Mechanical Engineering Answers

30. Compute the pressure drop of 35oC air flowing with a mean velocity of 7 m/s in a circular sheet-metal duct 450 mm in diameter and 25 m long. Use a friction factor, f = 0.04, and Pair = 1.3799 kg/m3.

29. A coil has an inlet temperature of 70oF and outlet of 80oF. If the mean temperature of the coil is 120oF, find the bypass factor of the coil.

28. Compute the specific volume of an air-vapor mixture in cubic meters pre kilogram of dry air when the following conditions prevail : t = 45oC, w = 0.015 kg/kg, and Pt = 100 kPa.

27. A classroom that normally contains 40 people is to be air-conditioned with window air-conditioning units of 5 KW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 KJ/hr. There are 10 light bulbs in the room, each with a rating of 100 watts. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000 KJ/hr. If the room air is to be maintained at a constant temperature of 21oC, determine the number of window air-conditioning units required.

26. An auditorium seating 1600 people is to be maintained at 80oF dry bulb and 65oF wet bulb temperature

when outdoor air is at 91oF dry bulb and 75oF wet bulb. Solar heat load is 120,000 Btu/hr and supply air is

at 60oF, determine the amount of supply air. (Use sensible heat load of 225 Btu/hr per person).

A vibration damper unit is composed of a rubber cylinder of diameter d compressed inside of a wrought-iron cylinder by a force F applied to the steel rod. Develop, in terms of d, F, and Poisson’s ratio ν for the rubber, the following expression for the lateral pressure p between the rubber and the wrought-iron cylinder.

Compute the value of 𝑝 for the following data: 𝑑 = 63.5 𝑚𝑚, 𝜈 =

0.5, 𝑎𝑛𝑑 𝐹 = 9 𝑘𝑁.

5. Compute for the enthalpy, internal energy, and entropy of steam at 72oC and 93%

quality.

10. A supercritical power generates steam at 25 Mpa and 560℃. The condenser pressure is 7 kpa. Determine

the exit quality of steam if it expands through a turbine in this power plant.

9. Steam enters a turbine at 1.4 Mpa and 320℃. The turbine internal efficiency is 70%, and the total requirement is 800 kw. The exhaust is to the back pressure system, maintains at 175kpa. Find the stean flow rate.

8. A steam power plant operates on the Rankine cycle. The steam enters the turbine at 7 Mpa and 550℃ with a velocity of 30 m/s. it discharges to the condenser at 20 kpa with a velocity of 90 m/s. Calculate the net work in kw for a flow of 37.8kg/s.