ESTABLISHMENT OF A PRIMARY LEVEL LAB FACILITY AT MEASUREMENT STANDARDS LABORATORY TO CALIBRATE AIR VELOCITY SENSORS

摘要

Air velocity measurements are a very common and important activity within Heating, Ventilating and Air Conditioning (HVAC), security, comfort and aerodynamic testing techniques. The most basic airflow measurement is the velocity and direction of the air flowing past a given point in space at a given time. Although it sounds simple, this has not been an easy thing to measure, particularly for small flows, because a measuring device placed in the air stream changes the airflow slightly. When air velocity is measured we need to know the mean value and its uncertainty, so air velocity sensors must be calibrated by means of a velocity standard to know their metrological performances. The correct position of the sensing probe is significant for reliable and accurate measurement of the air velocity. This paper will focus primarily on the design and operation of low speed wind tunnel to calibrate the air velocity sensors. The components involved in the construction of a typical wind tunnel will be presented and accompanied by brief commentary on the underlying physical processes most influential in determining optimal construction of each component. A summary overview of fluid dynamic principles concerning incompressible flow in tubes will include discussion on laminar and turbulent flow, fluid viscosity, Reynolds number criteria, and boundary layer formation. It should be designed flexible in order to make it suitable for research use and as well as laboratory teaching. This research grade wind tunnel will improve the metrological capabilities and will be of greater assistance to the industrial community in Saudi Arabia.