Specific heat, evolution

The heat evolution rate per unit mass, the vent capacity per unit area, physical properties (e.g.. latent heat of liquid, specific heat, and vapor/liqnid specific volumes) are constant. It allows for total vapor-liqnid disengagement of fluids that are not natural" surface active foamers. ... 

Here Q(t) denotes the heat input per unit volume accumulated up to time t, Cp is the specific heat per unit mass at constant pressure, Cv the specific heat per unit mass at constant volume, c is the sound velocity, oCp the coefficient of isobaric thermal expansion, and pg the equilibrium density. (4) The heat input Q(t) is the laser energy released by the absorbing molecule per unit volume. If the excitation is in the visible spectral range, the evolution of Q(t) follows the rhythm of the different chemically driven relaxation processes through which energy is... 

Experimental Methods In Differential thermal analysis (DTA) the sample and an inert reference substance, undergoing no thermal transition in the temperature range under study are heated at the same rate. The temperature difference between sample and reference is measured and plotted as a function of sample temperature. The temperature difference is finite only when heat is being evolved or absorbed because of exothermic or endothermic activity in the sample, or when the heat capacity of the sample changes abruptly. As the temperature difference is directly proportional to the heat capacity so the curves are similar to specific heat curves, but are inverted because, by convention, heat evolution is registered as an upward peak and heat absorption as a downward peak. 

A fermentation broth contained in a batch-operated stirred-tank fermentor, 2.4m in inside diameter D, is equipped with a paddle-type stirrer of diameter (L) of 0.8 m that rotates at a speed Af = 4s -. The broth temperature is maintained at 30 °C with cooling water at 15°C, which flows through a stainless steel helical coil that has a 50 mm outside diameter and is 5 mm thick. The maximum rate of heat evolution by biochemical reactions, plus dissipation of mechanical energy input by the stirrer, is 51000 kcal h , although the rate varies with time. The physical properties of the broth at 30 °C were density p = 1000 kg m " , viscosity p = 0.013 Pa s, specific heat Cp = 0.90 kcal kg °C , and thermal conductivity K = 0.49 kcal h m °C = 0.000136 kcals m °C . ... 

The concept of specific energy can be explained as follows. When we imagine the reaction of an explosive to proceed without volume expansion and without heat evolution, it is possible to calculate a theoretical thermodynamic value of the pressure, which is different from the shock wave pressure (- Detonation) if this pressure is now multiplied... 

By definition, the kinetic curve of a cement is the weighted sum of the curves for its constituent phases as they occur in that cement. The reactivities of individual clinker phases were considered in Section 4.5 and some effects of particle size distribution, which is a particularly important variable, in Section 4.1.4. Although many data relating particle size distribution directly to strength exist, much less is known about its relation to degrees of reaction. Parrott and Killoh (P30) presented data indicating that the rate of hydration, as represented by that of heat evolution, was proportional to the specific surface area during the period of hydration in which the rate was controlled by diffusion. 

The reverse process,. e. the production of heat when work is done, was discovered at the beginning of the nineteenth century. The exponents of the material theory of heat, guided by the assumption of the constancy of the heat substance in nature, explained the evolution of heat on turning metals by a supposed decrease in their specific heat. Count Rumford showed, however, by experiments on the large scale that the rise in temperature caused by the boring of a cannon cannot be accounted for by the decrease in the specific heat of the turnings. In 1798 he was the first to state clearly that the motion of the horses, which were used to drive the drill, was the true cause of the observed rise in temperature. 

In the summation the specific heats of the substances which are produced with evolution of heat are reckoned positive. The temperature coefficient of the heat of reaction is therefore equal to the change in the heat capacity of the system, consequent on the reaction. The heat of reaction increases with temperature when the substances formed in the reaction have a smaller heat capacity than the substances which disappear in the reverse case it decreases with temperature. For endothermic reactions in which Q is negative, an increase in Q means a diminution in the numerical value of the heat of reaction, and conversely. 

Fig. 5. Thermal evolution of the lithosphere along a cross-section of Africa through 34°E. Arrow shows the location of the plume relative to the northward-moving African plate since 45 Ma. It should be noted that lithosphere cools as y/t south of plume, as we have placed no restriction on maximum thickness of the continental lithosphere. The long-term effect of the plume heating can be crudely estimated, if we assume that a 40 km equivalent thickness of material that is 200 K hotter than normal mantle, and with specific heat 4 x 106 JK m", ponds beneath a craton every 300 Ma. The mantle heat flow is increased by 3.4 mWm, or 20-25% of typical mantle heat flow from cratonal areas (e.g. Jaupart et al. 1998). (b) Thickness of plume material ponded beneath lithosphere 45 Ma after plume onset.

Figure 21. Evolution of specific heat profiles in (Pbi-xSrj )3(P04)2 with increasing concentrations of Ba. Note change of Cp scales. Modified from Figure 2 in Bismayer et al. (1995).

Calder, W. (1986). Body temperature and the specific heat of water. Science, 324,418. Carroll, S. B. (2001). Chance and necessity the evolution of morphological complexity... 

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