Assume that the thickness of the food on the drum is 0.3 mm and the thermal conductivity of the food is 0.55 J m-1 s-1 °C-1. If the drum, 1 m diameter and 1 m in length, is rotating at 2 rev/min and the food occupies three-quarters of the circumference, estimate the moisture content of the film being scraped off. Assume the critical moisture content for the food material is 14% on a dry basis, and that conduction heat transfer is through the whole film thickness to give a conservative estimate.
Total quantity of material on drum
Assuming a density
of the food paste of 1000 kg m3,
Overall resistance to heat transfer, 1/U
Residence time of food on drum: at 2 rev min
1 revolution takes 30s, but the material is on for ¾ rev.
Residence time =
(3/4) x 30
Residual water =
(0.53 - 0.495)
= 0.035/(0.18 + 0.035)
Drying > DRYING EQUIPMENT
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