A bayonet cooleris used to reduce the temperature ofa

Chapter 8, Problem 8.104

(choose chapter or problem)

A bayonet cooleris used to reduce the temperature ofa pharmaceutical fluid. The pharmaceutical fluid flowsthrough the cooler, which is fabricated of 10-mm-diameter, thin-walled tubing with two 250-mm- longstraight sections and a coil with six and a half turnsand a coil diameter of 75 mm. A coolant flows outsidethe cooler, with a convection coefficient at the outsidesurface of ho?500 W/m2?K and a coolant tempera-ture of 20C. Consider the situation where the pharma-ceutical fluid enters at 90C with a mass flow rate of 0.005 kg/s. The pharmaceutical has the followingproperties: ??1200 kg/m3, ??4?10?3N?s/m2,cp?2000 J/kg?K, and k?0.5 W/m?K. (a) Determine the outlet temperature of the pharma- ceutical fluid.(b) It is desired to further reduce the outlet tempera-ture of the pharmaceutical. However, because thecooling process is just one part of an intricate pro-cessing operation, flow rates cannot be changed. Ayoung engineer suggests that the outlet temperaturemight be reduced by inserting stainless steel coiledsprings into the straight sections of the cooler withthe notion that the springs will disturb the flow adja-cent to the inner tube wall and, in turn, increase theheat transfer coefficient at the inner tube wall. Asenior engineer asserts that insertion of the springsshould double the heat transfer coefficient at thestraight inner tube walls. Determine the outlet tem-perature of the pharmaceutical fluid with the springsinserted into the tubes, assuming the senior engineeris correct in his assertion.(c) Would you expect the outlet temperature of thepharmaceutical to depend on whether the springshave a left-hand or right-hand spiral? Why?