THERMO Spoken Here! ~ J. Pohl © (A1160~11/15) | ( A1220 - 1.02 P) |
Analytic methods of physics and engineering select actual material of reality as the system. There is often some "physical scenario" in mind. Next, since matter of reality is complex, approximation of that matter must happen. Such approximations are called models. The models discussed here are the BODY (by way of review), the models of thermodynamics, the SUBSTANCE and the COMPLEX SUBSTANCE.
BODY is the approximation that the mass of a system does not occupy space - rather that the mass of a BODY is assumed to reside at a point. When BODY is used some call the system a mechanical system. In BODY proved effective in the 1700's to understand motion of projectiles and planets. The system associated with the BODY consists of the mass (at its point) and Earth. The BODY has one property, its mass, and two characteristics (relative to Earth): its elevation and its velocity. Also relevant to the BODY were the ideas: force, work and energy. Work, the only energy transfer mechanism, results in change of energy properties being potential energy and or kinetic energy. Some call work of a BODY, mechanical work.
Thermodynamics involves heat, work and temperature. The simplest model suited is the substance (or thermodynamic substance).
SUBSTANCE: One responsibility of thermodynamics has been to quantify and catalog properties of matter. Be the effort experimental or analytic, the model used is named the SUBSTANCE. (Terms used equivalently are pure substance or thermodynamic substance.) The substance has mass. For an analytic study the system is assumed to be ies the subject of analysis is assumed to be being composed of one molecular species.
Specific Studies such as, to establish an equation of state for a phase, to measure boiling temperature-pressures, and others are conducted using vitually pure material for an experimental study "assumed pure." Nothing is pure, nonetheless thermodynamics begins its studies with pure substances; substances of a single molecular species.
Thermodynamic work involves change of thermodynamic properties of the substance which by its special nature have inherently a thermodynamic "force-like property" and "displacement-like property." In similar action, "force acts through displacement" the substance energy is changed via work. A number of special types of such thermodynamic work are known and are called work modes.
All thermodynamic substances have one work mode which is compression work. This is to say the energy of all substances can be changed by its compression. Such work can be put to use for a gas as system but rarely for liquid or solid substances. The list of work modes (all thermodynamic) is: compression work, spring work, torsion work, surface work, electric work, electric polarization work, and magnetic polarization work. A substance with one (and only one) work mode is termed "simple."
Complex Substances: To the utter delight of engineers are the exotic substances having two significant work modes. Such a substance might experience work in its first work mode then immediately balance that energy change by work in its second mode.
Quite a few designs have sprung from such unique substances. Internet resources have details. You will need to "look around" in accord with your interest. Key words might be: Piezoelectric Sensor, Magnetostrictive Positioning, Oxygen Sensor.
Complex Substance Feasibility: Certainly, upon application of an enormous magnetic field to any substance, one would might expect it to levitate or at least, smoke. Extreme values of the force or displacement properties are no useful. Value of a complex substance is realized not in the extreme but in "being complex with within subtle, non-destructive, ranges" of its two force and two displacement properties. In looking for, evaluating potential of a substance - understanding of property ranges is important. Two example investigations are below. The first is numeric, the second algebraic.
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Example 1: Complex "Elastic/Compression" Substance: As an elastic substance is strained along the axis of extension concurrent strain happens prependicular ("perp") to the axis. Poisson's ratio quantifies this effect. Taken in combination, the strains amount to a decreased volume of the substance. Volume change of a substance within the surroundings (assumed ambient atmosphere) constitutes substance compression work. Compare these work effects. Most persons know the elastic work vastly overshadows the concurrent compression work. But how to show this.
Explanation: Strained along an axis a solid exhibits strain in perpendicular axes also. The relationship between axial and perpendicular strains, ε, for a linear Hookean media involves Poisson's Ratio, μ, as εperp = -με (μ ≤ 1/2)
The minus sign indicates that a circular member loaded in tension will be reduced in diameter. For the case, μ = 1/2, the system volume is constant otherwise the volume increases. This gives rise to compression work, pdV, accompanying the elastic work.
The above algebraic result is applied to results of a previous calculation: Linear Elastic Substance.
The example simply shows the procedure. As expected, the elastic work component is much greater than the compression component.
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Example 2: Complex "Surface/Compression" Substance: The phenomenon of boiling is critical to the design of steam power production, water-moderated nuclear reactors, phase-changing refrigeration systems, many industrial applications and cooking.
Boiling occurs when heat driven by high temperature becomes sufficient to locally vaporize a liquid. Formation of the vapor bubble and its growth into a liquid. Boiling involves at least two work mechanisms: surface work of the enlarging liquid-vapor interface and compression work of the expanding bubble.
Thus the relevance of surface to compression work depends upon the raius of the bubble. Work of an infinitesimally small bubble will be dominantly surface work in nature. Large bubbles will have compression ( -pdV ) as their work form. At some "transitional radius the work effects would be equal. For water boiling at 1 atm (σsurf = 58dyne/cm) the transitional radius, rt is:
The energy possessed by matter is classed as extrinsic (being observable) or intrinsic (not observable). Kinetic energy and potential energy of a mass are observable and quantifiable in terms of the system mass, its position and speed relative to Earth. The egergy properties of extrinsic energy are the system mass (m, elevation, (h) and speed. The single cause of change of extrinsic energy is work: the action of a force at the system boundary through a system displacement - work or wext. Substances of systems on with constant extrinsic energies can still experience energy change.
The matter or material of beginning level systems of thermodynamic analysis are assumed to be "pure." The term, "pure substance" is used and "substance," unmodified means pure. Energy changes of a substance happen in consequence of energy transfer (to or from) the system. Heat and work are the only mechanisms of energy change. Seven manners of system work have been identified. These are called work modes. A work mode is said to be "appreciable"
Premise presently unwritten!