Design considerations for ammonia-water rankine cycle

Han

2018

Energies

The Kalina flash cycle (KFC) is a novel, recently proposed modification of the Kalina cycle (KC) equipped with a flash vessel. This study performs a comparative analysis of the thermodynamic performance of KC and KFC utilizing low-grade heat sources. How separator pressure, flash pressure, and ammonia mass fraction affect the system performance is systematically and parametrically investigated. Dependences of net power and cycle efficiencies on these parameters as well as the mass flow rate, heat transfer rate and power production at the cycle components are analyzed. For a given set of separator pressure and ammonia mass fraction, there exists an optimum flash pressure making exergy efficiency locally maximal. For these pressures, which are higher for higher separator pressure and lower ammonia mass fraction, KFC shows better performance than KC both in net power and cycle efficiencies. At higher ammonia mass fraction, however, the difference is smaller. While the maximum power production increases with separator pressure, the dependence is quite weak for the maximum values of both efficiencies.

Section: Introductionmentioning

confidence: 99%

Comparative Thermodynamic Analysis of Kalina and Kalina Flash Cycles for Utilizing Low-Grade Heat Sources

Han

2018

Energies

“…When the source is low-temperature energy in the form of sensible heat, the thermal performance of a power generation cycle using a pure substance becomes quite poor, because pure fluids have thermal properties of boiling and condensing at a constant temperature under a constant pressure condition, which leads to large temperature differences in the vapor generator and condenser and, in turn, inevitably increases the irreversibilities in the system. However, the use of an ammonia-water mixture, which is a zeotropic binary-mixture, as a working fluid in power generating systems has been found to be a proven technology for efficiently utilizing low-temperature heat sources [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Entropy and Exergy Analysis of a Heat Recovery Vapor Generator for Ammonia-Water Mixtures

2014

Entropy

Abstract:Recently power generation systems using ammonia-water binary mixtures as a working fluid have been attracting much attention for their efficient conversion of low-grade heat sources into useful energy forms. This paper presents the First and Second Law thermodynamic analysis for a heat recovery vapor generator (HRVG) of ammonia-water mixtures when the heat source is low-temperature energy in the form of sensible heat. In the analysis, key parameters such as ammonia mass concentration and pressure of the binary mixture are studied to investigate their effects on the system performance, including the effectiveness of heat transfer, entropy generation, and exergy efficiency. The results show that the ammonia concentration and the pressure of the mixture have significant effects on the system performance of the HRVG.

“…The motivation of them is that heat can be supplied or rejected at variable temperature but constant pressure. The variable heat transfer processes reduce the temperature mismatch between the hot and cold streams and the cycle, which results in smaller exergy destruction in heat exchangers [10].…”

Section: Introductionmentioning

confidence: 99%

Influence of Pressure on the Performance of Heat Exchangers in Ammonia-Water Based Power Cycles

Han

2012

AMM

Recently the power generation systems using ammonia-water binary mixture as a working fluid have been attracted much attention for efficient conversion of low-temperature waste heat sources to useful energy forms. In this work, ammonia-water based Rankine (AWR) and regenerative Rankine (AWRR) power generation cycles are comparatively analyzed by investigating the effects of turbine inlet pressure on the performances of heat exchangers in AWR and AWRR systems. Temperature distributions of fluid streams in the heat exchanging devices are closely examined at different levels of turbine inlet pressure under the conditions that the minimum temperature difference of hot and cold streams reaches the prescribed pinch point. Results show that the position of pinch point and temperature distributions are sensitively affected by varying turbine inlet pressure, which might be the most important design consideration in the power systems using a binary working fluid.