## 4 Results and Analysis
### The Effect of the Rotation Speed on the Motion of the Suction Valve  
The flow velocity is the key factor affecting the low-pressure region, and the compressor rotation speed directly determines the flow velocity through the valve. Therefore, the low-pressure region at various rotation speeds is investigated. To eliminate the influence of other factors on the flow field, as shown in Figure 15, the pressure distribution on the surface of the suction reed valve was studied when the suction reed valve was fully open (i.e., the crank angle was at 90.0\({}^{\circ}\)) at different rotation speeds.  
With the rotation speed increasing from 1050 r-min\({}^{-1}\) to 1950 r-min\({}^{-1}\), the low-pressure zone on both sides of the position opposite the suction hole increased gradually, and the minimum pressure value decreased from 98,100 Pa to 95,667 Pa. The conclusion can be drawn that the Bernoulli effect in the valve gap strengthened with the increase of the rotation speed.  
When the valve was fully opened, as shown in Figure 16a, the pressure distribution along the X direction of the reed valve was investigated at different rotation speeds. It is obvious that the pressure fluctuation increased with the increase of the rotation speed. The pressure distribution along the Y direction had the same trend, as shown in Figure 16b.  
Figure 16: _Cont._  
Figure 15: Pressure distribution on the upper surface of the reed (1050, 1500, and 1950 r-min\({}^{-1}\)).  
The movement of the valve determines the flow capacity and backflow characteristics of the valve [23], which has a great influence on the performance of compressor. Therefore, the movement characteristics of the valve under various working conditions were studied in depth.  
Figure 17a shows the lift of the suction valve at various rotation speeds under the same working conditions. With the increase of the rotation speed, the opening delay of the suction valve increased, caused by the high-speed flow in the narrow region between the upper surface of the reed and the valve plate, while the closing time of the suction valve decreased first and then increased. The low-pressure region in the narrow region caused by the Bernoulli effect was beneficial to the quick closure of the valve. When the rotation speed was low, the flow velocity in the narrow region was low, which resulted in a longer delay closing time, such as at 1050 r\(\cdot\)min\({}^{-1}\). With the increase of the rotation speed, the Bernoulli effect was strengthened, and the valve was closed in time, such as at 1500 r\(\cdot\)min\({}^{-1}\). However, when the rotation speed was excessively high, the air flow velocity through the valve was overly high, which led to a stronger Bernoulli effect in the narrow region and premature closure of the valve. When the piston reached the bottom dead center (BDC), the insufficient flow region of the valve would cause the valve to reopen and eventually lead to a longer delay during the closure of the valve, such as at 1950 r\(\cdot\)min\({}^{-1}\).  
The mass flow rate through the suction valve was investigated as shown in Figure 17b. The backflow through the suction reed valve was at its minimum at 1500 r\(\cdot\)min\({}^{-1}\). The results show that the backflow characteristics of the suction valve were consistent with the movement characteristics of the suction reed valve. Furthermore, the low-pressure region in the pressure distribution had a direct impact on the capacity of the compressor.  
Figure 16: (**a**) The pressure distribution along X direction at various rotation speeds. (**b**) The pressure distribution along the Y direction at various rotation speeds.