Thermal measuring and testing – Temperature measurement – By a vibratory effect
Patent
1989-10-18
1992-08-25
Shoap, Allan N.
Thermal measuring and testing
Temperature measurement
By a vibratory effect
374117, 374 31, 356432, 73657, 73602, 73 2401, G01K 1122, G01K 1126, G01N 2900
Patent
active
051413310
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process and to an apparatus for measuring small temperature changes in a gas, as well as the uses thereof in optical spectroscopy calorimetry.
BACKGROUND OF THE INVENTION
A large number of different temperature measuring methods exists. For example, temperatures can be measured by means of thermal expansion (liquid thermometers, bimetallic strain gauges), the temperature dependence of the electrical resistance (resistance thermometers) or the thermoelectric voltage at the interface of different metals (thermocouple). Other methods are based on electromagnetic irradiation (infrared radiometers, pyrometers). These measuring methods are very suitable for determining the temperature in the case of solids and liquids.
Apart from gas expansion measurements performed in the gas thermometer, gas temperatures are generally indirectly measured, by bringing the gas into contact with a solid or liquid thermometer. Due to the poor thermal conductivity of gases and the low thermal energy transfer from the gas to the thermometer, such temperature measurements are relatively slow.
On the basis of the ideal gas law, the temperature of an enclosed gas can be determined via its pressure. The pressure fluctuations occurring in the case of a periodic gas temperature change, can be determined in a highly sensitive manner by means of a microphone. However, due to the aforementioned low thermal conductivity of gases, the temperature changes which occur are generally very small, so that it would be necessary to operate the microphone at very low frequencies in the subhertz range. However, microphones are not very suitable for such frequencies or even for static measurements. It is therefore of interest to seek a process permitting a direct and quasi-static measurement of the gas temperature.
Numerous uses are conceivable where it is desired to measure small temperature changes in a gas. For example, in optical gas spectroscopy, it is of interest to investigate the interaction of the radiation field with a gas. On the basis of a periodic light and in particular infrared irradiation, periodic temperature fluctuations occur in the gas.
Different devices exist for measuring the light power absorbed in a gas. The greatest significance is attached to solid radiation sensors based on the photoelectric effect. Using such sensors, use is generally made of the so-called extinction method. The absorption of the material being investigated is determined as a result of the comparison of two beams, one beam passing through the material and the other passing unimpeded to the detector. However, as opposed to this indirect method, preference is often given to a direct method, which consists of directly measuring the light absorption-caused signal. As stated, it has proved very satisfactory in this connection to measure pressure fluctuations building up in a closed cell on absorbing intensity-modulated light. This so-called photoacoustic effect is characterized by a very high sensitivity. As the measurement takes place with the aid of a microphone, it is not possible to prevent acoustic interference to the measurement, and in many cases this is not acceptable.
Another possible use of a direct gas temperature measuring method is calorimetry.
Calorimetric research is carried out in the standard calorimeter in an aqueous ambient. The measuring material is either placed directly in the water, or it is immersed in the calorimeter water in a closed vessel. The latter is located in a water tank thermally separated from the environment. The calorimetric test is based on following the temperature of this calorimeter water, to which the measuring material gives off its heat which is liberated, for example, by a chemical reaction. It must be borne in mind that the temperature distribution within the calorimeter must be as homogeneous as possible and must also coincide with that of the material being analyzed. For this purpose it is advantageous to use a stirrer.
Water is suitable as the heat transfer mediu
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Melchior Hans
Oehler Oscar
Farley Walter C.
Gutierrez Diego F. F.
Shoap Allan N.
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