Surfaces internal pressure

Whether we assume, however, the existence of a fixed angle of contact between a given liquid and a given solid, or derive it from a static molecular model, as above, we can proceed at once to explain all the common capillary phenomena. Tlie three ideas of tension at a surface, internal pressure, and angle of contact suffice with these concepts and the key expression (1.14) for the internal pressure inside a curved surface we can solve all common equilibrium capillary problems by the methods of dassical statics. This is not a field we wish to explore in detail but show here only how the rise in a capillary tube is treated, since this forms the basis of the commonest method of measuring surface tension. 

The calculation was carried out using the ANSYS F.E.M. code. The pressure vessel was meshed with a 4 nodes shell element. Fig. 18 shows a view of the results of calculation of the sum of principal stresses on the vessel surface represented on the undeformed shape. For the calculation it was assumed an internal pressure equal to 5 bar and the same mechanical characteristics for the test material. 

It may be shown (33) that when the inner surface of a cylinder made of components of the same material is subjected to an internal pressure, the bote of each component experiences the same shear stress provided all components have the same diameter ratio. For these optimum conditions,... 

The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

The nylon ring may be considered as a thick wall cylinder subjected to this internal pressure (see Appendix D). At the inner surface of the ring there will be a hoop stress, <7, and a radial stress, Cr. Benham et al. shows these to be... 

Let us start with a model situation there is a single bubble in the liquid, the gas is insoluble, and there is no flow. Internal pressure Pint in the equilibrium bubble is in this case counterbalanced by external pressure Pext and surface Laplace pressure PL = 2a/r (a is surface tension) ... 

The external diameter of the tube and its wall thickness determine the pressure which it will stand. Failure of a tube is due to the tension at the surface becoming too great. For a cylinder of internal radius r and external radius R, and vwth an internal pressure in the cylinder of P, the maximum circumferential (or hoop) tension S (see A. Morley, 1940) on the inner surface of the cylinder is... 

Foam Coalescence Coalescence is of two types. The first is the growth of the larger foam bubbles at the expense of the smaller bubbles due to interbubble gas diffusion, which results from the smaller bubbles having somewhat higher internal pressures (Adamson and Cast, Physical Chemistry of Surfaces, 6th ed., Wiley New York, 1997). Small bubbles can even disappear entirely. In principle, the rate at which this type of coalescence proceeds can be estimated [Ranadive and Lemlich,/. Colloid Interface Sci., 70, 392 (1979)]. 

When salts in groundwater precipitate and crystallize within the cavities of buried materials such as pottery, cement, and wood, they may generate internal pressures sufficient to disrupt these materials and turn them into gravel. Salts are also active in blistering and scaling painted surfaces on a variety of materials. 

Drums containing moist quinone self-heated, generating smoke and internal pressure. Investigation showed that the moist material showed an exotherm at 40-50°C and decomposed at 60-70°C, possibly owing to presence of impurities. Drums exposed to direct sunlight soon attain a surface temperature of 50-60°C. 

In the case of EC-DMC solutions, since the surface species are deposited quickly and form very compact passivating films, the passivation of the active mass is obtained before products such as ethylene gas have the chance to be accumulated in crevices and an internal pressure to grow. Indeed, in these solutions the irreversible capacity depends inversely on the size of the particles (as expected). 

In cases where the solid reduction products of the solvent molecules form highly cohesive and adhesive surface films, the surface reactions are quickly blocked before further massive reduction of solution species (which also form the gas molecules) takes place. When passivation of the graphite is not reached quickly enough (as in the case of PC solutions), intensive surface reactions build up the internal pressure that cracks the particles and leads to their deactivation. 

From the above discussion, it is clear that the stabilization or failure of graphite electrodes depends on a delicate balance between passivation phenomena (due to the formation of highly cohesive and adhesive surface films) and a buildup of internal pressure due to the reduction of solution species inside crevices in the graphite particles. This delicate balance can be attenuated by both solution composition (EC-DMC vs. EC-PC or PC, etc.) and the morphology of the graphite particles (i.e. the structure of the edge planes and the presence of crevices). 

A rotary drum with a filter area of 3 m3 operates with an internal pressure of 71.3 kN/m2 below atmospheric and with 30 per cent of its surface submerged in the slurry. Calculate the rate of production of filtrate and the thickness of cake when it rotates at 0.0083 Hz, if the filter cake is incompressible and the filter cloth has a resistance equal to that of 1 mm of cake. 

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