Calorimeter, representation

The differential equations Eqs. (10) and (29)3, which represent the heat transfer in a heat-flow calorimeter, indicate explicitly that the data obtained with calorimeters of this type are related to the kinetics of the thermal phenomenon under investigation. A thermogram is the representation, as a function of time, of the heat evolution in the calorimeter cell, but this representation is distorted by the thermal inertia of the calorimeter (48). It could be concluded from this observation that in order to improve heat-flow calorimeters, one should construct instruments, with a small... 

The development of the theory of heat-flow calorimetry (Section VI) has demonstrated that the response of a calorimeter of this type is, because of the thermal inertia of the instrument, a distorted representation of the time-dependence of the evolution of heat produced, in the calorimeter cell, by the phenomenon under investigation. This is evidently the basic feature of heat-flow calorimetry. It is therefore particularly important to profit from this characteristic and to correct the calorimetric data in order to gain information on the thermokinetics of the process taking place in a heat-flow calorimeter. 

Figure 15 gives a diagrammatic representation of a volumetric line which is used in connection with a high-temperature Calvet microcalorimeter 67). Other volumetric lines which have been described present the same general features (15, 68). In the case of corrosive gases or vapors, metallic systems may be used 69). In all cases, a sampling system (A in Fig. 15) permits the introduction of a small quantity of gas (or vapor) in a calibrated part of the volumetric line (between stopcocks Ri and Ro in Fig. 15) where its pressure Pi is measured (by means of the McLeod gage B in Fig. 15). The gas is then allowed to contact the adsorbent placed in the calorimeter cell C (by opening stopcock Ro in Fig. 15). The heat evolution is recorded and when it has come to completion, the final equi-...

Figure 10.5 Schematic representation of the stepwise heating mode of operation of an adiabatic calorimeter.

Figure 3.6 Schematic representation of the bomb calorimeter for measuring the changes in internal energy that occur during combustion. The whole apparatus approximates to an adiabatic chamber, so we enclose it within a vacuum jacket (like a Dewar flask)...

Heat recovery system (HRS), 23 190 energy demand in, 23 190-192 grid representation of, 23 188-189 Heat recovery system process, 23 786-787 Heat release calorimeters, 22 458 Heat removal, from direct HDC chlorination reaction, 25 638 Heat resistance... 

Figure 6.2 Schematic representation of (a) an adiabatic calorimeter, (b) an isoperibol calorimeter, and (c) a heat conduction (or heat flow) calorimeter. fc and 7] are the temperatures of the calorimeter proper and the external jacket, respectively, and is the heat flow rate between the calorimeter proper and the external jacket.

This highly sensitive calorimeter needs to be connected to a sensitive volumetric system in order to determine accurately the amounts of gas or vapor adsorbed. A schematic representation of the whole assembly is shown in Figure 13.4 [147]. The volumetric determination of the adsorbed amount of gas is performed in a constant-volume vessel linked to a vacuum pump. The apparatus consists of two parts the measuring section equipped with a capacitance manometer, and the vessels section that includes the cells placed in the calorimeter (a sample cell in which the adsorbent solid is set, and an empty reference cell). 

Fig. 1. Schematic representation of the time resolved photoacoustic calorimeter. Solid lines indicate light path heavy solid lines represent signal paths. (After Peters and Snyder)...

FIGURE 6.3 Schematic representation of a calorimeter and a volumetric system. 

Figure 4.3. Schematic representation of the isoperibohc Calvet s twin micro-calorimeter. A - thermocouple, B - calorimetric cell, C - thermal and electric shielding, D, F, H - three parts of the calorimetric block,...

The aim of this classification was to unquestionably classify any calorimeter within only one main class. The relationship existing between the sample temperature and that of the surrounding thermostat seems to be an appropriate criterion . For that purpose, a clear distinction is made between two parts of the calorimeter, namely (i) the sample together with the container with which it is in good thermal contact and (ii) the surrounding thermostat. To make this distinction clear, these two distinct parts are shown on the schematic representation of 11 types of calorimeters. This finally leads to the following classification ... 

The distinguishing of a central system consisting of only the sample and its container which are in good thermal contact is a simple one,and is easy to apply. It was therefore kept in the basic representation of a calorimeter given in section 4.1. 

Since the discovery by Kroto et al. [232] of the third molecular form of carbon, Ceoj named buckminsterfiillerene, and especially after the development of effective ways of production of these type of molecules, there has been great interest in the thermochemistry of these molecules. The enthalpy of formation of Cao is a key value in establishing its thermodynamic stability. Several micro- and macro-combustion calorimeters have been used for the experimental determination of the enthalpies of formation of Ceo in the crystalline state at 298.15 K [233]. A graphical representation of the available results collected in... 

Differential scanning calorimetry curve Graphical representation of the data collected by a differential scanning calorimeter, where the differential energy supplied is plotted as a function of temperature (scanning mode) or time (isothermal mode). 

Fig. 3. Representation of a two heat-flux calorimeter showing (a) Boersma thermocouple placement and (b) the Tian-Calvet design. The schematic diagram (c) is appropriate for analysis of the response of both types of calorimeters. Symbols in (c) are subscript T refers to temperature, R refers to reference the temperatures of the block, sample, container, reference, and reference containers given by Tb, Tsc, T-r, Trq, respectively capital R refers to heat transfer resistance in the instrument (9).

The representation of the calorimeter by mathematical models described by a set of heat balance equations has long traditions. In 1942 King and Grover [22] and then Jessup [23] and Chumey et al. [24] used this method to explain the fact that the calculated heat capacity of a calorimetric bomb as the sum of the heat capacities of particular parts of the calorimeter was not equal to the experimentally determined heat capacity of the system. Since that time, many papers have been published on this field. For example, Zielenkiewicz et al. applied systems of heat balance equations for two and three distinguished domains [25 8] to analyze various phenomena occurring in calorimeters with a constant-temperature external shield Socorro and de Rivera [49] studied microeffects on the continuous-injection TAM microcalorimeter, while Kumpinsky [50] developed a method or evaluating heat-transfer coefficients in a heat flow reaction calorimeter. 

Figure 1.5. A diagrammatic representation of an adiabatic (constant heat) calorimeter. The calorimeter consists of an insulated container filled with water in which the reaction chamber containing the sample and an excess of oxygen gas is immersed. In an exothermic reaction, the heat generated is transferred to the water and measured. Knowing the quantity of heat, the change in temperature, and the heat-absorbing characteristics of the system, the amount of heat evolved in the reaction may be calculated. ...

Figure 6.10 Top Schematic representation of an isoperibol calorimeter. Bottom Onedimensional simplification ofthe thermal path.

Figure 6.15 Schematic representation of the measuring system of a scanning calorimeter in a linear simplification with the corresponding temperature field in the presence of a steady-state heat flow.

For a clear-cut representation of the heat flows in a calorimeter as well as their combined effects and the consequences of their action, it is recommended to draw an analog electric representation diagram that translates the thermal relationships into electric circuits (for an example, see Section 7.9.2.3 on Calvet calorimeter). Thus, the temperature difference, the heat flow rate, and the thermal resistance become analogous to the voltage, the current, and the electric resistance, respectively. These electric circuits are often easier to interpret, and the electric laws are more familiar. 

Figure 4 is a schematic representation of a Perkin-Elmer DSC 2 differential scanning calorimeter, whose principles are given by Gray [17]. The calorimeter head is constituted of two identical plates in continuous contact with a cold source and heaters that supply the required energy to impose the programmed temperature Tp to the plates. The heaters run independently, and an electronic system compensates for temperatures between the plates. 

Figure 2 is a diagrammatic representation of the calorimeter. The vapour enters from the left and passes ovct a uniform heater of length L and power... 

Figure 2 Diagrammatic representation of flow calorimeter. At distance I to right of origin vapour has temperature T...

Figure 14.3 Schematic representation of the syringe mechanism and calorimeter cell of an ITC instrument as well as data from an ITC experiment. Controlled movement of the piston, which is driven by the injection motor, enables the exact injection of sub-pl amounts of a solution typically containing the ligand into the sample cell.

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