SECOND LAW OF THERMODYNAMICS ThermodynamicsEarly thermodynamic developments were centered around improving the performance ofcontemporary steam engines. It was desirable to construct a cycle that was as close to beingreversible as possible and would better lend itself to the characteristics of steam and processcontrol than the Carnot cycle did. Towards this end, the Rankine cycle was developed.The main feature of the Rankine cycle, shown in Figure 31, is that it confines the isentropiccompression process to the liquid phase only (Figure 31 points 1 to 2). This minimizes theamount of work required to attain operating pressures and avoids the mechanical problemsassociated with pumping a two-phase mixture. The compression process shown in figure 31between points 1 and 2 is greatly exaggerated*. In reality, a temperature rise of only 1°F occursin compressing water from 14.7 psig at a saturation temperature of 212°F to 1000 psig.Figure 31 Rankine Cycle* The constant pressure lines converge rapidly in the subcooled or compressedliquid region and it is difficult to distinguish them from the saturated liquid linewithout artificially expanding them away from it.In a Rankine cycle available and unavailable energy on a T-s diagram, like a T-s diagram of aCarnot cycle, is represented by the areas under the curves. The larger the unavailable energy,the less efficient the cycle.HT-01 Page 88 Rev. 0
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
