Chattering in dynamic mathematical two-phase flow models

Bonilla, Javier; Yebra, Luis J.; Dormido, Sebastián

doi:10.1016/j.apm.2011.08.013

Cited by 39 publications

(28 citation statements)

References 10 publications

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“…• Mean densities method: The mean densities method was originally proposed by Casella [4] and successfully tested by Bonilla et al [2]. It is also the method implemented in the ThermoPower Modelica library [7].…”

Section: Chattering and Flow Reversalsmentioning

confidence: 99%

ThermoCycle: A Modelica library for the simulation of thermodynamic systems

Quoilin¹,

Desideri²,

Wronski³

et al. 2014

Linköping Electronic Conference Proceedings

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This paper presents the results of an on-going project to develop ThermoCycle, an open Modelica library for the simulation of low-capacity thermodynamic cycles and thermal systems. Special attention is paid to robustness and simulation speed since dynamic simulations are often limited by numerical constraints and failures, either during initialization or during integration. Furthermore, the use of complex equations of state (EOS) to compute thermodynamic properties significantly decreases the simulation speed. In this paper, the approach adopted in the library to overcome these challenges is presented and discussed.

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Section: Chattering and Flow Reversalsmentioning

confidence: 99%

ThermoCycle: A Modelica library for the simulation of thermodynamic systems

Quoilin¹,

Desideri²,

Wronski³

et al. 2014

Linköping Electronic Conference Proceedings

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“…Other previous work related to the dynamics associated with the cycle charge includes Ref. [7], in which the authors study the effect of system oscillations and numerical instability resulting from variations in the density in an evaporator, as well as the work of Ref. [8], which discusses both chattering (oscillations around a phase boundary) and the selection of different state variables due to different parameterizations for the equations of state for various fluids.…”

Section: Introductionmentioning

confidence: 99%

On the influence of state selection on mass conservation in dynamic vapour compression cycle models

Laughman

Qiao

2017

Mathematical and Computer Modelling of Dynamical Systems

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Many dynamic models of vapour compression systems experience nonphysical variations in the total refrigerant mass contained in the system when common modelling approaches are used. Rather than using the traditional state variables of pressure and specific enthalpy, the use of density as a state variable can eliminate these variations. The reasons for these variations are explained, and a set of test models is developed to study the effect of the state variable selection on the overall system charge. Results from both a simplified cycle model and a realistic airsource heat pump model indicate that this alternative approach has significant benefits for maintaining a fixed mass of refrigerant in the cycle. ARTICLE HISTORY

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“…The comparison shows quite good agreement, though there is time-shift in some parts in the order of minutes, which could indicate the need for model improvement in thermal heat storage in metal components such as component casings and pipe walls. Bonilla et al (2012) also observe and discuss a chattering problem in a pipe model which can hinder the performance of said dynamic models. In this paper, they analyse this problem and present an approach to a solution which is based on the smooth interpolation of some thermodynamic properties.…”

Section: Heat Exchanger Modellingmentioning

confidence: 98%

Dynamic simulation and experimental validation of an Organic Rankine Cycle model

Twomey¹

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The aim of this thesis is to develop a methodology to model and simulate the dynamics of Organic Rankine Cycle (ORC) power plants, and to demonstrate and validate this methodology by performing experiments on a laboratory-scale ORC plant. Typical plant models for ORCs provide steady state analysis of thermodynamic cycles and losses, but for a system that has complex starting mechanisms and undergoes fluctuations in operating conditions due to environmental effects, dynamic models are needed to predict how the system will behave. Two main questions are interesting to an ORC designer. What is the start-up and shut-down time of the plant? And: What effect does an unprecedented slow or sharp transient in one or multiple physical variables have on the system? There are a number of modelling libraries available for the simulation of Rankine cycles, however there is no complete package that covers all potential dynamic scenarios and is fully documented with guidance on how to develop a stable dynamic model. Issues such as component selection and parameterisation criteria, compilation of stable models in large systems, simulation initialisation strategies, and heat transfer model selection present many challenges to the inexperienced modeller. This thesis aims to address these issues and document strategies to overcome them.Existing modelling libraries do not include extensive heat transfer models that can accurately simulate the heat exchange that occurs during dynamic transients in ORC heat exchangers. Void fraction is a critical variable for the dynamics of a closed thermodynamic cycle that depends on accurate heat transfer models, and models that switch between single-phase and two-phase heat transfer correlation are beneficial here. Development of an extension of the existing heat transfer models to better model these effects is another aim of this thesis.A smaller ORC laboratory that is separate to the main facility used in this project was available early in the thesis to test initial heat exchanger and cycle modelling results. An intermediate project goal was to use this laboratory to model and analyse a novel small-scale solar cogeneration unit that uses cheap and available components to heat water and produce power using a scroll expander. The completion of this goal was seen as a fundamental step toward understanding the physical characteristics of an ORC that is producing power, and to observe the system dynamics. The results of i the study include a typical day's power output for various times of the year, and show the competitiveness of this type of system.The major contributions that originate from the main body of work on the larger ORC facility are:• Development of extended pipe models that include an extra wall for heat transfer to a shell or the environment;• Development of detailed, deterministic plate heat exchanger models with descriptive parameters that can be quickly configured by an inexperienced modeller. These include extensions to heat transfer models and a new phase switching method ...

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Chattering in dynamic mathematical two-phase flow models

Cited by 39 publications

References 10 publications

ThermoCycle: A Modelica library for the simulation of thermodynamic systems

ThermoCycle: A Modelica library for the simulation of thermodynamic systems

On the influence of state selection on mass conservation in dynamic vapour compression cycle models

Dynamic simulation and experimental validation of an Organic Rankine Cycle model

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