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Determination of the sensible heat effectiveness and pressure loss of a rotary regenerative heat exchanger using CFD

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Building Simulation 2023年第6期16卷 869-887页

作者： Vladimír Zmrhal petr zelenský Jindřich Boháč Martin Barták Miroslav Kučera Roman Vavřička Faculty of Mechanical Engineering Department of Environmental EngineeringCzech Technical University in PragueTechnická416000Prague 6Czech Republic

The paper presents a new method to determine the sensible effectiveness and pressure loss of rotary regenerative heat exchangers using computational fluid dynamics(CFD).It is based on CFD simulations of a single thermal wheel microchannel with a small cross-sectional area and thin walls,with cyclic inlet and outlet boundary *** unique measurement set-ups were designed and built for the experimental measurement of the heat exchanger *** different types of thermal wheels were manufactured,measured,and simulated in ANSYS *** wheels achieve an effectiveness greater than 73%under certain(air flow)conditions,which is the minimum effectiveness required by Ecodesign(in the EU).For the examined exchangers,the effectiveness ranges from 66.5%to 83.3%,depending on the boundary conditions and geometric parameters of the *** highest sensible effectiveness is achieved by heat exchangers with the largest heat exchange surface Ac;on the other hand,these wheels have the largest pressure *** paper discusses the use of a simplifiedε-NTU correlation model for the HVAC systems(typically C*=1).The correlation model and CFD results were compared and found to be different from each *** results of the CFD simulation were compared with measurements to prove that the proposed simulation method can predict the behaviour of the real heat exchanger as a *** was demonstrated that the sensible effectiveness and pressure loss of the rotary heat exchanger predicted by the CFD simulations correspond well to the measured values within the measurement uncertainty±1.3%.The proposed method can be used for the comparison of different rotary regenerative heat exchangers before their manufacturing and for verification that they meet the EU Ecodesign requirements set by the current *** reduces the cost of the initial optimisation and testing of new designs.

关键词： rotary heat exchanger heat wheel microchannel heat recovery sensible effectiveness pressureloss computer fluid dynamics experiment

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Heavy rockbursts due to longwall mining near protective pillars:A case study

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International Journal of Mining Science and Technology 2018年第5期28卷 799-805页

作者： petr Konicek Jan Schreiber Department of Geomechanics and Mining Research Institute of Geonics Czech Academy of Science

Rockburst represents a very dangerous phenomenon in deep underground mining in unfavourable conditions such as great depth, high horizontal stress, proximity of important tectonic structures, and unmined pillars. The case study describes a recorded heavy rockburst in the Czech part of the Upper Silesian Coal Basin, which occurred during longwall mining near the protective pillar. The artificial dividing of geological blocks and creation of mining protective pillars(shaft pillars, crosscut pillars etc.) is a dangerous task in light of rockbursts occurring mainly due to overstressing of remaining pillars. A simple model of this situation is presented. Natural and mining conditions are analysed and presented in detail as well as registered seismicity during longwall mining in the area. Recorded rockbursts in the area of interest are described and their causes discussed. Many rockbursts near protective pillars were recorded in this mining region. Methodical instructions for rockburst prevention in proximity of protective pillars as well as for gates driving were devised based on the evaluation of rockburst causes. The paper presents these principles for prevention.

关键词： Rockburst Rockburst prevention Hardcoal longwall mining Induced seismicity Protective pillar

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A Comparison of Experimental and Numerical Studies Performed on a Low-Pressure Turbine Blade Cascade at High-Speed Conditions, Low Reynolds Numbers and Various Turbulence Intensities

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Journal of Thermal Science 2013年第5期22卷 413-423页

作者： Jan Michalek petr Straka VZLU - Aerospace Research and Test Establishment Beranovych 130 19500 PragueCzech Republic

This paper focuses on a comparison of experimental and numerical investigations performed on a low-pressure mid-loaded turbine blade at operating conditions comprised of a wide range of Math numbers （from 0.5 - 1.1）, Reynolds numbers （from 0.4e＋5 - 3.0e＋5）, flow incidence （-15 - 15 degrees） and three levels of free-stream tur- bulence intensities （2, 5 and 10%）. The experimental part of the work was performed in a high-speed linear cas- cade wind tunnel. The increased levels of turbulence were achieved by a passive grid placed at the cascade inlet. A two-dimensional flow field at the center of the blade was traversed pitch-wise upstream and downstream the cascade by means of a five-bole probe and a needle pressure probe, respectively. The blade loading was measured using the surface pressure taps evenly deployed at the blade mid-span along the suction and the pressure side. The inlet turbulence was investigated using the constant temperature anemometer technique with a dual sensor probe. Experimentally evaluated values of turbulent kinetic energy and its dissipation rate were then used as inputs for the numerical simulations. An in-house code based on a system of the Favre-averaged Navier-Stokes equation closed by a two-equation k-co turbulence model was adopted for the predictions. The code utilizes an algebraic model of bypass transition valid both for attached as for separated flows taking in account the effect of free-stream turbulence and pressure gradient. The resulting comparison was carried out in terms of the kinetic en- ergy loss coefficient, distributions of downstream wakes and blade velocity. Additionally a flow visualization was performed by means of the Schlieren technique in order to provide a further understanding of the studied phe- nomena. A few selected cases with a particular interest in the attached and separated flow transition are compared and discussed.

关键词： low pressure turbine high-speed flow low Reynolds number flow separation transition RANS

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Hybrid LES/RANS Simulations of Compressible Flow in a Linear Cascade of Flat Blade Profiles

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Journal of Thermal Science 2024年第5期33卷 1839-1850页

作者： Jaromír PRIHODA petr STRAKA David SIMURDA petr SIDLOF Jan LEPICOVSKY Institute of Thermomechanics of the Czech Academy of Sciences Dolejskova 1402/518200 Prague 5Czech Republic Aerospace Research and Test Centre Beranovych 13019905 PragueCzech Republic Technical University of Liberec Faculty of MechatronicsStudentska 246117 Liberec 1Czech Republic

The paper reports on 3D numerical simulations of unsteady compressible airflow in a blade cascade consisting of flat profiles using a hybrid LES/RANS approach including a transition *** a first step towards simulation of blade flutter in turbomachinery,various incidence angle offsets of the middle blade were *** simulations were run for the flow regime characterized by outlet isentropic Mach number M_(is)=0.5and zero *** results of the LES/RANS simulations(pressure and Mach number distributions)were compared to a baseline RANS model,and to experimental data measured in a high-speed wind *** numerical results show that both methods overpredict flow separation taking place at the leading *** this regard,the hybrid LES/RANS method does not provide superior results compared to the traditional RANS ***,the LES/RANS results also capture vortex shedding from the blunt trailing *** frequency of the trailing edge vortex shedding in CFD simulations matches perfectly the spectral peak recorded during wind tunnel measurements.

关键词： numerical simulation blade cascade hybrid LES/RANS

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Numerical Simulation of Separated Flows in Channels

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Journal of Thermal Science 2012年第2期21卷 145-153页

作者： petr Louda Jaromír Príhoda petr Sváek Karel Kozel Czech Technical University in Prague Fac. of Mechanical Engineering Karlovo nám. 13 CZ-121 35 Praha 2 Institute of Thermomechanics AS CR v.v.i. Dolejkova 5 CZ-182 00 Praha 8

The work deals with numerical modelling of turbulent flows in channels with an expansion of the cross-section where flow separation and reattachment occur. The performance of several eddy viscosity models and an explicit algebraic Reynolds stress model (EARSM) is studied. The used test cases are flows in channels with various backward facing steps where the step is perpendicular or inclined and the top wall is parallel or deflected. Furthermore, a channel with the circular ramp is considered. The numerical solution is achieved by the finite volume method or by the finite element method. The results of both numerical approaches are compared.

关键词： backward facing step flow EARSM model SST model

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Visualization of Large Amount of Spectra in Virtual Observatory Environment

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International Journal of Automation and computing 2014年第6期11卷 613-620页

作者： petr aloun David Andrei petr koda Ivan Zelinka Department of Computer Science Faculty of Electrical Engineering and Computer Science VB-Technical University of Ostrava17.listopadu 15 708 33 Ostrava-Poruba Czech Republic Astronomical Institute of the Academy of Sciences Fricova 298 251 65 Ondrejov Czech Republic

This paper presents overview of new features so far prepared for new version of spectral analysis tool SPLAT-VO that allows to retrieve a large amount of spectra(and other data) based on its characteristics by detailed querying a virtual observatory s resources. The overview is focused on enhancements of user experience, work with simple application messaging protocol(SAMP) and other interoperability that improves work with global list of spectra, plot window and analysis menu.

关键词： SPLAT-VO virtual observatory spectra simple application message protocol (SAMP) flexible image transport system (FITS)

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AN ANP/DNP ANALYSIS OF ECONOMIC ELEMENTS IN TODAY’S WORLD NETWORK ECONOMY

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Journal of Systems Science and Systems Engineering 2006年第2期15卷 131-140页

作者： petr FIALA Department of Econometrics University of EconomicsPragueThe Czech Republic

The network economy is a term for today＇s global relationship among economic elements characterized by massive connectivity. The central act of the new era is to connect everything to everything in deep web networks at many levels of mutually interdependent relations, where resources and activities are shared, markets are enlarged and costs and risk are reduced, Network systems contain both positive and negative feedback. A variety of feedback processes create complex system behavior. For such a network the Analytic Network Process （ANP） approach seems to be very appropriate. The ANP method makes it possible to deal systematically with all kinds of dependence and feedback in the system. Dynamic models try to reflect changes in real or simulated time and take into account that the network model components are constantly evolving. Dynamic models use concepts of state variables, flows, and feedback processes. The Dynamic Network Process （DNP） is an extension of ANP that can deal with time deoendent oriorities in a networked economv.

关键词： Network economy positive feedback complementarity Analytic Network Process,Dynamic Network Process

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Study on the Numerical Model of Transonic Wind Tunnel Test Section

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Journal of Thermal Science 2021年第1期30卷 231-241页

作者： LOUDA petr PŘÍHODA Jaromír Institute of Thermomechanics of the Czech Academy of Sciences Prague 818200Czech Republic Faculty of Mechanical Engineering Czech Technical UniversityPrague 212135Czech Republic

The authors consider numerical simulations of transonic flows through various turbine cascades in a confined channel which approximates boundaries of real wind *** boundaries of the wind tunnel are impermeable or there can be permeable tailboards to diminish shock wave *** mathematical model is based on Favre-averaged Navier-Stokes equations closed by a turbulence model and model of transition to *** mathematical model is solved by an implicit finite volume method with multi-block *** types of turbine blade cascades with subsonic or supersonic inlet are *** results are compared with optical measurements and simulations of periodic *** validity of experimental reference flow parameters in relation to computed flow patterns is discussed.

关键词： perforated wall model transonic wind tunnel turbine blade cascade

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Optimal Choice of Weighting Factors in Adaptive Linear Quadratic Control

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International Journal of Automation and computing 2014年第3期11卷 241-248页

作者： Jiri Vojtesek petr Dostal Tomas Bata University in Zlin Faculty of Applied Informatics

Most of the processes in the industry have nonlinear behavior. Control of such processes with conventional control methods could lead to unstable, suboptimal, etc., results. On the other hand, the adaptive control is a technique widely used for controlling of nonlinear systems. The approach here is based on the recursive identification of the external linear model as a linear representation of the originally nonlinear system. The controller then reacts to the change of the working point or disturbances which could occur by the change of the parameters, structure, etc. The polynomial synthesis together with the linear quadratic(LQ) approach is employed here for the controller synthesis. These techniques satisfy basic control requirements such as the stability, the reference signal tracking and the disturbance attenuation. Resulted controller could be tuned with the choice of weighting factors in LQ approach. This work investigates the effect of these factors on control results. Proposed methods are tested on the mathematical model of the isothermal continuous stirred-tank reactor and simulated results are also verified on the real model of the continuous stirred tank reactor.

关键词： Simulation adaptive control recursive identification linear quadratic(LQ) approach continuous stirred-tank reactor(CSTR).

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Accurate large-scale simulations of siliceous zeolites by neural network potentials

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npj Computational Materials 2022年第1期8卷 1662-1673页

作者： Andreas Erlebach petr Nachtigall LukášGrajciar Department of Physical and Macromolecular Chemistry Charles UniversityHlavova 812800Prague 2Czech Republic

The computational discovery and design of zeolites is a crucial part of the chemical *** highly accurate while computational feasible protocol for identification of hypothetical siliceous frameworks that could be targeted experimentally is a great *** tackle this challenge,we trained neural network potentials(NNP)with the SchNet architecture on a structurally diverse database of density functional theory(DFT)*** database was iteratively extended by active learning to cover not only low-energy equilibrium configurations but also high-energy transition *** demonstrate that the resulting reactive NNPs retain DFT accuracy for thermodynamic stabilities,vibrational properties,as well as reactive and non-reactive phase *** a showcase,we screened an existing zeolite database and revealed>20k additional hypothetical frameworks in the thermodynamically accessible range of zeolite ***,our NNPs are expected to be essential for future high-throughput studies on the structure and reactivity of siliceous zeolites.

关键词： synthesis zeolite zeolites

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