Application Notes:
Pro Tips: Examining Tanks and Vessels |
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Normally, people in industry use level indicators to tell how much product is inside a tank. So why do so many of them also use thermal imagers (infrared cameras) to do the same thing? It's because of the horror stories.
Typical thermal images seem to exhibit "x-ray vision" they show the contents of the container and give quantifiable verification of the material inside. Of course, x-rays aren't actually involved. Instead, the images show apparent thermal differences.
Because of that human deductive element, the meaningfulness of the examination depends on the person's knowledge and the type of result they desire.
Since these tanks are located outside, the tanks and their contents undergo thermal cycling. During the daylight hours the tank and contents absorb heat from the sun and the air, as well as from whatever processing might be taking place. During the night, the tank and the contents are giving up heat to the surrounding air.
These metal tanks in particular are un-insulated and highly thermally conductive. As night falls, the headspace begins to cool quickly while the liquid volume cools much more slowly. That makes the thermal gradient between the liquid and headspace readily apparent through a thermal imager.
Tanks hold materials other than liquids, too. Dry bulk materials tend to pile up against the sides and have very uneven levels. Thermal imagers enable you to see these irregularities (see Figure 3).
Industrial processes often involve other kinds of vessels that don't look like tanks, often referred to as "heat exchangers". The most common is a steam radiator.
While furnaces and ovens are often thought of as vessels and are examined for heat loss, another interesting industrial vessel is a process freezer. The freezer in this example was constructed to flash freeze meat patties.
Thermal imagers can analyze a great many more things than just temperature, once you embrace the spectral and thermal dynamics of your materials and processes. Start by considering how the thermal properties of materials are exhibited in different ways.
Moisture content is a most interesting parameter, because moisture can be measured directly using infrared analyzers. When light hits a surface that contains moisture, the moisture absorbs infrared radiation in the region of 1.8 microns. By measuring infrared absorbance, you can measure actual surface moisture.
The application of thermal imagers is limited only by the knowledge of the person using the equipment. Thermal imagers are rapidly becoming more economical and easy to use, but the camera is only as good as...
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