Chunhong Ma’s research while affiliated with Zhejiang University of Science and Technology and other places

The property of vaporization phase transition in liquid oxygen face seals is a key factor affecting the stability of mechanical face seals in many fields, especially under cryogenic conditions. Here, a numerical model based on the saturated vapor pressure is established to investigate the vaporization phase transition property of liquid oxygen sealing film. The novelty of this model is to take the influence of heat transfer and face distortions into consideration at the same time. The pressure and temperature distributions as well as face distortions are calculated, and then the property of vaporization phase transition and sealing performance are analyzed. It is found that spiral grooves may lead to the complex film temperature distributions and irregular vaporization distributions. With the increase in seal temperature and decrease in seal pressure, the vaporization area extends from the low-pressure side to the grooves area, and the vaporization rate increases rapidly. The more important thing is that the vaporization often brings a drastic fluctuation and non-monotonic change in opening force. Specifically, with the increase inin seal temperature from 55 K to 140 K, the opening force fluctuates violently, and the fluctuation range is more than 50%, showing an obvious instability. Finally, this study provides a design range of pressure and temperature values for liquid oxygen face seals. In these ranges, this kind of face seals can have a stable operation, which is beneficial to the practice engineering related to the complex properties of sealing fluid.

In order to obtain the leakage characteristics of an upstream pumping face seal with inclined ellipse dimples under high-temperature and high-speed liquid lubricating conditions, a thermo-hydrodynamic lubricating model is developed. The novelty of this model is that it takes the thermo-viscosity effect and cavitation effect into account. The influence of operating parameters, such as rotational speed, seal clearance, seal pressure, ambient temperature and structural parameters, such as dimple depth, inclination angle, slender ratio and dimple number on the opening force and leakage rate, is numerically calculated. The results obtained show that the thermo-viscosity effect makes the cavitation intensity decrease noticeably, leading to an increase in the upstream pumping effect of ellipse dimples. Moreover, the thermo-viscosity effect may make both the upstream pumping leakage rate and opening force increase by about 10%. It can also be found that the inclined ellipse dimples can produce an obvious upstream pumping effect and hydrodynamic effect. Based on the reasonable design of the dimple parameter, not only can the sealed medium achieve zero leakage, but the opening force can also increase by more than 50%. The proposed model has the potential to provide the theoretical basis for and guide the future designs of upstreaming liquid face seals.

The force equilibrium and moment equilibrium play a significant role on the sealing performance of gas split floating ring seals. A small deflection angle may generate seriously wear on sealing surface and cause seal failure. Therefore, the thermo-hydrodynamic lubrication analysis of gas split floating ring seal with Rayleigh grooves is investigated considering the deflection angle and frictional heat of surface contact, which is beneficial to grasp the hydrodynamic characteristics and rules under high-temperature and high-speed conditions. Pressure and temperature distributions of sealing rings are numerically calculated for the cases with different deflection angle, rational speed, seal pressure and ambient temperature. Then, the hydrodynamic effect and sealing performance are analyzed. The obtained results show that, the surface Rayleigh step grooves do not present obvious hydrodynamic effect when split seal ring has no deflection. While, a significant hydrodynamic effect can be obtained when the split seal ring presents a deflection angle about dozens of micro radians. Here, a 10% increase of opening force is achieved when the deflection angle reaches 80 μrad in the case of speed 30,000 r/min and seal pressure 0.2 MPa. Moreover, the hydrodynamic effect becomes obvious with increasing deflection angle as well as rotational speed. Meanwhile, the growth of rotational speed results in an obvious increase of film temperature. The increase of ambient temperature has a significant influence on the decrease of leakage rate. When the ambient temperature increases from 340 K to 540 K, the leakage rate reduces exceeding 50%, however, it does not present obvious effect on the opening force. The proposed model has the potential to provide the theoretical basis and design guidance for surface grooves of gas split floating ring seal in the future.

Thermal distortion characteristics of spiral groove gas face seals are investigated for cases of high temperature. The influence of ambient temperature and temperature difference on the thermal distortion and the sealing performance is analyzed with consideration of gas thermoviscosity effect. It is found that, the thermal distortion makes the opening force decrease slightly with the increasing ambient temperature, while the thermoviscosity effect causes the leakage rate decrease obviously. Temperature difference between the inner and outer diameters plays a more important role in thermal distortion of the seal face, which results in a sharp divergence distortion accompanying with decrease of the opening force and increase of the leakage rate. This means a large temperature difference may significantly reduce the sealing performance.

Purpose The purpose of this paper is to improve opening performance of bi-directional rotation gas face seals by investigating the hydrodynamic effect of non-closed elliptical grooves. Design/methodology/approach A model of non-closed elliptical groove bi-directional rotation gas face seal is developed. The distribution of lubricating film pressure is obtained by solving gas Reynolds equations with the finite difference method. The program iterates repeatedly until the convergence criterion on the opening force is satisfied, and the sealing performance is finally obtained. Findings Non-closed elliptical groove presents much stronger hydrodynamic effect than the closed groove because of drop of the gas resistance flowing into grooves. Besides, the non-closed elliptical groove presents significant hydrodynamic effect under bi-directional rotation conditions, and an increase of over 40 per cent is obtained for the opening force at seal pressure 4.5 MPa, as same level as the unidirectional spiral groove gas seal. In the case of bi-directional rotation, the value of the inclination angle is recommended to set as 90° presenting a structure symmetry so as to keep best opening performance for both positive and reverse rotation. Originality/value A model of non-closed elliptical groove bi-directional rotation gas face seal is established. The hydrodynamic mechanism of this gas seal is illustrated. Parametric investigation of inclination angle and integrity rate is presented for the non-closed elliptical groove bi-directional rotation gas face seal.

Thermoelastohydrodynamic characteristics of T-groove gas face seals are numerically investigated. The film pressure and temperature fields are calculated with consideration of the elastic and thermal distortions of the rings and the choked flow effect. The temperature difference between the outer radius and the inner radius is about 6 K below 1.0 MPa, and about 60 K above 1.0 MPa. Analysis results also show that a convergent gap is formed under 1.0 MPa and a divergent gap is formed when the sealing pressure is larger than 1.0 MPa. The thermoelastohydrodynamic effect becomes obvious and leads to significant decrease of the opening force when the sealing pressure is larger than 1.0 MPa. Besides, the dynamic opening force increases with the increasing rotational speed at low sealing pressures, exceeding 2% in degree in the case of sealing 0.5 MPa in the analysis, but it decreases at high pressures, exceeding 6% in degree in the case of sealing 3.0 MPa. T-groove gas face seal is more suitable to be applied under conditions of low sealing pressure and high rotational speed.

Thermo-hydrodynamic behaviors of spiral groove gas face seals are investigated for the cases of low seal pressure. Pressure and temperature fields of gas film are calculated, and then influence of thermal distortion on seal performance are analyzed. It is found that spiral grooves lead to complex film temperature distributions and rotational speed results in the increase of whole film temperature. But the shear heat and pumping effect of spiral grooves have little influence on film temperature gradient along the leakage direction. The face thermal distortion, forming divergent clearance along the leakage direction, makes the opening force decrease and the leakage increase. A higher seal pressure and clearance will result in a larger thermal distortion. And the rotational speed may enhance the face thermal distortion further in some low pressure cases.

A numerical modeling of thermoelastohydrodynamic gas spiral groove face seal behavior is presented. Temperature fields of the fluid film and the seal rings are computed, as they are the elastic and thermal distortions of the rings. Numerical analysis is carried out on a gas spiral groove face seal taking into account of choked flow effect. Analysis results show that both elastic and thermal distortions induce strong influence on the geometry of the fluid film, forming obvious divergent clearance which leads to significant decrease of minimum equilibrium clearance, exceeding 50% in degree. Thermal distortion may induce the same influence degree as elastic distortion on the minimum equilibrium clearance in high pressure cases, but the rotation speed has no obvious influence on the minimum clearance when both elastic and thermal distortions are considered. The thermal distortion as well as elastic distortion should be concerned in high pressure analysis.

The transient spreading behavior of water droplet is investigated on micro-structured SiC surfaces. Two types of texture, micro-convexes and micro-grooves, are prepared by laser processing method on SiC (silicon carbide) surfaces. And the evolution of contact angle over time is recorded by a high speed CCD. The results show that the initial transient spreading is rapid and the time to reach the equilibrium contact angle is much longer on the smooth surface than on the textured surfaces. Among the testing textured surfaces, the drop-spreading is fastest in the perpendicular direction on the grooved surface.