Cooler
Introduction
The large input of power by the fan is ultimately converted into heat – mostly from friction with the tunnel walls; this heat must be removed by the cooler. The cooler is made up of four rows of oval copper tubes. Cooling water is supplied to the top of the cooler and pumped down the rear two rows of tubes and back up the front two rows in order to maintain an even distribution of temperature.
Cooling Towers
Water flows through the cooler at a rate of 27000 litres (6000 gallons) per minute during which the water temperature increases by around 10°C (18F). On emerging from the cooler, the water is pumped through “forced draught” (fan powered) cooling towers where the water temperature drops by 10°C due to evaporation.
The cooling towers can be seen with steam rising from them in
the bottom right hand corner of the site photograph.
Technical Information
The cooler is preceded by a rapid change in the tunnel shape from an octagonal shape with a cross-sectional area of 55 sq. metres (592 sq. feet) at the end of the low speed diffuser to a rectangular shape with cross-sectional area of 103 sq. metres (1109 sq. feet) at the cooler. This rapid expansion would normally cause a severe disturbance to the flow but the cooler creates a back pressure which stabilises the air flow. The speed of the airflow at the cooler is approximately 13 metres per second (43 feet per second) when the air flow speed in the Test Section is Mach 0.8.
In addition to removing surplus heat from the tunnel, the cooler provides a significant amount of smoothing to the flow emerging from the fan section.
