The relationship between static, dynamic, and total pressure is precisely linked to Bernoulli’s equation. The interplay between these pressures is crucial in aerodynamics and wind tunnel experiments. If you’re curious about how to measure static and dynamic pressure, I recommend reading this article.
This article briefly explains the relationship between static, dynamic, and total pressure. We’ll also discuss how to measure dynamic and static pressure. Traditionally, pitot tubes were used. Today, pressure sensors are primarily used for more precise measurements.
What is Static Pressure?
Static pressure refers to the force exerted by a fluid on the container or the surface of an object when the fluid is at rest or moving at a constant velocity in a straight line. This force arises from the fluid’s own weight and the intermolecular forces within it. Also known as hydrostatic pressure, static pressure simply represents the force exerted when a fluid is at rest relative to an object. In flowing fluids, static pressure refers to the pressure component perpendicular to the flow direction. Static pressure is independent of fluid velocity.
The two formulas for calculating static pressure are: p = ρgh and P = F/A.
What is Dynamic Pressure?
Dynamic pressure is the pressure exerted by a fluid when it moves relative to an object. In other words, dynamic pressure is the pressure exerted by the fluid flow. When a fluid flows at a certain velocity, its kinetic energy is converted into a pressure exerted on the obstacle—this is dynamic pressure. The magnitude of dynamic pressure is proportional to the square of the fluid velocity and its density, typically expressed as P = 1/2 × ρ × v². You can use this formula to measure the velocity, density, and mass of a fluid.
Here, ρ represents the fluid’s density, and v denotes its flow velocity.
The relationship between pressure and fluid velocity
According to Bernoulli’s principle, as fluid velocity increases, dynamic pressure increases while static pressure decreases.
Bernoulli’s principle, also known as Bernoulli’s equation:
Here, p represents the pressure at a point in the fluid, v is the fluid velocity at that point, ρ is the fluid density, g is the gravitational acceleration, and h is the height of that point.
Bernoulli’s theorem is a physical law that describes the motion of fluids. It states that in fluids (liquids and gases), an increase in velocity causes a decrease in pressure, while a decrease in velocity causes an increase in pressure.
What is Total Pressure?
In fluid mechanics, Total Pressure is the algebraic sum of static pressure and dynamic pressure. Its calculation formula is P_total = P_static + P_dynamic. Total pressure represents the total energy per unit volume of fluid. It comprises both static pressure energy and kinetic energy.
Static Pressure and Dynamic Pressure Measurement
The Pitot tube is the most traditional instrument for measuring static and dynamic pressures. However, this method has certain limitations.
It consists of a cylindrical tube with a small orifice at its head and a tube for measuring static pressure. The total pressure of the airflow enters the Pitot tube through the small orifice at the head. Inside the tube, a row of static pressure ports is drilled perpendicular to the direction of the airflow. By measuring the static pressure at these ports, the total pressure of the airflow can be calculated.
When measuring total air pressure, a total pressure tube is typically used. The head of the total pressure tube has a small orifice through which the total air pressure enters. Inside the tube, a row of static pressure ports is arranged perpendicular to the airflow direction. By measuring the static pressure at these ports, the total air pressure can be calculated. This method of measuring total air pressure using a total pressure tube is based on Bernoulli’s principle. It states that total air pressure equals the sum of dynamic pressure and static pressure.
The most commonly used measurement instrument in industry today is the pressure sensor. Pressure sensors provide more precise measurements and offer simpler operation. Sino-Inst offers static pressure sensors and dynamic pressure sensors. Our sensors can directly measure static pressure and dynamic pressure.
Read More about: 7 Types of Pressure Sensors: Different Types, Working Principles, and Definitions
Static pressure sensors can measure liquid levels:
A static pressure level gauge is a pressure sensor used to measure liquid levels. It operates on the principle that the static pressure of a liquid is proportional to its height. Utilizing advanced isolated diffused silicon sensing elements or ceramic capacitive pressure sensors, it converts static pressure into an electrical signal. This signal undergoes temperature compensation and linear correction before being converted into a standard electrical signal.
Sino-Inst Featured Pressure Sensor
Static Pressure VS Dynamic Pressure VS Total Pressure
1. Static Pressure
The pressure generated by air molecules colliding with pipe walls due to their random motion is termed static pressure. When calculated with absolute vacuum as the reference zero point, it is called absolute static pressure. When atmospheric pressure serves as the zero point, it is termed relative static pressure. In HVAC systems, air static pressure always refers to relative static pressure.
Static pressure represents the potential energy per unit volume of gas, manifesting as a force that compresses the gas and exerts pressure on pipe walls. The absolute static pressure of gas within a duct can be positive (higher than ambient atmospheric pressure) or negative (lower than ambient atmospheric pressure).
2. Dynamic Pressure
Dynamic pressure refers to the force generated when a fluid (liquid or gas) flows relative to an object. It always acts in the direction of fluid flow and maintains a positive value. Any fluid flow within a pipe has dynamic pressure. It represents the kinetic energy per unit volume of fluid and acts as a force that alters the fluid’s velocity within the pipe.
3. Total Pressure
The total pressure is calculated as the total sum of static pressure and dynamic pressure. It represents the total energy contained within a unit volume of fluid (liquid or gas). Relative to atmospheric pressure, the total pressure value can be either positive or negative.
The Role of Static and Dynamic Pressure in Industrial Applications
The terms dynamic pressure and static pressure are common in aerodynamics, mechanical design and manufacturing. They also play a significant role in wind tunnel experiments. In summary, these concepts are frequently encountered in applications involving pressure-related issues. Here is a brief introduction to the application scenarios for dynamic and static pressure.
Static pressure finds widespread use across various industrial sectors, with specific applications including:
Static pressure plays an important role in aerospace development. It influences vital aircraft components. such as landing gear, thrust reversers, and turbines. It enhances aircraft maneuverability and safety while effectively reducing component wear and noise. Static pressure finds extensive application in energy engineering. It is utilized in energy equipment such as hydraulic systems, steam turbines, and gas turbines. It improves the transmission efficiency and operational stability of energy machinery.
Static pressure also plays an essential role in mechanical design and manufacturing. It effectively reduces friction and wear in mechanical components during processes like mechanical bearings, guide rails, cutting operations, and machining.
Dynamic pressure has important applications in aerodynamics, aerospace, and hydraulic transmission systems.
In aerodynamics, dynamic pressure is a key value in studying gas flow and pressure distribution. In hydraulic systems, dynamic pressure drives hydraulic cylinders and motors. Enable the transfer and conversion of mechanical energy. In aerospace, dynamic pressure guides the design and manufacturing of aircraft wings and tails to generate the desired lift and drag at a specific speed.
What are Static Pressure and Dynamic Pressure in HVAC?
In HVAC, the concepts of dynamic pressure and static pressure are defined as follows:
Dynamic Pressure:
From a fluid dynamics perspective, the kinetic energy possessed by a fluid due to its flow is termed dynamic pressure. Any airflow within ductwork possesses a certain dynamic pressure. It is an expression related to fluid density, the square of flow velocity, and gravitational acceleration.
Static Pressure:
The pressure exerted on the pipe wall due to the irregular motion of fluid molecules is called static pressure. In calculations, static pressure measured relative to absolute vacuum is termed absolute static pressure. Static pressure measured relative to atmospheric pressure is termed relative static pressure. All air static pressures in fresh air systems refer to relative static pressure.
Note: During fluid flow, friction occurs with the duct walls, and increased molecular collisions generate energy loss. This loss is termed pressure loss, or pressure drop.
What is the difference between DP（differential pressure）and static pressure?
Static pressure is the force exerted by a fluid on some objects when there is no relative motion between them. Static pressure is the pressure exerted by a fluid (gas or liquid) on its container or surrounding environment when at rest.
Differential pressure is the difference between the pressures detected at the high-pressure and low-pressure ends of a differential pressure sensor. It is measured by the pressure difference between the high-pressure and low-pressure ends and can be used for specific fluid pressure analysis.
What happens if the static pressure is too high in HVAC?
Excessive static pressure may cause system noise and prolonged operation of HVAC units. This translates to higher energy costs and additional stress on equipment.
High duct static pressure can cause serious problems for your HVAC system. Unstable static pressure has several causes. Some of the most common are related to system installation, either due to poor workmanship or improper duct and system sizing.
In other cases, using incorrect air filters or allowing clogged filters to remain in service can cause higher-than-expected static pressure in ductwork. Finally, minor issues like kinks in flexible ducting can restrict or alter airflow, increasing static pressure.
The following measures can help resolve high static pressure.
First, consider replacing the air filters. However, in severe cases, modifying the ductwork system or even replacing and reinstalling the entire system may be necessary.
The relationship between dynamic pressure, static pressure, and total pressure is common in aerodynamics and mechanical engineering. This article provides a general overview of their interactions, hoping it proves helpful.
All in all, if you’re facing challenges measuring dynamic pressure and static pressure, we offer specialized pressure sensors to solve your problems. We, Sino-Inst, are a measurement instrument supplier from China. Contact us immediately for a free quote!
