Utilities
Every point of residual moisture left in the load is bought again at the dryer, at about a kilowatt-hour per hundred kilos.
— x
Drying energy avoided per unit of extractor energy
Moisture is expressed on the dry mass, which is why a figure above one hundred per cent is ordinary rather than an error: a hundred kilos of dry cloth carrying a hundred and twenty per cent is holding a hundred and twenty kilos of water. The drying energy is latent heat alone, at 2257 kJ per kilogram, divided by a stated thermal efficiency. That makes it a floor and not a forecast: it counts nothing for heating the cloth and the machine to temperature, nothing for the air changes a dryer needs to carry vapour away, and nothing for the last few per cent of moisture, which comes out far more slowly than the first. A real dryer will use more than this figure and never less. Residual moisture is deliberately an input rather than something predicted from g-force and time, because that relationship depends on the fibre, the construction, the batch density and how the load sits in the basket, and no general curve for it belongs in a calculator. Measure it off the machine, or enter the figure the process is specified to. The g-force is geometry and holds regardless: it is the force at the basket wall, and cloth packed toward the centre sees less.
Hydroextraction: G-Force, Residual Moisture & Drying Load — free, with the formula and a worked example, at Textile School.