In a small textile industry processing unit, dyed and washed cotton yarn is dried in an insulated chamber through which hot air is blown. Bundles of yarn are kept suspended from the roof of the chamber. 200kg of wet yarn with 1kg water per kg of yarn is taken in a batch. Air at 25^oC (wet bulb temperature=15^oC) is heated to 65^oC before it enters the chamber. Assume that the airflow rate is large enough for its temperature and humidity to remain essentially constant. From the operating data is known that the constant rate of drying under the given conditions is 0.5kg moisture per hour per kg of dry yarn. The critical moisture, X_c = 0.15 and the equilibrium moisture X*=0.001. Calculate the time required for drying the yarn to final moisture of X_f = 0.0033 if the falling rate of drying is linear in X.