Parametric Study
In order to complete the project Excel and MATLAB were used to carry out the calculations. Excel and matlab in conjunction with CoolProps puts the property tables less than a click away CoolProps is a seperate program and is an ‘add-in’ in excel. All is needed is a basic code inputted into your excel graph with the given values and the variables needed are automatically given. To ‘coding’ for both MATLAB and Excel the inputter needs two given variables of state.
The first variable inputted into the cell is what you are trying to find. This could be “s” for entropy,”T” for temperature, “h” for enthalpy, “Q” for quality, or “P” for pressure. For this project enthalpy was our variable of interest. After the pressure and the quality have been inputted as the given values along with the information that the cycle is a water cycle and the entire code is divided by 100 for units sake. An example of this can be seen in Table 1 below. Once the quality has been solved for more formulas are created to solve for the Power of each and every component, and efficiency for the entire system.[2]
After the results are obtained from excel they need to be check with MATLAB. The coding process is extremely similar however MATLAB has greater capabilities used with more ease. Example of the coding used can be found in Appendix A, B, C, and D. Once a MATLAB code is written graphs depicting the performance of the cycle are generated. These graphs will be used to help analyze which cycle is the most efficient one for our purpose.
For this project four variations of the rankine cycle were analyzed. These included a modified open feedwater heater, modified closed feed water heater, modified high/low pressure turbine and the rankine cycle. They were all analyzed under the same conditions to determine which of the four operating cycles had the best efficiency. An Open feedwater heater, Closed feedwater heater, modified high/low pressure turbine were all compared with the simple rankine cycle to see what the effects of Increasing the pressure and power to the system would do.
The first variable inputted into the cell is what you are trying to find. This could be “s” for entropy,”T” for temperature, “h” for enthalpy, “Q” for quality, or “P” for pressure. For this project enthalpy was our variable of interest. After the pressure and the quality have been inputted as the given values along with the information that the cycle is a water cycle and the entire code is divided by 100 for units sake. An example of this can be seen in Table 1 below. Once the quality has been solved for more formulas are created to solve for the Power of each and every component, and efficiency for the entire system.[2]
After the results are obtained from excel they need to be check with MATLAB. The coding process is extremely similar however MATLAB has greater capabilities used with more ease. Example of the coding used can be found in Appendix A, B, C, and D. Once a MATLAB code is written graphs depicting the performance of the cycle are generated. These graphs will be used to help analyze which cycle is the most efficient one for our purpose.
For this project four variations of the rankine cycle were analyzed. These included a modified open feedwater heater, modified closed feed water heater, modified high/low pressure turbine and the rankine cycle. They were all analyzed under the same conditions to determine which of the four operating cycles had the best efficiency. An Open feedwater heater, Closed feedwater heater, modified high/low pressure turbine were all compared with the simple rankine cycle to see what the effects of Increasing the pressure and power to the system would do.
Simple Rankine Cycle results WT = h3 - h4 = 1687.57kW WP = h2 - h1 = 4.54kW Eta = (WT - WP) / QB = 0.432 = 43.2% Results for High/Low Pressure Turbine WT = (h3-h4) + (h5-h6) = 2304.09kW WP = h2-h1 = 4.54kW Eta = (WT-WP)/QB = 0.484 = 48.4% |
Results for a Modified Closed Feedwater heater
WT = y(h6 - h7) + (1-y)(h6 - h8) = 981.162kW WP = (1-y)(h2-h1)+(h4-h3)y = 1633.84kW Eta = (WT - WP)/QB = 0.273 = 27.3% Results for Modified Open Feedwater heater WT = (h5 - h6)+(1-y)(h5-h7) = 1482.51kW WP = (1-y)(h2-h1) + (h4 - h3) = 51.675kW Eta = (WT - WP)/Qb = 0.457 = 45.7% |
Above shows the results of what will be analyzed compared to the simple rankine cycle as a base model. By adding a High/Low pressure turbine the efficiency and work produced by the turbine increases and the work done by the pump is the same. With a closed feed water system the efficiency and work done by the turbine is decreased and the work done by the pump is increased. Finally the open feedwater system increases the efficiency and work done by pump, however the work done by the turbine stays decreases. The closed feedwater system would be the poorest system do utilize as its has the lowest efficiency while increasing total work which would drive up cost. On the other hand the high/low pressure turbine and open feedwater system increases efficiency but also greatly increase work done by the pump or turbine. This would make it more cost effective than the closed feed system and make them good options to use.