申論題

Problem 10 Fill-in-the-Blank (10 points)
0.126 kg/s of a solid product containing 4 per cent water is produced in a dryer from a wet feed containing 42 per cent water on a wet basis. Ambient air at 294 K and of40 per cent relative humidity is heated to 366 K in a preheater before entering the dryer from which it leaves at 60 per cent relative humidity. Assuming that the dryer operates adiabatically, what must be the flowrate of air to the preheater (a) 2pt ? and how much heat must be added to the preheater (b) 3pt ? Conditions change if the air enters the dryer at 340 K and sufficient heat is supplied within the dryer so that the air again leaves at 340 K with a relative humidity of 60 per cent, what must be the flowrate of air to the preheater (c) 2pt ? and how much heat must be added to the preheater (d) 3pt ? (Hint. The following humidity chart can be used)