Operation adiabatic scanning

A schematic of the operation of the Sinku Riku ULVAC SH-3000 adiabatic, scanning calorimeter is shown in Fig. 4.38. The calorimeter is detailed on the right It is a miniaturization of the classical calorimeter in Fig. 4.30. The sample is indicated by 1. It is heated by supplying constant power, outlined in the block diagram on the... 

Adiabatically operated single scanning calorimeters were used for determinations of the specific heat capacities of copper and brass (Sykes, 1935) and of silver, nickel, brass, quartz, and quartz glass (Moser, 1936). Sykes calorimeter is shown schematically in Figure 7.35. 

Figure 5. Mechanical/thermal design of a computer-controlled calorimeter capable of operating in the a.c. mode or in relaxation modes including non-adiabatic scanning [34, 35].

The methods used for the isothermal reactor can also be used here, but must be completed by a thermal study over the total temperature range in which the reactor will be operated. Therefore, DSC in the scanning mode, or adiabatic calorimeters such as the Accelerating Rate Calorimeter or simply the Dewar flask, can be used. 

The scanning or dynamic mode of operation ensures that the whole temperature range of interest is explored. This must be ensured also in adiabatic experiments, where it is essential to force the calorimeter to higher temperatures, in order to avoid missing an important exothermal reaction (see Exercise 2 in Chapter 4). 

Notice that this means that the TS-PFR can be operated under isothermal or adiabatic conditions as well as any other. One way to envision this flexibility is to see isothermal reactors as operating under conditions where the heat transfer is infinite, allowing the reaction to track the control temperature perfectly. Adiabatic reactors in that view have zero heat transfer and no heat is lost from the reaction. Temperature scanning reactors operate with any value of heat transfer coefficient, including the above two extremes. 

Now only the first term on the right hand side is the thermodynamic heat capacity. The second term is a kinetic contribution that will only vanish if the system is at equilibrium (i.e., independent of time). But this can never happen when the DSC is operating in the scanning mode. Furthermore, since the kinetic term is inversely proportional to the scanning rate, dT/dt, the error in assuming that dH/dT is the true heat capacity, increases as the scanning rate is reduced Why, then, has the DSC yielded such excellent results in comparison with the adiabatic calorimeter ... 

The requirements with regard to a calorimeter can be derived on the basis of the above analysis of the measuring problem. The necessary operating conditions have to be defined first an isothermal, isoperibol, adiabatic, or a scanning calorimeter What temperature range What heating rate Any other boundary conditions a constant pressure, constant volume, gas flow rate, and so on ... 

Another development in calorimetry, at least in retrospect, was the construction of adiabatic calorimeters operating at constant heating rate. In such an instrument the heating was carried out continuously (scanning calorimeter), i.e., the measurement was not interrupted every 20 K or so to check the isothermal condition, but was carried out in one, continuous run. In such operation, the heat losses were minimized since the experiment could be completed faster, but the accuracy of such scanning calorimeters was considerably less than that of the standard adiabatic calorimeters. The reason for the lesser accuracy is the fact that the heat could not be distributed nearly as uniformly in the sample as in the adiabatic calorimeter. In addition, the loss calibration was also less accurate. 

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