Calorimeter high pressure

Figure Bl.27.9. High-temperature heat-leak calorimeter. (Reproduced by pemiission from Cliristensen J J and Izatt R M 1984 An isothemial flow calorimeter designed for high-temperature, high-pressure operation...

A high-temperature and high-pressure reaction calorimeter. 

The adsorption experiment is conducted until a relatively high pressure is reached without significant evolution of heat and the adsorbed amount becomes negligible. Owing to the high sensitivity of the method, only small quantities of sample are required. The error may be around 1%, as for the Tian-Calvet calorimeter [129]. 

Other thermal techniques are Thermogravimetric Analysis (TGA) [55,68], High Pressure Calorimeter (HPC) [1], Thermomechanical Analysis (TMA) [1,141], and Differential (or Dynamic) Thermal Analysis (DTA) [74]. These are rarely used and will not be discussed here. 

Thermal conductivity data are even more difficult to obtain. In the case of calorimetric data of heat capacity and heats of dissociation, the measurements though still reasonably challenging are aided by significant improvements in commercial calorimeters that can operate at high pressures. Thermal property data are presented in Section 6.3.2. 

In the CSM laboratory, Rueff et al. (1988) used a Perkin-Elmer differential scanning calorimeter (DSC-2), with sample containers modified for high pressure, to obtain methane hydrate heat capacity (245-259 K) and heat of dissociation (285 K), which were accurate to within 20%. Rueff (1985) was able to analyze his data to account for the portion of the sample that was ice, in an extension of work done earlier (Rueff and Sloan, 1985) to measure the thermal properties of hydrates in sediments. At Rice University, Lievois (1987) developed a twin-cell heat flux calorimeter and made AH measurements at 278.15 and 283.15 K to within 2.6%. More recently, at CSM a method was developed using the Setaram high pressure (heat-flux) micro-DSC VII (Gupta, 2007) to determine the heat capacity and heats of dissociation of methane hydrate at 277-283 K and at pressures of 5-20 MPa to within 2%. See Section 6.3.2 for gas hydrate heat capacity and heats of dissociation data. Figure 6.6 shows a schematic of the heat flux DSC system. In heat flux DSC, the heat flow necessary to achieve a zero temperature difference between the reference and sample cells is measured through the thermocouples linked to each of the cells. For more details on the principles of calorimetry the reader is referred to Hohne et al. (2003) and Brown (1998). 

Lievois, J.S., Development of an Automated, High Pressure Heat Flux Calorimeter and Its Application to Measure the Heat of Dissociation of Methane Hydrate, Ph.D. Thesis, Rice University, TX (1987). 

The latter is measured in a small container under high pressure and in pure oxygen, conditions that are not representative of real fires. The conditions in bench-scale calorimeters such as the cone calorimeter resemble those in real fires much more closely. For some fuels, in particular gases, both values are nearly identical. However, for charring solids such as wood, AHc is significantly lower and equal to the heat of combustion of the volatiles during flaming combustion. 

The energy expenditure of an animal or human may also be determined by the method of direct calorimetry. Direct calorimetry requires the use of an insulated room, chamber, or suit for the human or animal. The enclosure contains a water jacket. The water passes from one end of the jacket to the other, maintaining the room, chamber, or suit at a constant temperature. The temperature of the water leaving the jacket is used to calculate the energy expended by the subject. The principles behind the use of the chamber are identical to those behind the use of the bomb calorimeter. The major difference is that in bomb calorimetry combustion is catalyzed by a small spark. In addition, in the bomb calorimeter oxygen is present at a high pressure to facilitate combustion. With direct calorimetry, combustion is catalyzed by enzymes. This combustion proceeds more slowly than that catalyzed by a spark, and the temperature of the subject does not increase much over the normal resting body temperature with the various activities. 

A bomb calorimeter is useful for measuring the energy released in combustion reactions. The reaction is carried out in a constant volume bomb with a high pressure of oxygen. How much heat is evolved when 54.0 g glucose (C6Hi20s) is burned according to this equation ... 

Figure 2. Heat flow vs. temperature obtained with a high pressure differential scanning calorimeter for two samples of YBa2Cu307 x.

Christensen, J. J., L. D. Hansen, R. M. Izatt, and D. J. Eatough. 1981. Isothermal, isobaric, elevated temperature, high-pressure, flow calorimeter. Rev. Sci. Instrum. 52 1226-1231. 

Figure 6 22. High-pressure DTA apparatus of KubaMa and Schneider (75). (u) a. r = coolers. b, n = pyrophillite insulating disk c = heating block d = high-pressure vessel e. m — copper seals f, I = Zr02 blocks g = copper shield h = calorimeter block i = thermocouple k = corundum capillary o = fastening screw p = support c] = in- and outlet of refrigerant. (/ )(i) Open Pt/Ir well In) closed teflon well with brass holder lh = steel-sheathed thermocouple).

High-pressure DTA and DSC systems have been described by Wurflinger et al. (132-135). These instruments can be used in the temperature range —200-150CC at up to 3 kbar pressure. The DTA cell is a cylindrical pressure vessel made of copper-beryllium, closed al the top by a Bridgman piston. From the bottom, two steel-sheathed thermocouples were introduced into the inner volume of the vessel where identical DTA wells were fastened onto the two thermocouple junctions and inserted into a symmetrical calorimeter block. 

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