Abstract
In one manufacturing process ICI, Nobel Division it became necessary to measure the moisture content, around 60 per cent, of a hot, sticky solid. The normal laboratory method involved drying in an oven at 100°C for 16 hours, the lengthy time required being due to the fact that on drying the material forms a hard external skin which greatly reduces the rate of loss of water. Such a delay meant that the results were of little value in the day to day running of the plant, and a rapid method was sought. Among numerous methods which were considered, in some cases tested, and rejected were measurement of conductivity, dielectric constant, density and microwave attenuation. The principal difficulty was the intractable condition of the sample and the fact that it contained much occluded air.
Finally the effect of radio frequency heating was tried, and it was found that a 5 gm sample could be dried completely in 10 min. This was used as the basis for a successful laboratory method for determining moisture and subsequently a request was received for an automatic instrument operating on this principle and capable of being used by unskilled labour.
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