One way to improve the performance of waste-heat activated cooling systems, such as adsorption systems, is by targeted application of ultrasonic energy, which may make possible the use of abundant low-temperature heat sources to provide cooling. This project explores how ultrasonic energy, combined with low-temperature heat sources, can realize higher-efficiency adsorption cooling by increasing the rate at which refrigerant vapor is released from the surface of a solid adsorbent. This in effect creates a thermal compressor that replaces the conventional electric-powered compressor. At this point, however, the mechanisms by which ultrasound interacts with adsorbed liquid refrigerant are not clear, and these are examined through both experiments and theoretical modeling. This project also involves significant educational and outreach activities. To date there has been no central, online, open-source resource for thermally activated heat pump technologies. In addition to assembling and making available open-source simulation codes and performance data that make it easier to design improved systems, online educational modules are developed for enhancing the understanding of students and practitioners in this field and thus promote wider development and adoption of environmentally friendly heat pump technologies.
Although prior work clearly indicates the potential to improve desorption by applying ultrasonic energy, in general this prior work focused on system-level effects rather than local detailed measurements that would enable improved fundamental understanding. For example, how much of the improved desorption is due to localized heating, and how much is due to other effects such as mechanical compression/decompression, acoustic softening, etc.? Our work, rather than emphasizing such system-level performance, instead focuses on detailed, localized measurements and analysis to improve fundamental understanding of these coupled heat and mass transport processes that are crucial not only for adsorption cooling, but also for desiccant drying, food drying, etc. We also explore a much wider range of adsorbents/refrigerants, in addition to the silica gel/water system studied earlier. Interestingly, the application of ultrasound may enable new adsorbent materials to be utilized, such as superabsorbent polymers (commonly used in disposable diapers) that can absorb up to 2000 times their own weight in water. Without ultrasound, the use of polymers is limited or even prohibited because of the high temperatures needed for regeneration. By examining alternative materials like superabsorbent polymers we are able to greatly expand the variety of adsorbent/refrigerant pairs that can be considered for application in adsorption cooling.
