Heat capacity extraction

Fig. 12. Modulated DSC curve for Makroblend UT-400, an impact-modified polycarbon-ate/poly(ethylene terephthalate) blend. Curve A shows the conventional DSC curve curve B shows the heat capacity extracted from the reversing component of the signal curve C shows the modulus of the same material measured by DMA (Hale and Bair, in Ref 5).

The important question remains is this second critical point the key to understanding the anomalies of water, or does the cooperation of the configurational excitations at some parameter or some thermodynamic field choice produce a critical point The cooperation of the configurational excitation is implied by the form of the heat capacity extracted by confined water, in particular, that of water confined in silica gel materials [128] at < = 1.1 nm. In this case, water remains in the liquid state at very low T and shows a Cp peak at approximately 227K (see, e.g.. Fig. 21). The hump at 227K supports the order disorder process hypothesis of water molecules in the liquid state. This silica gel sample —dH/dt does not give a water GT at this temperature, the 227K peak can be attributed to an order-disorder process, and the Tg is located at lower temperatures. 

Consider the simple flowsheet shown in Fig. 6.2. Flow rates, temperatures, and heat duties for each stream are shown. Two of the streams in Fig. 6.2 are sources of heat (hot streams) and two are sinks for heat (cold streams). Assuming that heat capacities are constant, the hot and cold streams can be extracted as given in Table 6.2. Note that the heat capacities CP are total heat capacities and... 

Ultrasonic Spectroscopy. Information on size distribution maybe obtained from the attenuation of sound waves traveling through a particle dispersion. Two distinct approaches are being used to extract particle size data from the attenuation spectmm an empirical approach based on the Bouguer-Lambert-Beerlaw (63) and a more fundamental or first-principle approach (64—66). The first-principle approach implies that no caHbration is required, but certain physical constants of both phases, ie, speed of sound, density, thermal coefficient of expansion, heat capacity, thermal conductivity. 

In this book we have decided to concentrate on purely synthetic applications of ionic liquids, just to keep the amount of material to a manageable level. FFowever, we think that synthetic and non-synthetic applications (and the people doing research in these areas) should not be treated separately for a number of reasons. Each area can profit from developments made in the other field, especially concerning the availability of physicochemical data and practical experience of development of technical processes using ionic liquids. In fact, in all production-scale chemical reactions some typically non-synthetic aspects (such as the heat capacity of the ionic liquid or product extraction from the ionic catalyst layer) have to be considered anyway. The most important reason for close collaboration by synthetic and non-synthetic scientists in the field of ionic liquid research is, however, the fact that in both areas an increase in the understanding of the ionic liquid material is the key factor for successful future development. 

The condition of air or water entering or leaving a coil or heat exchanger Tons of refrigeration capacity Tons of refrigeration capacity extracted Tons refrigeration rejected (at final cooler)... 

Although Equation (4) is conceptually correct, the application to experimental data should be undertaken cautiously, especially when an arbitrary baseline is drawn to extract the area under the DSC melting peak. The problems and inaccuracy of the calculated crystallinities associated with arbitrary baselines have been pointed out by Gray [36] and more recently by Mathot et al. [37,64—67]. The most accurate value requires one to obtain experimentally the variation of the heat capacity during melting (Cp(T)) [37]. However, heat flow (d(/) values can yield accurate crystallinities if the primary heat flow data are devoid of instrumental curvature. In addition, the temperature dependence of the heat of fusion of the pure crystalline phase (AHc) and pure amorphous phase (AHa) are required. For many polymers these data can be found via their heat capacity functions (ATHAS data bank [68]). The melt is then linearly extrapolated and its temperature dependence identified with that of AHa. The general expression of the variation of Cp with temperature is... 

Heat capacity measurements can also be used to extract A7 ad in addition to Sm(T) (Equations 9.3a and 9.3b), where CM is the heat capacity of magnetization for a more complete analysis fHt... 

Continuous Multicomponent Distillation Column 501 Gas Separation by Membrane Permeation 475 Transport of Heavy Metals in Water and Sediment 565 Residence Time Distribution Studies 381 Nitrification in a Fluidised Bed Reactor 547 Conversion of Nitrobenzene to Aniline 329 Non-Ideal Stirred-Tank Reactor 374 Oscillating Tank Reactor Behaviour 290 Oxidation Reaction in an Aerated Tank 250 Classic Streeter-Phelps Oxygen Sag Curves 569 Auto-Refrigerated Reactor 295 Batch Reactor of Luyben 253 Reversible Reaction with Temperature Effects 305 Reversible Reaction with Variable Heat Capacities 299 Reaction with Integrated Extraction of Inhibitory Product 280... 

Thermally enhanced extraction is another experimental approach for DNAPL source removal. Commonly know as steam injection, this technique for the recovery of fluids from porous media is not new in that it has been used for enhanced oil recovery in the petroleum industry for decades, but its use in aquifer restoration goes back to the early 1980s. Steam injection heats the solid-phase porous media and causes displacement of the pore water below the water table. As a result of pore water displacement, DNAPL and aqueous-phase chlorinated solvent compounds are dissolved and volatilized. The heat front developed during steam injection is controlled by temperature gradients and heat capacity of the porous media. Pressure gradients and permeability play a less important role. 

Interestingly, the standard entropies (and in turn heat capacities) of both phases were found to be rather similar [69,70]. Considering the difference in standard entropy between F2(gas) and the mixture 02(gas) + H2(gas) taken in their standard states (which can be extracted from general thermodynamic tables), the difference between the entropy terms of the Gibbs function relative to HA and FA, around room temperature, is about 6.5 times lower than the difference between enthalpy terms (close to 125 kJ/mol as estimated from Tacker and Stormer [69]). This indicates that FA higher stability is mostly due to the lower enthalpy of formation of FA (more exothermic than for HA), and that it is not greatly affected by entropic factors. Jemal et al. [71] have studied some of the thermodynamic properties of FA and HA with varying cationic substitutions, and these authors linked the lower enthalpy of formation of FA compared to HA to the decrease in lattice volume in FA. 

Groundwater has a huge capacity to store heat (4181 J/kg/K). Rocks and minerals have a lesser (around 800 J/kg/K Mellon 2001), but still significant, heat capacity. They also have a certain thermal conductivity and these properties allow them to act as enormous subsurface heat storage and exchange reservoirs. Table 1 provides some examples of specific heat capacities and thermal conductivities. This heat, stored in the geological environment, can be extracted, manipulated and utilized. 

The Fowler-Guggenheim statement follows immediately from (5.77b), because lowering the temperature by heat extraction cannot be effective if the heat capacity CP vanishes faster than the desired temperature lowering. 

In these last formulas we have split up the enthalpy by extracting the chemical energy from it Q0(n0) is the heat capacity of the original mixture and qx is the heat capacity of the incomplete combustion at the point xlt where the amount of unreacted material at this point is determined from condition (30) in order to yield a reaction rate which balances the losses,... 

With additional information, including the heat capacity of the buffer solvent, the partial specific volumes (volume per gram of the solute), and the specific volume of the solvent, one can extract the partial specific heat capacity (J K 1g I) of the solute. Privalov has summarized these calculations.8 Because the solutions are studied at very low concentrations, it is assumed that the contribution to the total heat capacity from the solvent cancels out when one calculates the excess heat capacity. With only minor exceptions, the procedures used to calculate parameters associated with the transformations in nucleic acids and in proteins are the same and yield quantities that are interpreted in similar ways, although researchers in these two fields may use a different notation for the same quantity. 

Three pound moles of nitrogen at 450(°F) is contained in a piston/cylinder arrangement. How much heat must be extracted from this system, which is kept at constant pressure, to cool it to 100(°F) if the heat capacity of the piston and cylinder is neglected ... 

Pure component physical property data for the five species in our simulation of the HDA process were obtained from Chemical Engineering (1975) (liquid densities, heat capacities, vapor pressures, etc.). Vapor-liquid equilibrium behavior was assumed to be ideal. Much of the flowsheet and equipment design information was extracted from Douglas (1988). We have also determined certain design and control variables (e.g., column feed locations, temperature control trays, overhead receiver and column base liquid holdups.) that are not specified by Douglas. Tables 10.1 to 10.4 contain data for selected process streams. These data come from our TMODS dynamic simulation and not from a commercial steady-state simulation package. The corresponding stream numbers are shown in Fig. 10.1. In our simulation, the stabilizer column is modeled as a component splitter and tank. A heater is used to raise the temperature of the liquid feed stream to the product column. Table 10.5 presents equipment data and Table 10.6 compiles the heat transfer rates within process equipment. 

As stated earlier, the most important applications of chemical and metallurgical thermodynamics are in the processes of synthesis, extraction, refining, etc. The free energy change is by far the most important of the thermodynamic properties as it is linked to identifying the limits of an actual process. The free energy in turn is dependent on other parameters like activity, interaction co-efficient, entropy, enthalpy, heat capacity, etc. 

It is possible, and perhaps generally believed, that the high reproducibility of an isotherm justihes the extraction of thermodynamic values from data that show hysteresis. However, hysteresis would still be a source of systematic error in the values. There is a poorly documented impression that small samples or thin films display less hysteresis. Hysteresis was not found for the heat capacity isotherm (Yang and Rupley, 1979), which may he taken as support for the view that meaningful free-energy information also can be derived from sorption isotherms. 

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