How to Measure Air Temperature in Tunnel.

Several temperature measurements are used for tunnel calculations. A pair of wet and dry bulb thermometers are located near the test section. These can be used to predict humidity of the air if this information is required for the experiment.

The static temperature of the air inside the tunnel is measured using a thermocouple located in the tunnel return leg. This temperature measurement is the one that should be used to accurately estimate air density of the tunnel flow. While the tunnel test section is vented to the surrounding air in the lab, this only means that tunnel static pressure is equivalent to the ambient pressure in the lab. Temperature of the air in the tunnel will be higher than ambient laboratory temperature when the tunnel is in operation due to the energy imparted to the flow by the driving fan and by friction with the walls, corner vanes and screens.

For conditions shown on the right the temperature of the air in the tunnel is