Hel's Phi-tec system is a computer-controlled adiabatic calorimeter designed to simulate the thermal behaviour of larger-scale chemical reactors.
The Phi-tec is available in two different models: the entry-level Phi-tec I uses high-pressure cells, or bombs, of approximately 8ml volume to determine the heat evolved and pressure developed during the reaction.
It features a high-precision and rugged solid copper adiabatic furnace and a stainless-steel containment vessel.
Control is by the latest in-house developed Windows software.
Phi-tec II incorporates the same furnace and containment vessel, however, it also includes a pressure tracking facility, which allows for the use of low phi-factor test cells.
These cells are of 100ml volume, but are very thin walled and have very low thermal inertia (a low phi-factor).
This allows the Phi-tec II to simulate the behaviour of a full-scale plant during 'worst-case' scenarios and to provide information for calculations such as vent sizing and flow restrictors.
A complete system includes dedicated software for control and data analysis.
Sample temperatures can be tracked at up to 200C/min, up to 500C maximum and up to a pressure of 138 bar pressure.
A wide range of test cells enable the precise simulation of plant conditions, including overhead agitation and specialist materials of construction.
Adiabatic calorimetry is used primarily for the study of thermal hazards and the consequences of a maloperation during a process, for instance a misfeed or loss of cooling.
This is because on larger scales the effective natural cooling rates are negligible in comparison to heat generation, and many large process vessels can therefore be considered to be adiabatic.
Adiabatic calorimeters invariably maintain adiabatic conditions by using electric heaters surrounding the sample cell.
These are maintained fractionally above the sample temperature so that there is no net heat flow between the sample and its surroundings.
Therefore, the system is adiabatic.
With high phi factor calorimeters, such as the Phi-tec I, that use 'bomb-type' sample cells, when a reaction runaway is initiated the thermal mass of the sample cell is high when compared to the sample itself.
A large fraction of the energy released is absorbed by the container, thus limiting the adiabatic temperature rise.
In theory this can be corrected for using the equation discussed previously.
However, this can not be used to correct the rate of temperature rise.
Because the maximum temperature rise is limited, the consequences of side reactions initiated at high temperatures may not be seen.
The Phi-tec II uses a pressure tracking system and high volume (100-120 ml) sample cells with very thin walls and low thermal mass.
Test conditions are much more like plant conditions and very different data can be obtained.
