## 3 Results and Discussion
### System Performance According to Quality Variation
Due to the loss of the mass flow rate caused by a back flow of liquid refrigerant into the suction chamber mentioned above, the heating capacity rapidly decreased under a quality of 0.91, 0.88, and 0.84 for EWT of OD HEX at 10 \({}^{\circ}\)C, 5 \({}^{\circ}\)C, and 0 \({}^{\circ}\)C, respectively. Due to the larger increase in the mass flow rate, the slope of heat capacity, with respect to the quality, was steeper when the EWT of OD HEX increased. When the EWT of OD HEX was 10 \({}^{\circ}\)C, 5 \({}^{\circ}\)C, and 0 \({}^{\circ}\)C, compared to that of SH 10 \({}^{\circ}\)C, the heating capacity increased by a maximum of ca. 21%, 23%, and 22%, respectively. Figure 10: Suction and discharge pressure in the compressor as a function of quality for different EWT of OD HEX: (**a**) suction pressure; (**b**) discharge pressure. Figure 3:0 Measured mass flow rate at the condenser outlet as a function of quality for different EWT of OD HEX. Figure 12 shows the power input as a function of the quality for different EWT of OD HEX. As can be seen from the figure, the power input remained almost unchanged during dry compression in the range between SH 10 \({}^{\circ}\)C and a quality of one. On the other hand, due to the increasing liquid droplets at the compressor suction, the power input linearly increased with a decreasing quality during wet compression. Generally, the compressor power decreases with respect to the reduction in the discharge temperature of the compressor (Figure 8), as the process approaches the isentropic compression process. However, due to the increasing refrigerant inflow to the compressor, the compressor power increased, in spite of a decrease in the discharge temperature with quality during wet compression. In previous research, it was observed that the increasing number of liquid droplets results in a rise in the compressor load [21]. In Figure 12, the power input rapidly decreased after the maximum value. This could be explained by the decrease in the mass flow rate by a back flow of liquid refrigerant into the suction chamber [5; 18]. In our study, when the EWT of OD HEX was 10 \({}^{\circ}\)C, 5 \({}^{\circ}\)C, and 0 \({}^{\circ}\)C, the power input increased by maximum of 10%, 12.7%, and 14.4%, respectively, when compared to that of SH 10 \({}^{\circ}\)C.  
Figure 3:1 Heating capacity as a function of quality for different EWT of OD HEX. Figure 3:2 Power input as a function of the quality for different EWT of OD HEX. Figure 13 shows the COP (Coefficient of Performance) as a function of quality for different EWT of OD HEX. With an increasing EWT of OD HEX, the COP increased, resulting from the increase in the mass flow rate. From SH10, the COP also increased, until it reached the maximum value at a quality of ca. 0.94 to 0.90 in the two-phase mixture region, according to the EWT of OD HEX, and then decreased with the quality. This trend can be explained as follows. As the COP depends on the rate of the heating capacity to power input, the heating capacity consistently increases more than the power input with a decreasing quality, until the abrupt decrease, since the power input in the wet compression region is proportionally larger than the increase in the heating capacity, in accordance with the decreasing quality. Thus, a maximum COP occurs at specific qualities, i.e., as mentioned above, ca. 0.94 to 0.90. When the EWT of OD HEX was 10 \({}^{\circ}\)C, 5 \({}^{\circ}\)C, and 0 \({}^{\circ}\)C, the COP increased by a maximum of ca. 12.4%, 10.6%, and 10.2%, respectively, when compared to that of SH 10 \({}^{\circ}\)C.  
Figure 14 shows the process line of the vapor-liquid mixture at a quality of 0.94 at a EWT of OD HEX of 10 \({}^{\circ}\)C, and compares it to that of SH 10 \({}^{\circ}\)C in a pressure-enthalpy diagram. The discharge temperature for a quality of 0.94 and SH 10 \({}^{\circ}\)C is 75 \({}^{\circ}\)C and 110 \({}^{\circ}\)C, respectively, with a difference of ca.