Sp. Proj. PPE IPE

Calculate the energy transfer rate across 6 in. wall of firebrick with a temperature

difference across the wall of 50 °C. The thermal conductivity of the firebrick is 0.65 BTU/hrft-°

F at the temperature interest.

• 285 W/m2

• 369 W/m2

• 112 W/m2

• 429 W/m2

At an average temperature of 100˚C, hot air flows through a 2.5 m long tube with an inside diameter of 50 mm. The temperature of the tube is ˚C along its entire length. Convective film coefficient is 20.1 W/m2-K. Determine the connective heat transfer from air to the tube.

• 900 W

• 909 W

• 624 W

• 632 W

Steam, initially saturated at 2.05 MPa, passes through a 10.10 cm standard steel pipe for

a total distance of 152 m. The steam line is insulated with 5.08 cm thickness of 85%

magnesia. For an ambient temperature of 22˚C, what is the quality of the steam which

arises at its destination if the mass flow rate is 0.125 kg steam per second?

Properties of Steam:

Pressure=2.05 MPa, Temperature=213.67 ˚C

Enthalpy: hf=914.52 kJ/kg hfg=1885.5 kJ/kg hg=2800.00 kJ/kg

Note: k for 85% magnesia is 0.069 W/m-K and ho for still air is 9.36 W/m2-K

• 93%

• 98%

• 84%

• 76%

The sun generates 1 kW/m2 when used as a source for solar collectors, a collector withan area of 1 m2 heat water. The flow rate is 3.0 liters per minute. What is the temperature rise in the water? The specific heat of water is 4,200 J/kg ˚C.

• 4.8 ˚C

• 0.48 ˚C

• 0.50 ˚C

• 0.84 ˚C

The hot combustion gases of a furnace are separated from the ambient air and its

surrounding which are a 25˚C, by a brick wall 0.15 m thick. The brick has a thermal

conductivity of 1.2 W/m-K and a surface emissivity of 0.80. Under steady state conditions

and outer surface temperature of 100 ˚C is measured. Free convection heat surface

temperature of 100 ˚C is measured. Free convection heat transfer to the air adjoining this

surface is characterized by a convection coefficient of 20 W/m2-K. What is the inner

temperature in ˚C?

• 623.7

• 352

• 461.4

• 256.3

A 6 in. x 20 ft. uninsulated B.I. pipe conveys steam at 385 ˚F wit han average ambient temperature of 85˚F. If the cost of the fuel is P 250.00 per 106 BTU with the net energy conversion efficiency of 75%, what is the annual cost of the heat lost?

• P60, 482.00

• P 65, 482.00

• P 70, 482.00

• P 75, 482.00

What is the external heating area in square feet of a tube with the following dimensions: tube inside diameter = 5 in. wall thickness = ½ in. length = 18 ft.

• 26.5

• 24.25

• 19.25

• 28.26

Determine the vacuum efficiency of a surface condenser which operates at a vacuum of 635 mm Hg and exhaust steam enters the condenser at 45.81 ˚C, the barometric pressure is 760 mm Hg and the saturation pressure at 45.81 ˚C is 0.010 MPa.

• 80.4%

• 85.2%

• 92.7%

• 98.3%

A heat exchanger was installed purposely to cool 0.50 kg of gas per second. Molecular weight is 28 and k=1.32. The gas is cooled from 150 ˚C to 80 ˚C. Water is available at the rate of 0.30 kg/s and at a temperature of 12 ˚C. Calculate the exit temperature of the water.

• 48

• 42

• 46

• 44

An uninsulated steam pipe passes through a room in which the air and walls are at

25 ˚C. The outside diameter of the pipe is 70 mm, and its surface temperature and emissivity

are 200 ˚C and 0.80 respectively. If the coefficient associated with free convection heat

transfer from the surface to the air is 15 W/m2-K, what is the rate of heat loss from the surface

per unit length of pipe?

• 997.84 W/m

• 897.84 W/m

• 797.84 W/m

• 697.84 W/m