The Ben & Jerry's Project
A prototype thermoacoustic chiller has been designed, constructed and tested that has a greater power density than any other electrically driven thermoacoustic refrigerator to date. The prototype machine, which is 10 inches (25.4 cm) in diameter and about 19 inches (48.3 cm) tall, has a cooling capacity of 119 W at a temperature of -24.6 ºC. The overall coefficient-of-performance (defined as the ratio of the cooling capacity to the electrical power consumption) of the chiller is measured to be 0.81 or 19% of the Carnot COP at the capacity and temperature listed above. For more information about how this machine moves heat and more performance data, see the paper in Acoustic Research Letters Online (ARLO) published by the Acoustical Society of America.
A cut-away solid model of the entire machine is shown on the right and a cross-sectional view is shown on the left. The cold heat exchanger (dark grey) is identical to the hot heat exchanger and is contained within a thermally-insulating Ultem plastic plate (brown). The cold heat exchanger plate is in contact with the “platform” plate (yellow) that contains the regenerator and sensor signal lines. A second thermally-insulating Ultem plastic plate (green) provides the contoured plenum space that directs the oscillating cold helium gas in and out of the thermal buffer spaces (“windows”) through the platform. A solid stainless steel plate (dark grey) is used to seal the platform, cold heat exchanger plate, and plenum plate to the pressure vessel (green) and provide the force necessary to resist the 10 atmospheres of internal helium gas pressure. Enclosing the hot heat exchanger is the vibromechanical multiplier comprised of the compliance volume within the multiplier's cylinder (orange) that is terminated by an ordinary loudspeaker cone (purple). Directly below the speaker cone is the power piston cone (light green) that is attached to the bellows (gray). The moving-magnet linear motor, which moves the power piston cone, is shown as a gray rectangle with yellow straps. It is attached to the bottom plate (black) that forms the lower boundary of the pressure vessel. The cylindrical portion of the pressure vessel is shown in green.
In 1999, Ben and Jerry’s Homemade Ice Cream began a company wide audit of their refrigeration machinery and realized that they could make a difference in the emission of global warming gasses by finding an alternative to the HFC based refrigerants found in virtually all small refrigeration units. In collaboration with Greenpeace, IEER and other organizations that have interest in environmental protection, they were made aware thermoacoustic technology. In late spring of 2002, they began to fund our team at PSU to develop a prototype that could meet the stringent cost, capacity and reliability targets required for in-store ice cream storage cabinets. By February 2003 we had a working prototype and in April of 2004 the prototype was interfaced to a standard ice cream storage cabinet that had the compressor and condenser removed. For more information about this project, check out the Ben and Jerry’s website which has a great 10 minute piece about the B&J/PSU collaboration.
This photographs shows the stainless steel resonator of the thermoacoustic machine (with Matt uselessly “fiddling with it” for the photographer) as it is removing heat from the off-the-shelf (200 liter storage volume) ice cream cabinet in the foreground. You can see cold pints of Ben and Jerry’s ice cream under the clear sliding lids of the cabinet. The only modification made to the cabinet was to remove the compressor and condenser coils. The evaporator tubing now carries a single phase liquid that is circulated through a heat exchanger in the thermoacoustic machine where heat is removed from it.
This photograph shows the whole team gathered in front of the cabinet ready to enjoy some thermoacoustically cooled Ben and Jerry’s ice cream. From right to left, the team is Robert Smith, Steven Garrett and Matt Poese.