Leakage Flow Analysis for a MEMS Rotary Engine

2003 ◽  
Author(s):  
Joshua D. Heppner ◽  
David C. Walther ◽  
Albert P. Pisano
Keyword(s):  
Power System ◽  
Compression Ratio ◽  
Flow Analysis ◽  
Design Parameters ◽  
Working Fluid ◽  
Leakage Flow ◽  
Engine Operation ◽  
Rotary Engine ◽  
Leakage Flows ◽  
Macro Scale

An internal leakage flow analysis is presented for a MEMS fabricated rotary engine in order to establish design parameters for micro engine sealing systems. This research is part of the MEMS Rotary Engine Power System (REPS) group effort to develop a portable power system based on an integrated generator and Wankel rotary internal combustion engine. In order to have acceptable system efficiency, it is necessary to suppress internal leakage and thereby maintain a critical level of compression ratio. There are two inherent leakage paths in rotary engines, which result in blowby and reduced compression ratio: leakage around the apexes of the rotor and leakage across the rotor faces. These sealing issues arise due to the large pressure gradients, which occur along these leakage paths in the combustion chamber. It is the aim of this work to examine the effects of reduced scale on both traditional and novel rotary engine apex sealing mechanisms. In contrast to the macro scale, viscous forces have an increased importance in micro scale engines since Re~.01. A simplified Poiseuille-Couette flow model has been developed to analyze the leakage flows of rotary type engines. Since the Reynolds number for the MEMS REPS is extremely small, the model assumes that the flow is laminar, viscous, incompressible, and steady with air as the working fluid. The model indicates that if a 1 μm gap can be maintained between the housing and moving parts (rotor apexes and faces), leakage flows at expected engine operation speeds will only reduce the compression ratio from 8.3:1 to 6.1:1 so long as the rotation speed is greater than 10,000 rpm. It is doubtful that a traditional or simple micromachine design will yield such a gap and therefore several novel, integrated sealing approaches are under investigation. The model will determine design specification for one of these approaches, an integrated cantilever flexure apex. In conjunction with the theoretical model, a scaled engine experiment at the macro scale is used to verify the modeling effort. The scaling of the experiment complies with Reynolds scaling and ensures that Hele-Shaw flow within the leakage paths is maintained. The experiment does not operate as a functional engine, rather the experiment is designed to maintain a precise clearance between the rotor and housing. In order to preclude additional pressure driven flow effects, an electric motor is used to spin the rotor and simulate the rotation expected due to the combustion pressure acting on the rotor face.

Application of Computational Fluid Dynamics Analysis for Rotating Machinery—Part II: Labyrinth Seal Analysis

2005 ◽  
Vol 127 (4) ◽  
pp. 820-826 ◽  
Author(s):  
Toshio Hirano ◽  
Zenglin Guo ◽  
R. Gordon Kirk
Keyword(s):  
Research Work ◽  
Flow Analysis ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Working Fluid ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Eccentric Rotor ◽  
Computational Fluid Dynamics Analysis ◽  
Force Components

Labyrinth seals are used in various kinds of turbo machines to reduce internal leakage flow. The working fluid, or the gas passing through the rotor shaft labyrinth seals, often generates driving force components that may increase the unstable vibration of the rotor. It is important to know the accurate rotordynamic force components for predicting the instability of the rotor-bearing-seal system. The major goals of this research were to calculate the rotordynamic force of a labyrinth seals utilizing a commercial CFD program and to further compare those results to an existing bulk flow computer program currently used by major US machinery manufacturers. The labyrinth seals of a steam turbine and a compressor eye seal are taken as objects of analysis. For each case, a 3D model with eccentric rotor was solved to obtain the rotordynamic force components. The leakage flow and rotor dynamics force predicted by CFX TASCFlow are compared with the results of the existing bulk flow analysis program DYNLAB. The results show that the bulk flow program gives a pessimistic prediction of the destabilizing forces for the conditions under investigation. Further research work will be required to fully understand the complex leakage flows in turbo machinery.

Performance Analysis of Photovoltaic Thermal (PVT) Panels Considering Thermal Parameters

2016 ◽  
Author(s):  
W. J. A. Jayasuriya ◽  
A. U. C. D. Athukorala ◽  
A. T. D. Perera ◽  
M. P. G. Sirimanna ◽  
R. A. Attalage
Keyword(s):  
Wind Speed ◽  
Performance Analysis ◽  
Mass Flow ◽  
Flow Analysis ◽  
Operating Conditions ◽  
Solar Irradiation ◽  
Heat Transfer Fluid ◽  
Design Parameters ◽  
Working Fluid ◽  
Fluid Temperature

Solar PVT panels are getting popular for wider spectrum of applications for concurrent heat and power generation (CHP). These panels can provide the heating demand of buildings while generating electricity which becomes ideal for building applications of urban energy systems. Energy flow analysis of such panels and performance analysis of such systems becomes essential to design PVT systems matching with the operating conditions. A number of studies have used both theoretical and experimental methods to optimize PVT. However, this task is challenging due to interrelation of CHP production based on two different phenomena where classical optimization methods cannot be applied directly. Hence basic performance analysis considering primary design parameters plays a major role. In this study, a computational model is developed to evaluate sensitivity of design, operating and climatic parameters for a hybrid PVT system and to analyze the performances of PVT for five different design configurations. Five main configurations of the PVT system are considered based on the heat transfer fluid and the arrangements of glass and tedlar layers of PVT collector. This study presents comprehensive performance analysis conducted to evaluate the sensitivity of mass flow rate and working fluid temperature for the five different design configurations of PVT panels. Results show that glass-tedlar water collector performs better when compared to other configurations. Subsequently, the sensitivity of wind speed and solar irradiation is evaluated. The behavior of thermal and electrical efficiencies is analyzed at different wind speed and solar irradiation levels for a range of mass flow rates and working fluid temperatures. Important conclusions on the performance of PVT panels are given based on this detailed analysis.

The Deviation Function Method of Rotary Engine Design by Geometric Parameters

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Sarah Warren Rose ◽  
Daniel C. H. Yang
Keyword(s):  
Compression Ratio ◽  
Design Method ◽  
Geometric Parameters ◽  
Performance Criteria ◽  
Engine Operation ◽  
Deviation Function ◽  
Rotary Engine ◽  
Engine Design ◽  
K Factor ◽  
Wankel Engine

Rotary engines require seals inserted into each rotor apex to maintain contact with the housing and prevent leaks during internal combustion. These seals are called apex seals and their effectiveness directly influences the engine operation and efficiency. The deviation function (DF) method of rotary engine design has several advantages over the conventional design method with regard to the apex seals, and also finds many more possibilities. The DF method can be used to incorporate the profile of the apex seal into the design process and the rotor profile itself. In the DF method, the seal profile is used as a generating curve and the housing bore profile is a generated curve. The housing is conjugate to the apex seal, and therefore conforms to the seal profile, unlike the conventional rotary engine. Another advantage the DF method has over the conventional method is that different apex seal profiles can be used, resulting in a larger variety of rotary engine designs. This paper introduces the DF method of rotary engine design and selection by the geometric parameters rotor radius, R, and eccentricity, l. In conventional rotary (Wankel) engine design, these parameters are used as a ratio called the K factor. The K factor uniquely identifies a conventional rotary engine profile and is therefore used to associate performance criteria such as displacement, compression ratio, and apex sealing. The DF method can be used to employ the same ratio as a selection tool. Instead of a single profile for each K factor, there is a range of possible DF-designed engine profiles associated with each R/l ratio. The resulting design flexibility is shown using two example deviation functions and the design criteria swept area and maximum theoretical compression ratio. Furthermore, the R/l ratio is not an indication of apex sealing effectiveness because the DF method of rotary engine design and selection separates the engine profile geometry from the apex seal geometry. An apex sealing index is presented to show how the DF method can be used to quantify, analyze, and improve apex sealing.

Application of CFD Analysis for Rotating Machinery: Part 2 — Labyrinth Seal Analysis

2003 ◽  
Author(s):  
Toshio Hirano ◽  
Zenglin Guo ◽  
R. Gordon Kirk
Keyword(s):  
Research Work ◽  
Flow Analysis ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Working Fluid ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Eccentric Rotor ◽  
Force Components ◽  
Unstable Vibration

Labyrinth seals are used in various kinds of turbo machines to reduce internal leakage flow. The working fluid or, the gas passing through the rotor shaft labyrinth seals, often generates driving force components that may increase the unstable vibration of the rotor. It is important to know the accurate rotordynamic force components for predicting the instability of the rotor-bearing-seal system. The major goals of this research was to calculate the rotordynamic force of a labyrinth seals utilizing a commercial CFD program and to further compare those results to an existing bulk flow computer program currently used by major US machinery manufacturers. The labyrinth seals of a steam turbine and a compressor eye seal are taken as objects of analysis. For each case, a 3D model with eccentric rotor was solved to obtain the rotordynamic force components. The leakage flow and rotor dynamics force predicted by CFX TASCFlow are compared with the results the existing bulk flow analysis program DYNLAB. The results show that the bulk flow program gives a pessimistic prediction of the destabilizing forces for the conditions under investigation. Further research work will be required to fully understand the complex leakage flows in turbo machinery.

Elliptical Shape Hole-Pattern Seals Performance Evaluation Using Design of Experiments Technique

2016 ◽  
Author(s):  
Hanxiang Jin ◽  
Alexandrina Untaroiu
Keyword(s):  
Design Of Experiments ◽  
Design Parameters ◽  
Working Fluid ◽  
Leakage Flow ◽  
Linear Regression Models ◽  
Analysis And Design ◽  
Seal Design ◽  
Elliptical Shape ◽  
Cylindrical Cavities ◽  
Gas Seals

Hole-pattern annular gas seals have been proven to be very effective in reducing leakage flow between high and low pressure sections in turbomachinery. This type of seal has two distinct flow regions: an annular jet-flow region between the rotor and stator, and cylindrical indentions in the stator that serve as cavities where flow recirculation occurs. As the working fluid enters the cavities and recirculates, its kinetic energy is reduced, resulting in a reduction of leakage flow rate through the seal. The geometry of the cylindrical cavities has a significant effect on the overall performance of a hole-pattern annular gas seal. Previous studies have been primarily focused on cylindrical cavities that are perpendicular to the axis of the seal and have indicated that the performance may be improved by varying the depths, spacing, and diameters of the cavities. However, to date the effects of elliptical cylinder cavities has yet to be investigated. In this study, the effects of elliptical shape hole pattern geometry on the leakage and dynamic response performance of an industry-relevant hole-pattern seal design are investigated using a combination of computational fluid dynamics (CFD), hybrid bulk flow/CFD analysis, and design of experiments techniques. A CFD model of the baseline hole-pattern seal was first developed and validated against experimental data. A design of experiments (DOE) study was then performed to investigate the effect that various elliptical shape cavities had on the leakage rate through the seal. CFD simulations were run for multiple geometry configurations of the cylindrical cavities to evaluate the seal performance at each of the design points. The design space was defined by varying the values of five geometrical characteristics: the major and minor radius of hole, the angle between the major axis and the axis of the seal, the spacing between holes along the seal axis, and hole spacing in the circumferential direction. Quadratic polynomial fitting was then used to analyze the sensitivity of different design variables with respect to the different outputs. This detailed analysis allowed for a greater understanding of the interaction effects from varying all of these design parameters together as opposed to studying them one variable at a time. Response maps generated from the calculated results demonstrate the effects of each design parameter on seal leakage as well as the relationships between the design parameters. The data from this analysis was also used to generate linear regression models that demonstrate how these parameters affect the leakage of the seal. The results of this study could aid in improving future designs of hole-pattern annular gas seals.

Performance Analysis and Comparison Study of Transcritical Power Cycles Using CO2-Based Mixtures as Working Fluids

2016 ◽  
Author(s):  
Jiaxi Xia ◽  
Jiangfeng Wang ◽  
Pan Zhao ◽  
Dai Yiping
Keyword(s):  
Critical Temperature ◽  
Parametric Optimization ◽  
Design Parameters ◽  
Working Fluid ◽  
Comparison Study ◽  
Software Environment ◽  
Working Fluids ◽  
Power Cycles ◽  
Power Cycle ◽  
Thermodynamic Performance

CO2 in a transcritical CO2 cycle can not easily be condensed due to its low critical temperature (304.15K). In order to increase the critical temperature of working fluid, an effective method is to blend CO2 with other refrigerants to achieve a higher critical temperature. In this study, a transcritical power cycle using CO2-based mixtures which blend CO2 with other refrigerants as working fluids is investigated under heat source. Mathematical models are established to simulate the transcritical power cycle using different CO2-based mixtures under MATLAB® software environment. A parametric analysis is conducted under steady-state conditions for different CO2-based mixtures. In addition, a parametric optimization is carried out to obtain the optimal design parameters, and the comparisons of the transcritical power cycle using different CO2-based mixtures and pure CO2 are conducted. The results show that a raise in critical temperature can be achieved by using CO2-based mixtures, and CO2-based mixtures with R32 and R22 can also obtain better thermodynamic performance than pure CO2 in transcritical power cycle. What’s more, the condenser area needed by CO2-based mixture is smaller than pure CO2.

Flow Structures in the Tip Region for a Transonic Compressor Rotor

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Juan Du ◽  
Feng Lin ◽  
Jingyi Chen ◽  
Chaoqun Nie ◽  
Christoph Biela
Keyword(s):  
Numerical Simulations ◽  
Reference Frame ◽  
Three Dimensional ◽  
Flow Structures ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Three Dimensional Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Tip Leakage Flows

Numerical simulations are carried out to investigate flow structures in the tip region for an axial transonic rotor, with careful comparisons with the experimental results. The calculated performance curve and two-dimensional (2D) flow structures observed at casing, such as the shock wave, the expansion wave around the leading edge, and the tip leakage flow at peak efficiency and near-stall points, are all captured by simulation results, which agree with the experimental data well. An in-depth analysis of three-dimensional flow structures reveals three features: (1) there exists an interface between the incoming main flow and the tip leakage flow, (2) in this rotor the tip leakage flows along the blade chord can be divided into at least two parts according to the blade loading distribution, and (3) each part plays a different role on the stall inception mechanism in the leakage flow dominated region. A model of three-dimensional flow structures of tip leakage flow is thus proposed accordingly. In the second half of this paper, the unsteady features of the tip leakage flows, which emerge at the operating points close to stall, are presented and validated with experiment observations. The numerical results in the rotor relative reference frame are first converted to the casing absolute reference frame before compared with the measurements in experiments. It is found that the main frequency components of simulation at absolute reference frame match well with those measured in the experiments. The mechanism of the unsteadiness and its significance to stability enhancement design are then discussed based on the details of the flow field obtained through numerical simulations.

Feasibility Study of a MEMS Viscous Rotary Engine Power System (VREPS)

2004 ◽  
Author(s):  
Thomas H. Cauley ◽  
Jose D. Rosario-Rosario ◽  
Albert P. Pisano
Keyword(s):  
Power System ◽  
Permanent Magnet ◽  
Electrical Power ◽  
Rotating Disk ◽  
Creeping Flow ◽  
Magnetic Pole ◽  
Rotary Engine ◽  
Magnetic Circuits ◽  
Isentropic Efficiency ◽  
Engine Power

In this paper is presented an analytic, theoretical and numerical study of the Viscous Rotary Engine Power System (VREPS). In addition, a proposed process flow for the fabrication of the VREPS using DRIE of silicon is described. The design premise of the VREPS is to derive mechanical power from the surface viscous shearing forces developed by a pressure driven flow present between a rotating disk or annulus and a stationary housing. The resulting motion of the rotating disk or annulus is converted into electrical power by using an external permanent magnet, embedded nickel-iron magnetic circuits, and an external switched magnetic pole electric generator similar to the design proposed by M. Senesky for the UC Berkeley micro-Wankel Engine [1]. This paper will examine the power output, isentropic efficiency, and operating characteristics of the disk and annular viscous turbines using the lubrication approximation and the Creeping Flow Equations (Stokes Flow). The viscous turbine is optimized for maximum isentropic efficiency using MATLAB numerical optimization routines. Finally, a unique triple-wafer micro-fabrication process for VREPS is presented. The proposed design consists of a 250 μm thick, 3.4 mm OD / 2.4 mm ID annular rotor with embedded magnetic poles and four 10 μm driving channels on each side of the rotor. Electrical power is generated with a switched magnetic pole generator, external permanent magnet, and integrated magnetic circuits. Calculations with water predict an output power of 825 mW at an isentropic efficiency of 25% using a pressure drop of 5 MPa cross the device.

Influence of regenerator matrix and working fluid on optimisation of design parameters of Stirling cryocoolers

Cryogenics ◽  
1994 ◽  
Vol 34 ◽  
pp. 211-214 ◽  
Author(s):  
M.D. Atrey ◽  
S.L. Bapat ◽  
K.G. Narayankhedkar
Keyword(s):  
Design Parameters ◽  
Working Fluid
Sign in / Sign up

Export Citation Format

Share Document