Wind Tunnel Review
Choosing a wind tunnel for a laboratory for thermal studies for electronics must factor in cost and space constraints.
Omega Engineering’s wind tunnel is designed to give a highly uniform flow rate over a 6" (152 mm) test section. A 12 A motor with variable speed from 0 to 10,000 rpm is adjustable to give a particular flow rate using a motor control unit. The uniform flow rate is determined by monitoring a repeatable differential-pressure sensor that has been calibrated to each individual wind tunnel as a system. Each wind tunnel is supplied with two restrictive plates for achieving optimum low flow rates. The established differential pressure measurements vs. flow rates are listed from 25 to 9,000 ft/min. Calibration sheets are included, which makes calibrating different flow sensors simple.
The differential pressure measurements used to establish known flow rates will be affected by barometric pressure and temperature conditions during testing. Depending on the application, humidity may also be a factor. To control these issues, Omega offers a wind tunnel package with an environmental monitoring system that measures barometric pressure, room temperature, humidity and differential pressure. By monitoring room conditions, standard differential pressures can be converted to actual differential pressure readings to ensure accurate flow rates.
The CLWT-115 from Advanced Thermal Solutions Inc. is a closed-loop wind tunnel that provides a system for thermally characterizing PCBs and individual components at controlled temperatures from ambient to 85°C. This wind tunnel produces airflows up to 1000 ft/min (5 m/s). With customization, it can generate flows up to 10,000 ft/min (50 m/s) using orifice plates. It has a clear plastic test section so the user can view the test specimen and airflow. Unlike open-loop wind tunnels, the closed-loop version recirculates internal air. This allows the system heater to quickly warm the air to a specific temperature. The testing of boards and components in hot air is a requirement in some NEBS and other standards.
The precise controls and temperature range of this kind of closed-loop wind tunnel allow its use for testing heat sink performance and for calibrating air and temperature sensors. The complete wind tunnel fits on most laboratory benches and is powered from standard AC outlets. It has a smaller footprint than traditional, closed-loop wind tunnels or environmental test chambers. The wind tunnel’s test section can be accessed from the top door or sides for mounting and repositioning of boards, components and sensors. Internal rail guides provide a mechanism to install test specimens of different sizes (e.g., PCB, heat sink). Instrument ports are provided in the side walls of the test section for placing temperature and velocity sensors such as thermocouples, Pitot tubes and hotwire anemometers.