11. A cast iron flywheel is to be designed for a
single cylinder double acting steam engine which delivers
150 kW at 80 r.p.m. The maximum fluctuation of energy per
revolution is 10%. The total fluctuation
of the speed is 4 per cent of the mean speed. If the mean diameter
of the flywheel rim is 2.4 metres,
determine the following :
(a) Cross-sectional dimensions of the rim, assuming that the hub
and spokes provide 5% of the
rotational inertia of the wheel. The density of cast iron is 7200
kg/m3 and tensile stress 16 MPa.
Take width of rim equal to twice of thickness.
(b) Dimensions of hub and rectangular sunk key. The shear stress
for the material of shaft and key is
40 MPa.
(c) Cross-sectional dimensions of the elliptical arms assuming
major axis as twice of minor axis and
number of arms equal to six.
In: Mechanical Engineering
. A punching machine makes 24 working strokes per minute and is capable of punching 30 mm diameter holes in 20 mm thick steel plates having an ultimate shear strength of 350 MPa. The punching operation takes place during 1 10 th of a revolution of the crankshaft. Find the power required for the driving motor, assuming a mechanical efficiency of 76%. Determine suitable dimensions for the rim cross-section of the flywheel, which revolves at 9 times the speed of crankshaft. The permissible coefficient of fluctuation of speed is 0.4. The flywheel is to be made of cast iron having a safe tensile stress of 6 MPa and density 7250 kg/m3. The diameter of the flywheel must not exceed 1.05 m owing to space restrictions. The hub and spokesmay be assumed to provide 5% of the rotational inertia of the wheel. Check for the centrifugal stress induced in the rim.
In: Mechanical Engineering
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Steam is to be condensed on the shell side of a heat exchanger at 50°C. Cooling water enters the tubes at 15°C at a rate of 55 kg/s and leaves at 23°C. Assuming the heat exchanger to be well insulated, determine (a) the rate of heat transfer in the heat exchanger and (b) the rate of exergy destruction in the heat exchanger. Take T0 = 25°C. |
In: Mechanical Engineering
5. Design a cast iron flywheel for a four stroke cycle
engine to develop 110 kW at 150 r.p.m. The work
done in the power stroke is 1.3 times the average work done during
the whole cycle. Take the mean
diameter of the flywheel as 3 metres. The total fluctuation of
speed is limited to 5 per cent of the mean
speed. The material density is 7250 kg / m3. The permissible shear
stress for the shaft material is
40 MPa and flexural stress for the arms of the flywheel is 20
MPa.
In: Mechanical Engineering
A flat plates surface tempertures are initially at 120 deg C and 60 deg C with one surfaces temperature being lower due to air at 20 deg C flowing over it with a velocity of 2m/s having a heat transfer coefficient of 30 W/m ^2K. The themal conductivities of the sheet metal and air are 35 W/m K. and 0.0262 W/mK. respectively.
Without following the problem solving guide answer the following question providing detaied justifications:
A. What are the modes of heat transfer?
B. Is this a time dependent or steady state problem? Why or why not?
C. The themal conductivities in the sheet metal and air are significantly different. Recalling the definition of thermal conductivity, What can you conclude about the materials abilitys to transfer heat?
D. How would the heat transfer in the system differ if the cooling was through natural convection? Explain your reasoning.
E. Draw a schematic of the energy flow?
In: Mechanical Engineering
السؤال 27
The water flux of RO membranes ______ as water viscosity lowers.
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Increases |
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Decreases |
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Alters |
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Fluctuates |
السؤال 28
RO membranes are made of _______
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Plastic |
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Cotton |
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Silk |
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Polymer |
السؤال 29
A reverse osmosis membrane is a semi-permeable membrane that allows the passage of _________
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Water |
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Dissolved salts |
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Organics |
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Bacteria |
In: Mechanical Engineering
A refrigeration cycle absorbs 20,000 kJ/h of heat from a space
maintained at -45oC and rejects heat to the surrounding
air at 30oC.
i. Determine the actual power input to the refrigeration cycle if
the coefficient of performance (COP) of the refrigeration cycle is
25% of that of a reversible refrigerating cycle operating between
the same two temperature reservoirs (kW).
ii. Determine the minimum work input to the refrigeration cycle
(kW).
iii. Will the heat rejected to the surrounding by the actual
refrigeration be greater, smaller or the same as the heat rejected
to the surrounding by the reversible refrigeration cycle?
In: Mechanical Engineering
Newton's second law of motion can always be used to derive the equations of motion of a vibrating system
In: Mechanical Engineering
At 180°C the heat of vaporization, AvapH of a certain liquid is 14.4 kJ mol'1 . The molar volumes of the liquid and the vapour at the boiling point are 115 cm3 mol'1 and 14.5 dm3 mol' 1 , respectively. Estimate the change in the boiling point of the liquid at 180°C per bar change in atmospheric pressure, dT/dp using the Clayperon equation. Briefly discuss the physical significance of the sign of dT/dp .
In: Mechanical Engineering
Hibbeler said in Engineering Mechanics Statics page 167 (14th Edition):
"Notice that FR is independent of the location of point O since it's simply a summation of the forces"
What I want to ask, It's known that a couple moment is a free vector and it can be moved arbitrary to any point on the body but how can I insist the same concept for Resultant Force, although I can't assure that point O is on the line of the action of FR
In different words, how can I move FR freely while not the Principle of Transmissibility nor free vector is applied to it.
In: Mechanical Engineering
A hot silver plate is having its upper surface cooled by air forced convection of 15 °C with heat transfer coefficient of 220 W/m.K. The 10-cm thick plate (mass density ρ=8530 kg/m3, Cp=380J/kg.K, k=110 W/m.K, and α=33.9×10-6 m2/s) has a uniform initial temperature of 650 °C, and the bottom surface of the plate is insulated.
(a) calculate the Bi number and determine whether the lumped capacitance method can be used. (2 points)
(b) Determine the temperature at the center plane of the plate after 3 minutes of cooling. Solve this problem using the analytical one-term approximation method. (Hint: use table 5.1 in the lecture slides) (8 points)
In: Mechanical Engineering
3. (a) Among thin-film and emerging photovoltaic technologies, explain two photovoltaic cells you understand well, in terms of working principle, structure, materials used, fabrication techniques, advantages, and disadvantages.
(b) Assume you are about to start a business in photovoltaic technologies. Based on what you have studied in this course; what type of photovoltaic cell business would you like to run? Explain the reasons.
In: Mechanical Engineering
The air, which has a temperature of 120 ° C, flows
over a plate with a length of 1.2 m and a constant temperature of
30 ° C across the surface, and its speed flows at a speed of 2 m /
s. According to this,
a.) Calculate the speed and temperature boundary layer thickness at
the end of the plate.
b.) Find the local heat transfer coefficient and heat flux at the
end of the plate.
c.) Find the average heat transfer coefficient and heat flux at the
end of the plate.
(Properties of the air will be taken from the table)
all informations are given
In: Mechanical Engineering