Search

The second‐law analysis evaluates the irreversibilities of a process. Systematic study of the relationship between thermodynamic efficiency and process modifications enhances process synthesis. The Allam cycle is an oxy‐fuel combustion cycle with nearly complete carbon capture that offers greater efficiency than current electricity generating systems. This study applies lost work analysis to the original Allam cycle and three modifications to obtain the distribution of irreversibilities and the effects of different configurations among potential process improvements for more sustainable power generation. The major inefficiencies are from the combustors and heat exchangers. We also examine the economic profitability of the alternatives. The largest equipment costs are for the turbines, compressors, and recuperators. We find that improving efficiency leads to less economic return; a configuration with partial compression has the highest efficiency, while the original Allam cycle has the highest profitability. We discuss how to resolve this apparent conflict between sustainability and profitability. [ABSTRACT FROM AUTHOR]

The Ranque‐Hilsch vortex tube is a device for continuously separating an inlet pressurized fluid stream into two outlet streams of warmer and cooler temperatures at lower pressures, with no moving parts and without any heat or work effects. It has been applied to cool or heat small systems where refrigeration is impractical. Studies of the fluid mechanics inside the tube have not fully established the flow structure that provides the separation. Thermodynamic energy and entropy balances giving relations among properties and the relative amounts of the three fluid streams have been examined to determine consistency among measured data along with sensitivity of the phenomena to tube configuration, measurement error, and properties. The strong response of the temperature separation to small variations in entropy generation is shown to limit the possibilities for generalized prediction of vortex tube behavior. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1067–1074, 2018 [ABSTRACT FROM AUTHOR]