Analysis of the inaccuracy of the oxygen bomb calorimeter (calorimeter) verification results

Analysis of the inaccuracy of the oxygen bomb calorimeter (calorimeter) verification results

The oxygen bomb calorimeter (calorimeter) is a nationally mandated metrological verification instrument. For many years, the Shanghai Testing Technology Institute is authorized by the Shanghai Municipal Bureau of Quality and Technical Supervision to perform mandatory verification of oxygen bomb calorimeters and oxygen bombs in society. Unit, through more

Years of practice, groping, summing up, affecting the results of oxygen bomb calorimeter verification, the data is inaccurate with the following various factors for reference.

1, oxygen bomb calorimeter (calorimeter) verification of heat capacity calibration is not accurate

Inaccuracies in heat capacity calibration often introduce systematic errors. This is mostly due to the failure of the benzoic acid used. The heat capacity of the instrument should be calibrated using a secondary reference mass, benzoic acid, which has been qualified by the metrology department, and the calculation is correct. In addition, the amount of inner cylinder water at the time of calorific value measurement is not completely consistent with the thermal capacity calibration, and the marked heat capacity is also not suitable for the calorific value measurement test. After calibrating the heat capacity, the quality of the inner cylinder water (including the inner cylinder itself) should be recorded to ensure that the internal cylinder water volume is completely consistent in all subsequent tests.

2, oxygen bomb calorimeter (calorimeter) to verify the mixer failure or uneven stirring speed

Sometimes the contact part of the agitator of the calorimeter is in poor contact and there is a virtual connection phenomenon, which will cause the stirring speed to be fast and slow, and stop when the time is turned; sometimes the stirring paddle is not suitable, and it is stuck and cannot move freely, which will result in the inside. The heat locally obtained in the cylinder water cannot be dissipated evenly in time, so that the measured inner cylinder temperature changes to a false temperature change. The calorific value calculated with this temperature rise is necessarily the wrong result. When the heat capacity or calorific value is found to be high and low, and the difference is very far, the reason can be found from this aspect.

3, oxygen bomb calorimeter (calorimeter) verification using Beckman thermometer did not perform or failed to correct the capillary diameter and the average division value. The Beckman thermometer is used to measure the temperature change of the inner cylinder. If the capillary diameter value and the average division value are not corrected correctly, the measured temperature rise will be inaccurate, resulting in an error in the calorific value measurement.

4, oxygen bomb calorimeter (calorimeter) verification that the amount of water in the inner cylinder can not be consistent. The heat capacity of the inner cylinder water accounts for a considerable proportion of the heat capacity of the whole instrument. Because the specific heat of water is very large, the amount of water in the inner cylinder is Inaccuracies will cause the heat capacity of the instrument to change, resulting in a measurement error in the amount of heat generated.

5, oxygen bomb calorimeter (calorimeter) verification using adiabatic calorimeter, the balance point of the calorimeter has problems If the balance point of the adiabatic calorimeter has problems, it will affect the ability of the outer cylinder temperature to track the inner cylinder temperature, so that The temperature of the outer cylinder often coincides with the inner cylinder, resulting in excessive heat exchange between the inner and outer cylinders. This heat exchange is not corrected in the adiabatic calorimeter, and therefore, this part of the heat exchange will cause a measurement error of the calorific value. There is a problem with the balance point, which means that the balance point is unstable or does not appear. One reason may be that the operator did not carefully check and adjust the balance point before using the calorimeter, and the second may be that the instrument's automatic temperature control line has a problem. The phenomenon that the balance point does not appear or is unstable is that the inner cylinder temperature cannot be constant for a long time, or the balance appears, and the next time it does not appear. In this case, the operator should carefully check and adjust the balance point of the instrument. If it is not successful after repeated debugging, the manufacturer should be repaired or help find the cause.

6, oxygen bomb calorimeter (calorimeter) verification performance is not very stable. Some automatic calorimeters, especially those that deviate from the classical calorimetry theory and the calorimetric method, cause unstable temperature measurement or other properties of the calorimeter due to unstable design or electronic components such as sensors used. Large fluctuations, resulting in inaccurate calorie determination results.

Mainly due to the above reasons, the oxygen bomb calorimeter is not accurate. Of course, there are other reasons. For example, the instrument itself is inherently insufficient at the time of purchase, and the materials and components do not meet the requirements. After a period of use, the change will also lead to the accuracy of the instrument.

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