## 3 Results and Discussion
### Lubrication Performance in SSCs of Different Machine Sizes
#### 3.3.3 MDMT Calculation Results  
The calculation results of MDMT in machines of different discharge capacity are shown in Figure 19.  
Figure 19: The MDMT curves in different machines.  
In the 3 m\({}^{3}\cdot\)min\({}^{-1}\) SSC, it is found that the MDMT curves of the SSLT and the SCT coincide with the straight line of \(\delta=\delta_{\rm{lim}}\) in a whole period of \(\gamma\). It implies that \(|T_{\rm{b}}|\) is always larger than \(T_{\rm{a}}\) and contact at leading flank is inevitable. It is observed that the MDMT curve of MCT coincides with the straight line of \(\delta=\delta_{\rm{lim}}\) in a small region about \(5^{\circ}\) (\(\varphi_{\rm{gr}}\) varies from \(-19.19^{\circ}\) to \(-14.22^{\circ}\)). In the remaining region of the whole period, the MDMT curve of MCT does not coincide with \(\delta=\delta_{\rm{lim}}\) anymore. This indicates that wear occurs in part of the period and the water film at leading flank is unable to bear the load of \(|T_{\rm{b}}|\) in the whole period.  
The calculation results of the 6 m\({}^{3}\cdot\)min\({}^{-1}\) SSC under 0.8 MPa are shown in Figure 15 and analyzed in Section 3.2.3. In order to facilitate the comparison among the three machines, the calculation results are replotted in Figure 19. It is worth mentioning that in Ref. [20], a 6 m\({}^{3}\cdot\)min\({}^{-1}\) prototype adopting the MCT has been made and a 2000 h endurance test under 0.8 MPa has been carried out. In the experiment, the test result does not show any sign of the discharge capacity loss during the whole 2000 h and the tooth flank basically remains in its original shape. The calculated MDMT curve of MCT for the 6 m\({}^{3}\cdot\)min\({}^{-1}\) machine in Figure 19 does not contact with the leading side or with the trailing side in the whole period. The calculated curve is in good agreement with the experimental results.  
In the 12 m\({}^{3}\cdot\)min\({}^{-1}\) SSC, it is found that the MDMT curve of the SSLT coincides with the straight line of \(\delta\)=\(\delta_{\rm{lim}}\) in a small region about \(8.67^{\circ}\) (\(\varphi_{\rm{gr}}\) varies from \(-20.17^{\circ}\) to \(-11.5^{\circ}\)). In this range, \(T_{\rm{a}}\) cannot balance \(T_{\rm{b}}\) and contact occurs at leading side. The MDMT curve of the SCT reaches \(\delta\)=\(\delta_{\rm{lim}}\) when \(\varphi_{\rm{gr}}\) ranges from \(-18.79^{\circ}\) to \(-13.48^{\circ}\). In the rest range of \(27.41^{\circ}\), the SCT MDMT curve is between \(\delta_{\rm{lim}}\) and -\(\delta_{\rm{lim}}\). The MCT MDMT curve does not reach \(\delta=\delta_{\rm{lim}}\) or \(\delta=-\delta_{\rm{lim}}\) in a whole period. It indicates that contact will occur neither at the leading flank nor at the trailing flank. The water films at both sides regulate the gate-rotor effectively. The gate-rotor floats in the water films of both sides.  
Overall, in the studied range, with the increment of compressor discharge capacity, the MDMT curves of different MPPs move towards the straight line of \(\delta=-\delta_{\rm{lim}}\). The liquid films get thicker at the leading side and thinner at the trailing side when \(\delta=\delta_{\rm{bal}}\). The lubrication performance is improved. The phenomenon that wear occurs at leading flank will reduce. The SSLT and SCT cannot achieve meshing without contact in all of the three SSCs, despite the improvements in the larger machines. The MCT gate-rotor can achieve this goal in the 6 m\({}^{3}\cdot\)min\({}^{-1}\) and 12 m\({}^{3}\cdot\)min\({}^{-1}\) machines.  
Further, with increment of the relative velocity, the hydrodynamic effect of leading side increases quicker than that at trailing side. This may mainly be because the relative velocity at tooth tip at leading side is larger than that at trailing side.