Water is pumped from a lower reservoir to a higher reservoir by a pump that provides 20 kW of shaft power. The free surface of t
he upper reservoir is 45 m higher than that of the lower reservoir. If the flow rate of water is measured to be 0.03 m3 /s, determine mechanical power that is converted to thermal energy during this process due to frictional effects.
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Answer:
The net energy transfer from the student's body during the 20-min ride to school is 139.164 BTU.
Explanation:
From Heat Transfer we determine that heat transfer rate due to electromagnetic radiation (), measured in BTU per hour, is represented by this formula:
(1)
Where:
- Emissivity, dimensionless.
- Surface area of the student, measured in square feet.
- Stefan-Boltzmann constant, measured in BTU per hour-square feet-quartic Rankine.
- Temperature of the student, measured in Rankine.
- Temperature of the bus, measured in Rankine.
If we know that ,
,
,
and
, then the heat transfer rate due to electromagnetic radiation is:
Under the consideration of steady heat transfer we find that the net energy transfer from the student's body during the 20 min-ride to school is:
(2)
Where is the heat transfer time, measured in hours.
If we know that and
, then the net energy transfer is:
The net energy transfer from the student's body during the 20-min ride to school is 139.164 BTU.