# Relationship between air velocity and pressure

### What is the relationship between pressure and velocity for a liquid and gas? | How Things Fly

There are other systems where velocity is related to pressure, so please qualify on your there is inverse relationship between P and v as by Bernoulli's eq. The higher the velocity of a fluid (liquid or gas), the lower the pressure it exerts. This is called Bernoulli's Principle. Fluid pressure is caused by. Relation between pressure, velocity and area. This principle is what creates lift on the wings of aircraft—the air traveling over the top of the wing is moving.

What is the Cost of Over-Pressurizing the System? The artificial demand in this case is 25 psig. A rule of thumb to remember is that for every 2-psi increase in discharge pressure, the energy measured at the compressor goes up by 1 percent.

Obviously, there are pressure drops across the clean-up equipment dryers and filterswhich could equate to 10 to 15 psig or more. But if the system was properly sized and maintained, this should be easily factored into what to set the discharge pressure of the compressor. Assuming that the clean-up equipment and piping distribution system were poorly sized and maintained, which equates to a psig pressure drop, you could still cut the pressure on the compressor operating at psig to psig, and still maintain the desired 75 psig on the production floor.

Dialing the pressure down by 25 psig, the plant could save To calculate the energy savings, use the energy equation below: To calculate kW, multiply BHP by the constant. Typically compressor manufacturers utilize a 1. Therefore, a hp rotary screw air compressor actually pulls on average BHP at full load, depending on the manufacturer.

If the compressed air system was properly audited on the supply and demand side, which resulted in adding the proper amount of storage, pressure flow controller, etc.

Keep doing this over a period of time, and you will eventually have someone scream at you. Then turn it up 2 psig, and leave it alone. Another way to reduce leaks is to have a leak audit performed and implemented.

However, remember that you can effectively reduce leaks, but you can never completely eliminate them. My philosophy to sales has always been to be a consultant and to educate the end user, not to merely be a salesman.

## The Relationship Between Pressure and Flow in a Compressed Air System

If you help an end user solve a problem, that person is much more apt to buy something from you in the future. In addition, an educated customer is a quality customer.

For more information, please contact Chris DownsTel. If we ignore gravity, then the pressures over the inlet and outlet areas are constant.

### Basics of Air Velocity, Pressure and Flow

Along a streamline on the centerline, the Bernoulli equation and the one-dimensional continuity equation give, respectively, These two observations provide an intuitive guide for analyzing fluid flows, even when the flow is not one-dimensional. For example, when fluid passes over a solid body, the streamlines get closer together, the flow velocity increases, and the pressure decreases.

Airfoils are designed so that the flow over the top surface is faster than over the bottom surface, and therefore the average pressure over the top surface is less than the average pressure over the bottom surface, and a resultant force due to this pressure difference is produced.

This is the source of lift on an airfoil. Lift is defined as the force acting on an airfoil due to its motion, in a direction normal to the direction of motion. Likewise, drag on an airfoil is defined as the force acting on an airfoil due to its motion, along the direction of motion. An easy demonstration of the lift produced by an airstream requires a piece of notebook paper and two books of about equal thickness.

Place the books four to five inches apart, and cover the gap with the paper. When you blow through the passage made by the books and the paper, what do you see? Example 1 A table tennis ball placed in a vertical air jet becomes suspended in the jet, and it is very stable to small perturbations in any direction. Push the ball down, and it springs back to its equilibrium position; push it sideways, and it rapidly returns to its original position in the center of the jet.

In the vertical direction, the weight of the ball is balanced by a force due to pressure differences: To understand the balance of forces in the horizontal direction, you need to know that the jet has its maximum velocity in the center, and the velocity of the jet decreases towards its edges. The ball position is stable because if the ball moves sideways, its outer side moves into a region of lower velocity and higher pressure, whereas its inner side moves closer to the center where the velocity is higher and the pressure is lower.

The differences in pressure tend to move the ball back towards the center. Example 3 Suppose a ball is spinning clockwise as it travels through the air from left to right The forces acting on the spinning ball would be the same if it was placed in a stream of air moving from right to left, as shown in figure Spinning ball in an airflow.

A thin layer of air a boundary layer is forced to spin with the ball because of viscous friction. At A the motion due to spin is opposite to that of the air stream, and therefore near A there is a region of low velocity where the pressure is close to atmospheric.

At B, the direction of motion of the boundary layer is the same as that of the external air stream, and since the velocities add, the pressure in this region is below atmospheric.

The ball experiences a force acting from A to B, causing its path to curve. If the spin was counterclockwise, the path would have the opposite curvature. The appearance of a side force on a spinning sphere or cylinder is called the Magnus effect, and it well known to all participants in ball sportsespecially baseball, cricket and tennis players.