared with the size of molecules of the liquid. The predictions of the theory are found to be in good agreement with the measured values of the viscosity of liquids containing colloidal particles in suspension. The presence of these obstacles increases the apparent viscosity of the liquid, and Einstein found1 that the increment is proportional to the total volume v of the foreign particles in unit volume, that is to say, the sum of the volumes of the particles that are present in unit volume of the liquid thus,... 

Cavitation occurs in a rapidly moving fluid when there is a decrease in pressure in the fluid below its vapor pressure and the presence of such nucleating sources as minute foreign particles or definite gas bubbles. As a result, vapor bubble forms that continues to grow until it reaches a region of pressure... 

Usually adsorption, i.e. binding of foreign particles to the surface of a solid body, is distinguished as physical and chemical the difference lying in the type of adsorbate - adsorbent interaction. Physical adsorption is assumed to be a surface binding caused by polarization dipole-dipole Van-der-Vaals interaction whereas chemical adsorption, as any chemical interaction, stems from covalent forces with plausible involvement of electrostatic interaction. In contrast to chemisorption in which, as it has been already mentioned, an absorbed particle and adsorbent itself become a unified quantum mechanical system, the physical absorption only leads to a weak perturbation of the lattice of a solid body. 

The USP has numerous requirements, e.g., ophthalmic solutions [need be] essentially free from foreign particles, suitably compounded and packaged for instillation into the eye, or ophthalmic suspensions [need contain] solid particles dispersed in liquid vehicle intended for application to the eye [1]. Ophthalmic suspensions are required to be made with the insoluble drug in a micronized form to prevent irritation or scratching of the cornea. A finished ophthalmic ointment must be free from large particles and must meet the requirements for leakage and for metal particles under ophthalmic ointments . These and other requirements will be discussed further in subsequent sections. 

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