Liquid substances
Semi-fluid substances are dried in their natural form. Large
amount of grease (fat) occurring in some of substances makes
moisture content determination difficult. In such case it is
recommended to use additional components, which increase
sample’s active surface and aid moisture content releasing
process from a sample. Such components are: high-silica sand,
blotting paper and filter. Prior to drying, initially dry the additional
component, so that its humidity is close to zero.
Solid substances
Depending on solid object’s structure (dense or loose), moisture
content determining process may take short or long time. The size
of solid’s surface determines the speed of drying process, and
measurement reliability. Thus, the surface of a solid object should
be as large as possible. Since solid objects release moisture
through their outer surface, sample thickness is another important
factor.
16. SELECTION OF DRYING PROCESS PARAMETERS
16.1. Optimum Sample Mass
Sample mass influences the accuracy of measurement result and measurement time. Higher
mass of a sample causes higher amount of water (moisture content) which needs to
evaporate, and therefore the measurement takes more time.
Obtaining short measurement time is possible in case of small sample mass, but sample
mass cannot be too small, as it may negatively influence required measurement accuracy.
16.2. Influence of Sample Mass on Measurement Repeatability
Sample mass considerably influences repeatability of measurement results obtained on a
moisture analyzer. Relation between sample mass and repeatability is presented in a table
below.
The above data refers to a model, uniform sample, containing no moisture due to the
evaporation process and showing no signs of decomposition (e.g. wet high-silica sand).
The results uncertainty cannot be avoided, this is due to sample nature and moisture
analyzer repeatability. In practice, it means that obtained measurement result may exceed
repeatability values provided above.
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