Consider the cylindrical. 0.12-m-diamter radiation shield of Example 9.5 that is installed concentric with a 0.10-m-diameter tube carrying steam. The spacing provides an air gap of L = 10 mm . (a) Calculate the heat loss per unit length of the tube by convection when a second shield of 0.14-mdiameter is installed, with the second shield maintained at 35°C. Compare the result to that for thesingle shield of the example. (b) In the two-shield configuration of part (a), the air gaps formed by the annular concentric tubes are L = 10 mm . Calculate the heat loss per Unit length if the gap dimension is L = 15 mm . Do you expect the heat loss to increase or decrease?
Consider the cylindrical. 0.12-m-diamter radiation shield of Example 9.5 that is installed concentric with a 0.10-m-diameter tube carrying steam. The spacing provides an air gap of L = 10 mm . (a) Calculate the heat loss per unit length of the tube by convection when a second shield of 0.14-mdiameter is installed, with the second shield maintained at 35°C. Compare the result to that for thesingle shield of the example. (b) In the two-shield configuration of part (a), the air gaps formed by the annular concentric tubes are L = 10 mm . Calculate the heat loss per Unit length if the gap dimension is L = 15 mm . Do you expect the heat loss to increase or decrease?
Solution Summary: The author explains the heat loss per unit length of the radiation shield, the air gap, and the thermal conductivity of air.
Consider the cylindrical. 0.12-m-diamter radiation shield of Example 9.5 that is installed concentric with a 0.10-m-diameter tube carrying steam. The spacing provides an air gap of
L
=
10
mm
.
(a) Calculate the heat loss per unit length of the tube by convection when a second shield of 0.14-mdiameter is installed, with the second shield maintained at 35°C. Compare the result to that for thesingle shield of the example. (b) In the two-shield configuration of part (a), the air gaps formed by the annular concentric tubes are
L
=
10
mm
. Calculate the heat loss per Unit length if the gap dimension is
L
=
15
mm
. Do you expect the heat loss to increase or decrease?
A piston–cylinder device contains 3 kg of nitrogen initially at 100 kPa and 25°C. Nitrogen is now compressed slowly in a polytropic process during which PV1.3 = constant until the volume is reduced by one-half. Determine the work done and the heat transfer for this process. The gas constant of N2 is R = 0.2968 kPa·m3/kg·K. The cv value of N2 at the anticipated average temperature of 350 K is 0.744 kJ/kg·K (Table A-2b).
The work done for this process is kJ.
The heat transfer for this process is kJ.
A 4-m × 5-m × 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 5 to 25°C within 10 min. 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. The properties of air are R = 0.287 kJ/kg·K and cv = 0.718 kJ/kg·K (Table A-2a).
The required power of the resistance heater is kW.
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