In the adiabatic system the environment is controlled so that no energy is lost or gained. To achieve this state, the Calorimeter Vessel (Bomb Vessel) and bucket are surrounded by a water jacket which is strictly temperature controlled by a system or circulators, heaters and coolers, so that it has the same temperature as the inner bucket.
Isoperibol (Isothermal Calorimeter)
With an isoperibol calorimeter a water jacket surrounds the bucket in which the vessel sits. The surrounding water jacket is controlled to be at a constant temperature. When a sample is fired, the heat from the vessel is transferred to the water in the bucket and the temperature rise of the bucket water is measured to determine the calorific value of the sample.
The Isothermal Calorimeter measures the effect that the environment has on the bucket before and after the determination and corrects the results accordingly. This implies that the environment is stable during the determination. To achieve stability a large body of water surrounds the vessel and bucket assembly, which is thermally stable.
DDS developed their first calorimeter system in 1972. The system was a full isothermal system with water jacket. Prior to development of the CP500, it was demonstrated by Digital Data Systems that a polystyrene jacket, which has very little thermal mass and negligible heat conductivity, could replace the water jacket. The system was referred to as the "dry method".
"Dry" Static Jacket (Isothermal) Calorimeter
The "dry" static jacket isothermal method has no water inside the calorimeter. An aluminium sleeve that is an integral part of the vessel, replaces the bucket. The sleeve transfers the heat from the combustion process rapidly and evenly around the outside shell of the vessel. The temperature sensors are located between the combustion vessel and the sleeve. The temperature rise of the vessel is measured to determine the calorific value of the sample .The surrounding water jacket is replaced by polystyrene that is insulated from the outside environment by an aluminium box. The timing of the determination and the quality of the insulation is such that the environment has negligible effects on the determination.
Advantages of "dry" static jacket isothermal method
- No complicated water pipes and valves.
- The associated switching circuitry is not required.
- This makes the unit virtually maintenance free.
- The electronic control circuits are reduced, thus making the unit very easy to fault find in case of failure.
- With reduced electronics in the calorimeter, the training of a service technician or operator is reduced to an absolute minimum.
- Precise and reproducible determination of gross calorific values according to ISO 1928, DIN51900, and BS1016:105 International Standards.
By making the vessel removable and by removing the cooling of the vessel from the calorimeter, the speed of each determination is greatly increased.
Once the result is obtained for a determination, the hot vessel can be removed and cooled in a separate unit. This allows for another vessel to be inserted into the calorimeter and another determination to be started even before the previous vessel has been cooled.
This allows for higher throughput in a single calorimeter.
The use of the dry static jacket method allows water to be removed from the vessel surrounds which in turn allows electronics to be built into the vessel.
The advantages to this are:
- The temperature measurements of the vessel are totally independent of the calorimeter and all calibration data is stored inside the vessel.
- Multiple vessels can be used in a single calorimeter.
- Any vessel can be used in any calorimeter without re-calibration.
- If a vessel needs reconditioning or fails, the calorimeter can still be used, using another vessel.