The calorimeter's principle and development history

Calorimeter development:

At present, domestic use of calorimeter in addition to domestic production of instruments, that is, some scientific research institutions are used by the United States LECO company and Germany IKA company's production, and its models are also thermostatic, thermal insulation and double dry type. However, regardless of the model or manufacturer, it has not been separated from the basic model since the birth of the first calorimeter in 1881. It includes water jackets (usually called outer cylinders), inner cylinders, and combustion chambers (usually A system consisting of basic components such as oxygen bombs. For more than one hundred years, especially in the past 20 years, with the rapid development of computer technology, the calorimeter has undergone great improvements in structure and operation mode, the degree of automation has been greatly improved, the test speed is faster, precision, and More accurate.

Due to the very complex structure of the oxygen bomb and the strict requirements on the environmental conditions, the adiabatic calorimeter has a high requirement for automatic temperature tracking technology. This type of calorimeter is relatively rare in the market, so the basic Not on the production, and basically all domestic use is a constant temperature calorimeter. Now we introduce the history of calorimeters. From the earliest calorimeters to modern calorimeters, we have made some major improvements in the following aspects:

Before the 1970s, the calorimeter's temperature measurement tool was a Beckman thermometer similar to an ordinary mercury thermometer. It also reflected the temperature change through the thermal expansion and contraction of mercury in the glass tube. The difference was that in order to read The temperature is more accurate, so the scale is finer (actually the capillaries in the glass tube are made finer), but this requires the thermometer to be very long, inconvenient to use and easily damaged. At the same time taking into account that the test process only needs to measure the temperature difference between the starting point and the end point, does not require the actual temperature value, and the actual temperature difference of the actual testing process is below 4 °C, so the thermometer scale range 5 ~ 6 °C can be, but when the actual When the water temperature is low, the temperature may not be read, that is, the mercury shrinks into the storage room below, and when the water temperature is high, the temperature may not be read, that is, the mercury expands beyond the maximum range. To solve this problem, add a storage room above the thermometer to store the reserve mercury. When the water temperature is too low, a part of the mercury is poured back into the capillary from the upper storage room. When the water temperature is too high, the mercury in the capillary tube is returned to a part of the upper storage room. This ensures that at any water temperature, The Beckman thermometer can read temperature.

Although the Beckman thermometer is more accurate than ordinary mercury thermometers, it can only be read at 0.001°C (and read with a magnifying glass). The operation is also cumbersome, and because of manufacturing technology, the capillary capillary inner diameter and scale It is impossible to be very uniform, so capillary aperture correction and average division value correction must be performed, and these tasks are also quite tedious.

The second improvement of the calorimeter is to change the artificial weighing of the inner cylinder water to automatic weighing. The amount of water in the inner cylinder and its repeatability are important factors affecting the precision and accuracy of the calorimeter. At present, the quantity of water in the calorimeter inside the domestic market is mainly about 2000 g and about 3000 g. According to the requirements of national standards, the reproducibility of the water volume of any type of calorimeter should be less than 1 g. The use of electronic platform scales to manually weigh the inner cylinder water is not only troublesome but also brings about errors caused by non-standard human operation. The automatic weighing method improves the working efficiency and avoids the influence of human factors, thus improving the calorimeter. The repeatability makes the measured result more accurate. The method for automatically weighing the inner cylinder water has so far been of the following three types: measuring cup type, automatic balance type and electronic measuring cup.

After the amount of water in the inner cylinder was changed from manual weighing to automatic weighing, the work efficiency was greatly improved. It took 40 minutes for the original sample to be produced, and now it takes only about 15 minutes. After the original experiment was finished, the water volume of the inner cylinder was replaced. After the test was finished, the water in the inner cylinder was poured back into the outer cylinder. After each test, the water temperature in the inner cylinder was increased by 1.5 to 3. At about 5°C, although the amount of water in the inner cylinder is only one-tenth to one-tenth of the amount of water in the outer cylinder, the water temperature of the outer cylinder can be increased by about 0.3 to 0.5°C after each test. About a sample, the temperature of the outer cylinder can be increased by about 3 to 5°C.

According to the environmental requirements for the calorimeter used by the national standards, the difference between the room temperature and the outer cylinder water temperature cannot exceed 1.5°C. If the inner cylinder water after each test is directly cooled into the outer cylinder without cooling treatment, the difference is at least 3 times. As many as five times, the water temperature of the outer cylinder may exceed 1.5°C, which will affect the accuracy of the test results. For this purpose, the inner cylinder water after the test must be cooled first, and then enter the outer cylinder to participate in the next round of circulation, so as to ensure that the difference between the water temperature and the room temperature of the outer cylinder can always meet the requirements of the national standards. The current cooling methods are as follows: Three types: semiconductor refrigeration, compressor refrigeration, and natural cooling.