Units, Conversions and Calculations

The following information applies to the : CAL3K-AP , CAL3K-A , CAL3K-U, CAL3K-F.


This section gives a short summary of related mathematical info.

3.6MJ = 3410BTU = 1KWh = 860Kcal

1J = 1 Watt second = 1Ws


Point to ponder:

0.5g Benzoic Acid (BA) releases 26.454*0.5=13.227KJ

This means it releases 13227 Ws. This means:

13227Watt in 1 second or 13227/60 = 220 Watts for 1 minute or 40 Watts for 5.5 minutes. This is the energy of a typical light bulb. It would burn for 5.5 minutes except for the less than 100% heat to electrical current conversion efficiency in a coal burning power station.

CONVERSIONS

1MJ/Kg = 1KJ/g
BTU to KJ = BTU/429.92255
BTU to CAL = BTU/1.8
CAL to KJ = CAL *0.004187 (1.8/429.92255)
CAL to BTU = CAL *1.8
KJ to BTU = MJ * 429.92255
KJ to CAL = MJ * 238.84586 (429.92255/1.8)

CALCULATIONS

The KJ/g (=MJ/Kg) is used because the CAL3K uses Gramm (g) as an input.

The Bomb Factor (BF) is a factor describing the heat capacity of the combustion vessel. It is measured in: KJ/C

BF = 26.454KJ/g x Mass / Temperature Rise

KJ/C = KJ/g x g / C


Therefore:

Heat capacity = BF = 26.454 x 0.5 /13°C Rise =~ 1

The Heat capacity of a CAL3K vessel is Approx. 1.0

The Calorific Value (CV) is calculated from:

CV (KJ/g) = Compensated Rise (C) x BombFactor (KJ/C) / Mass (g)

The CV calculation includes other important corrections:

FIRING WIRE + COTTON

This is the energy released from the electrical firing current and from the cotton fuse. It is labelled ‘Cotton Correction’ but includes the firing current and the cotton. Since it is CONSTANT unless you change the firing voltage or the cotton it is measured as a TEMPERATURE RISE. It is directly subtracted from the RISE temperature.

SUPLHUR CORRECTION

Sulphuric Acid is formed from the sulphur contained in the sample (Coal) and the oxygen. This formation causes a heat release. This is normally not the case if a sample is burned and the correction must be subtracted. The Sulphur correction is subtracted on the end of the determination. For the purest mathematicians: It changes with each sample mass and should be included in the mass calculation. BUT: It is so small that it can be entered as a constant if the sample mass is reasonably constant.

ENVIRONMENTAL COMPENSATIONS

The CAL3K is not perfect: The environment (room) temperature influences the determination. The CAL3K measures the vessel temperature to within 0.000001 (1ppm) and is constructed in a way that the environment influence is minimized, but it still gets through. The changes are very small and well within the specifications. The ‘IntelCal’ procedure measures these influences and instructs the determination process to compensate for them. In absence of a IntelCal the defaults are loaded which contain a ‘reasonable’ average obtained by running multiple vessels on multiple calorimeters.

MOISTURE CORRECTION

If the moisture of a sample is known then the CAL3K can subtract the entry in percent from the mass. The result will rise. The moisture correction is NOT applied to a calibration. The moisture compensation must be enabled in the System Configuration.

FIBRE CORRECTION

This applies to FOOD/FEED determinations. The calorific value of Protein and Carbohydrates can be set (Default : ~4Kcal = 16.7Kj/g) and the fibre content can be set in percent as a portion of the mass. The fibre correction reduces the result. The fibre correction is NOT applied during calibration. The fibre correction must be enabled in the System Configuration.

GELATINE CAPSULE CORRECTION

Gelatine capsules are used for powdery sample substances to prevent a sample explosion or sample scattering. The capsule correction is entered as an ABSOLUTE temperature rise. The rise is subtracted from the temperature rise in the same fashion as the cotton + wire correction. It reduces the result. The gelatine correction is not used during calibration. The capsule correction must be enabled in the System Definition.


HEAT CAPACITY

The Heat capacity is a measurement which describes the amount of energy (heat) needed to raise the vessel temperature by 1 degree. The exact heat capacity is calculated by the CAL3K every 6 seconds after the Start record (parameter) during a calibration and then saved to the vessel as a ‘Bomb Factor’.

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BOMB FACTOR

This is a conventional term, but related to the heat capacity. The Bomb factor is approx. 1 KJ/C. In practice this means that 0.5g Benzoic Acid results in ~13.2°C rise. Then the calorific value CV=13.2C / 0.5g x 1KJ/C = 25.4KJ/g.

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BENZOIC ACID STANDARD VALUE

The BA (Benzoic Acid) standard is normally 26.454 MJ/Kg. Sometimes it is required to change the setting to the supplied certification standard. Fire up the CAL3K PC software, set the communications port to USB or RS232 at 115.2Kb, plug in the communications cable and observe that the data is displayed.

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