Fluid-mechanical aspects

Kawahara A, Chung PM, Kawaji M (2002) Investigation of two-phase flow pattern, void fraction and pressure drop in a micro-channel. Int J Multiphase Plow 28 1411-1435 Kawaji M (1999) Fluid mechanics aspects of two-phase flow Flow in other geometries. In Kand-likar SG, Shoji M, Dhir VK (eds) Handbook of phase change boiling and condensation. Taylor and Francis, Washington, DC, pp 205-259... 

Chapters 6 and 7 discuss many of the underlying fluid mechanical aspects of stagnation flows and channel flows. The intent here is to put those fundamentals to use in terms of practical, chemically reacting flows. There are numerous applications that could be discussed. We choose a few to illustrate salient points about the modeling. 

Two of this year s articles discuss the fluid-mechanical aspects of systems where material transfer may occur, accompanied by chemical reaction or heat transfer. Fulford analyzes thin-film flow in terms of the flow regimes and of surface disturbances, and relates recent experimental findings to the theoretical framework. Rietema discusses segregation phenomena in heterogeneous reactions, in relation to conditions of flow and of mass transfer. 

The analysis can be significantly simplified by reahzing that the rate with which the vorticity diffuses inwards, and hence establishes the fluid motion, is represented by the kinematic viscosity coeflBcient, which is of the order of 10 cmVsec and is at least one order of magnitude greater than the droplet surface regression rate. Hence quasi-steadiness for both the gas and liquid motion, with a stationary droplet surface and constant interfacial heat and mass flux, can be assumed. Once the fluid mechanical aspect of the problem is solved, the transient liquid-phase heat and mass transfer analyses, with a regressing droplet surface, can be performed. 

As discussed in the previous section, the convective droplet vaporization case has yet to be analyzed completely. The major difficulty lies with describing the fluid mechanical aspect of the phenomena, particularly for large Reynolds number flow when separation and reverse flow occur towards the rear stagnation point in both the gas and liquid phases. The difficulty is further compounded when the components in the droplet are not completely miscible, as is the case for emulsified fuels. The drop-... 

Because a polymer-forming luminous gas phase such as the tail-flame portion of an inductively coupled radio frequency glow discharge behaves as a fluid, the deposition mechanism can be investigated by examining the influence of the fluid mechanical aspects of luminous gas phase on the deposition rate of polymer. 

The fluid mechanical aspect of luminous gas is also evident with non-polymer-forming plasma. It has been observed that the degradation of polymer exposed to N2 plasma is very severe in the constricted portion a polyethylene film inserted in the constricted portion suffered permanent deformation due to partial melting, whereas polyethylene films placed in wider portions of the tube (before and after the constriction) did not show any visible difference after they were exposed to N2 glow discharge simultaneously as depicted in Figure 20.27. 

The present results differ significantly from those of Clark and Wilson ( [3 ], pp. 9—128) who discussed some fluid mechanical aspects of flotation processes. The reason for this disagreement is the different dimensions of both particles and hubbies taken in their theoretical treatment and those determined here experimentally. The particle diameters determined under the non-stationary conditions as the most probable values are in the range 100—150 pm. As it has been already mentioned, the air bubble diameters are comparable to these values and are equal to 40 and 65 pm in the DAF and DIS system, respectively. In contrast to this tha above authors assumed the air bubble diameters (about 200 pm) to be much larger from the particle diameter (about 0.2 pm). 

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

FLUID DYNAMICAL ASPECTS AND MACROSCOPIC THEORY. The following section shows that one can join statistical mechanics with fluid dynamics in the spirit of the global simulations this link is essential. The conceptual, intellectual and practical importance of this link is equally important and we are confident to have opened an important path to further understand physical phenomena. 

The major reason for these effects is of a chemical nature, namely the hydration of clays. Borehole instabilities were observed even with the most inhibitive fluids, that is oil-based mud. This demonstrates that the mechanical aspect is also important. In fact, the coupling of both chemical and mechanical mechanisms has to be considered. For this reason, it is still difficult to predict the behavior of rock at medium-to-great depth under certain loading conditions. 

Ho, C. M., and E. Gutmark. 1987. Vortex indnction and mass entrainment in a small-aspect ratio elliptic jet. J. Fluid Mechanics 179 383. 

At high flow rates, and for other transport processes, however, it is useful to have some information on the fluid mechanics of the system. Therefore, a semi-empirical description of this aspect of slug flow is given below, as developed by Nicklin et al. (N4) as an extension of the work of Laird and Chisholm (L2). 

The general notion of a boundary later is found in many aspects of modeling physical systems. Recognizing boundary-layer behavior can very often lead to important simplifications in the analysis and modeling of such systems. Certainly the analysis and study of fluid mechanics is greatly facilitated by the exploitation of boundary-layer approximations. 

A review including fluid mechanical considerations and useful applications among other aspects of dust explosions [7], and a collection of abstracts covering 20 years to 1977 [8] have been published. In a comparative study of laboratory methods available... 

Fluid flow, also known as fluid mechanics, momentum transfer and momentum transport, is a wide-ranging subject, fundamental to many aspects of chemical engineering. It is impossible to cover the whole field here, so we will concentrate upon a few aspects of the subject. 

Mechanical Aspects of Sampling—We have thus far discussed sampling methods in a general way. There are certain situations in which it is desired to predetermine exactly the influence of sampling devices themselves on the universe under consideration. For example, it is relatively easy to deal with particles in a fluid medium so long as the fluid is still,... 

It is safe to say that most graduate courses in chemical reaction engineering today suffer from an excess of mathematical sophistication and insufficient contact with reality. Because of the complexity of many reaction engineering models, it is essential that students be given a balanced and realistic view of what can and cannot be achieved. For example, they must learn that if the intrinsic kinetics of a reaction are not known accurately, this deficiency cannot be made up by a more detailed understanding of the fluid mechanics. In this connection, it would be useful pedagogically to take a complex model and illustrate its sensitivity to various aspects, such as the assumptions inherent in the model, the reaction kinetics, and the parameter estimates. 

The basis of chemical engineering is application of scientific and engineering principles to solve problems of industrial and societal importance. Chemical reaction engineering is unique to chemical engineering and is at the core of its identity as a separate discipline because it combines chemistry, chemical kinetics, catalysis, fluid mechanics, and heat and mass transfer. Other disciplines involve some of these aspects, but none brings the reaction chemistry and the transport together in the same way. 

A cutaway drawing of the rotating-cylinder reactor is shown in Fig. 35. The mechanical aspects of the reactor system were designed to provide temperature control, fluid containment, and process measurements. The apparatus consists of a stainless steel (SS) holder and glass cylinder in which rides an SS piston, sealed by two Viton O-rings. Piston movements is monitored by a linear variable differential transformer (type 250 HCD, Schaevetz Engineering) attached to the piston and fixed relative to the cylinder. 

Landau, L. D., and Lifshitz, E. M., Fluid Mechanics, Pergamon Press, New York, 1959. Lanza, A. J., in Silicosis and Asbestosis, Oxford University Press, New York, 1938. Lawton, J., and Weinberg, F. J., Electrical Aspects of Combustion, Clarendon Press, Oxford, 1969. 

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