Environmental priorities are forcing chloro­-fluorocarbons out of market place thereby creating a new demand for cooling technologies. This paper presents an outcome of researches done to design, construct and evaluate a CFC free refrigeration system. A prototype Thermo acoustic cooling system utilizing high amplitude sound waves in an inert gas is discussed.





Thermo Acoustic Engines


A thermo acoustic engine converts some heat from a high Temperature heat source into acoustic power rejecting waste heat to a low temperature heat sink. The figure shown is very similar to appearance of a heat engine. The apparatus absorbs heat per unit time Qh from the heat source at high temperature Th rejects heat per unit time QC to a heat sink at low temperature TC and produces acoustic power W. According to first law of thermodynamics W + QC = Qh. The second law of thermodynamics show that the efficiency W/Qh is bounded by the carnot efficiency (Th-TC)/Th.


One of the most important scales in a thermo acoustic device is the length of its resonator which determines the operating frequency. Just as the length of an organ pipe determines its pitch. The gas sound speed is also an important criterion. In the figure with both ends of resonator are closed, the west resonant mode is that which fits a half wavelength.