# Piston problem

1. Dec 1, 2013

### Hsol

Hi people, I need help to this problem

Someone has suggested that the device shown in the figure below be used to improve the maximum force F against the spring, which has a spring constant of k. This is accomplished by changing the temperature of the liquid-vapor mixture in the container. You are to design such a device to close sun-blocking window-shutters that require a maximum force of 0.5 lbf. The piston must move 6 inches to close those shutters completely. You elect to use R-134a as the working fluid and arrange the liquid-vapor mixture container such that he temperature changes from 70 degrees F when shaded from the sun to 100 degrees F when exposed to the full sun. Select the sizes of the various components in this system to do this task. Also select the necessary spring constant and the amount of R-134a to be used.

2. Dec 1, 2013

### SteamKing

Staff Emeritus
No figure attached to post.

3. Dec 1, 2013

### Simon Bridge

... need the figure.

Just reading it over suggests several approaches - how have you been thinking about this so far?

4. Dec 2, 2013

5. Dec 2, 2013

### Simon Bridge

Good - so, do you have a list of the properties of the liquid in question?
Have you translated the design parameters into terms appropriate to the mechanism?

6. Dec 2, 2013

### Hsol

I assume that when the system is 100 degrees F is not applying any bone strength the system is in equilibrium. I was able to determine that the saturation pressure of R-134a table are as follows:

100 degrees F the saturation pressure is 138.93 psia.
70 degrees F the saturation pressure is 85,858 psia.

That's what I've been able to determine so far.

7. Dec 2, 2013

### Simon Bridge

OK - so how does this work: you warm the gas reservoir (the small container), what happens?
This is the basics of the operation that you have to work with. Make sure you understand it.

Do you have no idea how the piston should move to open and close the shutters?

Never mind about the gas part just yet - just get the mechanical details down.
How would you rig a piston so that it moves the shutters?

Once you know that, you can get an idea of the dimensions of the piston chamber.
What shape should it be? How long should it be?
What determines the cross-section area?

What is the maximum force needed?
Can you turn that into a pressure?

Start to see how to proceed?