Sand particles (sg = 2.7), approximately spherical with diameters from 100 to 250 µm are introduced into a water tank at 20˚c. what is the velocity of the slowest settling particles? what is the velocity of the fastest settling particles? this same collection of sand is introduced into an upward flowing stream of water at 20˚c. what is the minimum water velocity that will carry all of the particles upward?

Along 8-cm diameter steam pipe whose external surface temperature is 900c connects two buildings. the pipe is exposed to ambient air at 70c with a wind speed of 50 km/hr blowing across the pipe. determine the heat loss from the pipe per unit length. (b) air at 500c enters a section of a rectangular duct (15 cm x 20 cm) at an average velocity of 7 m/s. if the walls of the duct are maintained at 100c. a) the length of the tube for an exit temperature of the air to be 40 0c. b)the rate of heat transfer from the air. c) the fan power needed to overcome the pressure drop in this section of the duct.