## 5 Analysis of Simulation Model and Experimental Results
### Simulation Analysis of the Impact of OCR on Compressor Performance
#### 5.2.3 Simulation Results on the Impact of OCR on Compressor Performance  
Using the theoretical model from the previous section, simulations were conducted, and the experimental and simulated data of the compressor performance were compared. Figures 10-12 present the comparison of simulated and experimental data for isentropic efficiency, volumetric efficiency, and the discharge temperature, respectively. Figure 10 indicates that the simulation error for isentropic efficiency is within 10%, and the average error is 1.3%. At high compressor speeds and a low pressure ratio of 2.41, the experimental values are lower than the simulated ones, where the oil content is the highest. Conversely, at low compressor speeds and a high pressure ratio of 4.02, the experimental values are higher than the simulated ones, where the oil content is the lowest. These two cases have relatively large errors. Figure 11: Calculated data vs. test data for volumetric efficiency. Figure 10: Calculated data vs. test data for isentropic efficiency. Figure 11 shows that the simulation error for volumetric efficiency is within 5%, with an average error of 0.5%. Therefore, the influence of oil content on the model is not significant when compared to the experimental data. The simulation model shows good applicability with a maximum 10% OCR from the experimental data. Figure 12 indicates that the simulation error for the discharge temperature is within 5 \({}^{\circ}\)C, with an average error of 0.68 \({}^{\circ}\)C. The largest deviations occur at low or high compressor speeds. As can be seen from Figure 9, discharge temperatures at low and high compressor speeds are higher than those at rated compressor speeds. By comparing simulation model data with experimental data, it is shown that the discharge temperature is significantly affected by the oil content, suggesting that further optimization regarding the impact of the OCR is needed. In addition to the simulation and experimental comparison for compressor performance, simulations for compressor power, cooling capacity, and the COP were also conducted. Figures 13-15 compare the deviations between simulated and experimental values for compressor power, cooling capacity, and COP, respectively. In Figure 13, the minimum error for power between simulated and experimental values is 0.12%, with a maximum error of 9.8% and an RMS deviation of 2.6%. In Figure 14, the minimum error for cooling capacity is 0.06%, with a maximum error of 9.4% and an RMS deviation of 2.8%. In Figure 15, the minimum error for the COP is 0.47%, with a maximum error of 10.3% and an RMS deviation of 2.9%. However, when the OCR is within the range of 2-10%, the simulation model matches well with deviations under 5%, with RMS errors of 3.0%, 2.8%, and 2.1%, respectively. The figures indicate that when the oil content under working conditions exceeds 10%, the deviation in simulated values is relatively large. Since the relationship between isentropic efficiency and the compressor speed in Figure 7 is more akin to a fourth-degree polynomial, using a second-degree polynomial for the simulation model results in larger deviations. Particularly, with the inflection point at low compressor speeds, in Figure 13, the power deviation is larger at low compressor speeds and smaller at high compressor speeds. From the previous discussion on the solubility characteristics of refrigerant and oil, more refrigerant is dissolved in the oil at the inlet of the evaporator, and a significant amount of liquid refrigerant dissolved in the oil volatilizes at the outlet of the evaporator. While the simulation retains calculations on solubility, the actual process may be more unstable, with greater deviations in cooling capacity as the oil content increases, as shown in Figure 14. Consequently, the added deviations in power and cooling capacity result in even larger deviations in COP, as seen in Figure 15.  
Figure 12: Calculated data vs. test data for discharge temperature. Figure 14: Calculated data vs. test data for cooling capacity.