Community Digest

Top new questions this week:

Can a Peltier's device (i.e.Thermoelectric cooler) achieve cryogenic temperature efficiently?

Does the stacking of peltiers device shows promising results in achieving the cryogenic temperature? I have tried doing the experiment, the overall temperature of the system increased around 80ºC and ...

mechanical-engineering thermodynamics heat-transfer refrigeration cryogenics  
asked by Adarsh Shubhananda 4 votes
answered by niels nielsen 3 votes

How do I determine what hardness to change the bearing or the track?

We have a project that requires us to use a qty of 4, Ø2" yoke roller bearings mounted two per side on a trolley that roll on a steel track. The maximum total weight that we estimate on the track at ...

mechanical-engineering stresses  
asked by sgwilliams 2 votes
answered by blacksmith37 2 votes

Can I submerge a pneumatic cylinder in oil?

I am looking for a linear pneumatic cylinder to raise and lower a fixed object. Everything will be submerged in oil (for electrical purposes). I am new to engineering and pneumatics in particular, and ...

mechanical-engineering pneumatic  
asked by snasvak 2 votes
answered by Solar Mike 1 vote

Drained and undrained shear strength of clay correlated?

When we measure the undrained strength of clay via CPT or triaxial test for instance, is there a way to correlate this to drained strength? How? I ask because measuring drained strength takes very ...

asked by user3600630 1 vote
answered by ingenørd 1 vote

analysis of PD controller vs static-gain

I have a plant $G(s)$ which gives position and velocity as output $$ G = [G_{ru}(s)\quad G_{vu}(s)]^T $$ where $G_{ru}$ is the integral of $G_{vu}$, and $u$ is the input to the system. Now if I want ...

control-engineering control-theory pid-control  
asked by venom 1 vote
answered by fibonatic 2 votes

How to convert output of controller (control signal) into PWM signal?

I am trying to control a mechanical system with some transfer function T (output is position & input is voltage). I have implemented a state feedback controller in order for the output of the ...

mechanical-engineering control-engineering control-theory  
asked by Teo Protoulis 1 vote
answered by morbo 2 votes

How do nuclear power plants prevent fuel rods from depleting nonuniformaly?

Power output of nuclear reactors is controlled by control rods that sit in between the fuel rods: These are pulled out to increase fission rates - and lowered to decrease them. The control rods are ...

asked by yippy_yay 1 vote

Greatest hits from previous weeks:

How does width and thickness affect the stiffness of steel plate?

I have a 2 mm thick steel plate which is 300 mm long and 30 mm wide, supported at either end. It supports a weight-bearing wheel that can roll along the plate. It currently supports the maximum weight ...

mechanical-engineering steel stiffness  
asked by jhabbott 18 votes
answered by William S. Godfrey- S.E. 15 votes

How to determine reinforcement design strip widths and locations

When designing reinforced concrete slabs it is common to divide the slab into 'design strips', which are then used to rationalise the reinforcement design along (typically orthogonal) lengths of the ...

concrete reinforcement  
asked by thomasmichaelwallace 5 votes
answered by hazzey 5 votes

How was Volkswagen able to trick the lab pollution test?

The recent Volkswagen pollution test cheating scandal has shocked many people with its widespread extent as well as how it was hidden for so many years. Last year, the International Council on ...

automotive-engineering product-testing air-quality emissions  
asked by March Ho 48 votes
answered by Air 61 votes

Why is air pressure in all directions?

Here is a typical definition of air pressure: Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of air molecules that ...

mechanical-engineering pressure  
asked by oyvey 13 votes

What are the pros and cons of a traffic circle versus a traffic light intersection?

The debate of traffic circles (also called roundabouts or rotaries) versus traffic light intersections has been in progress for a while. Those in favor of traffic circles say that, among other things, ...

traffic-light highway-engineering  
asked by APerson 29 votes
answered by jhabbott 27 votes

How to determine the characteristic length in reynolds number calculations in general?

I understand that the reynolds number is given by the expression $Re=\frac{\rho v L}{\mu}$, where $\rho$ is the density, $v$ is the fluid velocity and $\mu$ is the dynamic viscosity. For any given ...

asked by Paul 10 votes
answered by nluigi 5 votes

Why is kVA not the same as kW?

I thought my electric car charging unit uses 6.6 kW of power. However, I found the label and it actually says 6.6 kVA. When I saw this I thought something along the lines of... Well, $ ...

asked by jhabbott 53 votes
answered by Chris Mueller 59 votes

Can you answer these questions?

How to modify Airfoil thickness

I'm writing a fusion360 adding to model windmill blades. My first goal is to model the NREL Phase IV in which the airfoils (S809) definitions come with thickness and also span station (wich I¿dont ...

asked by efirvida 1 vote

How to furnace-melt bismuth oxide into optical glass?

I have been experimenting with a furnace at my house and am looking to attempt the more difficult process of creating bismuth-oxide based optical glass for the purposes of creating optical elements ...

asked by nikk wong 1 vote
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