Instant coffee is dried in a spray dryer. Calculate the mass transfer coefficient on the surface of a coffee droplet that falls through the air in the spray dryer at the initial stages of drying if the diameter of the droplet is 0.5 mm, the relative velocity between the air and the droplet is 50 m/s, and the air temperature is 180C. Assume that the droplet surface temperature is at 60 C. Note 1: use the air properties equations from heat transfer lectures to calculate air properties ( and ) at the temperatures of the question. What temperature should you use? Note 2: for DAB of water vapor in air, at 25C and 1 atm, it is 2.610-5 m2 /s. You may then estimate the DAB at other temperatures using DAB ~ T1.5, where T is in K