PPE Looks Fam 2 Flashcards by Jonathan cabrito

A single acting, twin cylinder, Ammonia compressor with bore equal to stroke is driven by an engine at 250 rpm. The machine is installed in a chilling plant to produce 700 kW of refrigeration at -18°C evaporating temperature. At this temperature the cooling effect per kg mass is 1160 kJ. The specific volume of vapor entering the compressor is 0.592 m3 per kilogram. Assume 85% volumetric efficiency, determine the bore in mm.
A. 400 mm
B. 300 mm
C. 450 mm
D. 500 mm

400 mm

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If the specific weight of a liquid is 58.5 lbf per cubic foot, what is the specific volume of the liquid in cm3/g?
A. 0.5321 cm3/g
B. 0.6748 cm3/g
C. 0.9504 cm3/g
D. 1.0675 cm3/g

1.0675 cm3/g

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How long must a current of 5.0 amperes pass through a 10 ohm resistor until a charge of 1200 coulombs passes through?
A.1 min
B. 2 min
C. 3 min
D. 4 min

4 min

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A boy pulls a sled with a mass of 20 kg horizontally over a surface with a coefficient of friction of 0.20. It takes him 10 minutes to pull the sled 100 yards. What is his average power output over these 10 minutes?
A. 4 W
B. 6 W
C. 8 W
D. 10 W

6 W

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A copper bar is 90 centimeters long at 86°F. What is the increase in its length when the bar is heated to 95°F? The linear expansion coefficient for copper, α, is 1.7 x 10-5/°C.
A. 2.12 x 10 -5 m
B. 3.22 x 10 -5 m
C. 5.25 x 10 -5 m
D. 7.65 x 10 -5 m

7.65 x 10 -5 m

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Calculate the energy transfer rate across a 6” wall of firebrick with a temperature difference across the wall of 50°C. The thermal conductivity of firebrick is 0.65 BTU/hr-ft-°F at the temperature of interest.
A. 112 W/m2
B. 285 W/m2
C. 369 W/m2
D. 429 W/m2

369 W/m2

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A house has brick walls 15 millimeters thick. On a cold winter day, the temperature of the inner and outer layers of the walls are measured and found to be 20°C and -12°C, respectively. If there is 120 m2 of exterior wall of race, and the thermal conductivity of bricks is 0.711 J/m-s-
°C, how much heat is lost through the walls per hour?
A. 182 J
B. 12.5 kJ
C. 655 kJ
D. 655 MJ

655 MJ

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A power of 6 kW is supplied to the motor of a crane. The motor has an efficiency of 90%. With what constant speed does the crane lift the 800 lbf weight?
A. 0.09 m/s
B. 0.32 m/s
C. 0.98 m/s
D. 1.52 m/s

1.52 m/s

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An engine has an efficiency of 26%. It uses 2 gallons of gasoline per hour. Gasoline has a heating value of 20,500 BTU/lbm and a specific gravity of 0.8. What is the power output of the engine?
A. 0.33 kW
B. 20.8 kW
C. 26.0 kW
D. 41.7 kW

20.8 kW

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Two liters of an ideal gas at a temperature of T1 = 25°C and a pressure of P1 = 0.101 MPa, are in a 10 cm diameter cylinder with a piston at one end. The piston is depressed so that the cylinder is shortened by 10 centimeters. The temperature increases by 2°C. What is the change in pressure?
A. 0.156 MPa
B. 0.167 MPa
C. 0.251 MPa
D. 0.327 MPa

0.167 MPa

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The average power output of a cylinder in a combustion engine is given by:
where:
p = average pressure on the piston during the stroke L = length of the piston stroke
A = area of the piston head
N = number of strokes per second
An 8-ylinder engine has the following specifications p = 283 kPa
L = 14 cm
d = diameter of piston head = 12 cm N = 1500 strokes/min
What is the average power output of this engine?
A. 89.5 N/s
B. 89.5 kW
C. 89.5 x 103 J-m/s
D. 89.5 kJ

89.5 kW

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is the power required to transfer What 97,000 coulombs of charge through a potential rise of 50 volts in one hour?
A. 0.5 kW
B. 0.9 kW
C. 1.3 kW
D. 2.8 kW

1.3 kW

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A current of 7 amperes passes through a 12 ohm resistor. What is the power dissipated in the resistor?
A. 84 w
B. 0.59 hp
C. 0.79 hp
D. 7 hp

0.79 hp

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What is the pressure at point A in the tank if h = 2 feet? (g = 32.2 ft/s2 and ρ = 1.94 slug/ft3)
A.75 lbf/ft2
B. 85 lbf/ft2
C. 100 lbf/ft2
D. 125 lbf/ft2

125 lbf/ft2

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A pipe has a diameter 4” at section AA, and a diameter of 2” at section BB. For an ideal fluid flow, the velocity given is 1 ft/s at section AA. What is the flow velocity at section BB?
A. 4 ft/s
B. 0.5 ft/s
C. 1.0 ft/s
D. 2.0 ft/s

4 ft/s

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A mixing tank mixes two inlet streams containing salt. The salt concentration in stream 1 is 5% by weight, at stream 2 it is 15% by weight. Stream 1 flows at 25 kg/s, and stream 2 flows at 10 kg/s. There is only one exit stream. Find the salt concentration in the exit stream.
A. 5%
B. 8%
C. 11%
D. 13%

11%

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Water is pumped at 1 m3/s to an elevation 5 meters through a flexible hose using a 100% efficient pump rated at 100 kilowatts. Using the same length of hose, what size motor is needed to pump 1 m3/s of water to the tank, with no elevation gain? In both cases, both ends of the hose are at the same temperature and pressure. Neglect kinetic energy effects.
A. 51 kW
B. 22 kW
C. 36 kW
D. 43 kW

51 kW

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The Reynold’s number of a sphere falling in air is 1x106. If the sphere’s radius is 1 ft, what is its velocity? (ρ = 0.00234 slug/ft3, μair = 3.8x10-7 lbf-s/ft2).
A. 2.5 ft/s
B. 5.1 ft/s
C. 40.6 ft/s
D. 81.2 ft/s

81.2 ft/s

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The flow rate of water through a cast iron is 5000 gallons per minute. The diameter of the pipe is 1 foot, and the coefficient of friction is f = 0.0173. What is the pressure drop over a 100 foot length of pipe?
A. 21.078 lbf/ft2
B. 23.78 lbf/ft2
C. 337.26 lbf/in2
D. 337.26 lbf/ft2

337.26 lbf/ft2

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A cylindrical flash tank mounted with its axis horizontal is used to separate liquid ammonia from ammonia vapor. The ammonia bubbles through the liquid with 70 m3/min leaving the disengaging surface. The disengaging rate is limited to 60 m/min and the liquid level is to operate with the liquid level one-third to the diameter from the top. Determine the diameter if the tank is 1.5 m long.
A. 830 mm
B. 730 mm
C. 860 mm
D. 760 mm

830 mm

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A 150 Hp motor is used to drive the compressor. If the heat loss from the compressor is 25 kW and the mass flow rate of the refrigerant entering the compressor is 0.50 kg/s, determine the difference of the enthalpies between the inlet and outlet of the compressor.
A. 143.80 kJ/kg
B. 153.80 kJ/kg
C. 173.80 kJ/kg
D. 183.80 kJ/kg

173.80 kJ/kg

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To cool farm products, 300 kg of ice at -4.4°C are placed in bunker. Twenty four hours later the ice has melted into water at 7.2°C. What is the average rate of cooling provided by the ice in kJ/hr?
A. 2679.28 kJ/hr
B. 5679.28 kJ/hr
C. 3679.28 kJ/hr
D. 4679.28 kJ/hr

4679.28 kJ/hr

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If the load on water-cooled condenser is 150,000 Btu/hr and the temperature rise of the water in the condenser is 10°F, what is the quantity of water circulated in gpm?
A. 30 GPM
B. 40 GPM
C. 20 GPM
D. 50 GPM

30 GPM

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The load on a water-cooled condenser is 90,000 Btu/hr. if the quantity of water circulated through the condenser is 15 gpm, determine the temperature rise of the water in the condenser.
A. 12°F
B. 14°F
C. 16°F
D. 18°F

12°F

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The weight of ammonia circulated in a machine is found to be 21.8 lb/hr. if the vapor enters the compressor with a specific volume of 9.6 ft3/lb, calculate the piston displacement, assuming 80% percent volume efficiency. A. 261.6 ft3/hr B. 271.6 ft3/hr C. 281.8 ft3/hr D. 291.6 ft3/hr

261.6 ft3/hr

A single-stage ammonia compressor is producing 10 tons of refrigeration and the power consumed is 15 Hp. Suction pressure is 25 psi, condensing pressure is 180 psi. Brine temperature is 20°F off brine cooler. Determine the actual coefficient of performance. A. 10.14 B. 11.14 C. 12.14 D. 13.14

13.14

In an ammonia condensing machine (compressor plus condenser) the water used for condensing is 55°F and the evaporator is at 15°F. Calculate the ideal COP. A. 11.875 B. 12.875 C. 10.875 D. 13.875

11.875

A cubical tank of 2 m sides is constructed of metal plate 12 mm and contains water at 75°C. The surrounding air temperature is 16°C. Calculate the overall heat transfer coefficient from water to air. Take the coefficient of thermal conductivity of the metal as 48 W/m-K, the coefficient of heat transfer of water is 2.5 kW/m2-K and the coefficient of heat transfer of the air is 16 W/m2-K. A. 15.84 W/m2-°C B.14.84 W/m2-°C C. 16.84 W/m2-°C D. 13.84 W/m2-°C

15.84 W/m2-°C

One insulated wall of a cold-storage compartment is 8 m long by 2.5 m high and consists of an outer steel plate 18 mm thick. An inner wood wall is 22.5 m thick. The steel and wood are 90 mm apart to form a cavity which is filled with cork. If the temperature drop across the extreme faces of the composite wall is 15°C. Calculate the heat transfer per hour through the wall and the temperature drop across the thickness of the cork. Take the coefficients of thermal conductivity for steel, cork and wood as 45, 0.045, and 0.18 W/m-K respectively. A. 408.24 kJ, 12.12°C B. 708.24 kJ, 11.12°C C. 608.24 kJ, 13.12°C D. 508.24 kJ, 14.12°C

508.24 kJ, 14.12°C

A cold storage compartment is 4.5 m long by 4 m wide by 2.5 m high. The four walls, ceiling and floor are covered to a thickness of 150 mm with insulating material which has a coefficient of thermal conductivity of 5.8x10-2W/m-K. Calculate the quantity of heat leaking through the insulation per hour when the outside and inside face temperature of the material is 15°C and -5°C respectively. A. 2185.44 kJ B. 2285.44 kJ C. 3185.44 kJ D. 4185.44 kJ

2185.44 kJ

A furnace wall consists of 35 cm firebrick (k = 1.557 W/m-K), 12 cm insulating refractory (k = 0.346) and 20 cm common brick (k = 0.692) covered with 7 cm steel plate (k = 45). The temperature at the inner surface of the firebrick is 1,230°C and at the outer face of the steel plate is 60°C. Atmosphere is 27°C. What is the value of the combined coefficient for convection and radiation from the outside wall? A. 31.13 W/m2-K B. 30.13 W/m2-K C. 41.3 W/m2-K D. 40.13 W/m2-K

41.3 W/m2-K

Hot gases at 280°C flow on one side of the metal plate 10 mm thickness and air at 35°C flows on the other side. The heat transfer coefficient of the gases is 31.5 W/m2-K and that of the air is 32 W/m2-K. Calculate the over-all heat transfer coefficient. A. 15.82 W/m2-K B. 16.82 W/m2-K C. 14.82 W/m2-K D. 17.82 W/m2-K

15.82 W/m2-K

The surface temperature of the hot side of the furnace wall is 1200°C. It is desired to maintain the outside of the wall at 38°C. A 152 mm of refractory silica is used adjacent to the combustion chamber and 10 mm of steel covers the outside. What thickness of insulating bricks is necessary between refractory and steel, if the heat loss should be kept at 788 W/m2? Use k = 13.84 W/m-K for refractory silica; 0.15 for insulating brick, and 45 for steel. A. 220 mm B. 240 mm C. 260 mm D. 280 mm

220 mm

An insulated steam pipe located where the ambient temperature is 32°C, has an inside diameter of 50 mm with 10 mm thick wall. The outside diameter of corrugated asbestos insulation is 125 mm and the surface coefficient of still air, ho = 12 W/m2-K. Inside the pipe is steam having a temperature of 150°C with film coefficient hi = 6000 W/m2-K. Thermal conductivity of pipe and asbestos insulation are 45 and 0.12 W/m-K respectively. Determine the heat loss per unit length of pipe. A. 110 W B. 120 W C. 130 W D. 140 W

120 W

A wall with an area of 10 m2 is made of a 2 cm thickness of white pine (k = 0.133 W/m-°C) followed by a 10 cm of brick (k = 0.649 W/m-°C). The pine is on the inside where the temperature is 30°C while the outside temperature is 10°C. Assuming equilibrium conditions exist, what is the temperature at the interface between the two metals? A. 15.65 °C B. 17.64 °C C. 18.21 °C D. 19.31 °C

19.31 °C

With three different quantities x, y, and z of the same kind of liquid of temperatures 9, 21 and 38°C respectively, it is found that when x and y are mixed together the resultant temperature is 17°C and when y and z are mixed together the resultant temperature is 28°C. Find the resultant temperature if x and z were mixed. A. 25.87°C B. 25.92°C C. 20.85°C D. 24.86°C

25.92°C

The journals of a shaft are 380 mm diameter, it runs at 105 rpm and the coefficient of friction between journals and bearings is 0.02. If the average load on the bearings is 200 kN, find the heat generated per minute at the bearings. A. 501.375 kJ B. 505.575 kJ C. 401.375 kJ D. 501.575 kJ

501.575 kJ

A reverse Carnot cycle requires 3 Hp and extracts energy from a lake to heat a house. If the house is kept at 70°F and requires 2000 Btu per minute, what is the temperature of the lake? A. 35.29°F B. 36.29°F C. 39.29°F D. 40.29°F

36.29°F

An oxygen cylinder of volume 2.3 ft3 has a pressure of 2200 psig and is at 70°F. Determine the mass of oxygen in the cylinder. A. 25.66 lbs B. 26.66 lbs C. 27.66 lbs D. 28.66 lbs

28.66 lbs

A group of 50 persons attend a secret meeting in a room which is 12 m wide by 10 m long and a ceiling height of 3 m. The room is completely sealed off and insulated. Each person gives off 150 kCal per hour of heat and occupies a volume of 0.20 m3. The room has an initial pressure of 101.3 kPa and temperature of 16°C. Calculate the room temperature after 10 minutes. Use R = 0.287 kJ/kg-K and Cv = 0.171 kCal/kg-K. A. 33.1°C B. 37.7°C C. 38.7°C D. 31.7°C

33.1°C

One kilogram of wet steam at a pressure of 8 bar (υg = 0.2404 m3/kg, υf = 0.0011148 m3/kg) and dryness of 0.94 is expanded until the pressure is 4 bar (υg = 0.4625 m3/kg, υf = 0.0010836 m3/kg). If expansion follows the law PVn = C, where n = 1.12, find the dryness fraction of the steam at the lower pressure. A. 0.9072 B. 0.4197 C. 0.2260 D. 0.2404

0.9072

2.5 liters of superheated steam at 25 bar and 400 C (υ = 0.1252 m3/kg) is expanded in an engine to a pressure of 0.1 bar (υg = 14.674 m3/kg, υf = 0.0010102 m3/kg) when its dryness fraction is 0.9. Find the final volume of the steam. A. 163.74 liters B. 263.74 liters C. 363.74 liters D. 463.74 liters

263.74 liters

A 1.5 kg of wet steam at a pressure of 5 bar (hf = 640 kJ/kg, hfg = 2109 kJ/kg) dryness 0.95 is blown into 70 liters of water 12°C (h = 50.4 kJ/kg). Find the final enthalpy of the mixture. A. 74.80 kJ/kg B. 84.80 kJ/kg C. 94.80 kJ/kg D. 104.80 kJ/kg

104.80 kJ/kg

A typical industrial fuel oil, C16H32 with 20% excess air by weight. Assuming complete oxidation of the fuel, calculate the actual air-fuel ratio by weight. A. 17.56 kgair/kgfuel B. 15.76 kgair/kgfuel C. 16.75 kgair/kgfuel D. 17.65 kgair/kgfuel

17.65 kgair/kgfuel

A 650 BHP diesel engine uses fuel oil of 28°API gravity, fuel consumption is 0.65 lb/BHP-hr. Cost of fuel is P7.95 per liter. For continuous operation determine the minimum volume of cubical day tank in cm3, ambient temperature is 45° C. A. 4,372,890 cm3 B. 5,987,909 cm3 C. 5,291,880 cm3 D. 7,352,789 cm3

5,291,880 cm3

A diesel electric plant supplies energy for Meralco. During a 24 hr Period, the plant consumed 200 gallons of fuel at 28°C and produced 3930 Kw-hr. Industrial fuel used is 28°API and was purchased at P5.50 per liter at 15.6°C. What should the cost of fuel be produce one kw-hr.? A. P 1.05 B. P 1.10 C. P 1.069 D. P 1.00

P 1.05

A certain coal has the following ultimate analysis: C = 70.5% H = 4.5% O2 = 6% N2 = 1.0% S = 3.0% Ash = 11% Moisture = 4% A stoker fired boiler of 175,000 kg/hr steaming capacity uses this coal as fuel. Calculate the volume of air in m3/hr with air at 60°F (15.6°F) and 14.7 psia (101.325 kPa) the coal is burned with 30% excess air. Boiler efficiency is 70% and factor of evaporation of 1.10. A. 212,861.04 m3/hr B. 221,861.04 m3/hr C. 218,261.04 m3/hr D. 281,261.04 m3/hr

212,861.04 m3/hr

A diesel power plant consumed 1 m3 of fuel with 30°API at 27°C in 24 hrs. Calculate the fuel rate in kg/hr. A. 36.21 B. 26.25 C. 29.34 D. 39.42

36.21

A diesel power plant uses fuel with heating value of 43,000 kJ/kg. What is the density of the fuel at 25°C? A. 840 kg/m3 B. 873 kg/m3 C. 970 kg/m3 D. 940 kg/m3

970 kg/m3

Steam with an enthalpy of 800 kCal/kg enters a nozzle at a velocity of 80 m/s. Find the velocity of the steam at the exit of the nozzle if its enthalpy is reduced to 750 kCal/kg, assuming the nozzle is horizontal and disregarding heat losses. Take g = 9.81 m/s 2 and J constant = 427 kg m/kCal. A. 452.37 m/s B. 245.45 m/s C. 651.92 m/s D. 427.54 m/s

651.92 m/s

A 6 MW steam turbine generator power plant has a full-load steam rate of 8 kg/kW-hr. Assuming that no-load steam consumption as 15% of full-load steam consumption, compute for the hourly steam consumption at 75% load, in kg/hr. A. 37,800 kg/hr B. 38,700 kg/hr C. 30,780 kg/hr D. 30,870 kg/hr

37,800 kg/hr

Steam is expanded through a nozzle and the enthalpy drop per kg of steam from the initial pressure to the final pressure of 60 kJ. Neglecting friction, find the velocity of discharge and the exit area of the nozzle to pass 0.20 kg/s if the specific volume of the steam at exit is 1.5 m3/kg. A. 346.4 m/s, 879 mm2 B. 356.7 m/s, 278 mm2 C. 765.6 m/s, 467 mm2 D. 346.4 m/s, 866 mm2

346.4 m/s, 866 mm2

A 4 kg of air enters a turbine with enthalpy of 600 kJ and velocity of 250 m/s. The enthalpy at exit is 486 kJ and velocity of 170 m/s. What is the work developed if there is a heat loss of 10 kJ? A. 122.83 kJ B. 171.2 kJ C. 80.2 kJ D. 28.3 kJ

171.2 kJ

Calculate the drive horsepower for pumping 1703 L/min cold water to a tank suction at 127 mmHg vacuum, delivery at 5.3 kg/cm2 ga., both measured close to pump, ep = 0.65. A. 31.42 Hp B. 20.42 Hp C. 35.42 Hp D. 23.02 Hp

31.42 Hp

An ideal gas turbine operates with a pressure ratio of 10 and the energy input in the high temperature heat exchanger is 300 kW. Calculate the air flow for temperature limits of 30°C and 1200°C. A. 0.25 kg/s B. 0.34 kg/s C. 0.41 kg/s D. 0.51 kg/s

0.34 kg/s

Kerosene is the fuel of a gas turbine plant: fuel-air ratio, mf = 0.012, T3 = 972 K, pressure ratio, rp = 4.5, exhaust to atmosphere. Find the available energy in kJ per kg air flow. Assume k = 1.34 and Cp = 1.13. A. 352.64 kJ/kg B. 452.64 kJ/kg C. 252.64 kJ/kg D. 552.64 kJ/kg

352.64 kJ/kg

Consider a refrigerator whose 40 watts light bulb remains on continuously as a result of a malfunction of the switch. If the refrigerator has a COP of 1.3 and the cost of electricity is 8 cents per kW-hr, determine the increase in the energy consumption of the refrigerator and its cost per year if the switch is not fixed. A. P 49.59 B. P 47.59 C. P 45.59 D. P 43.59

P 49.59

A household refrigerator that has a power input of 450 watts and a COP of 2.5 is to cool five large watermelons, 10 kg each, to 8°C. If the watermelons are initially at 20°C, determine how long it will take for the refrigerator to cool them. The watermelons can be treated as water whose specific heat is 4.2 kJ/kg-K. A. 2220 seconds B. 2230 seconds C. 2240 seconds D. 2250 seconds

2250 seconds

When a man returns to his wall-sealed house on a summer day, he finds that the house is at 32°C. He returns on the air conditioner which cools the entire house to 20°C in 15 minutes. If COP is 2.5, determine the power drawn by the air conditioner. Assume the entire mass within the house is 800 kg of air for which cv = 0.72 kJ/kg-K, cp = 1.0 kJ/kg-K. A. 1.072 kW B. 2.072 kW C. 3.072 kW D. 4.072 kW

3.072 kW

A heat source at 800 K losses 2000 kJ of heat to a sink at 500 K. Determine the entropy generated during this process. A. 1.5 kJ/K B. 2.5 kJ/K C. -2.5 kJ/K D. 4 kJ/K

1.5 kJ/K

Helium gas is compressed in an adiabatic compressor from an initial state of 14 psia and 50°F to a final temperature of 320°F in a reversible manner. Determine the exit pressure of Helium. A. 38.5 psia B. 40.5 psia C. 42.5 psia D. 44.5 psia

40.5 psia

Air passes thru a nozzle with efficiency of 90%. The velocity of air at the exit is 600 m/s. Find the actual velocity at the exit. A. 382 m/s B. 540 m/s C. 458 m/s D. 568 m/s

568 m/s

A 50 kg block of iron casting at 500 K is thrown into a large lake that is at a temperature of 285 K. The iron block eventually reaches thermal equilibrium with the lake water. Assuming average specific heat of 0.45 kJ/kg-K for the iron, determine the entropy generated during this process. A. -12.65 kJ/K B. 16.97 kJ/K C. 4.32 kJ/K D. 6.32 kJ/K

-12.65 kJ/K

A windmill with a 12 m diameter rotor is to be installed at a location where the wind is blowing at an average velocity of 10 m/s. Using standard condition of air (1 atm, 25°C), determine the maximum power that can be generated by the windmill. A. 68 kW B. 70 kW C. 72 kW D. 74 kW

70 kW

Consider a large furnace that can supply heat at a temperature of 2000°R at a steady rate of 3000 Btu/s. Determine the exergy of this energy. Assume an environment temperature of 77°F. A. 2305.19 kW B. 2315.19 kW C. 2325.19 kW D. 2335.19 kW

2315.19 kW

A heat engine receives heat from a source at 1200 K at a rate of 500 kJ/s and rejects the waste heat to a medium at 300 K. The power output of the engine is 180 kW. Determine the irreversibility rate for this process. A. 190 kW B. 195 kW C. 200 kW D. 205 kW

195 kW

A dealer advertises that he has just received a shipment of electric resistance heaters for residential buildings that have an efficiency of 100 percent. Assuming an indoor temperature of 21°C and outdoor temperature of 10°C, determine the second law efficiency of these heaters. A. 8.74% B. 6.74% C. 3.74% D. 4.74%

3.74%

A rigid tank contains 2 kmol of N2 and 6 kmol of CO2 gases at 300 K and 115 MPa. Find the tank volume using the ideal gas equation. A. 7.33 m3 B. 5.33 m3 C. 3.33 m3 D. 1.33 m3

1.33 m3

A spherical balloon with a diameter of 6 m is filled with helium at 20°C and 200 kPa. Determine the mole number. A. 9.28 kmol B. 10.28 kmol C. 11.28 kmol D. 13.28 kmol

9.28 kmol

A rigid tank contains 20 lbm of air at 20 psia and 70°F. More air is added to the tank until the pressure and temperature rise to 35 psia and 90°F, respectively. Determine the amount of air added to the tank. A. 11.73 lb B. 13.73 lb C. 15.73 lb D. 17.73 lb

13.73 lb

A rigid tank contains 5 kg of an ideal gas at 4 atm and 40°C. Now a valve is opened, and half of mass of the gas is allowed to escape. If the final pressure in the tank is 1.5 atm, the final temperature in the tank is? A. -38°C B. -30°C C. 40°C D. 53°C

-38°C

Water is boiling at 1 atm pressure in a stainless steel pan on an electric range. It is observed that 2 kg of liquid water evaporates in 30 min. The rate of heat transfer to the water is? A. 2.07 kW B. 0.47 kW C. 2.51 kW D. 3.12 kW

2.51 kW

The air in an automobile tire with a volume of 0.53 ft3 is at 90°F and 20 psig. Determine the amount of air that must be added to raise the pressure to the recommended value of 30 psig. Assume the atmospheric pressure to be 14.7 psia and the temperature and the volume to remain constant. A. 0.026 lb B. 0.046 lb C. 0.066 lb D. 0.086 lb

0.026 lb

Consider a person standing in a breezy room at 20°C. Determine the total rate of heat transfer from this person if the exposed surface area and the average outer surface temperature of the person are 1.6 m2 and 29°C, respectively, and the convection heat transfer coefficient is 6 W/m2 with emissivity factor of 0.95. A. 86.40 watts B. 81.70 watts C. 198.1 watts D. 168.1 watts

168.1 watts

Water is boiler in a pan on a stove at sea level. During 10 minutes of boiling, it is observed that 200 grams of water has evaporated. Then the rate of heat transfer to the water is: A. 0.84 kJ/min B. 45.1 kJ/min C. 41.8 kJ/min D. 53.5 kJ/min

45.1 kJ/min

A 5 cm diameter spherical ball whose surface is maintained at a temperature of 70°C is suspended in the middle of a room at 20°C. If the convection heat transfer coefficient is 15 W/m2-°C and the emissivity of the surface is 0.8, determine the total heat transfer from the ball. A. 23.56 watts B. 32.77 watts C. 9.22 watts D. 43.45 watts

32.77 watts

An aluminum pan whose thermal conductivity is 237 W/m-°C has a flat bottom whose diameter is 20 cm and thickness of 0.4 cm. Heat is transferred steadily to boiling water in the pan through its bottom at a rate of 500 watts. If the inner surface of the bottom of the pan is 105°C, determine the temperature of the surface of the bottom of the pan. A. 95.27°C B. 105.27°C C. 115.27°C D. 125.27°C

105.27°C

For heat transfer purposes, a standing man can be modeled as a 30 cm diameter, 170 cm long vertical cylinder with both the top and bottom surfaces insulated and with the side surface at an average temperature of 34°C. For a convection heat transfer coefficient of 15 W/m2-°C, determine the rate of heat loss from this man by convection in an environment at 20°C. A. 316.46 watts B. 326.46 watts C. 336.46 watts D. 346.46 watts

336.46 watts

A frictionless piston-cylinder device and a rigid tank contain 1.2 kmol of an ideal gas at the same temperature, pressure and volume. Now heat is transferred, and the temperature of both systems is raised by 15°C. The amount of extra heat that must be supplied to the gas in the cylinder that is maintained at constant pressure is? A. 0 B. 50 kJ C. 100 kJ D. 150 kJ

150 kJ

A supply of 50 kg of chicken at 6°C contained in a box is to be frozen to -18°C in a freezer. Determine the amount of heat that needs to be removed. The latent heat of the chicken is 247 kJ/kg, and its specific heat is 3.32 kJ/kg-°C above freezing and 1.77 kJ/kg-°C below freezing. The container box is 1.5 kg, and the specific heat of the box material is 1.4 kJ/kg-°C. Also the freezing temperature of chicken is -2.8°C. A. 15,206.4 kJ B. 50.4 kJ C. 15,156 kJ D. 1,863 kJ

15,206.4 kJ

Water is being heated in a closed pan on top of a range while being stirred by a paddle wheel. During the process, 30 kJ of heat is transferred to the water, and 5 kJ of heat is lost to the surrounding air. The paddle wheel work amounts to 500 N-m. Determine the final energy of the system if its initial energy is 10 kJ. A. 35.5 kJ B. 40.5 kJ C. 25.5 kJ D. 14.5 kJ

35.5 kJ

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 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 is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required. A. 1 units B. 2 units C. 3 units D. 4 units

2 units

hoping that the room will be cooler when she comes back in the evening. Assuming all the doors and windows are tightly closed and disregarding any heat transfer through the walls and the windows, determine the temperature in the room when she comes back 10 hours later. Use specific heat values at room temperature, and assume the room to be at 100 kPa and 15°C in the morning when she leaves. A. 28.13°C B. 38.13°C C. 48.13°C D. 58.13°C

58.13°C

A 4 m x 5 m x 6 m room is to be heated by a baseboard resistance heater. It is desired that the resistance heater be able to raise the air temperature in the room from 7 to 23°C within 15 minutes. Assuming no heat losses from the room and an atmospheric pressure of 100 kPa, determine the required power of the resistance heater. Assume constant specific heats at room temperature. A. 2.34 kW B. 1.91 kW C. 4.56 kW D. 6.34 kW

1.91 kW

In order to cool 1 ton (1000 kg) of water at 20°C in an insulated tank, a person pours 80 kg of ice at -5°C into the water. Determine the final equilibrium temperature in the tank. The melting temperature and the heat of fusion of ice at atmospheric pressure are 0°C and 333.7 kJ/kg, respectively. A. 12.43°C B. 14.43°C C. 16.43°C D. 18.43°C

12.43°C

A fan is powered by 0.5 hp motor and delivers air at a rate of 85 m3/min. Determine the highest value for the average velocity of air mobilized by the fan. Take the density of air to be 1.18 kg/m3. A. 18.23 m/s B. 21.12 m/s C. 25.34 m/s D. 32.23 m/s

21.12 m/s

An Ocean-Thermal Energy Conversion power plant generates 10,000 kW using a warm surface water inlet temperature of 26°C and cold deep-water temperature of 15°C. On the basis of a 3°C drop in the temperature of the warm water and a 3°C rise in the temperature of the cold water due to removal and addition of heat, calculate the power required in kW to pump the cold-deep water to the surface and through the system heat exchanger if the required pumping pressure increase is 12 kPa. Assume a Carnot cycle efficiency and density of cold water to be 100 kg/m3. A. 108 B. 250 C. 146 D. 160

250

A plate-type solar energy collector with an absorbing surface covered by a glass plate is to receive an incident radiation of 800 W/m2. The glass plate has a reflectivity of 0.12 and a transmissivity of 0.85. The absorbing surface has an absorptivity of 0.90. The area of the collector is 5 m2. How much solar energy in watts is absorbed by the collector? A. 2500 B. 2880 C. 3510 D. 3060

3060

A tank contains liquid nitrogen at -190°C is suspended in a vacuum shell by three stainless steel rods of 0.80 cm in diameter and 3 meters long with a thermal conductivity of 16.3 W/m2- °C. If the ambient air outside the vacuum shell is 15°C, calculate the magnitude of the conductive heat flow in watts along the support rods. A. 0.168 B. 0.0587 C. 0.182 D. 0.176

0.168

An elastic sphere containing gas at 120 kPa has a diameter of 1.0 m. Heating the sphere causes it to expand to a diameter of 1.3 m. During the process the pressure is proportional to the sphere diameter. Calculate the work done by the gas in kJ. A. 41.8 B. 50.6 C. 87.5 D. 35.4

87.5

An ideal gas with a molecular weight of 7.1 kg/kg mol is compressed from 600 kPa and 280 K to a final specific volume of 0.5 m3/kg. During the process the pressure varies according to P = 620 + 150υ + 95 υ2 where p is in kPa and υ in m3/kg. Calculate the work of compression in kJ/kg. A. 32.8 B. 28.7 C. 35.6 D. 33.3

33.3

A one cubic meter container contains a mixture of gases composed of 0.02 kg-mol of oxygen and 0.04 kg-mol of helium at a pressure of 220 kPa. What is the temperature of this ideal gas mixture in Kelvin? A. 441 B. 350 C. 400 D. 450

441

A 12 DC electrical motor draws a current of 15 amps. How much work in kJ does this motor produce over a 10-minute period of operation? A. 108.0 B. 129.6 C. 216.0 D. 318.2

108.0

Methyl alcohol (CH3OH) is burned with 25% excess air. How much unburned oxygen in kg- moloxygen/kg-molfuel will there be in the products if the combustion is complete? A. 0.35 B. 0.45 C. 0.37 D. 0.65

0.37

A 4 liter (2-liter per revolution at standard pressure and temperature) spark ignition engine has a compression ratio of 8 and 2200 kJ/kg heat addition by the fluid combustion. Considering a cold air-standard Otto cycle model, how much power will the engine produce when operating at 2500 rpm? A. 166.53 hp B. 73.12 hp C. 97.4 hp D. 148 hp

166.53 hp

A simple Rankine cycle produces 40 MW of power, 50 MW of process heated and rejects 50 MW of heat to the surroundings. What is the utilization factor of this cogeneration cycle neglecting the pump work? A. 50% B. 60% C. 64% D. 80%

64%

The rate of heat transfer to the surroundings from a person at rest is 400 kJ/hr. Suppose that the ventilation system fails in an auditorium containing 120 people and assuming that the energy goes into the air of volume 1500 m3 initially at 300 K and 101 kPa, calculate the rate in °C /min of air temperature change. A. 0.81 B. 0.53 C. 0.63 D. 1.0

0.63

An insulated box containing helium gas falls from a balloon 4.5 km above the earth’s surface. Calculate the temperature rise in °C of the helium when box hits the ground. A. 15.2 B. 12.6 C. 25.3 D. 14.1

14.1

A Carnot cycle operates between the temperature limits of 300 K and 1500 K, and produces 600 kW of net power. The rate of entropy change of the working fluid during heat addition process is? A. 0 B. 0.4 C. 0.5 D. 2.0

0.5