Temperature concept

Basic to the sandwich model is the two-temperature concept. According to this concept, the linear regression rate of the fuel and oxidizer sandwiches must be nearly identical i.e.,... 

Practical measurements of temperature long preceded the theory of this important concept. Thermodynamics clearly requires the temperature concept, but thermometry (the theory of temperature measurements) is so deeply intertwined with general thermodynamic theory that we must take care to avoid logical circularity. 

The cross-polarization (CP), i.e. the transfer of I-spin polarization to the dilute spins (S), is a double resonance experiment in which the I and S spins are coupled by a certain interaction, determined by the cross relaxation time tb. From the dynamics of the CP process, usually described with the spin temperature concept, the following equation for the time dependence of S-spin polarization could be derived ... 

R.B. Lindsay, The Temperature Concept for Systems in Equilibrium in Tempera-... 

First let us give some further consideration to the bulk-temperature concept which is important in all heat-transfer problems involving flow inside closed channels. In Chap. 5 we noted that the bulk temperature represents energy average or mixing cup conditions. Thus, for the tube flow depicted in Fig. 6-1 the total energy added can be expressed in terms of a bulk-temperature difference by... 

The question should be raised as to whether it is meaningful to introduce the temperature concept in a nonequilibrium situation. The answer is in the affirmative if the following sufficiency conditions have been met The two portions of the system are very large, and the heat transfer occurs very slowly. In this event T and T" are sensibly uniform over both regions and most of the temperature variation takes place in the immediate volume Ai of the interface. 

The linear velocity of polymer combustion propagation (v) may be represented in terms of the ignition temperature concept (Tj J by a simple fundamental formula... 

The introduction of this artifice is equivalent to employing the physical concept of an ignition temperature 7], below which the chemical reaction rate vanishes [see equations (19) and (33)]. An alternative procedure for determining a finite, nonzero value for A involves the assumption that a flame holder serves as a weak heat sink [18], removing an amount of heat per unit area per second equal to kdTjdx)i = mCp(T — TQ)(dx/d )i. Since 6 = 0 at the flame holder (that is, there is no reaction upstream), equation (19) implies that (dx/d )i = r,-, whence the heat-sink concept is seen to be mathematically equivalent to the ignition-temperature concept at the cold boundary. 

By using countercurrent columns the two-temperature concept becomes more acceptable since the selectivity of ion-exchange resins may be changed by varying such process conditions as solution concentration, solution pH, the composition of solvent, and the presence of complexing reagents. 

We follow here the presentation provided by H.A. Buchdahl, The Concepts of Classical Thermodynamics, Cambridge University Press, 1966, Chapters 5, 6. Readers interested in a somewhat more detailed exposition of Carath6odory s approach and in the introduction of the thermodynamic temperature concept may also consult Chapter 9, where it was placed so as not to interrupt the current derivation. In retrospect it seems to be more direct to start with the formulation of the Second Law adopted here rather than working with the more elegant theory developed by Caratheodory. 

In this connection it has to be stressed that the ceiling temperature concept should be applied to the polymerization of lactams very carefully. At elevated temperatures, the reversible transacylation reactions are accompanied by decomposition of the polymer and/or monomer and by other side reactions. With respect to the low ASp values (as compared to vinyl monomers), very high ceiling temperatures can be expected for most lactams. Therefore, the calculated values of lie high above the decomposition temperature of the polymer and monomer except for five-, six- and substituted seven-membered lactams. In addition, for very large rings the heat of polymerization approaches zero and the polymerization entropy becomes positive, so that the value of T<, = AHp/ASp becomes meaningless. 

Kesidou, S., Duit, R. Students conceptions of the Second Law of thermodynamics, an interpretive study. Journal of Research in Science Teaching 30 (1993), 85 Lewis, E., Linn, M. Heat, energy and temperature. Concepts of adolescents, adults and experts implications for curriculum development. Journal of Research in Science Teaching 31 (1994), 657... 

The basic mechanism of the critical temperature concept is simple. Lubrication failure is envisioned as occurring at the conjunction of the rubbing surfaces, and it is the critical temperature at this conjunction that controls the lubricating action. This temperature, T, is made up... 

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