| This work is an investigation of a novel concept to produce power and cooling with the energy contained in low-temperature (<200°C), thermal resources. These resources can be obtained from non-concentrating solar thermal energy, low-grade geothermal resources, and a near infinite variety of waste heat sources. The concept under investigation uses thermal energy in a low-temperature boiler to partially boil an ammonia-water working fluid mixture. This produces an ammonia rich vapor that drives an expander. The expander's output is mechanical power; however, under certain operating conditions its exhaust can be cold enough to use for cooling. This possibility is the focus of the present study.; An analytical study is presented which identifies expander efficiency, expander inlet conditions, and exhaust pressure as the factors determining exhaust temperature. Estimated expander efficiencies are based on a consideration of the operating conditions and a review of current technology. Preferred inlet conditions are identified; however, they are linked to the overall operation of the cycle, as is absorption pressure. An optimal balance between vapor generation and expander exhaust temperature is found for cooling production.; Purifying the vapor is shown to enhance cooling production, but it penalizes work output. A new coefficient of performance is defined as the ratio of the cooling gained to the work output lost and is used to determine the optimal purification. Additionally, another performance coefficient is defined and used to judge the overall value of cooling produced.; An experimental study is presented that verifies the predicted trends. Furthermore, a measurement of sub-ambient exhaust temperatures is provided that demonstrates the key concept of this cycle. It is concluded that with improved expander performance, practical power and cooling production can be achieved with this concept. Deviations between measured and simulated performance are discussed as they relate to improving future modeling and system design efforts. |
