Journal articles: '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.

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Abbas, G., and A. Ditta. "Accretion onto a charged Kiselev black hole." Modern Physics Letters A 33, no. 13 (April 30, 2018): 1850070. http://dx.doi.org/10.1142/s0217732318500700.

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Accretion of matter onto a compact is one of the interesting astrophysical processes. Here, we study the accretion of matter onto a charged Kiselev black hole. The problem of static and spherically symmetric accretion of a polytropic fluid is explored for the analytic solution of equations of motion. We have investigated the necessary conditions for existence of the critical flow points and the mass accretion rate. Finally, we discuss the polytropic gas accretion in detail. It has been found that in the accretion process the quintessence and charge parameters play a dominant role.

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Fu, Min, and Leslaw Mleczko. "Metallorganic reactions in the polytropic microreactors." Journal of Flow Chemistry 9, no. 2 (March 7, 2019): 89–100. http://dx.doi.org/10.1007/s41981-019-00030-3.

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Shin, Y. G. "Estimation of instantaneous exhaust gas flowrate based on the assumption of a polytropic process." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 215, no. 5 (May 2001): 637–43. http://dx.doi.org/10.1243/0954407011528220.

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Qian, Ye, and Meng GuoXiang. "Computation of Instantaneous Polytropic Exponent of Discharge Process of a Tank with Pressurised Gas." International Journal of Fluid Power 9, no. 2 (January 2008): 27–33. http://dx.doi.org/10.1080/14399776.2008.10781302.

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Kim, Kyoung Hoon, and Chul Ho Han. "Performance Analysis of Wet Compression Process under Critical Conditions of Water Injection." Applied Mechanics and Materials 229-231 (November 2012): 2541–45. http://dx.doi.org/10.4028/www.scientific.net/amm.229-231.2541.

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In wet compression process water is injected at an inlet of compressor and continuous cooling occurs due to evaporation of water droplets during the compression process of air, which can save the compression work and enhance the performance of gas turbine system. In this work, performance analysis of the wet compression process is carried out under the critical conditions of water injection which are defined as the maximum water injection which can be evaporated completely inside the compressor. For various ambient conditions the important variables of wet compression process such as water injection ratio, temperature-averaged polytropic coefficient, compressor outlet temperature, and compression work are estimated under the critical injection conditions. Parametric studies show that compression work decreases with ambient temperature, however, the reduction ratio of compression work relative to dry increases with ambient temperature.

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Kim, Kyoung Hoon, Dong Joo Kim, Kyoung Jin Kim, and Seong Wook Hong. "An Assessment of Wet Compression Process in Gas Turbine Systems with an Analytical Modeling." Applied Mechanics and Materials 234 (November 2012): 23–27. http://dx.doi.org/10.4028/www.scientific.net/amm.234.23.

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Recently humidified gas turbine systems in which water or steam is injected have attracted much attention, since they can offer a high efficiency and a high specific power with a relatively low cost compared to combined-cycle gas turbine systems, and therefore they have a potential for future power generation. In this study, performance analysis of the wet compression process is carried out with an analytical modeling which was developed from heat and mass transfer, and thermodynamic analyses based on droplet evaporation. Wet compression variables such as temperature-averaged polytropic coefficient, compressor outlet temperature, and compression work are estimated. Parametric studies show the effect of system parameters such as droplet size, water injection ratio or compression ratio on transient behavior.

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Osherovich, V. A., C. J. Farrugia, L. F. Burlaga, R. P. Lepping, J. Fainberg, and R. G. Stone. "Polytropic relationship in interplanetary magnetic clouds." Journal of Geophysical Research 98, A9 (1993): 15331. http://dx.doi.org/10.1029/93ja01012.

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Jin, Yingzi. "SIMPLIFICATION AND DETERMINATION OF POLYTROPIC EXPONENT OF THER- MODYNAMIC PROCESS IN THE FILLING AND EXHAUSTING PROCESS IN A PNEUMAITIC SYSTEM." Chinese Journal of Mechanical Engineering 41, no. 06 (2005): 76. http://dx.doi.org/10.3901/jme.2005.06.076.

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Durrive, Jean-Baptiste, and Mathieu Langer. "Analytic growth rate of gravitational instability in self-gravitating planar polytropes." Journal of Fluid Mechanics 859 (November 16, 2018): 362–99. http://dx.doi.org/10.1017/jfm.2018.837.

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Gravitational instability is a key process that may lead to fragmentation of gaseous structures (sheets, filaments, haloes) in astrophysics and cosmology. We introduce here a method to derive analytic expressions for the growth rate of gravitational instability in a plane stratified medium. First, the main strength of our approach is to reduce this intrinsically fourth-order eigenvalue problem to a sequence of second-order problems. Second, an interesting by-product is that the unstable part of the spectrum is computed by making use of its stable part. Third, as an example, we consider a pressure-confined, static, self-gravitating slab of a fluid with an arbitrary polytropic exponent, with either free or rigid boundary conditions. The method can naturally be generalised to analyse the stability of richer, more complex systems. Finally, our analytical results are in excellent agreement with numerical solutions. Their second-order expansions provide a valuable insight into how the rate and wavenumber of maximal instability behave as functions of the polytropic exponent and the external pressure (or, equivalently, the column density of the slab).

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Liu, Shuang, Zhen-Hua Wan, Rui Yan, Chao Sun, and De-Jun Sun. "Onset of fully compressible convection in a rapidly rotating spherical shell." Journal of Fluid Mechanics 873 (July 1, 2019): 1090–115. http://dx.doi.org/10.1017/jfm.2019.436.

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The onset of thermal convection in a rapidly rotating spherical shell is studied by linear stability analysis based on the fully compressible Navier–Stokes equations. Compressibility is quantified by the number of density scale heights $N_{\unicode[STIX]{x1D70C}}$, which measures the intensity of density stratification of the motionless, polytropic base state. The nearly adiabatic flow with polytropic index $n=1.499<n_{a}=1.5$ is considered, where $n_{a}$ is the adiabatic polytropic index. By investigating the stability of the base state with respect to the disturbance of specified wavenumber, the instability process is found to be sensitive to the Prandtl number $Pr$ and to $N_{\unicode[STIX]{x1D70C}}$. For large $Pr$ and small $N_{\unicode[STIX]{x1D70C}}$, the quasi-geostrophic columnar mode loses stability first; while for relatively small $Pr$ a new quasi-geostrophic compressible mode is identified, which becomes unstable first under strong density stratification. The inertial mode can also occur first for relatively small $Pr$ and a certain intensity of density stratification in the parameter range considered. Although the Rayleigh numbers $Ra$ for the onsets of the quasi-geostrophic compressible mode and columnar mode are different by several orders of magnitude, we find that they follow very similar scaling laws with the Taylor number. The critical $Ra$ for convection onset is found to be always positive, in contrast with previous results based on the widely used anelastic model that convection can occur at negative $Ra$. By evaluating the relative magnitude of the time derivative of density perturbation in the continuity equation, we show that the anelastic approximation in the present system cannot be applied in the small-$Ra$ and large-$N_{\unicode[STIX]{x1D70C}}$ regime.

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Macia, Ll, R. Castilla, P. J. Gamez-Montero, S. Camacho, and E. Codina. "Numerical Simulation of a Supersonic Ejector for Vacuum Generation with Explicit and Implicit Solver in Openfoam." Energies 12, no. 18 (September 17, 2019): 3553. http://dx.doi.org/10.3390/en12183553.

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Supersonic ejectors are used extensively in all kind of applications: compression of refrigerants in cooling systems, pumping of volatile fluids or in vacuum generation. In vacuum generation, also known as zero-secondary flow, the ejector has a transient behaviour. In this paper, a numerical and experimental research of a supersonic compressible air nozzle is performed in order to investigate and to simulate its behaviour. The CFD toolbox OpenFOAM 6 was used, with two density-based solvers: explicit solver rhoCentralFoam, which implements Kurganov Central-upwind schemes, and implicit solver HiSA, which implements the AUSM+up upwind scheme. The behaviour of the transient evacuation ranges between adiabatic polytropic exponent at the beginning of the process and isothermal at the end. A model for the computation of the transient polytropic exponent is proposed. During the evacuation, two regimes are encountered in the second nozzle. In the supercritic regime, the secondary is choked and sonic flow is reached. In the subcritic regime, the secondary flow is subsonic. The final agreement is good with the two different solvers, although simulation tends to slightly overestimate flow rate for large values region.

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Pudovkin, Mikhail I., Claudia-Veronika Meister, Bruno P. Besser, and Helfried K. Biernat. "The effective polytropic index in a magnetized plasma." Journal of Geophysical Research: Space Physics 102, A12 (December 1, 1997): 27145–49. http://dx.doi.org/10.1029/97ja02447.

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Belmont, Gerard, and Christian Mazelle. "Polytropic indices in collisionless plasmas: Theory and measurements." Journal of Geophysical Research 97, A6 (1992): 8327. http://dx.doi.org/10.1029/91ja02894.

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Agbadede, R., and B. Kainga. "Techno-economic analysis of the influence of different operating conditions on gas turbine centrifugal compressor set performance." Nigerian Journal of Technology 39, no. 4 (March 24, 2021): 1150–57. http://dx.doi.org/10.4314/njt.v39i4.23.

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In today’s world where fuel prices have increased drastically and there are great concerns about environmental issues, there is the need to properly match centrifugal compressors to their Gas Turbine (GT) drivers, so as to achieve an efficient overall package, lower turbine fuel consumption, longer time between overhauls, and most importantly, package operational flexibility in meeting alternate process conditions. This study highlights the influence of operating and environmental conditions on the overall performance of the gas turbine compressor set. GasTurb and CMap simulation softwares were employed to model and simulate the performances of the GT and centrifugal compressors respectively. The outcome of the performance plots show that at a design inlet flow volume of 15928 cubic meters per hour, the compressor required power from the gas turbine drive to transport RaNatGas is approximately 7450kW as against 7065kW and 6500kW for MaNatGas and LaNatGas mixtures respectively. Techno-economic analysis of the gas turbine compressor set shows that the fuel cost of transporting a given volume flow of RaNatGas to a specific location for a year gives about$13.5million when compared with MaNatGas and LaNatGas mixtures which cost about $13.02million and 12.3million respectively. Keywords: Natural Gas, Performance Simulations, Polytropic Efficiency, Polytropic Head, Gas Compositions

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Frost, T. H., A. Anderson, and B. Agnew. "A hybrid gas turbine cycle (Brayton/Ericsson): An alternative to conventional combined gas and steam turbine power plant." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 211, no. 2 (March 1, 1997): 121–31. http://dx.doi.org/10.1243/0957650971537042.

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A hybrid gas turbine cycle is proposed based on the conventional Brayton cycle for the high-temperature heat addition process while adopting the Ericsson cycle for the low-temperature heat rejection process. It thus incorporates the thermodynamic advantages of a combined gas and steam turbine (CCGT) cycle without the irrevcrsibilities of the boiler and the ancillarics of the steam turbine/condenser plant. Thermodynamic analysis shows that a similar overall thermal efficiency as current CCGT plant (i.e. 0.54) would be achieved at a maximum gas temperature of 1311 °C if polytropic efficiencies of 0.90 for compression and expansion could be realized and if a maximum temperature of 77 °C was obtained during isothermal compression in the bottoming Ericsson cycle. A novel method of achieving multistage isothermal compression using heat pipe technology is proposed.

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Nicolaou, Georgios, George Livadiotis, and Mihir I. Desai. "Significance of Bernoulli Integral Terms for the Solar Wind Protons at 1 au." Applied Sciences 11, no. 10 (May 19, 2021): 4643. http://dx.doi.org/10.3390/app11104643.

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The Bernoulli integral describes the energy conservation of a fluid along specific streamlines. The integral is the sum of individual terms that contain the plasma density, speed, temperature, and magnetic field. Typical solar wind analyses use the fluctuations of the Bernoulli integral as a criterion to identify different plasma streamlines from single spacecraft observations. However, the accurate calculation of the Bernoulli integral requires accurately determining the plasma polytropic index from the analysis of density and temperature observations. To avoid this complexity, we can simplify the calculations by keeping only the dominant terms of the integral. Here, we analyze proton plasma and magnetic field observations obtained by the Wind spacecraft at 1 au, during 1995. We calculate the Bernoulli integral terms and quantify their significance by comparing them with each other. We discuss potential simplifications of the calculations in the context of determining solar wind proton thermodynamics using single spacecraft observations.

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Zhang, Yahui, and Tielong Shen. "In-cylinder Pressure Pegging Algorithm Based on Cyclic Polytropic Coefficient Learning." International Journal of Automotive Engineering 8, no. 2 (2017): 79–86. http://dx.doi.org/10.20485/jsaeijae.8.2_79.

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Anderson, Kevin R. "Method of Determining a Nominal Index Value for the Polytropic Expansion Process of Supercritical Carbon Dioxide in Piston-Cylinder Devices." International Journal of Thermodynamics 17, no. 4 (December 4, 2014): 275. http://dx.doi.org/10.5541/ijot.582.

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Khanna, Abhishek, and Ramandeep S. Johal. "Maximum Power Point Characteristics of Generalized Heat Engines with Finite Time and Finite Heat Capacities." Journal of Thermodynamics 2012 (December 20, 2012): 1–7. http://dx.doi.org/10.1155/2012/246914.

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We revisit the problem of optimal power extraction in four-step cycles (two adiabatic and two heat-transfer branches) when the finite-rate heat transfer obeys a linear law and the heat reservoirs have finite heat capacities. The heat-transfer branch follows a polytropic process in which the heat capacity of the working fluid stays constant. For the case of ideal gas as working fluid and a given switching time, it is shown that maximum work is obtained at Curzon-Ahlborn efficiency. Our expressions clearly show the dependence on the relative magnitudes of heat capacities of the fluid and the reservoirs. Many previous formulae, including infinite reservoirs, infinite-time cycles, and Carnot-like and non-Carnot-like cycles, are recovered as special cases of our model.

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Petr, V., and M. Kolovratnik. "Modelling of the droplet size distribution in a low-pressure steam turbine." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 214, no. 2 (March 1, 2000): 145–52. http://dx.doi.org/10.1243/0957650001538245.

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Realization of numerous tests on the droplet size measurement with extinction probe, in a 200 MW low-pressure steam turbine, provides necessary experimental data for testing the theoretical models of the droplet nucleation process in steam turbines. The earlier computational model accounting for the unsteady and viscous effects given by Bakhtar and Heaton and by Guha and Young, where the steam particles follow randomly chosen different streamlines within the blade rows with prescribed polytropic efficiency distribution in the pitchwise direction, thus undergoing various nucleation conditions, has been extended in this paper to consider to some extent two-dimensional effects. Because several uncertainties still exist in the inversion methods, predicting the size distribution of droplets, this contribution is aimed at direct comparison of the computed and measured transmittance data I/I0.

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Martelli, F., S. Pazzi, and V. Michelassi. "Automatic computational fluid dynamics-based procedure for the optimization of a centrifugal impeller." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 219, no. 7 (November 1, 2005): 549–57. http://dx.doi.org/10.1243/095765005x31261.

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A typical centrifugal impeller characterized by a low flow coefficient and cylindrical blades is redesigned by means of an intelligent automatic search program. The procedure consists of a feasible sequential quadratic programming algorithm (Fletcher, R. Practical Methods of optimization, 2000 (Wiley)) coupled to a lazy learning (LL) interpolator 1 to speed-up the process. The program is able to handle geometric constraints to reduce the computational effort devoted to the analysis of non-physical configurations. The objective function evaluator is an in-house developed structured computational fluid dynamics (CFD) code. The LL approx-imator is called each time the stored database can provide a sufficiently accurate performance estimate for a given geometry, thus reducing the effective CFD computations. The impeller is represented by 25 geometric parameters describing the vane in the meridional and s-0 planes, the blade thickness, and the leading edge shape. The optimization is carried out on the impeller design point maximizing the polytropic efficiency with nearly constant flow coefficient and polytropic head. The optimization is accomplished by maintaining unaltered those geometrical parameters which have to be kept fixed in order to make the impeller fit the original stage. The optimization, carried out on a cluster of 16 PCs, is self-learning and leads to a geometry presenting an increased design point efficiency. The program is completely general and can be applied to any component which can be described by a finite number of geometrical parameters and computed by any numerical instrument to provide performance indices. The work presented in this paper was done under the METHOD EC funded project for the implementation of new technologies for optimization of centrifugal compressors.

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Lucas, Radika, Andy Jones, Wesley Ford, and Matt Doyle. "The effective use of data analytics in an advanced compressor performance and degradation monitoring system." APPEA Journal 58, no. 2 (2018): 723. http://dx.doi.org/10.1071/aj17086.

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Origin is the upstream operator and joint venture partner in Australia Pacific LNG. Origin’s integrated gas operations require reliable, sustainable delivery of gas to the downstream LNG facility on Curtis Island. This scale of operation requires establishing a ‘single source of truth’ regarding compressor condition and performance while achieving maximum and reliable compression capacities. Therefore, capability of monitoring performance of centrifugal compressors across the fleet is considered an essential component of production surveillance. Xodus leveraged Origin’s OSIsoft PI AF (PI Historian Asset Framework) tool. This system was used to build a compressor performance and degradation monitoring tool to accurately identify early indications of degradation in a multi-stage centrifugal compression train. The tool utilises live data from the PI historian to calculate key performance indicators which define compressor and driver operation. Dimensionless parameter analysis allows Origin to accurately quantify performance degradation regardless of variations in plant inlet conditions at each gas processing facility. Deviation from baseline performance in dimensionless parameters such as polytropic efficiency, work input number and polytropic head coefficient is used to quantify capacity losses, additional power consumption and increase in suction pressure. The tool provided the ability to use performance indicators to confidently determine the mode and extent of compressor degradation and prevent accelerated fouling which can lead to premature bundle changes. Also, this information helps streamline and has led to a major step change for the decision-making process concerning maximum production from rotating equipment. Additionally, this allowed operations to be confident on the condition of the compressor bundle, continue operation with higher capacities during high demand periods and ensure compressor bundle changeout is optimised for availability and economic aspects.

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Bondar, V. P., V. O. Zhukov, and S. V. Zhukova. "MINIMUM OF EXERGY LOSSES IN NON-EQUILIBRIUN PROCESSE OF ACTUATING MEDIUMS HEAT EXCHANGE." Energy Technologies & Resource Saving, no. 1 (March 20, 2017): 39–44. http://dx.doi.org/10.33070/etars.1.2017.04.

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In course of calculation of heat-exchange equipment, major parameters at which heat-exchanging process between heat-carriers runs with possible lesser losses of operational part of heat are defined by methods of thermo-dynamic. In comparison to developed methods of equilibrium processes of actuating mediums heat-exchange calculation, non-equilibrium is at stage of improvement. The research, allowing the defining minimum of entropy production and, accordingly, minimum of exergy losses in non-equilibrium processes of actuating media heat-exchange, is performed. Results of researches are valid both to externally non-equilibrium processes and polytropic. There is defined a dependency of the thermodynamic system entropy growth from the relation of the upper and lower boundary temperatures, independently from the operating media flow process in the heat-exchangers. There is shown that in certain degree of irreversibility the numerical value of which is determined technologically and structurally, there are the relations of thermodynamic parameters for which the operation media heat exchange entropy growth reaches of the minimum numerical value. As confirmation of analysis results example is presented, in which, on several variants, is shown course of entropy production of thermo-dynamic system through minimum that corresponds to the performed research. The carried analysis can find its application both in engineering works and analytical investigations. Bibl. 8, Fig. 1, Tab. 1.

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Grabbe, Crockett L. "The polytropic index for the solar wind at Earth's bow shock." Journal of Geophysical Research: Space Physics 101, A5 (May 1, 1996): 11067–73. http://dx.doi.org/10.1029/96ja00364.

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Hesse, Michael, and Joachim Birn. "Three-dimensional MHD modeling of magnetotail dynamics for different polytropic indices." Journal of Geophysical Research 97, A4 (1992): 3965. http://dx.doi.org/10.1029/91ja03003.

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Mrazík, Lukáš, and Pavel Kříž. "Porous Medium Equation in Graphene Oxide Membrane: Nonlinear Dependence of Permeability on Pressure Gradient Explained." Membranes 11, no. 9 (August 29, 2021): 665. http://dx.doi.org/10.3390/membranes11090665.

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Membrane performance in gas separation is quantified by its selectivity, determined as a ratio of measured gas permeabilities of given gases at fixed pressure difference. In this manuscript a nonlinear dependence of gas permeability on pressure difference observed in the measurements of gas permeability of graphene oxide membrane on a manometric integral permeameter is reported. We show that after reasoned assumptions and simplifications in the mathematical description of the experiment, only static properties of any proposed governing equation can be studied, in order to analyze the permeation rate for different pressure differences. Porous Medium Equation is proposed as a suitable governing equation for the gas permeation, as it manages to predict a nonlinear behavior which is consistent with the measured data. A coefficient responsible for the nonlinearity, the polytropic exponent, is determined to be gas-specific—implications on selectivity are discussed, alongside possible hints to a deeper physical interpretation of its actual value.

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Lee, Youngbok, Seungha Lee, and Kyoungdoug Min. "Semi-empirical estimation model of in-cylinder pressure for compression ignition engines." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 234, no. 12 (June 2, 2020): 2862–77. http://dx.doi.org/10.1177/0954407020916952.

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There have been significant efforts in recent years to comply with automotive emission regulations. To resolve the issue, researchers have strived to reduce the emissions through combustion control. The heat release rate, or in-cylinder pressure information, is necessary to model engine-out emissions, and can also be used to optimize efficiency and emissions by controlling combustion and estimating torque for torque-based engine dynamic control. Piezoelectric pressure sensors are widely used. However, because of cost and durability issues, there have been studies which estimate the in-cylinder pressure using data available only from the engine control unit to reduce engine costs. Therefore, in this study, in-cylinder pressure was predicted, without additional pressure sensors, in light-duty diesel engines. A variable polytropic exponent model was first adopted during the compression stroke, assuming a polytropic process. A Wiebe function was then applied for describing cumulative heat release rate during the combustion phase. Using the in-cylinder pressure model, it was possible to calculate combustion-related parameters which are frequently used such as ignition delay, combustion duration, peaked pressure, and MFB50 (mass fraction burned: timing when 50% of the fuel is burned) without pressure sensors. Notwithstanding the simplification of the model which is targeting real-time applications, the model can predict the in-cylinder pressure at steady-state conditions. The pressure at the end of compression stroke, at start of main combustion timing, and when it has a peaked value by the main combustion were estimated with accuracy of R2 0.996, 0.993, and 0.956, respectively, in test engine. The model was also validated against a second engine. This study can contribute to emission models that need to calculate in-cylinder temperature using pressure data, and other studies to establish engine control strategies, including optimization through combustion control and torque prediction, which can be applied to engine dynamic control.

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Sonnerup, B. U. Ö., and L. N. Hau. "Vortex laws and field line invariants in polytropic field-aligned MHD flow." Journal of Geophysical Research 99, A1 (1994): 143. http://dx.doi.org/10.1029/93ja02082.

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Лабутин, Александр, Aleksandr Labutin, Владимир Невиницын, Vladimir Nevinitsyn, Галина Волкова, Galina Volkova, Владислав Сальков, and Vladislav Sal'kov. "THE CONTROL ALGORITHM FOR CONCENTRATION OF THE TARGET PRODUCT IN THE CHEMICAL REACTOR." Automation and modeling in design and management of 2018, no. 2 (February 20, 2019): 34–40. http://dx.doi.org/10.30987/article_5c387d62698a75.92047422.

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A chemicalreactor is one of the common apparatuses in chemical industry. Despite a large number of theworks related to automation and control of chemical reactors, the problem of synthesizing controlsystems that provide the maintenance of optimal modes of their operation remains practically unsolved.This is related to the principal feature of chemical reactors as controlled objects, namely,manifold, non-linearity, and multi-coupling. An outcome from this situation is to develop a physicaltheory of control, in particular synergetic control theory. The problem of analytical synthesis of nonlinear control law for the concentration of the target component in a chemical reactor has been solved.We use the methods of synergetic control theory, simulation methodsand methods of computational experiment. The paper deals with continuous stirred tank reactor equipped with a mechanicalstirrer and cooling jacket. The reactor operates in the polytropic mode. The multistep series-parallelexothermic process is carried out in the reactor. The objective of chemical reactor operationis to obtain the key product of specified concentration.

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Amaral, Francisco, Alex Santos, Ewerton Calixto, Fernando Pessoa, and Delano Santana. "Exergetic Evaluation of an Ethylene Refrigeration Cycle." Energies 13, no. 14 (July 21, 2020): 3753. http://dx.doi.org/10.3390/en13143753.

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The production of light olefins by selective steam cracking is an energy-intensive process, and ethylene and propylene refrigeration cycles are key parts of it. The objective of this study was to identify opportunities for energy savings in an ethylene refrigeration cycle through an exergetic analysis. Two main causes of lower operational efficiency were identified: (1) Lower polytropic efficiency of the refrigerant compressor and (2) operating with the compressor mini-flow valve open to ensure reliability. The evaluation showed that the amount of irreversibilities generated by the cycle in operation is 22% higher than that predicted by the original design, which represents a 14% lower exergy efficiency. There is a potential savings of 0.20 MW in the cycle’s energy consumption with the implementation of the following improvements: recover refrigerant compressor efficiency by performing maintenance on the equipment and optimize the flow distribution between the recycle valve, the level control valve, and the temperature control valve.

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Coronado-Hernández, Óscar E., Mohsen Besharat, Vicente S. Fuertes-Miquel, and Helena M. Ramos. "Effect of a Commercial Air Valve on the Rapid Filling of a Single Pipeline: a Numerical and Experimental Analysis." Water 11, no. 9 (August 31, 2019): 1814. http://dx.doi.org/10.3390/w11091814.

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The filling process in water pipelines produces pressure surges caused by the compression of air pockets. In this sense, air valves should be appropriately designed to expel sufficient air to avoid pipeline failure. Recent studies concerning filling maneuvers have been addressed without considering the behavior of air valves. This work shows a mathematical model developed by the authors which is capable of simulating the main hydraulic and thermodynamic variables during filling operations under the effect of the air valve in a single pipeline, which is based on the mass oscillation equation, the air–water interface, the polytropic equation of the air phase, the air mass equation, and the air valve characterization. The mathematical model is validated in a 7.3-m-long pipeline with a 63-mm nominal diameter. A commercial air valve is positioned in the highest point of the hydraulic installation. Measurements indicate that the mathematical model can be used to simulate this phenomenon by providing good accuracy.

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Fahr, H. J., and D. Rucinski. "Heliospheric pick-up ions influencing thermodynamics and dynamics of the distant solar wind." Nonlinear Processes in Geophysics 9, no. 3/4 (August 31, 2002): 377–86. http://dx.doi.org/10.5194/npg-9-377-2002.

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Abstract. Neutral interstellar H-atoms penetrate into the inner heliosphere and upon the event of ionization are converted into pick-up ions (PUIs). The magnetized solar wind flow incorporates these ions into the plasma bulk and enforces their co-motion. By nonlinear interactions with wind-entrained Alfvén waves, these ions are then processed in the comoving velocity space. The complete pick-up process is connected with forces acting back to the original solar wind ion flow, thereby decelerating and heating the solar wind plasma. As we show here, the resulting deceleration cannot be treated as a pure loading effect, but requires adequate consideration of the action of the pressure of PUI-scattered waves operating by the PUI pressure gradient. Hereby, it is important to take into proper account the stochastic acceleration which PUIs suffer from at their convection out of the inner heliosphere by quasi-linear interactions with MHD turbulences. Only then can the presently reported VOYAGER observations of solar wind decelerations and heatings in the outer heliosphere be understood in view of the most likely values of interstellar gas parameters, such as an H-atom density of 0.12 cm-3 . Solar wind protons (SWPs) appear to be globally heated in their motion to larger solar distances. Ascribing the needed heat transfer to the action of suprathermal PUIs, which drive MHD waves that are partly absorbed by SWPs, in order to establish the observed SWP polytropy, we can obtain a quantitative expression for the solar wind proton pressure as a function of solar distance. This expression clearly shows the change from an adiabatic to a quasi-polytropic SWP behaviour with a decreasing polytropic index at increasing distances. This also allows one to calculate the average percentage of initial pick-up energy fed into the thermal proton energy. In a first order evaluation of this expression, we can estimate that about 10% of the initial PUI injection energy is eventually transfered to SWPs independent of the PUI injection rate.

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Vlase, Aurelian, Marius Iacob, Ovidiu Blăjină, and Vlad Darie. "Study Concerning the Cutting Tool Wear at Drilling of the Stainless Steel X20Cr13." Advanced Materials Research 1036 (October 2014): 230–34. http://dx.doi.org/10.4028/www.scientific.net/amr.1036.230.

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The researches in the cutting domain have as purpose the cutting process economic optimization. This paper studies the cutting tool wear at drilling of the stainless steel X20Cr13. The experimental data and their subsequent processing represent the original contribution of the authors to the estimation of polytropic exponents and to the assessment in terms of structure of the calculus relation of the cutting tool wear. The obtained relationship of the cutting tool wear on the tool putting surface at drilling of the steel X20Cr13 permits the determination of the wear on the putting surface, in the case of a couple: stainless steel X20Cr13 - Rp5 high-speed spiral drill, depending on the work parameters and the cutting conditions. Putting the condition of wear limitation, from the obtained relation, the cutting speeds are exactly given. The paper also contains graphs for the variation of the tool wear with parameters of the cutting technology. The results can be taken into consideration in the educational studies and in the theoretical technical research. They can be implemented in the manufacturing activity.

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Vlase, Aurelian, Marius Iacob, Ovidiu Blăjină, and Vlad Darie. "Analysis of the Relationship of the Cutting Tool Wear at Drilling of the Stainless Steel X15CrNiSi20-12." Applied Mechanics and Materials 657 (October 2014): 8–12. http://dx.doi.org/10.4028/www.scientific.net/amm.657.8.

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The researches in the cutting domain have as purpose the cutting process economic optimization. This paper studies the cutting tool wear at drilling of the stainless steel X15CrNiSi20-12. The experimental data and their subsequent processing represent the original contribution of the authors to the estimation of polytropic exponents and to the assessment in terms of structure of the calculus relation of the cutting tool wear. The obtained relationship of the cutting tool wear on the tool putting surface at drilling of the steel X15CrNiSi20-12 permits the determination of the wear on the putting surface, in the case of a couple: stainless steel X15CrNiSi20-12 - Rp5 high-speed spiral drill, depending on the work parameters and the cutting conditions. Putting the condition of wear limitation, from the obtained relation, the cutting speeds are exactly given. The paper also contains graphs for the variation of the tool wear with parameters of the cutting technology. The results can be taken into consideration in the educational studies and in the theoretical technical research. They can be implemented in the manufacturing activity.

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Medica-Viola, Vedran, Sandi Baressi Šegota, Vedran Mrzljak, and Daniel Štifanić. "Comparison of conventional and heat balance based energy analyses of steam turbine." Pomorstvo 34, no. 1 (June 30, 2020): 74–85. http://dx.doi.org/10.31217/p.34.1.9.

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This paper presents a comparison of conventional and heat balance based energy analyses of steam turbine. Both analyses are compared by using measured operating parameters from low power steam turbine exploitation. The major disadvantage of conventional steam turbine energy analysis is that extracted energy flow streams are not equal in real (polytropic) and ideal (isentropic) expansion processes, while the heat balance based energy analysis successfully resolved mentioned problem. Heat balance based energy analysis require an increase of steam mass flow rates extracted from the turbine in ideal (isentropic) expansion process to ensure always the same energy flow streams to all steam consumers. Increase in steam mass flow rate extracted through each turbine extraction (heat balance based energy analysis) result with a decrease in energy power losses and with an increase in energy efficiency of whole turbine and all of its cylinders (when compared to conventional analysis). All of the obtained conclusions in this research are valid not only for the analyzed low power steam turbine, but also for any other steam turbine with steam extractions.

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Fahr, H. J. "Solar wind heating by an embedded quasi-isothermal pick-up ion fluid." Annales Geophysicae 20, no. 10 (October 31, 2002): 1509–18. http://dx.doi.org/10.5194/angeo-20-1509-2002.

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Abstract. It is well known that the solar wind plasma consists of primary ions of solar coronal origin and secondary ions of interstellar origin. Interstellar H-atoms penetrate into the inner heliosphere and when ionized there are converted into secondary ions. These are implanted into the magnetized solar wind flow and are essentially enforced to co-move with this flow. By nonlinear interactions with wind-entrained Alfvén waves the latter are processed in the co-moving velocity space. This pick-up process, however, also causes actions back upon the original solar wind flow, leading to a deceleration, as well as a heating of the solar wind plasma. The resulting deceleration is not only due to the loading effect, but also due to the action of the pressure gradient. To calculate the latter, it is important to take into account the stochastic acceleration that suffers at their convection out of the inner heliosphere by the quasi-linear interactions with MHD turbulences. Only then can the presently reported VOYAGER observations of solar wind decelerations and heatings in the outer heliosphere be understood in terms of the current, most likely values of interstellar gas parameters. In a consistent view of the thermodynamics of the solar wind plasma, which is composed of secondary ions and solar wind protons, we also derive that the latter are globally heated at their motion to larger solar distances. The arising heat transfer is due to the action of suprathermal ions which drive MHD waves that are partially absorbed by solar wind protons and thereby establish their observed quasi-polytropy. We obtain a quantitative expression for the solar wind proton pressure as a function of solar distance. This expression clearly shows the change from an adiabatic to a quasi-polytropic behaviour with a decreasing polytropic index at increasing distances, as has been observed by the VOYAGERS. This also allows one to calculate the average percentage of the intitial energy fed into the thermal proton energy. In a first-order evaluation of this expression we can estimate that under stationary flow conditions about 10% of the initial injection energy is eventually transfered to solar wind protons, independent of the actual injection rate. Key words. Interplanetary physics (energetic particles; interstellar gas; solar wind plasma)

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Habbal, Shadia R. "The formation of a standing shock in a polytropic solar wind model within 1-10Rs." Journal of Geophysical Research: Space Physics 90, A1 (January 1, 1985): 199–204. http://dx.doi.org/10.1029/ja090ia01p00199.

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Kneis, D., R. Knoesche, and A. Bronstert. "Model-based analysis of nutrient retention and management for a lowland river." Hydrology and Earth System Sciences Discussions 2, no. 6 (November 30, 2005): 2549–79. http://dx.doi.org/10.5194/hessd-2-2549-2005.

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Abstract. In the context of the European Water Framework Directive options for improving the water quality of the lowland river Havel (Germany) were assessed. The lower section of this river is actually a polytrophic river-lake system suffering from high external nutrient loading and exhibiting significant in-river turnover. In order to gain a better understanding of present conditions and to allow integrated scenarios of nutrient management to be evaluated the catchment models SWIM and ArcEGMO-Urban were coupled with a simple, newly developed nutrient TRAnsport Model (TraM). Using the TraM model, the retention of nitrogen and phosphorus in a 55 km reach of the Lower Havel River was quantified and its temporal variation was analyzed. It was examined that about 30% of the external nitrogen input to the Lower Havel is retained within the surveyed river section. A comparison of simulation results generated with and without consideration of phosphorus retention/release revealed that summer TP concentrations are currently increased by 100–200% due to internal loading. Net phosphorus release rates of about 20 mg P m−2 d-1 in late summer were estimated for the Havel lakes. Scenario simulations with lowered external nutrient inputs revealed that persistent phosphorus limitation of primary production cannot be established within the next decade. It was shown that a further reduction in nitrogen concentrations requires emissions to be reduced in all inflows. Though the TraM model needs further extension it proved to be appropriate for conducting integrated catchment and river modeling.

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Mathew, Sajay Sunny, and Christoph Federrath. "Implementation of stellar heating feedback in simulations of star cluster formation: effects on the initial mass function." Monthly Notices of the Royal Astronomical Society 496, no. 4 (July 6, 2020): 5201–10. http://dx.doi.org/10.1093/mnras/staa1931.

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ABSTRACT Explaining the initial mass function (IMF) of stars is a long-standing problem in astrophysics. The number of complex mechanisms involved in the process of star cluster formation, such as turbulence, magnetic fields, and stellar feedback, make understanding and modelling the IMF a challenging task. In this paper, we aim to assert the importance of stellar heating feedback in the star cluster formation process and its effect on the shape of the IMF. We use an analytical sub-grid model to implement the radiative feedback in fully three-dimensional magnetohydrodynamical (MHD) simulations of star cluster formation, with the ultimate objective of obtaining numerical convergence on the IMF. We compare a set of MHD adaptive mesh refinement simulations with three different implementations of the heating of the gas: (1) a polytropic equation of state, (2) a spherically symmetric stellar heating feedback, and (3) our newly developed polar heating model that takes into account the geometry of the accretion disc and the resulting shielding of stellar radiation by dust. For each of the three heating models, we analyse the distribution of stellar masses formed in 10 molecular cloud simulations with different realizations of the turbulence to obtain a statistically representative IMF. We conclude that stellar heating feedback has a profound influence on the number of stars formed and plays a crucial role in controlling the IMF. We find that the simulations with the polar heating model achieve the best convergence on the observed IMF.

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Chatterjee, Tapan K. "A Tidal Trigger of Starburst or Seyfert Activity." International Astronomical Union Colloquium 157 (1996): 458–60. http://dx.doi.org/10.1017/s025292110005020x.

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Some of the classical seyferts are observed to be prototypical ovals, e.g. NGC 1068 and 4151 (e.g., Bosma 1981; Kormendy 1982; Scoville et al. 1988). Such a non-axisymmetric potential corresponding to an oval disk can produce inward flow of gas and induce mild activity. To test the efficiency of this process, we study a collision between a face-on spiral with a high gaseous content and an equally massive compact elliptical, under marginally bound conditions, as such encounters are most frequent.We model the spiral galaxy by an exponential model disk (of radius R) with a (static) thickness and scale length α = 4/R and a spherical polytropic bulge (n=0,3,4, equally weighted combination) containing 1/3 of the mass (cf. Chatterjee 1990); about 20% of the mass of the disk contains gas particles. The elliptical is modeled identically as the bulge. The gravitational potential is softened with softening constants of ∊ = r∘/5, r∘/3, and 0.8r∘, for the bulge of the spiral as well as the elliptical, stellar and gaseous components of the disk, respectively. Here r∘ is the radius containing 75% of the total mass of the galaxy in question, while the mutual gravitational interaction is softened with a softening constant of r∘/4.

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Journal articles on the topic 'Polytrophic process'

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