Thermoacoustic Refrigeration of Large Food Storage Containers

Operational demonstration of a CFC-free, electrically-powered thermoacoustic refrigeration unit is proposed, enabled by cost-shared availability of proposer's patented STAR resonant drivers. STARs (developed in part through previous SBIR work and alreadyused in acoustic cryocoolers) uniquely resolve the primary performance problem demonstrated in all previous thermoacoustic refrigerators: the efficiency and power limitations of conventional drivers. STARs exhibit high electro-acoustic efficiency,intrinsic capacity modulation, and compact power delivery. The proposer's extensive experience with Stirling and thermoacoustic machine development assures similarly effective results in analysis, design, and production of specialized heat exchangers andother components proposed for this integrated thermoacoustic system.The work statement includes analysis, design, construction, and a proof test. There is a configuration study with cycle analyses to compare mechanical arrangement options in simulation(using DeltaE and Sage modeling codes). This is expected to show (for the optimal configuration) an average energy efficiency greater than existing vapor-compression equipment. Construction of a proof unit is included, using an existing STAR motor drivefrom the proposer's cryocooler products. Testing of the proof unit against a laboratory load will be done, to demonstrate electrically-driven thermoacoustic cooling power sufficient to serve the Army's 40 cubic foot field kitchen refrigerator (650Btu/hr).STAR-powered, modulating, thermoacoustic refrigeration can significantly improve the logistical impact of food storage on Army field operations. Commercialization of this technology depends on early demonstration of superior energy efficiency andoperational flexibility. The proposed Phase 1 project enables both military and commercial gains.For the Army's use, the anticipated results of this project provide a food storage cooling system that consumes less energy overall and exhibits significantlylower peak power, noise, and maintenance demand. Total field-use energy consumption includes not just steady-state operation, but transportation and support logistics. STAR-thermoacoustic cooling, lower peak power draws (through modulation) and lowermaintenance demand (of simpler, long-life non-lubricated components) can reduce the size of field generators and the spare parts inventory essential to fielded readiness. Less to haul means more energy savings and enhanced operational flexibility. Smallergenerators and higher efficiency mean less fuel carried and lower thermal signatures, too. The absence of conventional refrigerant in the proposed equipment also furthers the Army's mission to minimize adverse environmental impact in its operations.Forcommercial use, the proposed development of a military refrigerator is a necessary catalyst and a proving ground for advanced equipment that can address a huge number of civilian applications. The STAR-thermoacoustic cooling system is expected to offeroverall performance superior to conventional vapor-compression systems, at comparable cost and size, in most cases where the cooling is delivered directly adjacent to the refrigeration machinery. These include: household and commercial refrigerators andfreezers, grocery storage and display cases, vending machines, hotel room air conditioning/heat pumps, window and rooftop air conditioners, industrial cabinet and electronics cooling, and truck trailer and railcar cargo coolers. Only split system uses,like household central air conditioning, are not now practical to address. The proposers have identified a $16 billion/year addressable US market for these target applications. Present technologies use refrigerants that retain significant ozone-depletionor global-warming potentials and must be phased out soon. Other identified alternatives (e.g., absorption, thermoelectrics) have severe penalties in size, complexity, or efficiency. Adoption of the STAR-thermoacoustic technology proposed for this projectin even a small fraction of these applications can eliminate the environmental threat while reducing the enormous electric energy consumption applied to such cooling, without major changes to the packaging or production of most products and at areasonable cost.1) 1.9 Trillion kWhr/yr, $73Billion/yr for US Household 1997& commercial buildings 1995. This represents about 1/4 of total electric consumption for these sectors.