Mechanical variables

Mechanical, variable flow race Self-actuating and deriving its energy from the airscrearn to maintain the constant flow rate function and having facilities for resetting the required value depending on an external system. 

Mechanical variable flow rate controller See Flow rate controller. 

G. E. Leblanc, R. A. Secco, M. Kostic, in Mechanical Variables Measurement Solid, Fluid, and Thermal (J. G. Webster, ed.), CRC Press Boca Raton, 2000, chapter 11. 

Such a functional relationship indeed provides a feasible mechanical thermometer based only on measurements of the mechanical variables P, V. 

Although the definition (3.35) allows practical progress, it rests on other concepts of temperature and thermal capacity that border on circular reasoning. Accordingly, we shall first attempt to formulate an alternative mechanical definition of heat that is of no practical significance, but satisfies the thermodynamicist s penchant for logical order. As in the case of temperature (Section 2.3), we attempt to characterize heat in terms of mechanical variables only (e.g., P, V), which are well defined in a pre-thermodynamic context. 

Let us briefly summarize the mathematical formalism of thermodynamics to this point. A mathematical formalism begins with identification of the proper variables. We began with the standard mechanical variables of classical mechanics P, V, and N (the quantity of matter, held fixed for the present). To these have now been added three important thermal variables ... 

Piezoelectric materials are materials that exhibit a linear relationship between electric and mechanical variables. The direct piezoelectric effect can be described as the ability of materials to convert mechanical stress into an electric field and the reverse, to convert an electric field into a mechanical stress. The use of the piezoelectric effect in sensors is based upon the latter property. 

Piezoelectric materials are materials that exhibit a linear relationship between electric and mechanical variables. Electric polarization is proportional to mechanical stress. The direct piezoelectric effect can be described as the ability of materials to convert mechanical stress into an electric field, and the reverse, to convert an electric field into a mechanical stress. The use of the piezoelectric effect in sensors is based on the latter property. For materials to exhibit the piezoelectric effect, the materials must be anisotropic and electrically poled ie, there must be a spontaneous electric field maintained in a particular direction throughout the material. A key feature of a piezoelectric material involves this spontaneous electric field and its disappearance above the Curie point. Only solids without a center of symmetry show this piezoelectric effect, a third-rank tensor property (14,15). 

Sensing chemical species is a much more difficult task than the measurement of mechanical variables such as pressure, temperature, and flow, because in addition to requirements of accuracy, stability, and sensitivity, there is the requirement of specificity. In the search for chemically-specific interactions that an serve as the basis for a chemical sensor, investigators should be aware of a variety of possible sensor structures and transduction principles. This paper adresses one such structure, the charge-flow transistor, and its associated transductive principle, measurement of electrical surface impedance. The basic device and measurement are explained, and are then illustrated with data from moisture sensors based on thin films of hydrated aluminum oxide. Application of the technique to other sensing problems is discussed. 

Background. The term microsensor denotes a transducer that, in some fashion, exploits advanced miniaturization technology, whether an adaptation of integrated circuit technology, or some other microfabrication technique. Within the past decade, a myriad of microsensors have been developed, with capabilities for measurement of temperature, pressure, flow, position, force, acceleration, chemical reactions, and the concentrations of chemical species. The latter measurements, of chemical species, are intrinsically more difficult than the measurement of mechanical variables because in addition to requirements of accuracy, stability, and sensitivity, there is a requirement for specificity. 

The term piezoelectric nonlinearity is used here to describe relationship between mechanical and electrical fields (charge density D vs. stress a, strain x vs. electric field E) in which the proportionality constant d, is dependent on the driving field, Figure 13.1. Thus, for the direct piezoelectric effect one may write D = d(a)a and for the converse effect x = d(E)E. Similar relationships may be defined for other piezoelectric coefficients (g, h, and e) and combination of electro-mechanical variables. The piezoelectric nonlinearity is usually accompanied by the electro-mechanical (D vs. a or x vs. E) hysteresis, as shown in Figure 13.2. By hysteresis we shall simply mean, in the first approximation, that there is a phase lag between the driving field and the response. This phase lag may be accompanied by complex nonlinear processes leading to a more general definition of the hysteresis [2],... 

Computational fluid mixing Computer programs that use velocity data to calculate various types of flow patterns and various types of fluid mechanics variables used in analyzing a mixing vessel. 

Each mechanical variable is replaced by a wave variable ... 

As integers always appear in Nature associated with periodic systems, with waves as the most familiar example, it is almost axiomatic that atomic matter should be described by the mechanics of wave motion. Each of the mechanical variables, energy, momentum and angular momentum, is linked to a wave variable by Planck s constant E = hu = h/r, p = h/X = hi), L = h/27r. A wave-mechanical formulation of any mechanical problem which can be modelled classically, can therefore be derived by substituting wave equivalents for dynamic variables. The resulting general equation for matter waves was first obtained by Erwin Schrodinger. 

Just as for this model all similar approaches found in the literature suffer from the problem that not all fluid mechanical variables can be precalculated on the basis of the operating conditions. Instead, reasonable estimations or measurements in cold flow models are used... 

The preceding discussion points up a matter of tacit understanding. It is presumed that the reader possesses an intuitive grasp of the concept of mass and of mechanical variables, such as volume V or pressure P. By contrast, items relating to the transfer of energy must be very carefully explained through the various laws of thermodynamics before they are utilized. We shall also be able at a later point to supply better definitions for adiabatic and diathermic processes, and for steady-state conditions. 

The Zeroth Law of Thermodynamics is based on a statement which emphasizes the transitive property that two bodies in equilibrium with a third are in equilibrium with each other. Here we restrict ourselves to the case where the mechanical variables, namely pressure P and volume V, suffice to describe a system at equilibrium however, this approach can easily be generalized. 

If a uniform concentration of a miscible liquid is more desirable than the high intensity turbulent dispersion of these materials in the stream, then it may be well to have injection points out in a more uniform, less fluctuating environment. Thus evaluation of injection point conditions can be very critical in reactions that may take different paths, depending upon chemical concentrations and fluid mechanics variables. 

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