## 6 Results and Discussions
### Influence of Total-Flow Turbine  
As illustrated above, the crucial factor of the proposed TF-SF system is the efficiency of the total-flow turbine. In order to study the sensitivity of system performance to TF turbine efficiency, four reasonable efficiencies covering from 20% to 65% are assumed and compared. As to the wellhead condition chosen in this simulation, the pressure/temperature/mass flowrate/vapor quality are 655.7 kPa/162.3 \({}^{\circ}\)C/14.5 kg/s/0.23. An optimum system power of 851.1 kW would be reached under this condition when the TF turbine efficiency is 35%, as shown in Figure 3.  
As shown in Figure 6, power capacity of the SF part is only slightly influenced by the variable total-flow turbine efficiency (\(\eta_{\eta f}\)). The increment of total-flow turbine efficiency (\(\eta_{\eta f}\)) would slightly decrease the vapor quality at turbine outlet, meaning that slightly less vapor would go through  
Figure 5: Distribution of freshwater generation against wellhead pressure and separating temperature. the steam turbine in the SF part to generate power. The biggest decrement of SF power capacity is only 5.5%. However, a more efficient total-flow turbine can significantly improve the power capacity of the TF part. During the reduction of separating temperature from wellhead condition to condensation condition, the TF part's power can only exceed the SF part's as the separating temperature is lower than 110 \({}^{\circ}\)C when the total-flow turbine efficiency is pre-set as 20%. However, a separating temperature of 125 \({}^{\circ}\)C is enough for the TF part to exceed SF regarding power capacity when the total-flow turbine efficiency can reach 65%, in which case the TF part is comparable to the SF part in terms of power generation. The effects that total-flow turbine efficiency (\(\eta_{lf}\)) has on TF-SF system performance, including power generation and freshwater generation, are shown in Figure 7. As a comparison, power capacity of a single-flash-only power system is also added, as the black dash lines represents. Firstly, the power generation comparison shows clearly higher power production of the proposed TF-SF combined system. When the total-flow turbine efficiency (\(\eta_{lf}\)) reaches to a value of 50%, an optimal power capacity can reach up to 875.8 kW at the separating temperature of 147.9 \({}^{\circ}\)C, exceeding that of SF-Only system by 16.1%. Furthermore, a more effective total-flow turbine with an efficiency (\(\eta_{lf}\)) of 65% has an optimal power capacity of 933.0 kW at the separating temperature of 131.9 \({}^{\circ}\)C, higher than that of SF-Only system by 23.7%. As for the freshwater generation capacity, higher total-flow turbine efficiency leads to slightly lower system freshwater output because it leads to smaller amount of steam flowing into the following steam turbine. However, the biggest reduction regarding the freshwater production within the efficiency range is only 0.2 kg/s (<5%), making it ignorable. On average, one fourth to one third of wellhead flow is recoverable by the system. During the condensation of the steam, the produced freshwater is to a certain extent desalinated and good for application in human activity, such as industrial water supply, plants irrigation, daily washing consumption. This extra benefit helps address the local water scarcity problem. Figure 6: Effects of total-flow turbine efficiency (\(\eta_{lf}\)) on power capacities of TF and SF. In order to maintain the sustainability of the geothermal field, the rejection strategy is a key factor to be considered. However, since the geothermal field targeted here is a two-phase, liquid-dominated one with relatively low-to-medium production enthalpy (1100 kJ/kg \(<h<\) 1200 kJ/kg) [25; 26; 27], in general the pressure decline is not excessive for geothermal systems in this sort of fields. Besides, good permeability in this kind of field benefits itself with strong lateral recharge.