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Journal ArticleDOI

A numerical approach for the study of glass furnace regenerators

01 Oct 2005-Applied Thermal Engineering (Pergamon)-Vol. 25, Iss: 14, pp 2299-2320
TL;DR: In this article, an open method to simulate the behavior of a glass furnace regenerator is presented, based on the Boussinesq approximation with a "fictitious thermal expansion coefficient".
About: This article is published in Applied Thermal Engineering.The article was published on 2005-10-01 and is currently open access. It has received 28 citations till now. The article focuses on the topics: Forced convection & Regenerative heat exchanger.

Summary (3 min read)

1. Introduction

  • Regenerators are widely used in many industrial sectors such as cryogenic, metallurgical, chemical process and glass industry.
  • Regenerator operation relies on the successive alternation of hot and cold periods.
  • Heat exchange is indeed dominated by free turbulent convection mechanisms next to the entrance of the channel whereas, next to the exit, mechanisms of laminar forced convection prevail.
  • The closed methods only calculate the cyclic equilibrium and only the periodic conditions are taken into account in the problem.
  • That is the reason why the present work proposes an open method, using the Computational Fluid Dynamics (CFD) code Fluent, able to estimate the mean heat transfer coefficients with a satisfactory accuracy.

2.1. General equations

  • Its direction is characterized by the unity vector~s and the coordinates are defined by the vector~r (Fig. 2).
  • The authors consider an absorbing, emitting and grey medium in which scattering phenomena are negligible.
  • Under these assumptions, the radiant transport equation (RTE) can then be written ~s grad !ðLÞ ¼ jI eq jI ð5Þ where Ieq ¼.
  • I eqð~rÞ is the equilibrium radiant luminance, given by the Planck s function and j the absorption coefficient.

2.2. Similitude criteria for the cold period

  • The dimensionless form of the momentum equation (2) gives rise to two similitude criteria (see Padet [23,24]).
  • Dh of the channel and the velocity scale is the mass-flow velocity Um. Moreover, as the hydraulic diameter is constant, the mass conservation equation (1) involves qU = q0U0.
  • Two models can be considered to satisfy the similitude criterion on the Richardson number: First model.
  • For a buoyancy-driven flow, this model (called model 1) is known to give poorer results than those given with the use of the Boussinesq approximation.

2.3. Similitude criteria for the hot period

  • During the hot period, the effect of free convection is negligible so that the buoyancy term gq in the momentum equation (2) no longer exists and as a consequence the similitude criterion for the Richardson number.
  • The Peclet number and the Reynolds number are still two similitude criteria and are respected in the same way as in the cold period.
  • But, the dimensionless energy equation give rise to a new similitude criterion defined as (the refraction index is equal to unity, n = 1) The Planck number; jk n2rT 3 ð13Þ where r is the Stefan–Boltzmann constant.
  • As the dependence of the thermal conductivity with temperature is considered in their models, this similarity criterion will be respected when the absorption coefficient j is correctly taken into account.
  • The model WSGG is of great interest thanks to its reduced CPU time and some authors, as Denison and Webb [26], have recently made improvements on it.

2.4. Calculation procedure

  • The calculations need an initial temperature condition in the channel: the value (Tc,in + Th,in)/2 is then imposed.
  • The transient calculation starts with a hot period followed by a cold period.
  • This operation goes on until the cyclic equilibrium is reached.
  • For each period, only one step time is made as the evolution of temperature is linear with time and height in the channel [9].
  • The typical CPU time was approximately 4 weeks on one processor of a modern multiprocessor SUN powerstation.

3. Test results

  • As preliminary work, this section proposes to simplify the problem under consideration by comparing the results of their method to reliable experimental or analytical data from the literature describing each physical phenomenon (free convection, mixed convection, radiation) on a simple geometry (tube, vertical flat plate).
  • Thus, the simulation can be made with a two-dimensional grid, contrary to the complete simulation described in Section 5 which is three-dimensional.
  • For the cold period, a turbulence model using wall functions and a computation grid are chosen by studying both free convection along a vertical plate and aiding mixed convection in a smooth tube.
  • For the hot period, a model of radiation is chosen to describe the RTE.

3.1. Turbulent free convection

  • The well-known k–emodel combined with wall functions has been developed for forced convection flows.
  • Grid independence tests have been carried out, but only the results obtained with the most efficient grids are reported in this paper.
  • The two-dimensional calculation field is sufficiently wide (0.8 m) to neglect the interaction between the lateral boundary and the growing boundary layer along the vertical plate.
  • This statement leads to the conclusion that the heat transfer coefficient is constant.
  • As for forced convection, the ‘‘enhanced’’ wall functions are then much better than the ‘‘standard’’ wall functions for the determination of both heat exchange and flow pattern.

3.2. Mixed convection

  • Many papers reporting experimental studies deal with aiding mixed convection.
  • The authors use the lowReynolds number k–e model proposed by Launder and Sharma [34] which is a slight modification of the Jones and Launder model.
  • The results of Cotton and Jackson show that the low-Reynolds number k–e model is able to predict the aiding mixed convection regime with a good accuracy.
  • They use a fine mesh in their study and the calculation points which are close to the wall are located in the viscous sub-layer (yþw 0:5).
  • The mesh used is identical to the one validated for the study with free convection, as the authors use a 2D-axisymmetric approach.

3.3. Radiation

  • To simulate the thermal radiation exchange, the discrete ordinates (DO) method has been chosen.
  • This method has first been developed for other applications than radiant heat transfer [36,37] and has been extended for thermal radiation.
  • For their test, the dimensions of the geometry are given in Fig.
  • The use of the DO method gives satisfactory results whatever the value of the parameter N*.

4. Experimental set-up and instrumentation

  • The work presented below has been done in their laboratory by Lagarenne [9] and co-workers.
  • In addition, the internal envelop of the test section is insulated to minimize thermal losses.
  • On the contrary, the suction pyrometer enables us to minimize the impact of the radiation of the environment and to measure the real gas temperature.
  • To calculate the mean spatial temperature over the section of the regenerator, the authors found that it was helpful to maximize the measurement duration or the number, say N, of periods.
  • To realize local measurements, thermocouples were installed into the wings of the cruciforms at several heights in one of these insulated channels.

5. Results and discussion

  • The global results reported in [9] are given in Table 7.
  • The gas temperatures measured by SP1 and SP2 for the hot period (Tout,h) and the cold period (Tout,c), respectively, were recorded at each half period.

6. Conclusion

  • The authors have proposed an open method based on a CFD code which has been shown successful.
  • The k–e RNG turbulence model combined with the ‘‘enhanced’’ wall functions is chosen to describe the turbulent aiding mixed convection phenomena from the region where heat transfer is dominated by free convection to the region where heat transfer is controlled by forced convection.
  • So, convective heat exchange is correctly computed for the cold period and for the hot period.
  • Moreover, as the cold period is the limiting factor of the heat exchanges, the assumption of a grey medium for waste gas is proved to be adequate for a glass furnace regenerator.
  • Based on the Boussinesq approximation, it introduces a fictitious thermal expansion coefficient which includes the evolution of density with temperature.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, a new type of thermal energy storage process for large scale electric applications was presented, based on a high temperature heat pump cycle which transformed electrical energy into thermal energy and stored it inside two large regenerators, followed by a thermal engine cycle which transforms the stored thermal energy back into electrical energy.

212 citations


Cites background from "A numerical approach for the study ..."

  • ...Sensible heat storage is used in pebble bed, packed bed or molten salts for thermal solar power plants [3], in water heater storage [4], in blast or glass furn ace regenerators [5], and it is the most used technology for heating and cooling of buildings [3] ....

    [...]

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TL;DR: A literature survey on the Pumped Thermal Electricity Storage technology is presented with the aim of analysing its actual configurations and state of development in this article, which is the most promising one due to its long cycle life, no geographical limitations, no need of fossil fuel streams and capability of being integrated into conventional fossil-fuelled power plants.
Abstract: A large penetration of variable intermittent renewable energy sources into the electric grid is stressing the need of installing large-scale Energy Storage units. Pumped Hydro Storage, Compressed Air Energy Storage and Flow Batteries are the commercially available large-scale energy storage technologies. However, these technologies suffer of geographical constrains (such as Pumped Hydro Storage and Compressed Air Energy Storage), require fossil fuel streams (like Compressed Air Energy Storage) or are characterised by low cycle life (Flow Batteries). For this reason, there is the need of developing new large-scale Energy Storage Technologies which do not suffer of the above-mentioned drawbacks. Among the in-developing large-scale Energy Storage Technologies, Pumped Thermal Electricity Storage or Pumped Heat Energy Storage is the most promising one due to its long cycle life, no geographical limitations, no need of fossil fuel streams and capability of being integrated into conventional fossil-fuelled power plants. Based on these evidences, in the present work, a literature survey on the Pumped Thermal Electricity Storage technology is presented with the aim of analysing its actual configurations and state of development.

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TL;DR: A review of the heat transfer literature published in 2005 can be found in this article, where the authors restrict themselves to papers published in English through a peer-review process, with selected translations from journals published in other languages.

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TL;DR: In this article, a new Pumped Thermal Electricity Storage configuration is proposed and tested, where an electric heater is used to convert electrical energy into thermal energy, a single heat exchanger is installed and air is used as heat transfer fluid.

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TL;DR: In this article, a regenerator model is developed to estimate the actual performance of the regenerator and to compare it with the target performance, based on mass and energy balance of streams along with heat transfer characteristic equations.

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References
More filters
Journal ArticleDOI
TL;DR: In this article, robust and accurate collocation schemes are offered for the series solution of the classical Nusselt integral equations which describe the steady state temperature behaviour of a thermal regenerator.

5 citations

Journal ArticleDOI
TL;DR: The use of the Legendre orthogonal polynomials provides a significant improvement in the robustness and simplicity of the Galerkin series expansion methods for the solution of the classical Nusselt integral equations as mentioned in this paper.

5 citations

W. F. Schalkwijk1
01 Jan 1960
TL;DR: In this paper, a simplified equation for calculating regenerator efficiency is derived based on the fact that most regenerators encountered in practice have very simple linear ternperature changes in their central portions.
Abstract: A simplified equation for calculating regenerator efficiency is derived. Derivation of the equation is based on the fact that most regenerators encountered in practice have very simple linear ternperature changes in their central portions. (B. O. G.)

3 citations

Dissertation
01 Jan 1990
TL;DR: In this paper, the regenerateur d'echelle industrielle specialement concu et realise pour cette etude concerne la recuperation d'energie par des regenerateurs, echangeurs de chaleur a haute temperature, utilises dans l'industrie du verre.
Abstract: Cette etude concerne la recuperation d'energie par des regenerateurs , echangeurs de chaleur a haute temperature, utilises dans l'industrie du verre. Des essais sont menes en conditions realistes sur un regenerateur d'echelle industrielle specialement concu et realise pour cette etude. Une instrumentation abondante permet une caracterisation globale et une description locale approfondie du systeme. Differentes methodes d'evaluation de la performance thermique s ont comparees. Les mecanismes d' echange de chaleur sont analyses ; les phenomenes de convection mixte sont notamment pris en compte. Un nouveau logiciel de simulation thermique transitoire est valide pas l'experience et une geometrie originale de surface d 'echange est developpee pour intensifier les transferts.

2 citations