# Calculating pressure needed in a misting system.

• X1Y1Z1
In summary, the conversation discusses the calculation of pressure needed for a misting system used in aeroponics. The Bernoulli principle is mentioned as a key concept, which states that the sum of static and dynamic pressure is constant for an incompressible non viscid fluid. The conversation also mentions the effects of decreasing the pipe section area to increase the speed of the fluid, causing a decrease in pressure and creating the desired misting effect. More advanced concepts such as viscosity, Reynolds number, stall/flow separation, and boundary layer are also mentioned as possible factors to consider in the calculation.
X1Y1Z1
Not a homework problem, personal project.

High all, this is my first post. I am seeking information on how to calculate the pressure needed in a single pipe, closed at its end. The pipe will be used in a misting system for aeroponics [veggies, not cannabis! :-) ].

I am assuming a fixed radius for the main pipe, and misting nozzles with a radius of about half that (however, the total flow will be restricted heavily by the porous exits of each valve). Currently, my misting pipe will have two valves, evenly separated from the open and closed ends of the pipe and from each other.

The pipe will run parallel with the ground. Valves are attached to the top of the pipe, facing upward.

My question is how to go about roughly calculating the total pressure required for causing the valves to mist, and the pressure drop across each valve. I am assuming laminar flow, and that friction and gravity effects are mostly negligible (I will be multiplying the required pressure by some factor and selecting a pump based on this).

Take a look at the Bernoulli equation. The Bernoulli principle states that the sum of static and dynamic pressure is constant for an incompressible non viscid fluid. Static pressure is about the pressure that the fluid would exhibit at rest. On the other hand dynamic pressure relates to the speed of the fluid.

The concepts you should learn about are:

So what you want is to increase the speed of the fluid by decreasing the pipe (valve) section area. Because the static and the dynamic pressure is constant if you increase the speed the pressure decreases. If the water pressure decreases below the vapor pressure point it will turn into vapor, which makes the misting effect that you want.

The concepts you should look are:
http://en.wikipedia.org/wiki/Bernoulli%27s_principle
http://en.wikipedia.org/wiki/Vapor_pressure#Boiling_point_of_water_in_nature

There is also a point which is that the assumption of an inviscid fluid might not hold for really small orifices since the boundary layer might have to be accounted for, making the calculations a bit harder, even though i doubt it would make significant problem.
Also if the orifice is opened at high angles, say more than 10 angular degrees, there might be separation the can cause the water not to go out evenly.

The concepts for this are:
Viscosity
Reynolds number
Stall/flow separation
Boundary Layer

Hope that helps a bit

## 1. How do you calculate the pressure needed for a misting system?

To calculate the pressure needed for a misting system, you will need to know the flow rate of the misting nozzles, the size and length of the tubing, and the desired droplet size. Once you have this information, you can use the Bernoulli's equation or the nozzle flow rate equation to determine the pressure needed for your misting system.

## 2. What is the importance of calculating the pressure needed in a misting system?

Calculating the pressure needed in a misting system is important because it ensures that the misting nozzles will produce the desired droplet size and coverage. If the pressure is too low, the mist may not reach its intended area or may produce larger droplets, while too high of pressure can result in excessive misting and water waste.

## 3. How does the size and length of tubing affect the pressure needed in a misting system?

The size and length of tubing have a direct impact on the pressure needed in a misting system. Smaller diameter tubing will result in higher pressure requirements, while longer tubing will decrease the pressure due to friction losses. It is essential to choose the appropriate tubing size and length to ensure the misting system operates at the desired pressure.

## 4. What is the relationship between flow rate and pressure in a misting system?

The flow rate and pressure in a misting system have an inverse relationship. This means that as the flow rate increases, the pressure will decrease, and vice versa. This relationship is crucial to understand when designing a misting system, as adjusting one variable will impact the other.

## 5. Can I use a pressure regulator to adjust the pressure in a misting system?

Yes, you can use a pressure regulator to adjust the pressure in a misting system. Pressure regulators are useful in controlling the pressure and ensuring it stays within the desired range. However, it is important to note that pressure regulators can only reduce the pressure, not increase it. So, the misting system must have enough pressure to be reduced in the first place.

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