During manufacture at Super Radiator Coils, each of the copper tubes in a coil was carefully brazed to a copper header that will feed refrigerant to the tubes.
The NASA wind tunnel has been in continuous operation since 1944. Aeronautic design engineers, aircraft manufacturers and airline companies use the facility to test wing design and other aircraft components under icing weather conditions. Its closed-loop tunnel uses a 5,200 hp motor and 14' prop-fan to recirculate air at speeds of 50 to 300 knots/hr (31 to 186 mi/hr). Downstream from the bank of coils are misters that inject water into the airstream, which freezes upon contact with the test specimen.
“The new coils will incorporate the most advanced heat exchanger technologies available and have taken about four months to build,” said Jon Holt, chairman of Super Radiator Coils. “One of the main reasons we were chosen for this important project was because of our experience in custom designing and manufacturing coils for 14 other wind tunnels, including NASA’s Ames Research Center in Mountain View, California.”
Designing the high efficiency, cascade-style heat exchangers to meet NASA’s specifications was a collaborative effort between Super Radiator and Jacobs Technology Inc., Tullahoma, Tenn., a company that specializes in wind tunnel design. The innovative design tilts the heat exchanger coils forward in a slant configuration that effectively doubles the exposed face area of the coils. The result is an increase in the heat transfer capabilities of the coils while reducing the air velocity and preventing ice shedding from the coils.
Each of the six, 50'-long heat exchanger coils for NASA’s Icing Research Tunnel was assembled by hand.
The $1.2 million project includes six large coils, or modules of heat exchanger coils, that will be stacked on top of each other in the IRT to form a wall that air must pass through before entering the test chamber in the wind tunnel. Each module is 4.4' high, nearly 9' wide and 50' long.
More than 30 miles of 0.625" dia. copper tubing were used to form the coils, which have enough heat-dissipating aluminum fins around them to cover a football field. All told, the six banks of coils will weigh 110 tons when a refrigerant is put inside the tubes.
Besides the massive wall of heat exchanger coils, the IRT’s remodeling project involves replacing all of the refrigeration equipment, including compressors, piping, instrumentation and controls. The new system will use advanced low-temperature refrigerants. All of these upgrades will increase efficiency and provide better thermal controls, according to Super Radiator.
“A project like this was not without its many challenges, beginning with its sheer size and scope,” Holt said. “Although we have designed and manufactured coils for a number of wind tunnels, this is by far the largest.”
“The overall height, weight and length of the coils, along with the core weight of the multi-angled framework that will hold the coils in each module, were all manufactured to a non-standard design,” he continued. “Another challenge that is yet to come will be carefully placing all six coil modules on top of each other to perform as one gigantic heat exchanger coil, taking into account variances in thermal expansion and contraction.”
The company has been working on plans for this project for more than a year. The six modules were assembled and tested by Super Radiator at its facilities in Chaska. Once transported to the IRT, they will be lowered through the roof into the wind tunnel. After final assembly, installation and additional testing, the research facility is expected to become operational by late fall.