Quasi-adiabatic calorimeters

There are two different kinds of calorimeter adiabatic (or quasi-adiabatic calorimeters) and non-isothermal, non-adiabatic calorimeters (often referred to as n-n calorimeters). The accuracy of measurements made using such methods will be high if ... 

Adiabatic calorimeters the thermal conductance between the calorimetric vessel and the surrounding thermostat equals 0. These calorimeters integrate all heat effects. The heat measurement is based on the measurement of the sample temperature. The most perfect adiabatic calorimeters are those for which the temperature of the thermostat is brought to follow that of the internal vessel, like those proposed by Person (1849) and Richards (1905). In this group of adiabatic calorimeters, the authors also mention the Dewar vessel calorimeter (which they call quasi-adiabatic ) and the Berthelot calorimeter. 

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. 

The thermal resistance R is supposed to increase from the isothermal to the isoperibol and then to the adiabatic type of calorimeter. It would probably be more correct and general to base the distinction between the adiabatic and the isoperibol calorimeters on the heat transfer (involving simultaneously the thermal conductance and the temperature difference) rather than on the value of the thermal resistance. For instance, a simple Dewar vessel calorimeter provides a very high thermal resistance between the central system and the surroundings, though it is simply an isoperibol calorimeter (called quasi-adiabatic in section 4.2.), whereas Swietoslawski s adiabatic calorimeters, which do not use any vacuum insulation, certainly provide a much lower thermal resistance [15]. 

The operating conditions of calorimeters are defined first and foremost with regard to an ideal state. For this reason, the designations isothermal and adiabatic as used here are not in strict accordance with the concepts of thermodynamics. In calorimetric practice, it would be more appropriate to use the terms quasi-isothermal and quasi-adiabatic. There is a common tendency to use thermodynamic concepts even when the ideal conditions required by them are not complied with. This fact must be kept in mind, in particular in the uncertainty analysis. 

The construction principles of such chip calorimeters are similar to those of conventional calorimeters The heater corresponds to the furnace, and the center of the membrane corresponds to the calorimeter system, including the sample container. The thin membrane serves as the thermal path between the heater and the sample with very low thermal resistance and very low effective heat capacity. The thermopile measures the temperature difference between the sample site and the chip frame (surroundings). Because of the much larger lateral dimension of the membrane of at least two orders of magnitude, the heat exchange between the sample and the frame can be neglected. The chip calorimeter can therefore be considered a quasi-adiabatic calorimeter when vacuum is applied. 

The striking result is the observation that for the single supported films, the calorimetric glass transition is, within experimental uncertainty, film thickness independent down to film thicknesses of 1 nm. But a serious limitation of the quasi-adiabatic calorimeters is the not so well-defined cooling rate, which defines the state of the sample prior to heating. 

Hub, L. Medium-small-scale safety calorimeter, usable under isothermal, quasi-isothermal or adiabatic conditions. 

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