Is your refrigerator running? More importantly, what's it running on?

Inside of refrigerators is a substance with about 1,300 times greater climate change potential than carbon dioxide. HFC-134a, a hydrofluorocarbon, can leak from the appliances into the environment, trapping greenhouse gases in the atmosphere.

Professor of Mechanical Engineering Chuck Knisely would like to see HFC-134a eliminated, and he's enlisted two Bucknell undergraduate researchers, Evan Colarusso and Stephanie Snoich, both in the Class of '14, to help. With Knisely as their mentor, the students have worked to improve a potentially more sustainable cooling system: the reverse Brayton-cycle refrigerator. It refrigerates by compressing and expanding environmentally benign atmospheric gases like nitrogen.

Colarusso fabricated a Tesla turbine to replace an inefficient valve used in a basic or current reverse Brayton-cycle refrigerator. A Tesla turbine is a cylinder with disks lined up next to each other flat sides together. Air is shot inside the circumferences of the disks, causing them to rotate and spin a shaft, thus producing electricity. That electricity, says Colarusso, might eventually be useful in supplementing the power to the refrigerator's air compressor, making it more energy efficient.

"The turbine can be made from cheaper materials and is safer, quieter, smaller and easier to build," says Colarusso, who this fall will investigate whether the roughness or smoothness of the disks affect the turbine's efficiency.

Snoich designed, constructed and implemented a test-rig to check the thermodynamic efficiency of Colarusso's turbine and other proposed expansion and compression systems that emerge from Knisely's lab. The manually operated facility includes gas flow meters, pressure gauges and temperature sensors. From the data produced, researchers can calculate efficiency of each component, says Snoich.

"The apparatus gives immediate results to students," she says. "It's a hands-on learning tool and applicable in a variety of courses, ranging from introductory thermodynamics, to fluid dynamics and turbo-machinery."

Knisely in fact plans to use both Snoich's and Colarusso's projects in future courses.

"A marketable environmentally friendly refrigerator remains several years away," he says. "But Evan and Stephanie can feel proud that they're passing on their knowledge."

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