Steady-State Performance of Liquid Film Seal Considering Dissolution of Methane

As one of the core equipments of the multiphase mixing process, the multiphase pump has the advantages of low cost, high efficiency, light weight and small volume. The performance of the multiphase pump directly determines the extraction efficiency of oil and gas resources. Sealing stability and reliability are the key factors affecting the performance of oil-gas multiphase pump. Liquid film lubricated mechanical seal is widely used in oil-gas multiphase pumps due to their advantages of stable operation, low leakage and long service life. Under the condition of oil-gas mixed transportation, the change of gas content will lead to the instability of the liquid film bearing capacity, and the dissolution and precipitation of methane gas in the oil phase during the working process has an important impact on sealing performance. Therefore, in order to effectively improve the stability and sealing performance of mechanical seal, according to the working conditions of oil-gas mixed transportation, the solubility equation was introduced into the generalized steady-state Reynolds equation including Jakobsson-Floberg-Olsson (JFO) boundary conditions, and a single spiral groove liquid film sealing lubrication model considering the dissolution and precipitation effects of methane in the oil phase was established. The finite difference method was used to solve this numerical model, and the accuracy of the model and the solution method was verified by comparing the calculation results of the proposed model with the literature data. The distribution of the liquid film pressure field was obtained, and the interaction relationship between the liquid film pressure, the methane solubility and the oil phase viscosity was studied. Under different structural parameters and working conditions of the spiral groove, the liquid film sealing performance obtained by the model with and without methane dissolution was compared and analyzed, and the influence of methane dissolution on the sealing performance was explored. The results indicated that the dissolution of methane in the oil phase will reduce the viscosity of the oil phase medium and weaken the hydrodynamic pressure effect. Especially in the high pressure region of the liquid film, the solubility of methane was relatively large, the viscosity of the oil phase was greatly reduced, and the hydrodynamic pressure effect was greatly weakened, which had a greater impact on the sealing performance. The higher the rotational speed, the greater the effect of the methane dissolution effect on the sealing performance. The same as the rotational speed, the greater the pressure difference, the greater the influence of the methane dissolution on the sealing performance. Under different spiral angles, groove numbers, and groove-land ratios, the sealing performance considering methane dissolution effect was greatly different from that without methane dissolution effect. Compared with the methane dissolution effect under different spiral angles, groove numbers, and groove-land ratios, the methane dissolution effect under different groove depths was smaller. Under different spiral groove structural parameters and working conditions, compared with the calculation results without considering the dissolution effect, the methane dissolution effect will reduce the liquid film opening force, increase the cavitation rate of the liquid film, increase the friction coefficient of the end face, and reduce the leakage of the seal. In a word, it is very important to study the influence of methane dissolution effect on sealing performance under high pressure and oil-gas mixed transportation conditions, and the influence of methane dissolution on sealing performance cannot be ignored.