Heat-flowmeter calorimeters

Figure 8. Three heat-flowmeter calorimeters Tian-Calvet, 1950, left, after [33] Wadso, middle, after [34]and Du Pont DSC, right, after [35].

The temperature difference family includes most adiabatic and quasi-adiabatic calorimeters (in the time dependent temperature" group) together with most heat-flowmeter calorimeters. The total probably represents between 80 and 90 % of the calorimeters used today, so that, for practical use, the above classification looks somewhat unbalanced. Moreover, the calorimeters just mentioned shift to the first family as soon as they also make use of heat compensation, hence a real overlap exists between the two main families. 

C) True Isothermal (i.e. both in space and in time) or extended isothermal (i.e. only isothermal in space) calorimeters Tq follows Ts these are proportional systems and include phase-change, power-compensation and heat-flowmeter calorimeters. 

One sees that the use of Equation (2.79) requires a knowledge of the following experimental quantities dQm (heat measured by the calorimeter), dna (amount adsorbed), dp (increase in equilibrium pressure) and Vc (dead volume of the part of the cell immersed in the heat-flowmeter of the microcalorimeter cf. Figure 3.15.). If the conditions of small and reversible introduction of adsorptive are not fulfilled, the quantity assessed by Equation (2.79) can be described as a pseudo-differential enthalpy of adsorption (see Figure 3.16a). 

Diathermal-conduction calorimeters-, sample temperature follows surround temperature by simple conduction. Either a heat flowmeter or a phase chc detection system is used. 

Heat-flow adsorption microcalorimetry. The most important type of isothermal calorimeter in current use is that based on the principle of the heat flowmeter, which was first applied by Tian (1923) and improved by Calvet (Calvet and Prat, 1958,... 

Groszek (1966) early developed a simple flow-through adsorption calorimeter, which is somewhat similar to a differential thermal analysis (DTA) system (because of its single-point temperature detector) and is therefore well suited for the detection of thermal effects and for screening experiments. To obtain meaningful results requires more sophisticated equipment, however. A heat flowmeter microcalorimeter is normally used for this purpose. Such a microcalorimeter, especially designed for liquid-flow adsorption and for the complementary determination of AmitH, is illustrated in Figure 5.18. 

The most common way, to-day, of measuring the heat exchanged in a passive diathermal calorimeter is to make use of a heat flowmeter (Tian-Calvet, [32-33], Wads5, [34], Du Pont heat-flux DSC, cf Figure 8). 

Gaseous fuels are measured volumetrically by a calibrated flowmeter, and their compositions are analyzed by gas chromatography. The heating value can be calculated based on fuel composition or determined experimentally using a bomb calorimeter. 

---