KNOUNIDESIGNS.
by Stepan Knouni
Rankine Cycle Simulations
The following Matlab script is a Rankine Cycle simulation. The purpose of the simulation was to study the effect of the intermediate pressures on the various components of a Rankine Cycle. The script uses functions in order to generate values for the appropriate thermodynamic tables. You can download all the script files below:
Rankine Reheat Cycle
Simulation Results
W of Turbines vs. Inter. Pressure:
As the pressure of states 4s, 4, (Inter. Pressure) increases, the resulting work from state 3 to state 4 decreases as illustrated in the graph. This happens because as the intermediate pressure increases, it approaches the pressure at state 3, resulting to a decrease in their enthalpy differences. Thus the overall work of the turbines decreases as well.
W of Pump vs. Inter. Pressure:
The work of the pump does not get affected by the change of the intermediate pressure, since the work from state 1 to 2 does not depend on the intermediate pressure.
Heat inputs vs. Inter. Pressure:
As the pressure of states 4s, 4, (Inter. Pressure) increases, the resulting heat input from state 4 to state 5 decreases as illustrated in the graph. This happens because as the intermediate pressure increases, it approaches pressure at state 5, resulting to a decrease in their enthalpy differences. Thus the overall heat input of the turbines decreases as well.
Quality of state 6 vs. Inter. Pressure:
The quality of state 6 depends on the entropy of state 5, which is a function of the intermediate pressure and temperature of sate 5. As the intermediate pressure increases, the entropy at 5 decreases, and as a result so does the quality of 6s and 6 respectively. The reverse proportionality of the quality at state 6 and inter. pressure is illustrated on the graph.
Temperature (at state 6) vs. Inter. Pressure:
The the temperature at state 6 does not get affected by the change of the intermediate pressure, since it does not depend on the intermediate pressure.
Overall Efficiency vs. Intermediate Pressure:
This graph illustrates the effect of the change of intermediate pressure on the overall efficiency of the cycle, for various pump and turbine efficiencies. The graph illustrates that there is a specific intermediate pressure on which the cycle reaches maximum efficiency for each case. However, a change in the efficiency of the turbines affects the overall efficiency way more that a change in efficiency of the pump. This result is logical since there are two turbines and only one pump in the cycle.