Question

B2 The University has decided to commission a large iconic sculpture which is to be erected in place of the old library. The structure is intended to acknowledge the industrial heritage of the region whilst at the same time linking to the University's motto "Per Ardua Ad Alta" (through efforts to high things"). An (unimaginative) artist is suggesting that a large circular chimney (diameter D, height h) should be built using the bricks from the old library. Concern has been expressed that when the wind velocity reaches 10ms, vortex shedding (i.e., the vortices created as the wind flows around the chimney) may cause structural problems Assuming the shedding frequency (f) depends on the dimensions of the chimney, the velocity of the air (V) and the kinematic viscosity (v), show that the follow expression is valid a) [14] 1) Re b) In order to investigate this issue further you decide to undertake a series of wind tunnel experiments using a 1/20h scale model. Noting the above expression, what wind speed is required in the tunnel? If a shedding frequency of 800Hz is measured in the tunnel, what frequency would you expect the vortices to be observed on the sculpture? [10] C2 a) A central heating "radiator" has a surface temperature of 70 °C and heats a room maintained at 25 °C. The following data are available 5.67 x 10-8 W/m2 Ka PAIR 1.22 ka/m3 HAIR 1.836 x 109 kg/m s KAIR 0.03 W/m k g 9.81 m/s Pr 0.83 you may also find the following useful where B1T i) Determine the heat transfer per square metre from the radiator due [4] to radiation (qrad). Assume black body behaviour Use the following correlation for natural convection NuL-0125G 13 Pr1'3, to determine the heat transfer per square metre from the radiator due to natural convection (Qconv) ii) [5] ii) Calculate the total heat transfer from the radiator per square metre [4] (Qtotal) and determine the percentage contributions of radiation and natural convection to heat transfer b) A cylinder, closed by a piston, has a volume of 0.03m and contains air at 1 [13] bar and 15°C. The air is compressed isentropically to one quarter of its original volume. t is then cooled in a reversible constant pressure process until the temperature falls to its initial value. Finally, the air is expanded isentropically back to 1 bar. Find the final temperature and the net work done during the sequence of processes

Answer 1

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