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Did you know? The truth behind the magical unit of air flow!
Air flow, or airflow, refers to the movement of air. Air is a fluid, and particles naturally flow from areas of high pressure to areas of low pressure. Atmospheric pressure is closely related to altitude, temperature and composition. In engineering, air flow refers to the amount of air passing through a specific piece of equipment per unit time. This can be described in terms of volume flow or mass flow, with the connection between the two being determined by the density of the air, which is a function of the ideal gas law. The movement of air can be initiated by mechanical means (such as operating an electric or manual fan), or it can occur passively by pressure differences present in the environment.
Types of air movement
Like other fluids, air can exhibit both laminar and turbulent flow modes.
As air passes through geometries such as ducts, wide ducts, open channels, or airfoils, the size and shape of the flow profile can be affected by a variety of factors, including the properties of the fluid, its physical structure, and energy-adding components such as pumps. role.Laminar flow occurs when air flows smoothly and has a parabolic velocity profile; turbulent flow occurs when irregularities occur during fluid flow, changing the direction of motion and making the velocity profile flat.
Unit of air flow
Typical units for expressing air flow are:
- Calculated by volume: m3/min (cubic meters per minute), m3/h (cubic meters per hour), ft3/h (cubic feet per hour), ft3/min (cubic feet per minute), l/s (liters per second)
- Calculated by mass: kg/s (kilograms per second)
Air flow can also be described in terms of air changes per hour (ACH), which represents the complete replacement of the volume of air filling the space in question. In the field of building science, higher ACH values often correspond to more leaky envelopes in older buildings.
Instruments for measuring air flow
Instruments that measure air flow are called air flow meters, while anemometers can also be used to measure wind speed and indoor air flow. There are various types of anemometers, including straight probe anemometers designed to measure air velocity, rotating vane anemometers and hot bulb anemometers designed to measure airflow volume. These instruments may use ultrasonic or resistive wires to measure the energy transfer between the measuring device and passing particles.
For example, a hot wire anemometer can calculate air flow rates by analyzing the reduced wire temperature, since the resistance of metal changes with temperature, affecting the effects of convective cooling.
Air flow simulation
Air flow can be simulated through computational fluid dynamics (CFD) modeling or experimentally observed through the operation of a wind tunnel. This can be used to predict air flow patterns around cars, planes and ocean vessels, as well as gas infiltration of building envelopes. CFD models are able to track the flow of solids through the system and therefore can be used to analyze pollutant concentrations in indoor and outdoor environments.
Equipment for controlling air flow
A device used to regulate air flow in a duct is called a damper. Such a device can be used to increase, decrease, or stop airflow entirely. More sophisticated devices are called air handlers, which not only regulate airflow but also generate and process it.
Purpose of air flow
Measuring air flow is necessary in many applications such as ventilation (to determine how much air is being replaced), pneumatic transmission (to control air speed and transport phase), and engines (to control the air-to-fuel ratio). Pneumatics is a branch of fluid dynamics that focuses on the measurement, simulation, and control of airflow. Managing airflow is a focus in fields as diverse as meteorology, aviation, medicine, mechanical engineering, civil engineering, environmental engineering, and building science.
Air flow in buildings
In building science, there is often a focus on the desirability of air movement, such as contrasting ventilation and infiltration. Ventilation is defined as the introduction of fresh outdoor supply air into another indoor space and the simultaneous discharge of indoor exhaust air to the outdoors. This can be achieved through mechanical means (such as using air intake louvers or dampers and fans to induce airflow through ducts) or passive strategies (also known as natural ventilation).
Natural ventilation has an economic advantage over mechanical ventilation because it generally requires less energy to operate but can only be utilized at certain times and under outdoor conditions.
The relationship between airflow, thermal comfort and overall indoor environmental quality
Air movement is critical when considered in design to meet occupant thermal comfort standards. Different air movement rates can positively or negatively affect an individual's perception of heat or cold, thereby affecting their comfort. Adequate, properly controlled and designed air movement (ventilation) is important to overall indoor environmental quality (IEQ) and indoor air quality (IAQ) as it provides necessary fresh air and efficient exhaust emissions.
Understanding the mystery of air flow may allow us to better control and improve our living environment. Will you feel the charm of it?
