8. When supplying heated air for a building, one often chooses to mix in some fresh outside air with air that has been heated fr
om the building as it passes through the furnace. An insulated mixing chamber is used to combine two streams of air to be used in a building. One stream of air, brought from the outside, enters at 2 kg/s, at a pressure of 120 kPa, and a temperature of 5oC. The second stream of air, coming from the building’s furnace, has a mass flow rate of 8 kg/s, a pressure of 120 kPa, and a temperature of 35oC. The combined stream is then delivered to the warm space at 120 kPa. Determine the rate of entropy generation for this mixing chamber.
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Answer:
474.59 mg/L
Explanation:
Given that
BOD = 30 mg/L
Original BOD = 30 mg/L × dilution factor
Original BOD = 30 mg/L × 10 = 300 mg/L
here is the ultimate BOD ; BOD is the biochemical oxygen demand ; t = 0.20 /day
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.