## 3 Results and Discussion
### System Performance According to Quality Variation  
Generally, compared to the conventional R410A, the internal gas leakage of a compressor increases, because the molecular weight of R32 is small. It leads to a reduction in the performance of the compressor. Furthermore, the reliability of a compressor can be decreased by a high discharge temperature. In order to analyze the effect of vapor-liquid compression on the compressor performance in different operating conditions, the volumetric and isentropic efficiencies were calculated as follows:  
The volumetric efficiency (\(\varepsilon_{\mathrm{v}}\)) is given by Equation (6). \[\varepsilon_{\mathrm{v}}=\frac{\dot{m}/\rho}{\dot{V}_{\mathrm{d}}\dot{v}} \tag{6}\]  
where \(\dot{m}\) is the mass flow rate, \(\dot{V}_{\mathrm{d}}\) is the compressor displacement, \(\rho\) is the density of the refrigerant, and \(v\) is the compressor speed. The isentropic efficiency (\(\varepsilon_{\mathrm{s}}\)) is given by Equation (7). Figure 3: Quality as a function of the EEV (Electronic Expansion Valve) opening for different EWT of OD HEX (entering water temperature of the outdoor heat exchanger). Figure 2: Measured vs. calculated mass flow rate. \[\varepsilon_{\mathrm{s}}=\frac{h_{2,\mathrm{Isen}}-h_{1}}{h_{2}-h_{1}}\approx\frac{ \dot{m}(h_{2,\mathrm{Isen}}-h_{1})}{\dot{P}} \tag{7}\]  
where \(h_{2,\mathrm{Isen}}\) is the isentropic discharge enthalpy, \(h_{1}\) is the suction enthalpy, \(h_{2}\) is the discharge enthalpy, and \(\dot{P}\) is the compressor power. Figures 4 and 5 show the volumetric and isentropic efficiencies of the compressor as a function of quality for different EWT of OD HEX. As the quality decreased from SH 10 \({}^{\circ}\)C to the values of wet compression, the volumetric efficiency consistently increased up to ca. 0.9, due to the increasing mass flow rate, and then decreased with a decreasing quality. When considering the isentropic efficiency, it increased up to the maximum value at a quality of about 0.95, as the rise of the compressor power is smaller than that of the ideal power, owing to the rise of the mass flow rate. It then decreased with a decreasing quality. Figure 6 shows the variation in the pressure ratio against the quality from dry compression to wet compression. The pressure ratio decreases with a decreasing quality, as the evaporating pressure rise is higher than that of the condensing pressure. In addition, with an increase in the EWT of OD HEX, the rise in the evaporating pressure is generally higher than that of the condensing pressure; thus, the  
Figure 4: Volumetric efficiency as a function of quality for different EWT of OD HEX. Figure 5: Isentropic efficiency as a function of quality for different EWT of OD HEX. pressure ratio between them decreased, as the EWT of OD HEX increased. This can be calculated from the data in Figure 10a,b, which represent the variation in the suction and discharge pressure against the quality. Figure 7 shows the suction temperature as a function of quality at different EWT of OD HEX. Since the saturation pressure is largely influenced by the EWT of OD HEX [16], the suction temperature dropped when the EWT of OD HEX decreased, due to the drop in the saturation pressure. The suction temperature decreased from SH 10 \({}^{\circ}\)C to a quality of one, and it presents a minimum value at a quality of one in this study. As the quality decreases in the area of wet compression, the suction temperature increases. This is due to the fact that the suction pressure is increased by the rising refrigerant inflow to the compressor inlet, with respect to a decreasing quality. Figure 8 shows the discharge temperature as a function of quality for different EWT of OD HEX. The discharge temperature is largely dependent on the pressure ratio and suction temperature of the system [17], which increases by a decrease in the pressure ratio and a rise in the suction temperature.