A windmill takes a fraction of the wind kinetic energy out as power on a shaft. In what manner does the temperature and wind velocity influence the power? Hint: write the power as mass flow rate times specific work.

# Category: Statistics

## A wind turbine is rotating at 15 rpm

A wind turbine is rotating at 15 rpm under steady winds flowing through the turbine at a rate of 42,000 kg/s. The tip velocity of the turbine blade is measured to be 250 km/h. If 180 kW power is produced by the turbine, determine, (a) The average velocity of the air and, (b) The conversion efficiency of the turbine. Take the density of air to be 1.31 kg/m3.

## A window air conditioner that consumes 1 kW

A window air conditioner that consumes 1 kW of electricity when running and has a coefficient of performance of 4 is placed in the middle of a room, and is plugged in. The rate of cooling or heating this air conditioner will provide to the air in the room when running is,(a) 4 kJ/s, cooling, (b) 1 kJ/s, cooling, (c) 0.25 kJ/s, heating,(d) 1 kJ/s, heating, (e) 4 kJ/s, heating

## A freezer is maintained at 20°F

A freezer is maintained at 20°F by removing heat from it at a rate of 75 Btu/min. The power input to the freezer is 0.70 hp, and the surrounding air is at 75°F. Determine,(a) The reversible power,, (b) The irreversibility, and, (c) The second-law efficiency of this freezer.

## A windmill with rotor diameter of 30 m takes 40%

A windmill with rotor diameter of 30 m takes 40% of the kinetic energy out as shaft work on a day with 20oC and wind speed of 30 km/h. What power is produced?

## A water-filled reactor of 50 ft3 is at 2000 lbf/in

A water-filled reactor of 50 ft3 is at 2000 lbf/in 2, 550 F and located inside an insulated containment room of 5000 ft3 that has air at 1 atm. and 77 F. Due to a failure the reactor ruptures and the water fills the containment room. Find the final pressure.

## A gas contained within a piston-cylinder assembly undergoes thre

A gas contained within a piston-cylinder assembly undergoes three processes in serial:,Process1-2: Compression with PV = constant from p1= 1 bar V1 = 1.0 m3 to V2 = 0.2m3.,Process 2-3: Constant-pressure expansion to V3 = 1.0 m3.,Process 3-1: Constant Volume,Sketch the processes in series on a p-V diagram labeled with pressure and volume values at each numbered state.

## A 95 wt% Pt-5 wt% Ni alloy is known to have an electrical

A 95 wt% Pt-5 wt% Ni alloy is known to have an electrical resistivity of 2.35 x 10-7 ohm-m at room temperature (25oC). Calculate the composition of a platinum-nickel alloy that gives a room-temperature resistivity of 1.75 x 10-7 ohm-m. The room-temperature resistivity of pure platinum may be determined from the data in Table 18.1; assume that platinum and nickel form a solid solution.

## A water-heater is covered up with insulation boards over a total

A water-heater is covered up with insulation boards over a total surface area of 30 ft2. The inside board surface is at 175 F and the outside surface is at 70 F and the board material has a conductivity of 0.05 Btu/h ft F. How thick a board should it be to limit the heat transfer loss to 720 Btu/h?,