Evaluating energy dissipation during expansion in a refrigeration cycle using flue pipe acoustic resonators

Abstract

This research evaluates the feasibility of using a flue pipe acoustic resonator to dissipate energy from a refrigerant stream in order to achieve greater cooling power from a cryorefrigeration cycle. Two models of the acoustic operation of flue pipe resonant systems are examined: an electrical circuit analog that represents the linear approximation of the acoustic system and a numerical model based on empirical data. The electrical analog yields a symbolic representation for the power that can potentially be dissipated from the acoustic stream. Ongoing research into these acoustic systems, however, shows that the electrical analog, which neglects nonlinear effects, is incomplete and overestimates the operation of a pipe. However, the analogy can be used to quickly find the order of magnitude of power dissipated from the acoustic resonator. A subsequent data-based model allows for a more accurate quantitative estimation of the potential efficiency of the flue pipe in extracting work and thereby dissipating energy from a refrigerant stream. The efficiency of extracting work from a refrigerant stream using the acoustic system analyzed here ranges from 10% to 60%. The range is so large because the quality factor of the experimental flue pipe is unknown. This quality factor is imperative in determining the power dissipation. Further research should optimize the quality factor. A large quality factor causes less amplitude attenuation than a small one, but a smaller one dissipates more of the stored energy. The results of the models are compared to the efficiencies of existing technology, specifically the recently invented thermo acoustic expansion valve (TEV). It is found that the efficiency of the TEV is less than the theoretical results deduced from the numerical model. At an efficiency of approximately 10%, the technology represents a gain in cooling power, but further optimization using the results of this research can increase this gain even more.