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Homework Help for Mechanical Engineering
Mechanical Engineering uses applied math and physics along with materials science to create the mechanical systems around us. One of the broadest fields within engineering, it helped build cars, skyscrapers and prosthetic limbs!
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An ideal reheat Rankine cycle with water as the working fluid operates the boiler at 15,000 kPa, the reheater at 2000 kPa, and the condenser at 100 kPa. The temperature is 4500C at the entrance of the high-pressure and low-pressure turbines. The mass flow rate through the cycle is 1.74 kg/s. Determine the power used by pumps, the power produced by the cycle, the rate of heat transfer in the reheater, and the thermal efficiency of this system.
Figure P4.56 shows a small pressurized cylinder, attached at the one end and loaded with a pipe
wrench at the other. The internal pressure causes a tangential stress of 400 MPa and an axial stress
of 200 MPa that act on an element at point A. The pipe wrench superimposes a bending stress of
100 MPa and a torsional stress of 200 MPa.
(a) Make a Mohr circle representation of the state of stress at point A.
(b) What is the magnitude of the maximum shear stress at A?
(c) Make a sketch showing the orientation of a principal element (with respect to the original element
drawn at A), and show all stresses acting on it.
Consider the power transmission for the rollers in the HP inkjet printer. Assume the following:
- The motor has a speed of 1,500 RPM.
- The white toothed sheave has diameter 0.48 in, the other white sheave has diameter 0.28 in, and that the black one has diameter 1.75 in.
- The little gear has 31 teeth and the big one has 66 teeth.
- The output shaft has rollers of 0.75 in that contact the paper.
- The printer can print 7.5 pages per minute.
Do the following:
- Handwrite the main equations to solve the problems below:
- Find the mechanical advantage going from the motor shaft to the output shaft.
- Find the speed of the paper when in motion.
- As a page is being printed, what percentage of that time goes into moving the page?
You’re a mechanical designer at a company that makes machines that manufacture pills. To prevent damage to the pills, you often use helical gears to reduce vibrations. A new hire, Darcy Hogg, emails you for advice. Darcy didn’t learn about helical gears in college and he seems
nervous in his new role at your company. He has worked out specs for helical gears to achieve a 4.4:1 reduction but can’t find the gears in catalogs. In an email, gently correct Darcy’s misunderstandings and offer him advice on selecting gears. You can refer to things like a catalog page but you cannot select the gears for Darcy because you want Darcy to develop independence.
You should catch 4 conceptual errors.
Darcy’s email is as follows:
I need help finding gears with the attached specs on McMaster-Carr. I don’t think the website works right. Do you think we should go ahead and get custom gears?
A file is attached showing the specs for a pinion and gear to achieve a reduction of 4.4. I got 4.36. Is that okay?
To make the design as compact as possible, I wanted 11 teeth on the pinion. I picked the specs so the gears would have a ratio of about 4.4, to get the desired reduction. 11 times 4.4 is not an exact integer so I rounded to 48. I picked Q10 and stainless because we want smooth operation and because corrosion could cause problems with FDA approval. I matched the helix and pressure angles on each gear. I put a higher pressure angle on the gear because it carries more force; I also gave the gear a wider face so it could carry double the load. I made sure that both gears were right-handed because that’s the standard. I couldn’t get the diameters on the pinion to line up right so I just copied those numbers over from the Excel calculator for the gear.
The top and bottom surfaces of a flat plate are open to air. Here, the air flowing over the bottom surface has a free stream temperature of 330 degrees Celsius and a free stream velocity of 9 meters per second. Whereas, the air flowing over the top surface has a free stream temperature of 420 degrees Celsius and free stream velocity of 6.5 meters per second. Here, the plate's surface temperature is uncertain
Find the following:
a. Assuming that the plate is isothermal in its thickness and that conduction in the x axis of the plate can be ignored, find the temperature of the plate at a distance of 0.7 meters downstream of the plates leading edge?
b. write your though on if the local temperature of the plate is unaffected by x? That is, for every x value, is the plate the same temperature?
Note: evaluate the properties at a film temperature that is equal to the average of both the free stream temperatures of air, and the order of the temperatures in the equation shows the direction of heat flow for Newton's law of cooling.
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