Equation Calvet calorimeter

The overall calorimeter equation of the Calvet calorimeter is finally given by Eq. (4). The overall heat effect, AH, is equal to the time integral over the Peltier compensation, the major effect to be measured, corrected for two factors the time-integral over the just-discussed losses, 4>, and, if the temperature does not stay exactly constant during the experiment, a correction term which involves the heat capacity of the calorimeter and the sample, C. All three terms can be evaluated by the measurement of the Peltier current i, the measurement of the emf of the measuring thermocouples, and a measurement of the change of the emf with time. The last term is needed for the calculation of the heat capacity correction which is written in Eq. (4). The last two terms in Eq. (4) are relatively small as long as the operation is close to isothermal. 

The basic principle of heat-flow calorimetry is certainly to be found in the linear equations of Onsager which relate the temperature or potential gradients across the thermoelements to the resulting flux of heat or electricity (16). Experimental verifications have been made (89-41) and they have shown that the Calvet microcalorimeter, for instance, behaves, within 0.2%, as a linear system at 25°C (41)-A. heat-flow calorimeter may be therefore considered as a transducer which produces the linear transformation of any function of time f(t), the input, i.e., the thermal phenomenon under investigation]] into another function of time ig(t), the response, i.e., the thermogram]. The problem is evidently to define the corresponding linear operator. 

Another problem related to the validity of equation 9.9 is that equation 9.6 applies only to heat conduction. If T — 12 is large, some significant fraction of heat will be transferred by convection and radiation and thus will not be monitored by the thermopile. Consequently, the use of partial compensating Peltier or Joule effects was essential in the experiments involving Calvet s calorimeter, whose thermopiles had a fairly low thermal conductivity. 

---