The space heating of a facility is accomplished by natural gas heaters that are 85 percent efficient. The compressed-air needs of the facility are met by a large liquid-cooled compressor. The coolant of the compressor is cooled by air in a liquid-to-air heat exchanger whose airflow section is 1.0 m high and 1.0 m wide. During typical operation, the air is heated from 20 to 52°C as it flows through the heat exchanger. The average velocity of air on the inlet side is measured at 3 m/s. The compressor operates 20 hours a day and 5 days a week throughout the year. Taking the heating season to be 6 months (26 weeks) and the cost of the natural gas to be $1.25/therm (1 therm = 100,000 Btu = 105,500 kJ), determine how much money will be saved by diverting the compressor waste heat into the facility during the heating season.
The space heating of a facility is accomplished by natural gas heaters that are 85 percent efficient. The compressed-air needs of the facility are met by a large liquid-cooled compressor. The coolant of the compressor is cooled by air in a liquid-to-air heat exchanger whose airflow section is 1.0 m high and 1.0 m wide. During typical operation, the air is heated from 20 to 52°C as it flows through the heat exchanger. The average velocity of air on the inlet side is measured at 3 m/s. The compressor operates 20 hours a day and 5 days a week throughout the year. Taking the heating season to be 6 months (26 weeks) and the cost of the natural gas to be $1.25/therm (1 therm = 100,000 Btu = 105,500 kJ), determine how much money will be saved by diverting the compressor waste heat into the facility during the heating season.
Solution Summary: The author analyzes the amount of money saved by diverting the compressor waste heat into the facility during the heating season.
The space heating of a facility is accomplished by natural gas heaters that are 85 percent efficient. The compressed-air needs of the facility are met by a large liquid-cooled compressor. The coolant of the compressor is cooled by air in a liquid-to-air heat exchanger whose airflow section is 1.0 m high and 1.0 m wide. During typical operation, the air is heated from 20 to 52°C as it flows through the heat exchanger. The average velocity of air on the inlet side is measured at 3 m/s. The compressor operates 20 hours a day and 5 days a week throughout the year. Taking the heating season to be 6 months (26 weeks) and the cost of the natural gas to be $1.25/therm (1 therm = 100,000 Btu = 105,500 kJ), determine how much money will be saved by diverting the compressor waste heat into the facility during the heating season.
Problem 1.
Two uniform rods AB and CE, each of weight 3 lb and length 2 ft, are welded to each other at their
midpoints. Knowing that this assembly has an angular velocity of constant magnitude c = 12 rad/s,
determine:
(1). the magnitude and direction of the angular momentum HD of the assembly about D.
(2). the dynamic reactions (ignore mg) at the bearings at A and B.
9 in.
3 in.
03
9 in.
3 in.
Answers: HD = 0.162 i +0.184 j slug-ft²/s
HG = 2.21 k
Ay =-1.1 lb; Az = 0; By = 1.1 lb; B₂ = 0.
Problem 5 (Optional, extra 6 points)
A 6-lb homogeneous disk of radius 3 in. spins as shown at the constant rate w₁ = 60 rad/s. The disk
is supported by the fork-ended rod AB, which is welded to the vertical shaft CBD. The system is
at rest when a couple Mo= (0.25ft-lb)j is applied to the shaft for 2 s and then removed. Determine
the dynamic reactions at C and D before and after the couple has been removed at 2 s.
4 in.
C
B
Mo
5 in
4 in.
Note: 2 rotating around CD induced by Mo is NOT
constant before Mo is removed.
and ₂ (two
unknowns) are related by the equation: ₂ =0+ w₂t
3 in.
Partial Answer (after Mo has been removed):
C-7.81+7.43k lb
D -7.81 7.43 lb
Problem 4.
A homogeneous disk with radius and mass m is mounted on an axle OG with length L and a
negligible mass. The axle is pivoted at the fixed-point O, and the disk is constrained to roll on a
horizontal surface. The disk rotates counterclockwise at the constant rate o₁ about the axle. (mg
must be included into your calculation)
(a). Calculate the linear velocity of G and indicate it on the figure.
(b). Calculate ₂ (constant), which is the angular velocity of the
axle OG around the vertical axis.
(c). Calculate the linear acceleration ā of G and indicate it on the
figure.
(d). Determine the force (assumed vertical) exerted by the floor on
the disk
(e). Determine the reaction at the pivot O.
1
Answers: N = mg +mr(r/L)² @² |j
mr w
IIG
C
R
L
i+
2L
=
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