Showing papers by "D. Yogi Goswami published in 2011"

Analysis of a combined power and cooling cycle for low-grade heat sources

Abstract: SUMMARY This paper presents a parametric analysis of a combined power/cooling cycle, which combines the Rankine and absorption refrigeration cycles, uses ammonia–water mixture as the working fluid and produces power and refrigeration, while power is the primary goal. This cycle, also known as the Goswami Cycle, can be used as a bottoming cycle using waste heat from a conventional power cycle or as an independent cycle using low-temperature sources such as geothermal and solar energy. Optimum operating conditions were found for a range of ammonia concentration in the basic solution, isentropic turbine efficiency and boiler pressure. It is shown that the cycle can be optimized for net work, cooling output, effective first law and exergy efficiencies. The effect of rectification cooling source (external and internal) on the cycle output was investigated, and it was found that an internal rectification cooling source always produces higher efficiencies. When ammonia vapor is superheated after the rectification process, cycle efficiencies increase but cooling output decreases. Copyright © 2010 John Wiley & Sons, Ltd.

Method and system for generating power from low- and mid- temperature heat sources

Abstract: A method and system for generating power from low- and mid- temperature heat sources using a zeotropic mixture as a working fluid The zeotropic mixture working fluid is compressed to pressures above critical and heated to a supercritical state The zeotropic mixture working fluid is then expanded to extract power The zeotropic mixture working fluid is then condensed, subcooled, and collected for recirculation and recompression

Multi-Objective Optimization of a Combined Power and Cooling Cycle for Low-Grade and Mid-Grade Heat Sources

Abstract: Optimization of thermodynamic cycles is important for the efficient utilization of energy sources; indeed it is more crucial for the cycles utilizing low grade heat sources where the cycle efficiencies are smaller compared to high temperature power cycles. This paper presents the optimization of a combined power/cooling cycle, also known as the Goswami Cycle, which combines the Rankine and absorption refrigeration cycles. The cycle uses a special binary fluid mixture as the working fluid and produces power and refrigeration. In this regard, multi-objective genetic algorithms (GA) are used for Pareto approach optimization of the thermodynamic cycle. The optimization study includes two cases. In the first case the performance of the cycle is evaluated as it is used as a bottoming cycle, and in the second case as it is used as a top cycle utilizing solar energy or geothermal sources. The important thermodynamic objectives that have been considered in this work are, namely, work output, cooling capacity, effective first law and exergy efficiencies. Optimization is carried out by varying the selected design variables; boiler temperature and pressure, rectifier temperature, and basic solution concentration. The boiler temperature is varied between 70–150 °C and 150–250 °C for the first and the second cases, respectively.Copyright © 2011 by ASME

Optimizing Energy Conversion Using Organic Rankine Cycles and Supercritical Rankine Cycles

Abstract: The optimization of energy conversion systems is of great significance in the utilization of low-grade heat This paper presents an analysis of 6 working fluids in 12 thermodynamic cycles to optimize the energy conversion systems The optimal exergy efficiency of the system is dependent on the type of the thermodynamic cycle, the choice of appropriate working fluid, and the working conditions A zeotropic mixture of R134a and R245fa shows advantages in energy conversion process, as well as its heat exchange with the heat source and heat sink The exergy efficiency of a 05R134a/05R245fa-based supercritical Rankine cycle system is 0643–0689 for a turbine inlet temperature of 415–445K, which is about 30% improvement over the exergy efficiency of 0491–0521 for a pure R32-based organic Rankine cycle under the same temperature limits Furthermore, the 05R134a/05R245fa mixture saves more than 60% of the cooling water during the condensation process than the pure R32, R134a and R245faCopyright © 2011 by ASME

Performance Analysis of a Rankine-Goswami Combined Cycle

Abstract: Improving the efficiency of thermodynamic cycles plays a fundamental role in reducing the cost of solar power plants. These plants work normally with Rankine cycles which present some disadvantages due to the thermodynamic behavior of steam at low pressures. These disadvantages can be reduced by introducing alternatives such as combined cycles which combine the best features of each cycle. In this paper a combined Rankine-Goswami cycle (RGC) is proposed and a thermodynamic analysis is conducted. The Goswami cycle, used as a bottoming cycle, uses ammonia-water mixture as the working fluid and produces power and refrigeration while power is the primary goal. This bottoming cycle, reduces the energy losses in the traditional condenser and eliminates the high specific volume and poor vapor quality presented in the last stages of the lower pressure turbine in the Rankine cycle. In addition, the use of absorption condensation in the Goswami cycle, for regeneration of the strong solution, allows operating the low pressure side of the cycle above atmospheric pressure which eliminates the need for maintaining a vacuum pressure in the condenser. The performance of the proposed combined Rankine-Goswami cycle, under full load, was investigated for applications in parabolic trough solar thermal plants for a range from 40 to 50 MW sizes. A sensitivity analysis to study the effect of the ammonia concentration, condenser pressure and rectifier concentration on the cycle efficiency, network and cooling was performed. The results indicate that the proposed RGC provide a difference in net power output between 15.7 and 42.3% for condenser pressures between 1 to 9 bars. The maximum effective first law and exergy efficiencies for an ammonia mass fraction of 0.5 are calculated as 36.7% and 24.7% respectively for the base case (no superheater or rectifier process).Copyright © 2011 by ASME