Lynne Wong's PhD thesis

approached, that is, either by adsorption to constant mass or desorption of the moisture at
105 °C after adsorption. A higher value is obtained when a wet material loses moisture by
desorption than when a dry material gains it by adsorption (McMinn and Magee, 2003; Al-
Muhtaseb et al., 2004b; Arslan and Toğrul, 2005), in which case, the material is said to
exhibit hysteresis.
In the dynamic method, air is moved mechanically and is often moistened by air
conditioning units (Brooker et al., 1992; Viswanathan et al., 2003). The pre-dried sample
may be placed in a U-tube through which is drawn a continuous flow of controlledhumidity
air. The equipment is maintained at constant temperature. Again the sample is
weighed periodically until a constant mass is reached.
5.5.2 Manometric method
The manometric method measures the vapour pressure of water in the vapour space
surrounding the test sample. The whole system is maintained at constant temperature and
the test sample will lose water to equilibrate with the vapour space. This will be indicated
by the difference in height on the manometer (Gal, 1981).
5.5.3 Hygrometric method
The hygrometric method measures the equilibrium relative humidity of air in contact with
the test sample, at a given moisture content. Dew-point hygrometers detect the
condensation of cooling water vapour. Electric hygrometers measure the change in
conductance or capacitance of hygrosensors. Most hygrosensors are coated with a
hygrocopic salt, such as lithium chloride, which absorbs moisture from the test sample
(Gal, 1981).
5.6 DETERMINATION OF ADSORPTION ISOTHERMS FOR COMPONENT
PARTS OF CANE VARIETY R 570
The aims of the work described in this chapter were (i) to determine the water adsorption
for the fibres of nine component parts of variety R 570 of two ages (52 and 36 weeks) at
four temperatures (30, 45, 55 and 60 °C) by means of a static method (ii) to model the
sorption behaviour by testing the goodness of fit of 17 commonly used models and (iii) to
evaluate the constants of the isotherm models.
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