# Pressure and flow relationship equation

### Bernoulli's Equation

Flow through a pipe can be determined using the Darcy-Weisbach equation or one of the other equations for irreversible pressure drop. Relationship Between Pressure Drop and Flow Rate in a Pipeline Between two points, the Bernoulli Equation can be expressed as. Fluid flow occurs with the motion of liquid and gaseous materials and pressure Bernoulli's Equation is used to determine fluid velocities through pressure.

### Bernoulli's principle - Wikipedia

Total pressure is pressure of fluid when it is brought to rest, i. Total pressure can be calculated using Bernoulli theorem.

Imagining that flow is in one point of stream line stopped without any energy loss Bernoulli theorem can be written as: Dynamic pressure for liquids and incompressible flow where the density is constant can be calculated as: For compressible flow calculation gas state equation can be used. Equation for velocity in front of the wave is given bellow: You can download complete derivation of given equations Fluid flow rate for the thermal - heat power transfer, boiler power and temperature The flow rate of fluid required for the thermal energy - heat power transfer can be calculated as: The flow therefore satisfies all the restrictions governing the use of Bernoulli's equation.

Upstream and downstream of the contraction we make the one-dimensional assumption that the velocity is constant over the inlet and outlet areas and parallel.

One-dimensional duct showing control volume. When streamlines are parallel the pressure is constant across them, except for hydrostatic head differences if the pressure was higher in the middle of the duct, for example, we would expect the streamlines to diverge, and vice versa.

If we ignore gravity, then the pressures over the inlet and outlet areas are constant.

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.

• pressure drop, flow rate, pipe diameter
• Bernoulli's Equation
• Space Details

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.

### Flow in pipe - Bernoulli equation

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.

If the flow rate through the expansion is gpm, the velocity goes from 9. The change in static pressure across the expansion due to the change in velocity is: In other words, pressure has increased by almost 0.

Pressure Change due to Head Loss Since head loss is a reduction in the total energy of the fluid, it represents a reduction in the capability of the fluid to do work.

Demonstrate the Flow Rate Characteristic Change as Pressure Change in a System

Head loss does not reduce the fluid velocity consider a constant diameter pipe with a constant mass flow rateand it will not be effect the elevation head of the fluid consider a horizontal pipe with no elevation change from inlet to outlet.

Therefore, head loss will always act to reduce the pressure head, or static pressure, of the fluid.

There are several ways to calculate the amount of energy lost due to fluid flow through a pipe. The two most common methods are the Darcy-Weisbach equation and the Hazen-Williams equation.