Calorimeter works

One is the working principle of the calorimeter. The principle of the industrial calorimeter is to measure the calorific value of the entire calorimetric system with a known calorific value (usually the standard substance benzoic acid). That is, the calorimeter's heat capacity is measured. For example, it is known that the caloric value of benzoic acid is 26,500 J/g, and the combustion of 1 g of benzoic acid can increase the calorimetric system by 2.65°C, and the calorimeter's heat capacity is measured to be 10000 J/°C; The coal combustion can increase the calorimetric system by 2°C, then the calorific value of the tested coal sample is 20000 J/g, and if the temperature is increased by 2.5°C, the calorific value of the tested coal sample is 25000J/g.

The second is the development of calorimeter. In addition to domestically produced calorimeters, there are also produced by American LECO Company and German IKA Company. The models are also thermostatic, adiabatic and double dry. 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, so this article is mainly about the constant temperature calorimeter.

From the earliest calorimeters to modern calorimeters, the following improvements have been made:

Before the 1970s, the calorimeter's temperature measurement tool was a Beckman thermometer similar to a common mercury thermometer. It also reflected the temperature change through the thermal expansion and contraction of mercury in the glass tube. In order to read the temperature more accurately, 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 weigh the amount of water in the inner cylinder. 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 cylinder was changed from manual weighing to automatic weighing, the working efficiency was greatly improved. It took about 40 minutes to enter the outer cylinder directly for a sample, 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 water temperature of the outer cylinder must not exceed the temperature of the inner cylinder after the test without cooling. If the water temperature exceeds the room temperature, the temperature of the outer cylinder may exceed 1 at least 3 times and more than 5 times. .5°C, this 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 of the outer cylinder and the room temperature is always 1.5°C, if it can meet the national standard each time. Requirements, the current cooling method has the following three: semiconductor refrigeration, compressor refrigeration and natural cooling.

In addition to stirring the old blades, the stirring method adds a magnetic stirring method. A fast generator is installed below the bottom of the inner cylinder. A metal rail is mounted on the motor shaft, and a round magnet is fixed at both ends of the rail. A cylindrical magnet rod (usually called a stirrer) is placed in the cylinder. When the motor rotates, it drives the crosspiece to rotate, which in turn rotates the stirrer in the inner cylinder, thereby homogenizing the water in the inner cylinder, making the oxygen bomb Heat to the inner cylinder of water. Magnetic stirring can be achieved by adjusting the speed of the motor to increase the stirring efficiency and control the heat of stirring. And the heat generated by the rotation of the motor will not be directly transmitted to the water in the inner cylinder to affect the test results.

Oxygenation and deflation changed from the past manual mode to semi-automatic mode. The oxygenation instrument and the deflation valve that were separated in the past are made into a whole and combined into one, mounted on the lid of the thermostatic cylinder, and equipped with a gas valve and a circuit for control, and the oxygenation is performed when the oxygenation is performed. Deflate at the time. The accuracy of the mechanical processing of the automatic oxygenation and deflation apparatus is relatively high. If the oxygenation head and the oxygen warhead have poor cooperation, the oxygenation time is not oxygenated, and the deflation time is not deflated and the decompression is performed simultaneously. The demand is relatively high, requiring that the pressure reducing valve cannot run the watch (that is, how much MPa is set is the number of MPa, and there can be no change). If the stopwatch is run, it will seriously threaten the use of safety, and lowering the speed will affect the test results. small.

The control method also has great development. It is controlled by a single-chip computer and also controlled by a general-purpose computer. It has a computer to control a thermostatic cylinder, and a computer controls two thermostatic cylinders or controls four thermostatic cylinders. There are at most Control the eight thermostatic cylinders.

The oxygen bomb was changed from a three-headed oxygen bomb to a single-headed oxygen bomb. The other electrodes were mounted on the lid of a thermostatic cylinder. This way, the amount was changed to greatly simplify the structure of the oxygen bomb. The operation is more convenient and the fault will be more and more. less.