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1500 questions
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5 answers
What do you call the difference between the on and off temperatures in a simple thermostat?
A simple thermostat will turn on at one temperature and off at a higher temperature. This keeps the thermostat from cycling on and off too quickly. The difference between these values is sometimes called dead band and sometimes called hysteresis.…
ericnutsch
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2 answers
How are wind tunnel models used when designing supersonic aircraft?
There are two things involved: wave drag and boundary layer separation. The wave drag depends on the Mach number while the latter depends on the Reynolds number of the flow. It's easy to maintain the incoming Mach number as it is independent of the…
Subodh
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2 answers
How to calculate permittivity for higher frequencies?
In many books the permittivity of a material is only listed as dielectric constant for one or a couple of frequencies. 1 kHz is used often (for example in the Plastics Technology Handbook, 4th ed, ISBN-13: 978-0-8493-7039-7), but I'm looking for the…
Mast
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2 answers
Are small car engines designed to tolerate a higher duty cycle than large car engines?
For simplicity we're going to ignore aerodynamics and vehicle mass for a moment...
Are small (around 1 litre) car engines designed to tolerate a higher duty cycle than large (2+ litre) car engines?
Cars are usually all travelling at roughly the…
squigbobble
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1 answer
How do I choose operating parameters for input air to a methane reformer?
I'm interested in controlled oxidation of nickel in a methane reformer with diameter ~3 m and height ~1.5 m. In this reactor, CH4 is converted into H2 and CO, and CO into H2 and CO2 but for this problem, we assume that the methane and water stopped…
Corvinus
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1 answer
Are all pressure-volume processes polytropic?
I was searching for information about pressure-volume processes when I read, in a heat engineering book, "The process is polytropic with $PV^n = \text{constant}$."
How can I know that a real life process follows this model? Are all processes…
user2703642
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10
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2 answers
Why do we neglect the radial stress in case of a thin pressure vessel?
A cylindrical or a spherical pressure vessel, having inner diameter $d$ & thickness of wall $t$, is called thin if $\large \frac{t}{d}<\frac{1}{20}$.
$\bullet$ Thin cylindrical pressure vessel
hoop or circumferential stress $…
Harish Chandra Rajpoot
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2 answers
Do structural engineers carry insurance for catastrophic errors?
A friend of mine is a structural engineer and he often complains to me about how little sleep he gets at night worrying over whether or not he accounted for all the little details involved in his design.
For all the double and triple checking one…
Paul
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10
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4 answers
What is an engineer's liability for code changes that occur after submitting a design?
What if any liability would an engineer have in the following situation? This is specifically in reference to engineering within the USA.
An engineer produces a design and plans that meet the standards and codes in effect at that time. The design…
hazzey
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2 answers
How accurately are moveable span bridges balanced?
Movable span bridges (bascule and lift) typically employ a counterweight to help reduce the amount of energy and size of motor required to move the span. Due to variations in the the construction of the bridge and counterweight, the theoretical…
hazzey
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1 answer
Does weathering steel corrode the same as carbon steel when it doesn't develop a protective patina?
Weathering steel is supposed to form a protective patina when exposed to wetting and drying cycles. This protective patina prevents more corrosion from occurring. This is what differentiates it from regular (carbon) steel.
In a situation where the…
hazzey
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2 answers
Differential equations of a (simplified) loading bridge
I am having trouble to calculate the differential equations of a simplified loading bridge.
The system is build as shown in the picture below (just a sketch):
If I use the Newton approach, I am getting the following equations by neglecting…
tlp
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votes
4 answers
Does a transformer use power when output isn't under load?
I was reading about how AC to DC converters work with a step-down transformer and then a diode bridge to convert the lower, stepped down AC voltage into DC. What I don't understand is since the input AC appears to be connected to the primary coil of…
jhabbott
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4 answers
How are high gear ratios achieved in a small space?
I have a very basic understanding of how gears work, and while trying to learn more, I've run into a small point of confusion.
If a 2:1 gear ratio is achieved by having twice as many teeth on one gear than the other, then how are 250:1 ratios…
Soviero
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4 answers
Are there different solar panels for recapturing energy from household lighting?
I have been investigating recapturing energy from house lighting using solar panels.
Are there solar panels specifically designed to capture indoor lighting with a higher efficiency?
If so, what are the differences between the outdoor and indoor…
Mahendra Gunawardena
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