## 5 Results and Discussions
### Parametric Analysis
#### 5.1.1 Effects of the Compressor Pressure Ratio (PRc)  
Figure 2 depicts the influences of PRc on the system performance indicators, namely COPP, COHP, exergy efficiency \(\eta_{\text{ex}}\) and total product unit cost \(c_{\text{total}}\), for a single sCO\({}_{2}\) system, sCO\({}_{2}\)/DH system, sCO\({}_{2}\)/ammonia-water AHP system, and sCO\({}_{2}\)/LiBr-H\({}_{2}\)O AHP system, respectively. Obviously in Figure 2a, the thermodynamic and exergoeconomic performances for these four systems can be ranked according to \(\eta_{\text{ex}}\) and \(c_{\text{total}}\) as: sCO\({}_{2}\)/LiBr-H\({}_{2}\)O AHP \(>\) sCO\({}_{2}\)/ammonia-water AHP \(>\) sCO\({}_{2}\)/DH \(>\) sCO\({}_{2}\) (A \(>\) B means A is better than B). Thus, the combined cycles show better performances than the single sCO\({}_{2}\). This indicates that the performance of recompression sCO\({}_{2}\) cycle can be enhanced by assembling a waste heat recovery system based on the energy cascade utilization principle. Besides, by comparing three combined cycles, it can be concluded that AHP is a better choice than DH, and that the LiBr-H\({}_{2}\)O solution is a better working fluid than the ammonia-water solution for AHP. Thus, the proposed sCO\({}_{2}\)/LiBr-H\({}_{2}\)O AHP system is a desirable waste heat recovery system for the sCO\({}_{2}\) cycle, with which the combined cycle could achieve a high exergy efficiency with a low cost.  
Figure 2 shows the variation trends of system performance indicators with _PRc_ for different thermal systems: (a) \(\eta_{\text{ex}}\) and \(c_{\text{total}}\); (b) _COPP_ and _COHP_.  
Figure 2: Variation trends of system performance indicators with _PRc_ for different thermal systems: (**a**) \(\eta_{\text{ex}}\) and \(c_{\text{total}}\); (**b**) _COPP_ and _COHP_.  
In Figure 2a, \(c_{total}\) increases with \(PRc\) due to the significant increments of capital investment, operation, and maintenance costs for the turbine, compressors and pressure vessels. Differently, \(\eta_{ex}\) increases firstly but then decreases with \(PRc\) in the research range, indicating the existence of an optimal \(PRc\) to maximize the exergy efficiency. As \(\eta_{ex}\) reflects the overall system performance considering both power generation and heat production, the above phenomenon can be analyzed and explained using these two aspects. Figure 2b depicts the variations of \(COPP\) and \(COHP\) with \(PRc\). \(COPP\) represents the power generation capacity while \(COHP\) reflects the heat production capacity. Clearly, \(COHP\) increases with \(PRc\), but \(COPP\) increases firstly and then decreases. Figure 3 presents the turbine output power \(W_{\text{tur}}\), compressor power consumption \(W_{\text{com}}\) and net output power \(W_{\text{net}}\) varying with \(PRc\) for the sCO\({}_{2}\)/LiBr-H\({}_{2}\)O AHP system. The increase of \(PRc\) (turbine inlet pressure) strengthens the power generation capacity of the unit mass working fluid, and leads to the increase of \(W_{\text{tur}}\). At the same time, the increase of the turbine inlet pressure requires more power to drive the compressors and leads to the increase of \(W_{\text{com}}\). So, with the increase of \(PRc\), \(W_{\text{net}}\) increases firstly when the increment of \(W_{\text{tur}}\) is larger than that of \(W_{\text{com}}\), and then decreases for the opposite situation. It explains why \(COPP\) and \(\eta_{ex}\) increase firstly but then decrease with \(PRc\) in Figure 2a,b.  
Figure 3 shows the variation trends of \(W_{\text{tur}}\), \(W_{\text{com}}\), and \(W_{\text{net}}\) with \(PRc\) for the sCO\({}_{2}\)/LiBr-H\({}_{2}\)O AHP system.