Liquid media basic principles

Given the speed of these combustion reactions, establishing a detailed mechanism presents experimental challenges. Nonetheless, a few basic principles have emerged. In those reactions where a salt is a by-product, the heat released from the reaction melts the salt and provides a liquid medium in which the product and reactants can combine. This has been inferred from the results of syntheses that were deliberately loaded with additional product salt, which increased the heat capacity of the system. This additional heat capacity resulted in a lower peak reaction temperature. If enough salt was added, the peak reaction temperature was insufficient for reaching a self-sustaining reaction. 

A further special area of propulsion systems is Chemical Thermal Propulsion (CTP). CTP is defined in contrast to STP (solar thermal propulsion) and NTP (nuclear thermal propulsion). In CTP, in a very exothermic chemical reaction in a closed system, heat but no pressure is generated since the products of the reaction are solid or liquid. The heat energy is then transferred to a liquid medium (the propellant) using a heat exchanger, which is responsible for the propulsion of for example, the torpedo. Suitable propellants are e.g. water (the torpedo can suck it in directly from its surroundsings) or H2 or He, due to their very low molecular or atomic masses. The basic principles of CTP can also be used in special heat generators. A good example for a chemical reaction which is suitable for CTP is the reaction of (non-toxic) SF6 (sulfur hexafluoride) with easily liquified lithium (m.p. 180 °C) ... 

Instrumental techniques for measurement of particle size distribution of powders have had a tremendous advancement in recent times. Numerous methods and procedures have been developed at a steady pace over the years, and there is the possibility of covering the wide spectrum from nanosystems, to ultrafine powders, and to coarse particulate assemblies. Many instruments offer nowadays quick, reliable results for a wide variety of powders and particulate systems, and for a number of applications. There is still, however, the need to understand the basic principles under which sophisticated instruments operate, as well as to resource to direct measurements under some circumstances. Some of the most modern instrumental techniques are based on an indirect measurement and carry out transformations among the different ways of expressing particles size distributions, that is, by number, surface, or mass. Sometimes it is advisable to avoid transformations because instruments assume a constant shape coefficient on such transformation, which is not necessarily the case, and overestimation or underestimations of size of certain particles may arise. Also, in very specific applications, or in cases of basic or applied research, is better to measure directly the most relevant particle size and particle size distribution. For example, if research is carried out in modeling of solid-liquid separations, a direct measurement of the Stokes equivalent diameter would be most appropriate. The aim of the exercise is to measure the particle size distribution of a sample of medium-sized dolomite, and compare the results with those of the Andreasen Pipette method. 

A better understanding of the basic principles of ultrafiltration has permitted the development of much more efficient equipment and corresponding commerical applications. A detailed consideration of the theory of ultrafiltration was published by Porter (134), who dealt specifically with the problem Of concentration polarization. As shown in Figure 4.4, the movement of particles toward the membrane results in the formation of a concentrated sol layer of high viscosity. This can reduce the flux or rate of filtration to a small fraction of that of the liquid medium in the absence of colloid. The resistance to flow is not due to plugging of pores, or even to an actual solid layer (gel) of close-packed colloidal particles. In has been observed... 

The basic principle of the jet pump is that the liquid or gas jet exits the motive nozzle at a high velocity and low pressure and entrains and accelerates the surrounding liquid, gas or solid medium. The result of this action is the mixing of the driving and the entrained material at a mean velocity. In a second nozzle, this velocity of the mixture is reduced and the pressure increases to an outlet pressure that is higher than the suction pressure. 

Darcy s law is recognised as a principle governing liquid movement through a porous medium under conditions of laminar flow. The basic characteristic parameters of water permeability for geotextiles are permittivity and transmissivity, which are, respectively, the ease of flow of water, at normal angle, through the fabric surface, and the ease of flow within the plane of the fabric [6]. 

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