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Wright State UniversityDepartment of Mechanical and Materials EngineeringSpring 2016ME 3360/5360 HEAT TRANSFER: EXAM 2Open Book, Closed Notes, Do Not Write on this SheetShow All Work for Partial CreditProblem 1 (9 points): When a thermocouple (a temperature sensing device that is shaped like a sphere) ismoved from one medium to another medium at a different temperature, the thermocouple must be givensufficient time to come to thermal equilibrium with the new conditions before a reading is taken. Consider a0.10-cm-diameter copper/constantan thermocouple originally at 150 C. How long does it take for thethermocouple to read within 1.0% of the correct temperature when it is suddenly immersed in air at 40 C, wherethe convective heat transfer coefficient is h 10 W/m2-K?Problem 2 (7 points): Estimate the minimum depth xm at which one must place a water main below thesurface of the earth to avoid freezing. The soil is initially at a uniform temperature of 20 C. Assume that underthe worst conditions anticipated it is subjected to a surface temperature of 15 C for a period of 60 days. Usethe following properties for soil:ρ 2050 kg/m3k 0.52 W/m-K𝛼 cp 1840 J/kg-K𝑘 0.138 10 6 m2 /s𝜌𝑐𝑝Problems 3 and 4 are on back of this page.

Problem 3 (6 points): The top surface of a metal plate (kplate 237 W/m-K) is being cooled by air (kair 0.243W/m-K) while the bottom surface is exposed to a hot steam at 100 C with a convection heat transfer coefficientof 30 W/m2-K. If the bottom surface temperature of the plate is 80 C, determine the temperature gradient in theair and the temperature gradient in the plate at the top surface of the plate.Problem 4 (8 points): A 5-m 5-m flat plate maintained at a constant temperature of 80 C is subjected toparallel flow of air at 1 atm, 20 C, and 10 m/s. The total drag force acting on the upper surface of the plate ismeasured to be 2.4 N. Using the momentum-heat transfer analogy, determine the average convection heattransfer coefficient, and the rate of heat transfer between the upper surface of the plate and the air.

ME 3360/5360 HEAT TRANSFER: EXAM 2 Open Book, Closed Notes, Do Not Write on this Sheet Show All Work for Partial Credit Problem 1 (9 points): When a thermocouple (a temperature sensing device that is shaped like a sphere) is moved from one medium to another medium a