Seal Clearance Research Articles

Large Eddy Simulation of Rotationally Induced Ingress and Egress around an Axial Seal between Rotor and Stator Disks

In gas turbines, the hot gas exiting the combustor can have temperatures as high as 2000 °C, and some of this hot gas enter into the space between the stator and rotor disks (wheelspace). Since the entering hot gas could damage the disks, its ingestion must be minimized. This is carried out by rim seals and by introducing a cooler flow from the compressor (sealing flow) into the wheelspace. Ingress and egress into rim seals are driven by the stator vanes, the rotor and its rotation, and the rotor blades. This study focuses on the ingress and egress driven by the rotor and its rotation. This is carried out by performing wall-resolved large eddy simulation (LES) around an axial seal in a rotor–stator configuration without vanes and blades. Results obtained show the mechanisms by which the rotor and its rotation induce ingress, egress, and flow trajectories. Kelvin–Helmholtz instability was found to create a wavy shear layer and displacement thickness that produces alternating regions of high and low pressures around the rotor side of the seal. Vortex shedding on the backward-facing side of the seal and its impingement on the rotor side of the seal also produces alternating regions of high and low pressures. The locations of the alternating regions of high and low pressures were found to be statistically stationary and to cause ingress to start on the rotor side of the seal. Vortex shedding and recirculating flow in the seal clearance also cause ingress by entrainment. With the effects of the rotor and its rotation on ingress and egress isolated, this study enables the effects of stator vanes and rotor blades to be assessed.

Thermo-Hydrodynamic Lubricating Behaviors of Upstream Liquid Face Seals with Ellipse Dimples.

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.

Inter-Stage Pressure Drop of Multi-Stage Brush Seal With Differentiated Structure

Abstract Uneven pressure drops among stages of multistage brush seal (MBS) leads to early failure of single-stage seal units, which directly affects service life of the seal used in aeroengines, gas turbines, and steam turbines. In this paper, influence factors of interstage pressure drop were studied to analyze formation mechanism of the uneven pressure drops. Moreover, an MBS with differentiated structure was presented, and its interstage pressure drops were further investigated. The results showed that the MBS with several same single-stage seal units had uneven pressure drops among stages under high inlet/outlet pressure ratios. In view of remarkably increasing velocity and decreasing pressure in downstream region of bristle pack near rotor surface during flow of airflow, adjustments of structural parameters (i.e., increasing height of backing plate to rotor surface Hb, increasing seal clearance Hg, and decreasing axial width of bristle pack B) could improve the uneven pressure drops among different stages due to increasing outlet air flow area of the stage. The closer pressure drop proportions of different stages to ideal average value indicated increase of Hb had a more effective effect to balance the pressure drops among different stages compared to increase of Hg and decrease of B. An MBS with differentiated structure, in which both Hb and Hg of all the single-stage seal units were increased progressively and B was decreased step by step, showed a good performance to obtain even interstage pressure drops.

Numerical and experimental study of convergent integral embedded magnetic fluid seal

To enhance the pressure resistance of small clearance magnetic fluid seals, a new convergent integral embedded magnetic fluid seal (CIEMFS) structure was proposed. The magnetic field distributions in the radial sealing clearance and axial sealing clearance were studied, and the theoretical pressure resistance capability values were obtained. The effects of magnetic fluid injection volumes, pole tooth (PT) heights and sealing clearance on the pressure resistance capability of the CIEMFS were experimentally investigated and compared with that of the ordinary magnetic fluid seal (OMFS). The results showed that the experimental pressure resistance capability of the CIEMFS was in good agreement with the theoretical pressure resistance, and both of them were better than the OMFS. The pressure resistance capability of the CIEMFS is not only affected by the radial sealing clearance but also limited by the axial seal clearance. The height of the pole tooth and the magnetic fluid (MF) injection volume will also have an impact on the pressure resistance capability, the higher the pole tooth, the higher the pressure resistance capability of the magnetic fluid sealing (MFS) structure. As the magnetic fluid injection volume increases, the pressure resistance capability of the CIEMFS increases and then plateaus.

Numerical Investigation on the Leakage and Rotordynamic Characteristics for a Hole-Pattern Seal in Wet-Gas Conditions

Abstract For turbomachinery working in wet-gas conditions, liquid-phase fluid may worsen the rotordynamic characteristic of an annular seal, which induces a subsynchronous vibration problem and destabilizes the rotor-bearing system. The hole-pattern seal, demonstrated as effective to eliminate synchronous or subsynchronous vibrations for gas turbomachinery, is an ideal seal scheme to increase rotor stability and liquid tolerance capability of wet-gas turbomachinery. In this paper, the leakage and rotordynamic characteristics of a hole-pattern seal are numerically investigated under wet-gas conditions, using a three-dimensional transient CFD-based perturbation method. The accuracy and reliability of the present numerical method are demonstrated based on published experimental data. The rotordynamic force coefficients are presented and compared for the wet-gas hole-pattern seal with various inlet liquid volume fractions (LVF = 0%–20%), rotor speeds (ω = 0–20 krpm), inlet preswirl ratios (Sr = −0.2–0.5), and pressure ratios (Pr = 0.3–0.7). Numerical results show that the hole-pattern seal possesses desired tolerance capability for high inlet liquid volume fraction (LVF) of up to 20%. With inlet LVF increasing from 0 to 20%, the effective damping of the hole-pattern seal increases by about 50%, suggesting an improvement in rotor stability. The leakage flow rate of the oil-air mixture increases by 97.5%, combined with the sharply increasing oil leakage flow rate (by 636%) and decreasing air leakage flow rate (by 40%). The increasing rotor speed and inlet preswirl ratio both result in an obvious increase (by 50%) in the cross-coupled stiffness, yielding a smaller effective damping and worse rotor stability. With the increase in pressure ratio, all the rotordynamic force coefficients show a weaker frequency dependency and smaller magnitudes. The swirl velocity in the seal clearance can cause an accumulation of the liquid component in the hole cavities. With the increase of swirl velocity, more liquid component accumulates in the hole cavities, and the main accumulation position gradually moves upstream.

Nonuniform Clearance Effects on Pressure Distribution and Leakage Flow in the Straight-through Labyrinth Seals

Straight-through labyrinth seal is a simple and reliable noncontact seal structure widely used in aeroengines. During the actual operation of aeroengines, the labyrinth seal clearance might experience a nonuniform variation in the flow direction due to asymmetric structure and uneven temperature. In order to characterize the degree of nonuniformity, the nonuniformity coefficient is defined in current paper. The effect of nonuniform causes (rotor deformation or stator deformation), nonuniform type (convergent clearance or divergent clearance), and nonuniformity coefficient (nonuniformity degree) is carefully studied by numerical simulation. Comparative analysis has shown that there is no obvious difference in flow coefficient (less than 0.8% in current studies) between two nonuniform causes. As for nonuniform type, the nonuniformity impact of divergent type on the flow coefficient is more significant than that of convergent type, as a result of stronger axial inertia. Pressure distributions of teeth cavities indicate that the total pressure drop of the divergent type is more obvious than that of the convergent type when the pressure ratio is the same. With the same dimensionless minimum tip clearance, clearance nonuniformity would result in the increase of leakage flow of the straight-through labyrinth, particularly for the condition with small pressure ratio, large circumferential Mach number, and small dimensionless minimum tip clearance. When the nonuniformity coefficient is within the range of -0.1 to 0.1, the variation curves of nonuniformity impact factor versus the nonuniformity coefficient almost coincide (the maximum deviation is no more than 1.2%) under different operation conditions (Reynolds number, pressure ratio, circumferential Mach number, and dimensionless minimum tip clearance). Current work proves it that the effect of seal clearance nonuniformity on the leakage flow requires special attention for the refined design of aeroengines.

Numerical Investigations on Gas Ingestion Mechanism Based on Flow Instabilities in Rim Seal and Cooling Characteristics of Endwall in a 1.5-Stage Axial Turbine

Abstract The sealant flow and rim seal at the periphery of cavities formed between rotor and stator disks prevent the high-temperature gas from ingesting into disk cavities and reduce the use of secondary air bleeding from a compressor. The unsteady sealing performance of rim seal and the cooling characteristics of sealant flow on endwall of a 1.5-stage axial turbine are studied by solving the three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations via shear stress transfer (SST) turbulence model. Besides, mass transfer analogy is introduced to predict the sealant distribution which makes the numerical sealing effectiveness in front and aft cavities agree well with experimental data. The accuracy of the numerical method is verified. The sealing effectiveness in cavities and the flow field in rim seal clearance are analyzed, and the film cooling performance on endwall is explored. The results show that, compared with Φ0=0.0170, the area-averaged sealing effectiveness εc on stator face is increased by 19.05% when Φ0=0.500 in the front cavity, and compared with Φ0=0.0042, the area-averaged sealing effectiveness εc on stator face is increased by 9.82% when Φ0=0.096 in the aft cavity. The nonaxisymmetric pressure on the endwall near rim seal and Kelvin Helmholtz unstable vortices arise due to the circumferential velocity difference between main flow and cavity flow. The flow field in the rim seal clearance is jointly affected by these two factors. The flow pattern in the front rim seal clearance is mainly affected by unstable vortex while the flow pattern in the aft rim seal clearance depends on the circumferential pressure distribution. According to FFT, the most significant frequency of flow field variety is about 1200 Hz and 400 Hz (corresponding to two and six blades passing periods) in front and aft rim seals, respectively. The time-averaged cooling effectiveness increases with the increase of sealant flow on endwall and decreases gradually in the axial direction. The unsteady flow behavior of cooling effectiveness on endwall is also discussed in detail.

Validation of RELAP5 MOD3.3 for 1% reactor pressure vessel top head break loss of coolant accident via the ATLAS facility

The OECD/NEA ATLAS project conducted a 1% top head break LOCA experiment to analyze the accident progression with the suggested accident mitigation plan. The RELAP5 simulation to validate its capability against ATLAS experimental data was performed. The simulation includes the pre-and post-test calculation to see the user dependency and reduce the discrepancy between the simulation and experiment. In post-test calculation, the sensitivity studies in terms of discharge coefficient at the break, break line modeling, environmental heat loss on the secondary side, and CCFL at Fuel Alignment Plate were conducted. Factors improving the simulation results in terms of total integrated mass from break and timings of accident management were found. The shortcoming of RELAP5 capability in predicting the downcomer level and Loop Seal Clearance timing was identified.

Experimental investigation on piston offset and performance of helium valved linear compressor with an external gas bypass

The valved linear compressor(VLC) is a significant part of the Joule-Thomson (JT) cryocooler at the liquid helium temperature zone. The use of clearance seals in the VLC inevitably causes the piston offset which affects the VLC performance and the JT cryocooler performance. Based on the VLC developed in our lab, an experimental bench for studying piston offset inhibition using the external gas bypass is built. The external gas bypass connects the compressor shell to the suction line by a bypass regulating valve which controls the mass flow, a solenoid valve that controls the number of connections and a bypass mass flowmeter which measurs the mass flow rate. The experiments focus on the effects of bypass regulating valve opening and solenoid valve action frequency on the piston offset and performance of the VLC. The experimental results show that there is an optimal opening to minimize the offset and the VLC obtains the best performance at the same time. When the solenoid valve is activated at a high frequency(greater than 1 Hz), the VLC obtains the best performance. This research provides a scheme to inhibit the piston offset by using an external gas bypass to improve the VLC performance.

Analysis of an Elasto-Hydrodynamic Seal by Using the Reynolds Equation

This paper reports numerical studies of an Elasto-Hydrodynamic (EHD) seal, which is being developed for supercritical CO2 (sCO2) turbomachinery applications. Current sCO2 turbomachinery suffers from high leakage rates, which is creating a major roadblock to the full realization of sCO2 power technology. The high leakage rates not only penalize the efficiencies but also create environmental concerns due to greenhouse effects caused by the increased CO2 discharge to the atmosphere. The proposed EHD seal needs to work at elevated pressures (10–35 MPa) and temperatures (350–700 °C) with low leakage and minimal wear. The unique mechanism of the EHD seal provides a self-regulated constriction effect to restrict the flow without substantial material contact, thereby minimizing leakage and wear. This work utilizes a physics-based modeling approach. The flow through the gradually narrowing seal clearance is modeled by the well-known Reynolds equation in EHD lubrication theory, while the deformation of the seal is modeled by using the governing equations of three-dimensional solid mechanics. As for the solution methodology, COMSOL’s Thin-Film Flow and Solid Mechanics modules were employed with their powerful capabilities. The numerical results were presented and discussed. It was observed that the Reynolds equation fully coupled with the surface deformation was able to successfully capture the constriction effect. The maximum and minimum leakages were calculated to be 2.25 g/s and 0.1 g/s at P = 5.5 MPa and P = 11 MPa for the design seal, respectively. It was interesting to observe that the seal leakage followed a quadratic trend with increasing pressure differential, which can become advantageous for high-pressure applications such as sCO2 power generation technology.

Turbofan engine performance prediction methodology integrated high-fidelity secondary air system models

This research studies the performance of an ultra-high bypass ratio turbofan engine, and specifically its secondary air system (SAS). A co-simulation methodology is explored whereby a high-fidelity SAS model and an engine performance code featuring flexible modules can be coupled and interactively executed. The percentage of bleed flows and boundary conditions for the SAS are updated at each iteration step. For this purpose, a SAS model including different elements is developed. Furthermore, a commercial computational fluid dynamics (CFD) solver is adopted to capture the complex flow field in the pre-swirl system. The credibility of cycle calculation and SAS elements is validated by comparing with publicly available data. Subsequently, an elaborately designed SAS is modeled and co-simulated with the AGTF30 engine using a flow network simulation method. The coupling effect between the engine performance and the SAS is studied for eight different flight conditions. The correlation and prediction of engine performance due to seal clearance change is presented. The co-simulation approach clarifies the mutual interactions between the engine overall parameters and the SAS. The results reveal that the enhanced flow network model can improve the simulation accuracy of engine performance over a wide range of operating conditions.

A New Interpretation of Hot Gas Ingress Through Turbine Rim Seals Influenced by Mainstream Annulus Swirl

Abstract Rim seals are fitted at the periphery of the stator and rotor disks to reduce the adverse effects of hot gas ingress on highly stressed turbine components limited by temperature. Ingress is induced by rotational effects such as disk pumping, as well as by asymmetric pressure-driven unsteady phenomena. These influences superpose to form a complex flow-physics problem that is a challenge for computational fluid dynamics. Engine designers typically use practical low-order models that require empirical validation and correlating parameters. This paper identifies the swirl ratio in the mainstream annulus as a dominant characterizing parameter to predict ingress. This is a new interpretation that is supported by extending a low-order model based on turbulent transport using an effective eddy mixing length based on the difference in swirl between the annulus and seal clearance. Experimental measurements were made using a 1.5-stage turbine rig at low Reynolds number. The influence of annulus swirl ratio was investigated over a range of flow conditions and two rim-seal geometries, with the ingress quantified using CO2 tracer concentration in the sealing flow. The concentration data were complemented by measurements in the annulus using a five-hole aerodynamic probe.

Loss Analysis of Cavity Leakage Flow in a Compressor Cascade

Abstract The cavity flow of shrouded stators is quite complex and not yet completely understood, especially for its loss characteristics. In this paper, a matrix of numerical simulations was designed and conducted to investigate the loss characteristics of the cavity flow in a compressor cascade, with a wide range of incidence, two flow coefficients, and three seal clearances. The effect of the skewed boundary layer was introduced to simulate the practical compressor environment as far as possible. The results show that the total pressure loss coefficient is unable to evaluate the cavity leakage loss correctly since it ignores the temperature rise. With the reduction of the flow coefficient, the entropy loss coefficient and thermal entropy generation rate tend to increase, while the change of the viscous entropy generation rate is dependent on the incidence since the high tangential velocity deteriorates the flow of the pressure side at large negative incidence but significantly improves the flow of the suction side as the incidence increases. In addition, there is a significant difference in loss sensitivity to the seal clearance at various incidences. One of the major reasons is the change of pressure difference between the downstream and upstream. And the other major reason is the distribution difference of the high-loss fluid caused by the variation in the passage vortex. These key findings are able to provide insights leading to reducing the compressor loss due to the cavity leakage flow.

Research on a Large Diameter Magnetic Fluid Seal With Thin-Wall Parts

Magnetic fluid seal is a new type of sealing method, which has been applied in many fields. For some fields, such as aviation and aerospace, high sealing performance, large shaft diameter, and small design space are required, which brings difficulties to the sealing design. Therefore, it is necessary to study a large diameter magnetic fluid seal with thin-wall parts. In this article, the effects of seal clearance and shaft deflection on the magnetic field distribution of magnetic fluid seal are analyzed by the finite element method. At the same time, the force of seal shaft in the assembly process is also simulated. The influence of the amount of magnetic fluid on the pressure resistance is analyzed. The low-temperature starting torque and high-temperature pressure resistance of magnetic fluid seal are experimentally studied, and the optimal injection amount of magnetic fluid is obtained. The research content of this article can be used as a reference for the design of a large diameter magnetic fluid seal with thin-wall parts.

Turbulence dissipation of leakage flow in supercritical CO2 labyrinth seals

Supercritical CO2 (S-CO2) leakage through seals significantly reduces the efficiency of turbomachinery. Improving the labyrinth seal structure is potentially the key to the reduction of the leakage flow rate, but its application is greatly limited by the uncertainties of supercritical CO2 turbulent flow inside the turbomachines with irregular chambers. In this work, we numerically investigated the S-CO2 flow field and dissipation rate of turbulence kinetic energy in stepped labyrinth seals. The RANS method and hexahedral structural mesh were employed. The look-up table containing the real gas properties of carbon dioxide was created and imported into the flow solver. The developed numerical method was validated by experiment results and proved its applicability. We have discovered that the fully developed rotating vortices inside each chamber of the turbomachine significantly increase the turbulent dissipation rate and decrease the fluid carried energy, thus reducing the leakage flow rate. With the seal clearance increasing form 0.5 mm–1.3 mm at pressure ratio π = 0.7, the vortices development is gradually limited, causing the decrease of turbulent dissipation rate. The leakage rate is found to be heavily dependent on the distance between the seal tip and step. The increase in this distance from 2 mm to 6 mm results in greater space for the continued development of the vortices within the first chamber, thus the enhancement of the turbulent dissipation rate of fluid. Therefore, we defined a geometry coefficient, (δ-b)/s, and analyzed its effects on turbulent dissipation rate and leakage flow rate. With this geometry coefficient increases from 2.8 to 11.2 at π = 0.7, the maximum turbulent dissipation rate increases from 7.09 × 107 to 1.23 × 108 and the leakage flow rate decreases from 3.98 × 10−2 kg/s to 1.62 × 10−2 kg/s. An improved leakage model characterizing seal geometry, gas properties and compressibility effects was proposed.

SQUEEZE FILM DAMPER DYNAMIC STIFFNESS ANALYSIS, TAKING INTO ACCOUNT THE END GAP

One of the most common ways to reduce vibration in engines is the use of damping devices in the rotor supports. Damping devices may affect both the amplitude of the oscillations and the critical frequencies. The most commonly used damping devices are the squeeze film dampers (SFD), which can show dynamic stiffness that is proportional to frequency of oscillations and that is depends on the relative amplitude of oscillations. The stiffness of the damper is highly influenced by the end gap, which is also often seen as a non-contact radial clearance seal. In this work, a method is proposed that will take into account the effect of end gaps on the dynamic stiffness of a SFD. As a result of the calculations, it was found that the size of the end slots significantly affects the dynamic stiffness of a short SFD, and in some work modes it can exceed the stiffness of supports and bearings.

Effects of Snake-Bioinspired Surface Texture on the Finger-Sealing Performance under Varied Working Conditions

The tribological performance of the friction pair between the rotor and finger feet is a crucial index affecting the service life of finger seals. In recent years, the surface texture has attracted a considerable number of researchers owing to its extraordinary potential in improving antifriction and wear resistance. This paper, inspired by snakeskins, introduces three texture forms (e.g., diamond, ellipse, and hexagon) into the rotor. The effects on finger-sealing performance are analyzed by considering finger seals’ varied working conditions. First, a numerical model of textured finger seals under hydrodynamic lubrication is established based on the Reynolds equation. Then, the sealing performance analysis of textured finger seals is performed considering varied working conditions given rotation speed, pressure difference, seal clearance, and working temperature. The numerical results show that: (1) the textured domain produces a noticeable hydrodynamic pressure effect and cavitation, which effectively improves the bearing capacity of the fluid film; (2) the higher the rotation speed or the lower the inlet/outlet pressure difference, the stronger the dynamic pressure effect of textured finger seals and the better the antifriction and wear resistance; (3) for good antifriction and wear resistance of a textured finger seal, the seal clearance should be as shallow as possible (≤10 μm), and the working temperature should be as low as possible (≤120 °C); and (4) the ellipse texture has a higher average dimensionless pressure and a lower friction coefficient, which is superior to diamond and hexagon ones in terms of friction and wear performance.

Experimental research on static and dynamic magnetic powder sealing used by micro-nano composite magnetic particles

The focus of the paper is the experimental study of static and dynamic magnetic powder sealing by preparing micro-nano hybrid magnetic powders with different proportions. The magnetization curves of the magnetic powders are measured, and the formula for calculating saturation magnetization of mixed magnetic particles is fitted. In the static seal test, the maximum pressure resistances of magnetic powders are studied. It can be concluded that the nanoparticles can achieve a stable pressure resistance under low pressure and the micron particles have higher pressure resistance, but there is a small amount of leakage due to the microcavities between particles. The nanoparticles are introduced into the micron particles’ microcavities to form a hybrid magnetic powder, which significantly improves the pressure resistance. The microstructure models of magnetic powders in the sealing gap are proposed based on the static pressure curves. However, in the dynamic magnetic powder seal test, its pressure characteristic curve is different from that of the magnetic fluid seal. The relationship between the pressure resistance and the rotational speed of the shaft is studied. It is concluded that different microstructures’ fracture and recombination abilities under shear stress and external magnetic field in seal clearance are different. The thermal effect caused by the friction between the shaft and magnetic powder makes the magnetism of magnetic powder decrease and reduces the sealing ability. Experimental studies prove the application potential of magnetic powder seal.

Simplified Improvement of Higher Order Extended Bulk Flow Analysis Specialized for Derivation of Rotordynamic Coefficients of the Annular Plain Seal With Large Static Eccentricity

Abstract Rotordynamic (RD) fluid force of turbomachinery is known as one of the causes of the shaft vibration problem. Bulk flow analysis is the analytical method of RD fluid force, and it is widely used in design stage. Conventional bulk flow analysis has been basically carried out under the assumption of concentric circular whirl orbit. While, the actual turbomachinery is often operated with static eccentricity due to the effect of static load and so on. However, there are not many studies that have investigated the case with large static eccentricity, in particular, the case more than half the seal clearance. In this paper, the linear RD coefficient for the plain annular seal is focused on and examined for the range that static eccentricity is up to 65% of seal clearance. In this range of static eccentricity, it requires the nonlinear analysis extended to the fifth order and largely increases the number of equations to be solved. This paper proposed simplification of higher order extended bulk flow (SHEBF) analysis, and as a result, the number of analytical equations to be solved is significantly reduced. The validity of this method is confirmed both numerically and experimentally.

An Investigation on Phase Transitions in a Supercritical CO2 Dry Gas Seal

Dry gas seals with extremely low leakage are the preferred sealing technology in the supercritical carbon dioxide (SCO2) Brayton cycle. However, dry gas seals are subject to a significant risk of CO2 phase transitions on the seal face, which has yet to be numerically investigated. A comparison study of SCO2 dry gas seals with two typical inlet temperatures is presented in this paper. The seal clearance, leakage rate, and gas mass fraction under different inlet pressures and inlet temperatures are analyzed, along with further insights into the CO2 expansion process. Some operating and design considerations for CO2 dry gas seals to avoid going through the liquid and two-phase states are finally discussed. The results indicate that liquid CO2 and two-phase CO2 appear on the seal face when operating near the critical temperature. Vaporization of CO2 always occurs near the inner radius of the seal face. The CO2 expansion processes can be decomposed into two slowly decreasing stages and a rapidly decreasing stage. The starting point of the rapidly decreasing stage plays an essential role in CO2 phase transitions. Both low pressure and high temperature help avoid CO2 on the seal face transitioning to the liquid and two-phase states.