Heat Capacity of materials

Heat transfer is measured by calorimetry, q = Mc AT, where M is the mass of the heat-absorbing substance in the calorimeter (usually water) and Cg is the specific heat of the substance. A commercial calorimeter will have calibration factors that take into account the heat capacity of materials other than water used in its construction (for example, sample holder, walls, and so forth). 

The principle of heat capacity measurement is based on proportionality of the DSC response to the heat capacity. By definition, the heat capacity of materials under constant pressure is the... 

Specific heat capacity of material before decomposition, j, Specific heat capacity of material after decomposition, Decomposition heat,... 

The crystallization and melting behaviors of polymers are conventionally measured by the method of differential scanning calorimetry (DSC). One can obtain the heat flow or compensation power dQ/dt as a function of temperature, which is in principle proportional to the heat capacity of materials Cp and the scanning rate q, as given by... 

D4816 Test Method for Determining the Specific Heat Capacity of Materials by DSC... 

If we are dealing with the problem of industrial optimization or fault analysis of an existing plant, the flowsheet and equipment of this industrial process have been specified, the physico-chemical parameters such as the equilibrium constants of chemical reactions or the heat capacity of materials have been all specified, the process can be described by another series of dimensionless numbers such as the relative pressure (P/Po), relative temperature (T/To), relative volume (VA o), and so on. Based on the above-mentioned concept, we can see that the theoretical basis of the data processing methods for industrial optimization and fault diagnosis is relevant to dimensional analysis in this respect. 

DSC (Differential Scanning Calorimetry) has also been used in cement science investigations to some extent. It is based on a power compensated system. In this technique the reference and the sample imder investigation are maintained at a constant temperature throughout the heating schedule. The heat energy required to maintain the isothermal condition is recorded as a function of time or temperature. There are some similarities between DTA and DSC ineluding the appearance of thermal curves. DSC can be used to measure the heat capacities of materials. DSC measures directly the heat effects involved in a reaction. 

Classical thermod)mamics using the equipartition of energy principle predicts that the lattice molar heat capacity will be given by 1/2R for each of the six degrees of freedom in a solid (three kinetic and three potential energy) for a total of 3R. As the temperature is increased, the observed heat capacity of materials approaches this value, which is known as the Dulong-Petit limit. However, at low temperatures, the observed heat capacity approaches zero as 7. ... 

Heat tracing for insulated pipes is generally only required for the period when the material in the pipe is not flowing. The heat loss of an insulated pipe is veiy small compared to the heat capacity of a flowing fluid. Unless the pipe is extremely long (several thousands of feet), the temperature drop of a flowing fluid will not be significant. 

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. 

TABLE 6.2 Specific and Molar Heat Capacities of Common Materials ... 

In differential thermal analysis, a sample and reference material are placed in the same large metal heat sink. Changes in the heat capacity of the sample are measured by changes in temperature between the sample and the reference materials as they are heated at the same rate. 

The semiconducting properties of the compounds of the SbSI type (see Table XXVIII) were predicted by Mooser and Pearson in 1958 228). They were first confirmed for SbSI, for which photoconductivity was found in 1960 243). The breakthrough was the observation of fer-roelectricity in this material 117) and other SbSI type compounds 244 see Table XXIX), in addition to phase transitions 184), nonlinear optical behavior 156), piezoelectric behavior 44), and electromechanical 183) and other properties. These photoconductors exhibit abnormally large temperature-coefficients for their band gaps they are strongly piezoelectric. Some are ferroelectric (see Table XXIX). They have anomalous electrooptic and optomechanical properties, namely, elongation or contraction under illumination. As already mentioned, these fields cannot be treated in any detail in this review for those interested in ferroelectricity, review articles 224, 352) are mentioned. The heat capacity of SbSI has been measured from - 180 to -l- 40°C and, from these data, the excess entropy of the ferro-paraelectric transition... 

This is because the heat capacity of a wall of finite thickness is several orders of magnitude higher than that of the hot combustion products. However, some researchers did observe a small effect of the properties of the wall [17] on the quenching distance. This was interpreted in terms of some residual catalytic activity of the wall surface, poisoned by the combustion products from the preceding experiments [18]. With respect to this explanation, the surface of any material moistened through the condensation of the water vapor produced in the reaction is supposed to have very similar, low activity. 

A Z depends on the identity of the material. For instance, 50 J of heat increases the temperature of 1 mol of gold more than it increases the temperature of 1 mol of water. The dependence of AT on the identity of the material is expressed by the molar heat capacity (C, units J moP ° C ). The molar heat capacity is the amount of heat needed to raise the temperature of 1 mol of substance by 1 °C. Eveiy substance has a different value for C. The molar heat capacities of several chemical substances are listed in Table 6-1. 

Cp = specific heat capacity of the material, constant pressure,... 

As we said, the material of the regenerator of a PTR must have a high specific heat to provide a good heat storage. Unfortunately, below 20 K, the specific heat of most regenerators rapidly decreases, whereas the heat capacity of helium increases and has a maximum at 10K (see Fig. 5.20). 

Fig. 5.20. Volumetric heat capacity of 4He and some regenerator materials as functions of temperature. 

Nevertheless the heat capacity of a carbon resistor was not so low as that of crystalline materials used later. More important, carbon resistors had an excess noise which limited the bolometer performance. In 1961, Low [61] proposed a bolometer which used a heavily doped Ge thermometer with much improved characteristics. This type of bolometer was rapidly applied to infrared astronomy as well also to laboratory spectroscopy. A further step in the development of bolometers came with improvements in the absorber. In the early superconducting bolometer built by Andrews et al. (1942) [62], the absorber was a blackened metal foil glued to the 7A thermometer. Low s original bolometer [61] was coated with black paint and Coron et al. [63] used a metal foil as substrate for the black-painted absorber. A definite improvement is due to J. Clarke, G. I. Hoffer, P. L. Richards [64] who used a thin low heat capacity dielectric substrate for the metal foil and used a bismuth film absorber instead of the black paint. 

Equation 9-24 provides a conservative estimate of the required vent area. By considering the case of 20% absolute overpressure, assuming a typical liquid heat capacity of 2510 J/kg K for most organic materials, and assuming a saturated water relationship, we can obtain the following equation13 ... 

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