A heat engine has an efficiency of 31.4% and receives 8.72 kJ of heat per cycle
(a) How much work does it perform in each cycle?
(b) How much heat does it exhaust in each cycle?
(a) 2.74 Kj (b) 5.98 kJ
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Air at 30°C enters a rectangular duct 1-m-long and 4 mm by 16 mm in cross-section at a rate of 0.0004 kg/s. If a uniform heat flux of 500 W/m2 is imposed on both of the long sides of the duct, calculate (a) the air outlet temperature (b) the average duct surface temperature, and (c) the pressure drop.
GIVEN
• Air flowing through a rectangular duct
• Inlet bulk air temperature (Tb,in) = 30°C
• Duct length (L) = 1 m
• Duct height (H) 4 mm = 0.004 m
• Duct width (w) = 16 mm = 0.016 m
• Air mass flow rate ( m ) = 0.0004 kg/s
• Uniform heat flux (q/A) = 500 W/m2 on the long sides
FIND
(a) Air outlet temperature (Tb,out)
(b) The average duct surface temperature (Ts)
(c) The pressure drop (? p)
ASSUMPTIONS
• The short sides of the duct are insulated
• Entrance effects are negligible
SKETCH
Teflon tubing or 4 cm OD and 2.7 cm ID conducts 1.9 W/m when the outside temperature is 80ºC. Estimate the inside temperature of the tubing. Also predict the thermal resistance per unit length.
What will be an ideal response?
Kinetic Energy: A 1000-kg car is moving at 15 km/h. If a 2000-kg truck has 23 times the kinetic energy of the car, how fast is the truck moving?
A. 51 km/h B. 72 km/h C. 61 km/h D. 41 km/h
Which of the following has not been detected around other stars in the Galaxy?
A) a collapsing nebula of gas B) flattened, spinning disks C) jovian planets D) asteroids E) strong stellar winds