How to find force from volumetric flow rate and pressure

In summary, the conversation discusses a problem related to designing a RC hover craft and using a fan as thrust. The goal is to approximate the equation to a straight line and find the values for F0 and γ. The conversation also includes a discussion about relating pressure to force and volumetric flow. The participants are unsure about the exact problem statement and how to relate force to volumetric flow or velocity. They also discuss the orientation of the graph and the values for F0 and γ.
  • #1
bl965
18
0
1. Homework Statement
Hi. This is a problem related to designing a RC hover craft. We are given a datasheet for a fan used as thrust.
http://imgur.com/6liZSid Sorry image post no working, url: http://imgur.com/a/6XLwL
We have to approximate the equation to a straight line through the curve. Then relate it to Fthrust = F0+ γ*v. We have to find γ and what F0 represents.

Homework Equations


Q = velocity * Area
F = mass * acceleration

The Attempt at a Solution


I found that the slope is -0.285 [m3/s/mmH20]. To find F0, I think the graph has to be turned on its side: pressure is the independent variable and volumetric flow is the dependent. If pressure is zero, I can find F0 which is the y intercept. But how to relate force to volumetric flow or velocity.
 
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  • #2
If P is the pressure and A is the area that the pressure acts on, what is the force?
 
  • #3
If pressure is 0, volumetric flow is high, and small pressure * area is small force. As pressure increases, there will be more force with less flow. Makes sense. From start the fan is operating at atmosphere. I get high results when I search for one atmosphere in mm of water. Am I on the right track?
 
  • #4
bl965 said:
If pressure is 0, volumetric flow is high, and small pressure * area is small force. As pressure increases, there will be more force with less flow. Makes sense. From start the fan is operating at atmosphere. I get high results when I search for one atmosphere in mm of water. Am I on the right track?
I have no idea. Can you please provide an exact problem statement?
 
  • #5
(b) We can relate this linear relationship to Fthrust = F0-γv [Note: γ is a constant representing the slope of the F(v) line]. For each fan, based on your approximation in (a), what are the values for F0 and for γ?
 
  • #6
bl965 said:
I think the graph has to be turned on its side:
No, it looks the right way around already, with pressure on the vertical axis. Seems to me you flipped it around in order to get:
bl965 said:
I found that the slope is -0.285 [m3/s/mmH20].

bl965 said:
how to relate force to volumetric flow or velocity.
What do you think relates volumetric flow through an aperture to the linear flow rate through it?
As Chester asks, what relates pressure to force?
 

1. How do you calculate force from volumetric flow rate and pressure?

The formula for calculating force from volumetric flow rate and pressure is Force = Pressure x Area. You will need to know the area of the surface that the force is acting on in order to solve for force.

2. What units are used for volumetric flow rate and pressure?

Volumetric flow rate is typically measured in units of volume per time, such as cubic meters per second (m^3/s) or gallons per minute (gpm). Pressure is commonly measured in units of force per area, such as newtons per square meter (N/m^2) or pounds per square inch (psi).

3. Can force be calculated if there is no volumetric flow rate given?

No, force cannot be calculated without knowing either the volumetric flow rate or the pressure. These two values are both necessary to solve for force using the formula mentioned above.

4. How does changing the volumetric flow rate or pressure affect the resulting force?

The force will increase or decrease proportionally to changes in the volumetric flow rate or pressure. For example, if the volumetric flow rate doubles, the force will also double as long as the pressure remains constant.

5. Are there any other factors that can affect the calculation of force from volumetric flow rate and pressure?

Aside from changes in the volumetric flow rate and pressure, the force may also be affected by the properties of the fluid (such as density and viscosity) and the geometry of the system. It is important to consider these factors when calculating force in real-world applications.

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