Academic literature on the topic 'Polytrophic process'
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Journal articles on the topic "Polytrophic process"
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Li, Zhong, Da Long Zhang, Jian Feng Li, Ding Hua Yang, Wen Jun Qin, Gen Sheng Yang, and Xiao Lin Wang. "A Gas-Turbine with Approximate General Carnot Cycle and Its Performance Prediction." Advanced Materials Research 960-961 (June 2014): 1134–41. http://dx.doi.org/10.4028/www.scientific.net/amr.960-961.1134.
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Based on polytrophic process of air compression and gas combustion inside the turbine isothermally, an approximate gas-turbine with General Carnot cycle and relevant implementing schemes are suggested. Its performance was predicted with mathematics model compared with traditional one. The results show that the heat efficiency of the suggested gas turbine is higher than the traditional one. The suggested cycle combines the gas cycle and steam cycle, of which the NOx emission can be easily decreased
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Bąkowski, Andrzej, Leszek Radziszewski, and Žmindak Milan. "Determining the Polytrophic Exponent of the Process Occurring During the Working Cycle of a Diesel." Procedia Engineering 136 (2016): 220–26. http://dx.doi.org/10.1016/j.proeng.2016.01.201.
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Vestfálová, Magda, and Pavel Šafařík. "About the operational determination of the state and parameters of flowing moist air." EPJ Web of Conferences 213 (2019): 02091. http://dx.doi.org/10.1051/epjconf/201921302091.
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The presented paper deals with the solution of moist air parameters for the needs of aerodynamic research or design. From the thermodynamic theory of moist air, a p-t diagram of moist air is designed to allow the operative expression of the process and state of the moist air. Using this diagram, it is possible to illustratively describe the course of parameters at various state changes in moist air such as isentropic expansion and compression, isothermal expansion and compression, isobaric state change, isochoric state change, or general polytrophic state change. The initial state of moist air is determined by the pressure, temperature and moisture of the air. In the p-t diagram, the process is expressed by the applicable curve; the identification of the parameters in which the phase transformation occurs in moist air is significant. Uncertainty analysis is performed.
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Ye, Chang An, and Xiao Fen Zhang. "Analysis of Polycrystalline Silicon-Photovoltaic Industry’s Key Technologies Development and Influences on its Cost and Energy-Consumption." Advanced Materials Research 1008-1009 (August 2014): 1470–76. http://dx.doi.org/10.4028/www.scientific.net/amr.1008-1009.1470.
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Polycrystalline silicon-photovoltaic industry belongs to high-and-new technology industry, but it produces massive by-products (silicon tetrachloride and so on), even partial chloro-silicane and hydrogen chloride exude into the exhaust in its production process. As a consequence, it not only increases the exhaust processing cost in the polycrystalline silicon-photovoltaic industry, but also increases pollutant discharge of the enterprise. At present, Chinese polycrystalline silicon-photovoltaic enterprises cannot solve technical difficult problems in large-scale production due to lack of coordination of chemical industry. Moreover, polycrystalline silicon has high request of purity that needs quite advanced technology to achieve. This article introduces influences upon production cost and energy consumption with the use of improved Siemens method, and proposes that polytrophic-photovoltaic industry needs to be systematized, normalized and standardized for its healthy development.
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Li, Xuebing, Yintao Wei, and Yuan He. "Simulation on polytropic process of air springs." Engineering Computations 33, no. 7 (October 3, 2016): 1957–68. http://dx.doi.org/10.1108/ec-08-2015-0224.
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Purpose The purpose of this paper is to propose a method to simulate the polytropic process of air springs. Design/methodology/approach An iterative finite element method (FEM) is proposed. Findings The proposed method is reliable and effective in solving the polytropic process of air springs. Originality/value This work would be helpful for understanding the simulation of pneumatic structures, and the proposed modified FEM would be useful for improving the simulation of the mechanical behavior of an air spring.
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Nicolaou, Georgios, George Livadiotis, and Mihir I. Desai. "Estimating the Polytropic Indices of Plasmas with Partial Temperature Tensor Measurements: Application to Solar Wind Protons at ~1 au." Applied Sciences 11, no. 9 (April 28, 2021): 4019. http://dx.doi.org/10.3390/app11094019.
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We examine the relationships between temperature tensor elements and their connection to the polytropic equation, which describes the relationship between the plasma scalar temperature and density. We investigate the possibility to determine the plasma polytropic index by fitting the fluctuations of temperature either perpendicular or parallel to the magnetic field. Such an application is particularly useful when the full temperature tensor is not available from the observations. We use solar wind proton observations at ~1 au to calculate the correlations between the temperature tensor elements and the scalar temperature. Our analysis also derives the polytropic equation in selected streamlines of solar wind plasma proton observations that exhibit temperature anisotropies related to stream-interaction regions. We compare the polytropic indices derived by fitting fluctuations of the scalar, perpendicular, and parallel temperatures, respectively. We show that the use of the parallel or perpendicular temperature, instead of the scalar temperature, still accurately derives the true, average polytropic index value, but only for a certain level of temperature anisotropy variability within the analyzed streamlines. The use of the perpendicular temperature leads to more accurate calculations, because its correlation with the scalar temperature is less affected by the anisotropy fluctuations.
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LEJDA, Kazimierz, and Michał WARIANEK. "Assessment methods of the basic parameters of the combustion process in reciprocating internal combustion engines." Combustion Engines 179, no. 4 (October 1, 2019): 21–26. http://dx.doi.org/10.19206/ce-2019-403.
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The article presents selected methods of assessing the basic parameters of the combustion process, as well as assessing the usability and limitations of the methods used to determine the initiation and the end of the combustion process in reciprocating internal combustion engines. The methods considered are based on data contained in real, developed indicator diagrams. Basic thermodynamic assumptions and the scope of application of the combustion process evaluation method based on the actual work cycle of a combustion engine prepared in a double logarithmic scale were discussed. The article also mentions the application of the following methods: a direct pressure comparison method in the cylinder, the comparison of the first pressure derivative in the cylinder, logarithmic derivative method of pressure change in the cylinder, the method of the polytropic index, method of the first derivative of the polytropic index and the method of constant values of the polytropic index. The article presents the advantages and disadvantages of the research of our methods.
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Dragomirescu, Andrei. "On the Variation of the Polytropic Exponent in a High Pressure Fan Impeller." Applied Mechanics and Materials 841 (June 2016): 286–91. http://dx.doi.org/10.4028/www.scientific.net/amm.841.286.
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Fan impellers are usually designed considering that the pumped air is incompressible and homogeneous, i.e. its density remains constant. When the incompressibility hypothesis can lead to significant errors, as in the case of high pressure fans, the analysis of the air flow can be made by considering that the air undergoes a polytropic process of constant polytropic exponent. In this paper, the concept of polytropic process of variable exponent depending on impeller radius is introduced, in order to better approximate the phenomena that take place inside blade passages. Numerical results obtained for an impeller of a high pressure fan without spiral casing suggest that the pumped air undergoes two different processes: an expansion in the first part of the impeller and the usual compression in the second part. The two processes are reflected in the strong variation of the polytropic exponent, which shows a vertical asymptote where the change of the process takes place. The results also suggest that high pressure fan impellers could consist of two stages, each stage being designed according to the process that takes place inside it: expansion or compression.
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Nestler, F., V. P. Müller, M. Ouda, M. J. Hadrich, A. Schaadt, S. Bajohr, and T. Kolb. "A novel approach for kinetic measurements in exothermic fixed bed reactors: advancements in non-isothermal bed conditions demonstrated for methanol synthesis." Reaction Chemistry & Engineering 6, no. 6 (2021): 1092–107. http://dx.doi.org/10.1039/d1re00071c.
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A novel approach for the investigation of reaction kinetics using a polytropic miniplant reactor featuring a highly resolved fibre optic temperature measurement and FTIR gas phase analysis is presented for methanol synthesis.
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Livadiotis. "Connection of Turbulence with Polytropic Index in the Solar Wind Proton Plasma." Entropy 21, no. 11 (October 25, 2019): 1041. http://dx.doi.org/10.3390/e21111041.
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This paper improves our understanding of the interplay of the proton plasma turbulent heating sources of the expanding solar wind in the heliosphere. Evidence is shown of the connections between the polytropic index, the rate of the heat absorbed by the solar wind, and the rate of change of the turbulent energy, which heats the solar wind in the inner and outer heliosphere. In particular, we: (i) show the theoretical connection of the rate of a heat source, such as the turbulent energy, with the polytropic index and the thermodynamic process; (ii) calculate the effect of the pick-up protons in the total proton temperature and the relationship connecting the rate of heating with the polytropic index; (iii) derive the radial profiles of the solar wind heating in the outer and inner heliosphere; and (iv) use the radial profile of the turbulent energy in the solar wind proton plasma in the heliosphere, in order to show its connection with the radial profiles of the polytropic index and the heating of the solar wind.
Dissertations / Theses on the topic "Polytrophic process"
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Kopečný, Lukáš. "McKibbenův pneumatický sval - modelování a použití v hmatovém rozhraní." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-233458.
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This work describes exceptional properties of McKibben pneumatical muscle and introduces its state-of-the-art model. The mathematical model is extended especially in a field of a thermodymical behavior. A new model applies a method used for describing of a thermodynamical behavior of pneumatic cylinders until now. This method is significantly upgraded to fit a muscle behavior, particularly by considering a heat generated by a muscle internal natural friction. The model is than verified and discussed with a real system. The haptic part introduces a development and design of a haptic glove interface for the use in robotics, especially in telepresence, or in VR. The force and touch feedback is provided by Pneumatic Muscles controlled by an open loop algorithm using the introduced mathematical model. The design is light and compact.
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Rydén, Gustav, and Fredrik Anarp. "Beräkningsmodell för slagtider av pneumatiska manöverdon : En experimentell och teoretisk studie av beteendet för pneumatiska cylindrar samt manöverdon." Thesis, Linköpings universitet, Fluida och mekatroniska system, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-166356.
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Denna rapport redogör framtagningen av en beräkningsmodell för slagtider av pneumatiska cylindrar och manöverdon. Slagtiderna för ett manöverdon kan bestämmas genom experimentella tester. För att underlätta och minska tiden som krävs i samband med testerna skapas en beräkningsmodell som presenterar teoretiska värden för slagtiderna. Denna beräkningsmodell stämmer kvalitativt överens med de experimentella tester som också genomförs i detta arbete. Testerna genomförs först på en enkel pneumatisk cylinder vilket bidrar till kunskaper om slagkarakteristik och slagtider. Denna kunskap är till hjälp för utveckling av beräkningsmodellen. Under testerna mäts bland annat slagtid, kammartryck och kolvens förflyttning vid en mängd olika driftförhållanden. Testerna visar att en av de mest kritiska parametrarna för beräkningsmodellen är C-värdet, en parameter som beskriver flödeskarakteristiken för pneumatiska komponenter. För att få beräkningsmodellen att fungera väl behöver ett så korrekt C-värde som möjligt användas. Beräkningsmetodiken består i stora drag av samband för fyllning och tömning av pneumatiska volymer samt tryckförändringar i cylinderkamrarna vid kompression och expansion. Med en kombination av dessa ekvationer är det möjligt att beräkna slagtiden. Eftersom beräkningsmodellen vill hållas relativt enkel görs ett antal antaganden om systemets parametrar. Dessa antaganden utvärderas efter deras påverkan på slagtiden. Validering mot experimentella resultat visar att beräkningsmodellen generellt fungerar bättre vid höga matningstryck och kritiska flöden. När matningstrycket är lågt och underkritiska flöden erhålls påverkas slagtiden av många fler parametrar, vilket gör att beräkningsmodellen får något sämre precision. Detta resultat är inte helt oväntat eftersom sambandet för kritiskt flöde är relativt enkelt.This thesis work describes the development of a calculation model for stroke times of pneumatic cylinders and actuators. The stroke time of an actuator can be determined by experimental tests. To facilitate and reduce the time required in connection with the tests, a calculation model is created which presents theoretical values of the stroke time. This calculation model is qualitatively consistent with the experimental tests carried out in this work. The tests are first carried out on a simple pneumatic cylinder, which contributes to knowledge of stroke characteristics and stroke times. This knowledge is helpful for the development of the calculation model. During the tests the stroke time, chamber pressure and piston movement are measured in a variety of operating conditions. The tests show that one of the most critical parameters for the calculation model is the C value, a parameter that describes the flow characteristics of pneumatic components. To make the calculation model reliable, a reasonable C value need to be used. The calculation method consists largely of equations for filling and emptying of pneumatic volumes as well as pressure changes in the cylinder chambers during compression and expansion. With a combination of these equations it is possible to calculate the stroke time. Since the calculation model wants to be kept relatively simple, several assumptions are made about parameters in the system. These assumptions are evaluated according to their potential and impact on the stroke time. Validation experiments show that the calculation model generally works better at high supply pressures and critical flows. When the supply pressure is low and subcritical flow are obtained, the stroke time is affected by many more parameters, which lower the precision of the calculation model. This result is not entirely unexpected since the critical flow equations are relatively simple.
Conference papers on the topic "Polytrophic process"
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Sorli, Massimo, and Laura Gastaldi. "Thermic Influence on the Dynamics of Pneumatic Servosystems." In ASME 8th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2006. http://dx.doi.org/10.1115/esda2006-95545.
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The gains values that can be imposed in pneumatic systems controllers are bounded to the restricted actuator bandwidth. That limitation, with low damping and stiffness, due to the air compressibility, seriously affects accuracy and repeatability when varying payload or supply pressures. For modelling and control intent a correct characterisation of the pneumatic actuator natural frequency is indispensable. The aim of this paper is to evaluate how heat exchange process affects the proper characteristics of pneumatic drivers, and in particular their hydraulic stiffness. To this purpose dynamic stiffness had been studied both by imposing in the cylinder’s chambers a polytrophic transformation of the fluid with a prefixed index and by employing energy equations. Numerical results obtained by implementing the two formulations for different working conditions are reported and compared in order to point out the ranges in which they overlap, and hence both approaches produce accurate results, or the ones in which there is a difference, and then it is necessary to consider the temperature dynamics.
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Taher, Matt. "Mathematical Modeling of the Polytropic Process Using the Sequential Cubic Polynomial Approximation." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59715.
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Abstract The polytropic process is used to signify the effect of “energy degradation” associated with the equipment losses, which is as an inherent irreversibility in a compression process. The polytropic process is path dependent, which entails the irreversibility associated with the system. The change of gas composition and operating conditions affect the energy degradation. In this paper the polytropic process of real gas is explained and thermodynamics and mathematical model used in Taher-Evans Cubic Polynomial Method [1], [2] is presented. The elegance of Taher-Evans Cubic Polynomial Method is its rapid solution technique and high precision for calculating polytropic efficiency as required for compressor performance testing by the ASME PTC-10 [3].
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Oldrich, Jiri. "Advanced Polytropic Calculation Method of Centrifugal Compressor." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40931.
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The contribution deals with a new method for calculation of the polytropic change of real gas or gaseous mixture. This method can be used for high accurate polytropic analysis of centrifugal compressors compressing real gases. In the course of design and test evaluation of the compressor the most important is to decrease energy consumption. Advantage of the polytropic analysis is the fact that the polytropic change is very close to the actual process which is in progress in the centrifugal compressor. Several various methods for calculation of polytropic process have been developed till now. The new method is based on numerical solution of basic definition equation of polytropic change in form edH = Vdp where “polytropic efficiency” e has constant value along the whole polytropic path. This method enables to calculate arbitrary unknown parameters from set of quantities (polytropic efficiency, initial pressure and temperature and final pressure and temperature) if the remaining parameters and gas composition are known. Suitable real gas equation of state can be used to calculation of real gas thermodynamic properties. Presented method is independent of equation of state. Accuracy of this method depends only on chosen equation of state. Computer procedure based on above mentioned method can be incorporated into computer programs for calculation of compressors, refrigerating cycles, expansion turbines, gas or steam turbines etc.
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Hundseid, O̸yvind, Lars E. Bakken, and Tor Helde. "A Revised Compressor Polytropic Performance Analysis." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-91033.
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The compressor polytropic head and efficiency analysis are based on the assumption that the compression process follows the path of a constant polytropic exponent n. Both the ASME PTC10-97 and the ISO 5389 refer to the polytropic analysis by John M. Schultz. The procedure utilizes a head correction factor and two compressibility functions to obtain a solution of the integral Δhp = ∫vdp. Present computer technology renders possible a direct integration of the compression path where the variation in actual gas properties along the path is included. This method eliminates the averaging of gas properties which the Schultz procedure includes. This paper reports deviation in compressor performance using the Schultz procedure with different average gas properties. The implementation of a direct integration procedure, employing actual gas properties from the new GERG-2004 equation of state, is given. The GERG-2004 equation of state has proven to give accurate density values both in the vapour and liquid phases. Depending on how the polytropic compression analysis is implemented, the work has revealed up to 4% deviation in polytropic head and efficiency for some specific compressors. This adds an extra uncertainty in compressor performance verification. Even though the API 617 allows up to 4% deviation, some compressors have to meet a more stringent demand, for instance 2% at the Sno̸hvit LNG plant. Future challenges within oil and natural gas production are related to wet gas compressors. The present paper points out the advantages in using a direct integration method for wet gas performance predictions as this takes phase changes along the compression path into account.
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Gilarranz, Jose´ L. "Uncertainty Analysis of a Polytropic Compression Process and Application to Centrifugal Compressor Performance Testing." In ASME Turbo Expo 2005: Power for Land, Sea, and Air. ASMEDC, 2005. http://dx.doi.org/10.1115/gt2005-68381.
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In recent years, several papers have been written concerning the application of uncertainty analyses for isentropic compression processes under the assumption of ideal gas behavior. However, for high-pressure ratio machines, the ideal gas model fails to capture the physics of the process. Still, the estimation of test uncertainty for polytropic processes is hindered by the complexity of the equations used to calculate the performance parameters and by the incorporation of real gas equations into the models. This paper presents an uncertainty analysis developed to estimate the error levels in data gathered during factory aero-performance tests of single- or multi-stage centrifugal compressors. The analysis incorporates the effects of the variation and uncertainty levels of every parameter used to calculate centrifugal compressor aero-thermal performance. Included are the variables used to define the thermodynamic states of the fluid inside the compressor, as well as geometric and operational parameters associated with the machine and test loop. Two different methods have been utilized and the results compared to evaluate the advantages and drawbacks of each. The first method is based on the direct use of the Monte Carlo simulation technique combined with real gas equations of state. The second method employs uncertainty propagation equations and the methodology included in the ASME PTC-19.1 (1998) Test Code. Both approaches utilize the polytropic compression model and equations for performance evaluation that are included in the ASME PTC 10 (1997) Power Test Code for compressors and exhausters. The methods and results from this work may be easily extended to the isentropic compression model as well. The use of real gas equations of state make the methods applicable to virtually any gas composition. Although the analysis was intended to be applied to ASME PTC 10 Type 2 tests, the method can be extended to evaluate Type 1 and/or on-site field tests, as long as certain considerations are addressed. The uncertainty analysis presented is then used to evaluate data from several machines, ranging from a low-pressure ratio gas pipeline compressor to an eight-stage machine used for natural gas processing. Comments are offered concerning the effects of machine pressure ratio on the levels of uncertainty, as well as the importance of proper selection of instrumentation to minimize the error level of the test data. Special emphasis is placed on the benefits of using this analysis during the planning phase of the test program, to determine the optimal combination of instruments, to guarantee acceptable levels of uncertainty.
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Taher, Matt. "ASME PTC-10 and Heat Capacity Relations for Polytropic and Isentropic Compression Process of Real Gas." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63106.
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ASME PTC-10 (reaffirmed 2009) serves as an internationally recognized standard factory acceptance and field performance testing for centrifugal compressors. It provides a test procedure to determine the thermodynamic performance of centrifugal compressors for gases conforming to ideal gas laws and for real gases. ASME PTC-10 defines ideal gases as those, which fall within the limits of table 3.3. The ratio of heat capacities is one of the parameters used to determine the limits of departure from ideal gas in table 3.3. However, ASME PTC-10 does not clearly define whether to use the ideal gas or a real gas method to calculate the ratio of heat capacities. The relationship Ĉp – Ĉv = R, is valid for ideal gases, but not real gases. The validity of Ĉp – Ĉv = R is examined across a typical range of pressures and temperatures and a composition applicable to the natural gas industry. Isentropic processes of ideal gases are accurately described with a simple relationship with the ratio of heat capacities. However, for real gases, that relationship is not valid and a more complex relationship is required for similar accuracy. Thermodynamic relationships used in calculating isentropic and polytropic exponents are summarized. Limitations for real and ideal gas calculation methods are described. The deviations of real gas isentropic and polytropic volume and temperature exponents from ideal gas calculation methods are presented.
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Zhang, Chao, Terrence W. Simon, and Perry Y. Li. "Storage Power and Efficiency Analysis Based on CFD for Air Compressors Used for Compressed Air Energy Storage." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-88985.
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The compression process in a piston cylinder device in a Compressed Air Energy Storage (CAES) system is studied computationally. Twelve different cases featuring four different compression space length-to-radius aspect ratios and three different Reynolds numbers are studied computationally using the commercial CFD code ANSYS FLUENT. The solutions show that for compression with a constant velocity, the compression can be approximated by a polytropic pressure vs. volume relation. The polytropic exponent, n, characterizes the heat transfer and temperature rise of the air being compressed. For the cases computed, it varies from 1.124 to 1.305 and is found to be more affected by Reynolds number and less by the length-to-radius ratio. Since the efficiency and storage power of the compressor depend on pressure vs. volume trajectory during compression, they are written as functions of the pressure rise ratio and the polytropic exponent, n. The efficiency is high at the beginning of the compression process, and decreases as the compression proceeds. The effect of temperature rise or heat transfer on efficiency and storage power is shown by comparing the efficiency and storage power vs. volume curves having different n values. Smaller temperature rise always results in higher efficiency but lower dimensionless storage power for the same compression pressure ratio. The storage power is used in this study to distinguish the compression process effect (n effect) and the compressor’s size effect on the storage power. The likelihood of flow transitioning into turbulent flow is discussed. A k–ε Reynolds Averaged Navier Stokes (RANS) turbulence model is used to calculate one of the larger Reynolds number cases. The calculated polytropic exponent was only 0.02 different from that of the laminar flow solution. The CFD results show also that during compression, complex vorticity patterns develop, which help mix the cold fluid near the wall with the hot fluid in the inner region, beneficial to achieving a higher efficiency.
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Casey, Michael V., and Thomas M. Fesich. "On the Efficiency of Compressors With Diabatic Flows." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-59015.
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In most compressors the flow is adiabatic, but in micro-compressors, and in turbochargers at low speeds, the compression process has both heat transfer and work input. The classical adiabatic efficiency definition found in most text books is then incorrect. This paper extends the text book definitions of compressor efficiency to diabatic flows. The paper explains different compressor efficiency definitions in a logical way and identifies fundamental flaws in the use of isentropic efficiency for a diabatic flow. It shows that the polytropic efficiency can be used with or without heat transfer without ambiguities. Other significant advantages of the polytropic efficiency are also summarized, as they are not fully covered in any turbomachinery text books. The advantages of the polytropic approach for a practical application are demonstrated by analyzing the heat transfer in a turbocharger compressor. A simple model of the heat transfer allows a correction for this effect on the polytropic efficiency at low speed to be derived. Compressor characteristics that have been corrected for this surprisingly large effect maintain a much higher efficiency down to low speeds.
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Zhang, Hanqing, and Ruxin Song. "Theoretical Prediction of Tension-Stroke Relationship of Hydro-Pneumatic Tension Systems." In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-84071.
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Hydro-pneumatic tension systems have been widely used to support production and drilling risers on floating production systems (such as Spars and TLPs). A hydro-pneumatic tension system utilizes several hydro-pneumatic piston-cylinders (typically four) filled with a working gas (such as nitrogen) to provide the riser it supports with a tension. When the riser experiences strokes with respect to its supporting vessel caused by vessel motion (e.g. due to environmental change), the tensioner will accommodate most of the strokes by changing the volume and pressure of the cylinders. The riser tension will accordingly fluctuate with the pressure change about its design value. Such tension variation directly affects riser design and the vessel’s performance. Therefore, in the design of a hydro-pneumatic tension system, the stiffness of the tensioner, which describes the tension and stroke relationship of the tensioner, is one of the key design parameters to be concerned of. Since it is difficult to perform full-scale tests to determine the relationship for a tensioner, a theoretical model, which considers the tension’s stroke motion as a polytropic process, has been used to simulate the tension-stroke behavior of the tensioners. A polytropic process is well defined by a single parameter, the exponent. For nitrogen as the working gas, an exponent of 1.1 to 1.3 has been adopted in the offshore industry without theoretical or experimental verification. The objective of this study is to theoretically predict the pressure-stroke relationship of the hydro-pneumatic tension systems and to determine proper values of the exponent for the polytropic process used in the offshore industry. The study uses the first law of thermodynamics and the knowledge of heat transfer to predict status change of the working gas with piston stroke and then to calculate the pressure-stroke relationship of the tensioner. The status of the gas is determined from the work exchange induced by piston strokes and heat transfer through the outer surfaces of piston rods and cylinder barrels. As a numerical example, a tension system similar to those used in the Gulf of Mexico is analyzed for 100-year hurricane environments. The predicted pressure time traces are compared with those given by a polytropic process with a series of exponents (or gas constants). The comparisons show that an exponent of 1.3 or 1.4 is a proper value for the polytropic process.
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Liu, Yan, Li-hua Tao, Jian Wang, Yang Wang, Xue-jun Wang, and Wei Wang. "Influence of Reynolds Number on the Performance of Process Centrifugal Compressors." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56853.
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Over the past 60 years, effects of changes in Reynolds number on performance of centrifugal compressors have been widely investigated. However most of cases deal with those compressors with small or medium flow coefficients. Studies on the influence of Reynolds number on centrifugal compressors with large flow coefficients and high machine Mach number are rarely seen in the literature. This paper deals with two types of centrifugal compressors. One type of compressor (Model 1) has a relatively large capacity with high machine Mach number. The flow coefficient and machine Mach number are 0.16 and 1.05 respectively at the design condition. Those design parameters for the other type of compressor (Model 2) are 0.11 and 0.7 respectively. Both experimental and numerical results show that with increase in Re, aerodynamic performance of centrifugal compressors is improved. However, to what extent that improvement is gained depends on properties of the baseline compressor. When Reynolds number of Model 1 becomes about 5 times large due to increase in the inlet pressure, its polytropic efficiency is only improved 0.7% at the design point in experiment. Flow field inside the impeller is similar to its prototype. For Model 2, when Reynolds number becomes 1.78 times large due to scaling up, the polytropic efficiency of the enlarged one is improved about 2% at the design point. These results demonstrate that for a compressor with large flow coefficient and high machine Mach number, i.e. originally high Reynolds number, the influence of Reynolds number on its performance is limited. In addition to experiment and CFD, two empirical formulas are applied to work out performance correction due to a change in Reynolds number for Model 1 and Model 2. Although CFD results are more accurate than the empirical results, empirical formula is still useful to get relatively reliable performance correction.