The Impact of Real Gas Properties on Predictions of Static and Rotordynamic Properties of the Annular Gas Seals for Injection Compressors

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Yoon-Shik Shin ◽  
Dara W. Childs
Keyword(s):  
Energy Equation ◽  
Control Volume ◽  
Ideal Gas ◽  
Running Speed ◽  
Real Gas ◽  
Ideal Gas Law ◽  
Piston Seal ◽  
Gas Seals ◽  
The Impact ◽  
Gas Properties

Predictions are presented for an annular gas seal that is representative of the division-wall seal of a back-to-back compressor or the balance-piston seal of an in-line compressor. A two-control-volume bulk-flow model is used including the axial and circumferential momentum equations and the continuity equations. The basic model uses a constant-temperature prediction (ISOT) and an ideal gas law as an equation of state. Two variations are used: adding the energy equation with an ideal gas law (IDEAL), and adding the energy equation with real gas properties (REAL). The energy equations assume adiabatic flow. The ISOT model has been used for prior calculations. Concerning predictions of static characteristics, the calculated mass leakage rates were, respectively, 9.46 kg∕s, 9.55 kg∕s, and 7.87 kg∕s for ISOT, IDEAL, and REAL. For rotordynamic coefficients, predicted effective stiffness coefficients are comparable for the models at low excitation frequencies. At running speed, REAL predictions are roughly 40% lower than ISOT, which could result in lower predicted critical speeds. Predicted effective damping coefficients are also generally comparable. REAL and IDEAL predictions for the crossover frequency are approximately 20% lower than ISOT. REAL predictions for effective damping are modestly lower in the frequency range of 40–50% of running speed where higher damping values are desired.

The Influence of Real Gas Properties on Predictions of Static and Rotordynamic Properties of Annular Seals for Injection Compressors

2007 ◽  
Author(s):  
Yoon-Shik Shin ◽  
Dara W. Childs
Keyword(s):  
Energy Equation ◽  
Control Volume ◽  
Ideal Gas ◽  
Running Speed ◽  
Real Gas ◽  
Adiabatic Flow ◽  
Rotordynamic Coefficients ◽  
Ideal Gas Law ◽  
Piston Seal ◽  
Gas Properties

Predictions are presented for an annular gas seal that is representative of the division-wall seal of a back-to-back compressor or the balance-piston seal of an in-line compressor. A 2-control-volume bulk-flow model is used including the axial and circumferential momentum equations and the continuity equations. The basic model uses a constant temperature prediction (ISOT) and an ideal gas law as an equation of state. Two variations are used: adding the energy equation with an ideal gas law (IDEAL), and adding the energy equation with real gas properties (REAL). The energy equations assume adiabatic flow. The ISOT model has been used for prior calculations. Concerning predictions of static characteristics, the calculated mass leakage rate was, respectively, 9.46, 9.55 and 7.87 kg/s for ISOT, IDEAL, and REAL. For rotordynamic coefficients, predicted effective stiffness coefficients are comparable for the models at low excitation frequencies. At running speed, REAL predictions are roughly 40% lower than ISOT, which could results in lower predicted critical speeds. Predicted effective damping coefficients are also generally comparable. REAL and IDEAL predictions for the cross-over frequency is approximately 20% lower than ISOT. REAL predictions for effective damping are modestly lower in the frequency range of 40 to 50% of running speed where higher damping values are desired.

Measurement Versus Predictions of Rotordynamic Coefficients of a Hole-Pattern Gas Seal With Negative Preswirl

2012 ◽  
Author(s):  
Philip D. Brown ◽  
Dara W. Childs
Keyword(s):  
Control Volume ◽  
Pressure Ratio ◽  
Excitation Frequency ◽  
Ideal Gas ◽  
Rotor Speed ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
The Cross ◽  
Gas Seals ◽  
Stiffness And Damping

Test results are presented for rotordynamic coefficients of a hole-pattern annular gas seals at supply pressures to 84 bar and running speeds to 20,200 RPM. The principal test variable of interest was negative preswirl. Preswirl signifies the circumferential fluid flow entering a seal, and negative preswirl indicates a fluid swirl in a direction opposite to rotor rotation. The influences of pressure ratio and rotor speed were also investigated. Measured results produce direct and cross-coupled stiffness and damping coefficients that are a function of excitation frequency Ω. Changes in pressure ratio had only small effects on most rotordynamic coefficients. Cross-coupled stiffness showed slightly different profiles through the mid-range of Ω values. Increasing rotor speed significantly increased cross-coupled stiffness and cross-coupled damping. At 10,200 RPM, high negative inlet preswirl produced negative cross-coupled stiffness over an excitation frequency range of 200–250 Hz. Negative preswirl did not affect direct stiffness and damping coefficients. Effective damping combines the stabilizing effect of direct damping and the destabilizing effect of cross-coupled stiffness. The cross-over frequency is the precession frequency where effective damping transitions from a negative value to a positive value with increasing frequency. At 20,200 RPM with a pressure ratio of 50%, peak effective damping was increased by 50%, and the cross-over frequency was reduced by 50% for high-negative preswirl versus zero preswirl. Hence, reverse swirl can greatly enhance the stabilizing capacity of hole-pattern balance-piston or division-wall seals for compressors. A two-control-volume model that uses the ideal gas law at constant temperature was used to predict rotordynamic coefficients. The model predicted direct rotordynamic coefficients well, but substantially under predicted cross-coupled rotordynamic coefficients especially at high negative preswirls.

Numerical Simulation of Steam Flow Inside the Superheater Section of An Industrial Boiler Using a Real Gas Model

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Deepak Kumar Kanungo ◽  
Kirti Chandra Sahu
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Supercritical Fluids ◽  
Ideal Gas ◽  
Real Gas ◽  
Absolute Value ◽  
Ideal Gas Law ◽  
Maximum Value ◽  
Industrial Boiler ◽  
The Ideal

Abstract Flow mal-distribution inside manifolds hampers the overall efficiency of processes in industries. In supercritical boilers, improper flow of steam inside the superheater (SH) section is a common cause of thermal accidents. However, carrying out a numerical simulation of supercritical fluids flowing inside manifolds is challenging as the ideal gas law does not describe the behavior of these fluids properly. In the present work, numerical simulation of the flow of supercritical steam inside the superheater section of an industrial boiler has been performed using a real gas model. The proposed real gas model is first validated with experimental data associated with the steam properties. Subsequently, the effect of different inlet and outlet arrangements on the flow mal-distribution of steam in the superheater section of the boiler is investigated numerically using the real gas model. A modified inlet and outlet arrangement of the superheater header is proposed which reduces the maximum value of flow mal-distribution in the header by 19.7% and total pressure drop in the domain by 17%. The effect of the Reynolds number on flow mal-distribution in the header arrangement is found to be negligible. The absolute value of the heat absorption by the superheater tubes increases with an increase in the value of the Reynolds number.

The Use of Real Gas Properties for Design and Flow Field Simulations of a Small Centripetal Steam Turbine

2009 ◽  
Author(s):  
Jianjun Feng ◽  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen
Keyword(s):  
Steam Turbine ◽  
Design Procedure ◽  
Flow Fields ◽  
Ideal Gas ◽  
Real Gas ◽  
The Real ◽  
Real Gas Effects ◽  
Applied Design ◽  
Small Capacity ◽  
Gas Properties

In this paper, the applied design procedure for generation of a small-capacity ORC centripetal steam turbine working with the fluid 1, 1, 1, 3, 3-Pentafluoropropane (R245fa) is described with consideration of real gas effects. After specification of the turbine geometry in an iterative process using different commercial design tools which have been enhanced in order to work with real gas conditions, CFD simulations based on the real gas properties of the fluid have been conducted for the originated geometry. The simulations are performed by using the CFD code ANSYS-CFX11 with a pre-prepared real gas property (RGP) table, which comprises the required gas properties at different discrete pressure and temperature values. In addition, the flow fields inside the turbine obtained from the real gas model is compared to those flow fields which are obtained by the ideal gas model and also by the Redlich-Kwong model.

The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Dara W. Childs ◽  
Stephen Arthur ◽  
Naitik J. Mehta
Keyword(s):  
Performance Improvement ◽  
Test Data ◽  
Hole Diameter ◽  
Test Results ◽  
Running Speed ◽  
Hole Depth ◽  
Test Variable ◽  
Leakage Characteristics ◽  
Gas Seals ◽  
The Impact

Test results are presented for rotordynamic characteristics of hole-pattern-stator annular gas seals at a 70 bar supply pressures with a running speed of 20,200 rpm. Leakage results are presented for these conditions and the additional speeds: 10,200 and 15,300 rpm. Hole-depth is the principal test variable of interest. Most published annular test data for these seals have a hole diameter of 3.175 mm and a hole depth of 3.302 mm. For this work, with the 3.175 mm hole diameter, additional results are presented for shallow (1.905 mm) and deep (6.604 mm) hole depths. Test results show a pronounced dependence of leakage and rotordynamic behavior on hole depth. Test results show much better leakage performance for the shallow-hole-depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.

Measurement Versus Predictions of Rotordynamic Coefficients of a Hole-Pattern Gas Seal With Negative Preswirl

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Philip D. Brown ◽  
Dara W. Childs
Keyword(s):  
Control Volume ◽  
Pressure Ratio ◽  
Excitation Frequency ◽  
Ideal Gas ◽  
Crossover Frequency ◽  
Rotor Speed ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Ideal Gas Law ◽  
Stiffness And Damping

Test results are presented for the rotordynamic coefficients of a hole-pattern annular gas seal at supply pressures to 84 bar and running speeds to 20200 rpm. The principal test variable of interest was negative preswirl. Preswirl signifies the circumferential fluid flow entering a seal and negative preswirl indicates a fluid swirl in a direction opposite to rotor rotation. The influences of the pressure ratio and rotor speed were also investigated. The measured results produce direct and cross-coupled stiffness and damping coefficients that are a function of the excitation frequency Ω. Changes in the pressure ratio had only small effects on most rotordynamic coefficients. Cross-coupled stiffness showed slightly different profiles through the midrange of Ω values. Increasing rotor speed significantly increased the cross-coupled stiffness and cross-coupled damping. At 10,200 RPM, high negative inlet preswirl produced negative cross-coupled stiffness over an excitation frequency range of 200–250 Hz. Negative preswirl did not affect the direct stiffness and damping coefficients. Effective damping combines the stabilizing effect of direct damping and the destabilizing effect of cross-coupled stiffness. The crossover frequency is the precession frequency where effective damping transitions from a negative value to a positive value with increasing frequency. At 20,200 rpm with a pressure ratio of 50%, the peak effective damping was increased by 50%, and the crossover frequency was reduced by 50% for high-negative preswirl versus zero preswirl. Hence, reverse swirl can greatly enhance the stabilizing capacity of a hole-pattern balance-piston or division-wall seals for compressors. A two-control-volume model that uses the ideal gas law at constant temperature was used to predict rotordynamic coefficients. The model predicted direct rotordynamic coefficients well, however, substantially under-predicted cross-coupled rotordynamic coefficients, especially at high negative preswirls.

scholarly journals Numerical investigation of the thermal-caloric imperfections on entropy enhancement across normal shock waves

2020 ◽  
Vol 48 (4) ◽  
pp. 285-308
Author(s):  
MEROUANE SALHI
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
Molecular Size ◽  
Ideal Gas ◽  
Normal Shock ◽  
Wave Flow ◽  
Appreciable Effect ◽  
Real Gas ◽  
Normal Shock Wave ◽  
The Impact

Changes in flow properties across a normal shock wave are calculated for a real gas, thus giving us a better affinity to the real behavior of the waves. The purpose of this work is to develop shock-wave theory under the gaseous imperfections. Expressions are developed for analyzing the supersonic flow of such a thermally and calorically imperfect gas. The effects of molecular size and intermolecular attraction forces are used to correct a state equation, focusing on determination of the impact of upstream stagnation parameters on a normal shock wave. Flow through a shock wave in air is investigated to find a general form for normal shock waves. At Mach numbers greater than 2.0, the temperature rise is considerably below, and hence the density rise is well above, that predicted assuming ideal gas behavior. It is shown that caloric imperfections in air have an appreciable effect on the parameters developed in the processes considered. Computation of errors between the present model based on real gas theory and a perfect gas model shows that the influence of the thermal and caloric imperfections associated with a real gas is important.

Theoretic Analysis of the Effect of Carbon Dioxide Real Gas on the Performance of the T-Groove Dry Gas Seal

2013 ◽  
Vol 634-638 ◽  
pp. 3815-3820
Author(s):  
Xiao Peng Hu ◽  
Peng Yun Song
Keyword(s):  
Carbon Dioxide ◽  
Ideal Gas ◽  
Virial Equation ◽  
Real Gas ◽  
The Real ◽  
Dry Gas Seal ◽  
Virial Equation Of State ◽  
Gas Seals ◽  
Carbon Dioxide Co2 ◽  
The Ideal

Dry gas seals have widely used in many centrifugal compressors and other rotating machinery. The gas performance of the dry gas seal is generally regarded as an ideal gas when the gas seal is investigated, designed, and operated. However some real gases performance may be quite different from the ideal gas when the gas pressure is high. In this paper, the carbon dioxide (CO2) was taken as an example in some T-groove dry gas seal, and the virial equation of state, which expresses the effect of real gas, was used, and the finite difference method (FDM) was adopted to solve the Reynolds equation of gas lubrication. The effects of real gas on the opening force (Fo) and radial leakage (Q) of the T-groove gas seal had been obtained. The results show that the seal performance (Fo, Q) will be underestimated when the real carbon dioxide is considered as an ideal gas. In calculation conditions, Fo and Q were maximum underestimated 4.16% and 19.25% respectively when Po was 5MPa and ns was variable and the real carbon dioxide was considered as an ideal gas; Fo and Q were maximum underestimated 7.48%, and 29.25% respectively, when ns was 3000r/min and Po was variable and the real carbon dioxide was considered as an ideal gas.

scholarly journals Shock interactions in inviscid air and $$\hbox {CO}_2$$–$$\hbox {N}_2$$ flows in thermochemical non-equilibrium

Shock Waves ◽  
2021 ◽  
Author(s):  
C. Garbacz ◽  
W. T. Maier ◽  
J. B. Scoggins ◽  
T. D. Economon ◽  
T. Magin ◽  
...  
Keyword(s):  
Chemical Species ◽  
High Energy ◽  
Ideal Gas ◽  
Shock Interaction ◽  
Interaction Patterns ◽  
Shock Interactions ◽  
Wave Interference ◽  
Type V ◽  
The Impact ◽  
Non Equilibrium

AbstractThe present study aims at providing insights into shock wave interference patterns in gas flows when a mixture different than air is considered. High-energy non-equilibrium flows of air and $$\hbox {CO}_2$$ CO 2 –$$\hbox {N}_2$$ N 2 over a double-wedge geometry are studied numerically. The impact of freestream temperature on the non-equilibrium shock interaction patterns is investigated by simulating two different sets of freestream conditions. To this purpose, the SU2 solver has been extended to account for the conservation of chemical species as well as multiple energies and coupled to the Mutation++ library (Multicomponent Thermodynamic And Transport properties for IONized gases in C++) that provides all the necessary thermochemical properties of the mixture and chemical species. An analysis of the shock interference patterns is presented with respect to the existing taxonomy of interactions. A comparison between calorically perfect ideal gas and non-equilibrium simulations confirms that non-equilibrium effects greatly influence the shock interaction patterns. When thermochemical relaxation is considered, a type VI interaction is obtained for the $$\hbox {CO}_2$$ CO 2 -dominated flow, for both freestream temperatures of 300 K and 1000 K; for air, a type V six-shock interaction and a type VI interaction are obtained, respectively. We conclude that the increase in freestream temperature has a large impact on the shock interaction pattern of the air flow, whereas for the $$\hbox {CO}_2$$ CO 2 –$$\hbox {N}_2$$ N 2 flow the pattern does not change.

Making sense of sensemaking: using the sensemaking epistemic game to investigate student discourse during a collaborative gas law activity

2021 ◽  
Author(s):  
Kevin H. Hunter ◽  
Jon-Marc G. Rodriguez ◽  
Nicole M. Becker
Keyword(s):  
Problem Solving ◽  
Conceptual Understanding ◽  
Ideal Gas ◽  
Interactive Simulation ◽  
Structural Components ◽  
Student Discourse ◽  
Coding Scheme ◽  
Making Sense ◽  
Ideal Gas Law ◽  
The Ideal

Beyond students’ ability to manipulate variables and solve problems, chemistry instructors are also interested in students developing a deeper conceptual understanding of chemistry, that is, engaging in the process of sensemaking. The concept of sensemaking transcends problem-solving and focuses on students recognizing a gap in knowledge and working to construct an explanation that resolves this gap, leading them to “make sense” of a concept. Here, we focus on adapting and applying sensemaking as a framework to analyze three groups of students working through a collaborative gas law activity. The activity was designed around the learning cycle to aid students in constructing the ideal gas law using an interactive simulation. For this analysis, we characterized student discourse using the structural components of the sensemaking epistemic game using a deductive coding scheme. Next, we further analyzed students’ epistemic form by assessing features of the activity and student discourse related to sensemaking: whether the question was framed in a real-world context, the extent of student engagement in robust explanation building, and analysis of written scientific explanations. Our work provides further insight regarding the application and use of the sensemaking framework for analyzing students’ problem solving by providing a framework for inferring the depth with which students engage in the process of sensemaking.

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