Abstract
Despite the thoroughness of measuring systems today, the possibility cannot be excluded that several units, though possessing identical electric constituents, give for the same actual test value signals with differences that are beyond the range of tolerance. This is important when the signals are intermediate values when establishing target quantities. For the measurements of calorimeters this fact must also be taken into account. With calorimeters for isothermal reactions, the accuracy of signals of the different actual powers p 1, p 2 and p St2 must be checked and, if necessary, be standardized as follows.
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- 1.
For instance, variation in p 2 due to changes in the set value ΔT 2 to (ΔT 2 + δΔT 2), its change due to varied manual setting, a variation in p St2 due to a change in the consistency in the filling of the measuring kettle.
- 2.
In what follows, signals of the actual quantities are denoted by boldface type.
- 3.
The compensation of the heat flow change δΔT 2·(k·F)2 by δp 1 is correctly indicated because p 1 has already been adjusted.
- 4.
The compensation of the heat flow change δΔT 2·(k·F)2 by δ p 1 is correctly indicated because p 1 has already been adjusted.
- 5.
Used for dosage of the reaction mixture, measurement of pressure and as a holder system of the stirrer bearing/shaft.
- 6.
With the exception of non-isothermal experiments by an induced change in the temperature of a simplified apparatus (Sect. 2.1.2.1).
- 7.
The small change in the temperature T S of the base thermostat in the beginning due to the initial stirrer power or heat exchange with the occasionally slow and steadily changing surroundings (temperature in laboratory) occurs in a quasi-static way owing to the high heat capacity.
- 8.
With constant rotational velocity of all stirrers.
- 9.
Thermal equilibrium means that there are constant heat flows over time, i.e. stationary heat flows in the calorimeter system:
• From the measuring kettle
– supplied by the electric heating power p 2 and stirring power p St2 –
into the intermediate thermostat
• From the intermediate thermostat
– increased by the electric heating power p 1 and the stirring power p St1 minus a tiny heat loss to the laboratory due to the dosing pipes and the stirrer bearing application –
into the base thermostat
• From the base thermostat
– changed by the stirring power of the base thermostat as well as heat loss by radiation and convection into the laboratory –
into the socle thermostat
- 10.
The rate of heat release (e.g., heat of mixing, heat of reaction) in the measuring kettle is compensated by opposite and equal changes in the electric heating power p 2.
- 11.
It is advisable to set p 2 = 0.
- 12.
In addition, the heat flow can vary also due to the changing heat-transfer coefficient (k·F)2 owing to the reaction.
- 13.
Around 400 W/°C or 1600 W/°C respectively around 120000 J/°C or 2000000 J/°C.
- 14.
These changes entail maintaining a quasi-equilibrium state, phenomenologically in comparison with the raising of a ship due to a rising water level, with the distance of the deck to the water level remaining quasi-constant.
- 15.
If the heating power p 20 is switched off, then the process reverses, i.e. the temperature T 2 of the measuring kettle and the temperature T S of the base thermostat return to their initial values. For example, switch off of p 2 takes place in order to determine the effective heat capacity C 2. See Sect. 2.1.2.3.
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© 2015 Springer International Publishing Switzerland
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Litz, W. (2015). Practical Hints. In: Bench Scale Calorimetry in Chemical Reaction Kinetics. Springer, Cham. https://doi.org/10.1007/978-3-319-12532-9_3
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DOI: https://doi.org/10.1007/978-3-319-12532-9_3
Publisher Name: Springer, Cham
Print ISBN: 978-3-319-12531-2
Online ISBN: 978-3-319-12532-9
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