Calorimeter thermoelectric compensation

Calorimeters involving compensation of the thermal effect by phase transition or thermoelectric effects. 

Commercially available power compensation and heat flux calorimeters are competitive in stability, accuracy, and sensitivity, fractions of a millijoule being detectable with good reproducibility. Although thermoelectric compensation is more efficient in time (larger power values are detected in shorter time intervals), the kinetics of adsorption may impose limitations on this advantage. 

On the other hand, for slow reactions, adiabatic and isothermal calorimeters are used and in the case of very small heat effects, heat-flow micro-calorimeters are suitable. Heat effects of thermodynamic processes lower than 1J are advantageously measured by the micro-calorimeter proposed by Tian (1923) or its modifications. For temperature measurement of the calorimetric vessel and the cover, thermoelectric batteries of thermocouples are used. At exothermic processes, the electromotive force of one battery is proportional to the heat flow between the vessel and the cover. The second battery enables us to compensate the heat evolved in the calorimetric vessel using the Peltier s effect. The endothermic heat effect is compensated using Joule heat. Calvet and Prat (1955, 1958) then improved the Tian s calorimeter, introducing the differential method of measurement using two calorimetric cells, which enabled direct determination of the reaction heat. 

These authors were aware of the difficulty of establishing a comprehensive classification of calorimeters In every classification there are certain calorimeters which do not clearly belong to a particular category.The Calvet calorimeter, for instance, can be used eidier isothermally with electric compensation... or in an isoperibol manner involving the measurement of a local temperature difference. Moreover, a number of existing calorimeters remain outside our classification. One example is a calorimeter involving a compensation of the thermal effect other than by thermoelectric means or by phase transition. But such devices can be easily included in our classification by analogy. ... 

The heat released from a sample during a process flows into the calorimeter and would cause a temperature change of the latter as a measuring effect this thermal effect is continuously suppressed by compensating the respective heat flow. The methods of compensation include the use of latent heat caused by a phase transition, thermoelectric effects, heats of chemical reactions, a change in the pressure of an ideal gas (Ter Minassian and Million, 1983), and heat exchange with a liquid (Regenass, 1977). Because the last three methods are confined to special cases, only the compensation by a physical heat of transition and by electric effects are briefly discussed here. 

Scanning condition Tp = Tp(t) or Tm = TmW with Tp = constant Calorimeters involving the measurement of a temperature difference (heat flow calorimeters) or with a compensation of the thermal effect by thermoelectric effects (power compensation calorimeters). 

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