Aretxabaleta, Spain
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Barreno I.,Cs Centro Stirling S Coop | Costa S.C.,Cs Centro Stirling S Coop | Cordon M.,Cs Centro Stirling S Coop | Tutar M.,University of Mondragon | And 4 more authors.
International Journal of Thermal Sciences | Year: 2015

New correlation equations, to be valid for the pressure drop and heat exchange calculation under the developing transitional reciprocating flow encountered in Stirling heat exchangers are numerically derived. Reynolds-Averaged NaviereStokes (RANS) equations based turbulence models are used to analyse laminar to turbulent reciprocating flow, focussing on the onset of turbulence and transitional reciprocating flow regime. The relative performance of four turbulence models in more accurately capturing the characteristics of the flow of interest is assessed in relation to overcoming the problems identified in previous numerical studies. The simulation results are compared with published and wellknown experimental data for reciprocating pipe flows, indicating that the effects of the turbulence anisotropy need to be taken into account in order to accurately predict the laminar to turbulent transition. The anisotropic Reynolds stress turbulence model is selected as a best choice among the tested turbulence models for analysis of this transitory phenomenon based on the comparative qualitative and quantitative results. This model is used to evaluate the heat transfer and pressure drop and propose new correlations considering the working and dimensional characteristics of Stirling heat exchangers: 100 ≤ Reω ≤ 600, A0 ≤ 600, bcri 761 and 40 ≤ L/D ≤ 120. These correlation equations reduce the unsteady 2D behaviour in reciprocating pipe flow into a manageable form that can be incorporated into Stirling engine performance codes. It is believed that the validated numerical model can be used with confidence for studying the transitional reciprocating flow and the obtained correlations, can be applied as a cost effective solution for the development of Stirling engine heat exchangers. © 2015 Elsevier Masson SAS.


Costa S.C.,Cs Centro Stirling S Coop | Barrutia H.,University of Mondragon | Esnaola J.A.,University of Mondragon | Tutar M.,University of Mondragon | Tutar M.,Ikerbasque
Energy Conversion and Management | Year: 2013

Friction pressure drop correlation equations are derived from a numerical study by characterizing the pressure drop phenomena through porous medium of both types namely stacked and wound woven wire matrices of a Stirling engine regenerator over a specified range of Reynolds number, diameter and porosity. First, a finite volume method (FVM) based numerical approach is used and validated against well known experimentally obtained empirical correlations for a misaligned stacked woven wire matrix, the most widely used due to fabrication issues, for Reynolds number up to 400. The friction pressure drop correlation equation derived from the numerical results corresponds well with the experimentally obtained correlations with less than 5% deviation. Once the numerical approach is validated, the study is further extended to characterize the pressure drop phenomena in a wound woven wire matrix model of a Stirling engine regenerator for a diameter range from 0.080 to 0.110 mm and a porosity range from 0.472 to 0.638 within the same Reynolds number range. Thus, the new correlation equations are derived from this numerical study for different flow configurations of the Stirling engine regenerator. The results indicate flow nature and complex geometry dependent friction pressure drop characteristics within the present Stirling engine regenerator system. It is believed that the developed correlations can be applied with confidence as a cost effective solution to characterize and hence to optimize stacked and woven Stirling engine efficiency in the above specified ranges. © 2012 Elsevier B.V. All rights reserved.


Costa S.-C.,Cs Centro Stirling S Coop | Tutar M.,University of Mondragon | Tutar M.,Ikerbasque | Barreno I.,Cs Centro Stirling S Coop | And 5 more authors.
Energy | Year: 2014

This paper presents both preliminary experimental and numerical studies of pressure drop and heat transfer characteristics of Stirling engine regenerators. A test bench is designed and manufactured for testing different regenerators under oscillating flow conditions, while three-dimensional (3-D) numerical simulations are performed to numerically characterize the pressure drop phenomena through a wound woven wire matrix regenerator under different porosity and flow boundary conditions.The test bench operating condition range is initially determined based on the performance of the commercial, well-known Stirling engine called WhisperGenTM. This oscillating flow test bench is essentially a symmetrical design, which allows two regenerator samples to be tested simultaneously under the same inflow conditions. The oscillating flow is generated by means of a linear motor which moves a piston in an oscillatory motion. Both the frequency and the stroke of the piston are modified to achieve different test conditions.In the numerical study, use of a FVM (finite volume method) based CFD (computational fluid dynamics) approach for different configurations of small volume matrices leads to a derivation of a two-coefficient based friction factor correlation equation, which could be later implemented in an equivalent porous media with a confidence for future regenerator flow and heat transfer analysis. © 2014 Elsevier Ltd.


Costa S.C.,Cs Centro Stirling S Coop | Barreno I.,Cs Centro Stirling S Coop | Tutar M.,University of Mondragon | Tutar M.,Ikerbasque | And 2 more authors.
Energy Conversion and Management | Year: 2014

Different numerical methods can be applied to the analysis of the flow through the Stirling engine regenerator. One growing approach is to model the regenerator as porous medium to simulate and design the full Stirling engine in three-dimensional (3-D) manner. In general, the friction resistance coefficients and heat transfer coefficient are experimentally obtained to describe the flow and thermal non-equilibrium through a porous medium. A finite volume method (FVM) based non-thermal equilibrium porous media modelling approach characterizing the fluid flow and heat transfer in a representative small detailed flow domain of the woven wire matrix is proposed here to obtain the porous media coefficients without further requirement of experimental studies. The results are considered to be equivalent to those obtained from the detailed woven wire matrix for the pressure drop and heat transfer. Once the equivalence between the models is verified, this approach is extended to model oscillating regeneration cycles through a full size regenerator porous media for two different woven wire matrix configurations of stacked and wound types. The results suggest that the numerical modelling approach proposed here can be applied with confidence to model the regenerator as a porous media in the multi-dimensional (multi-D) simulations of Stirling engines. © 2014 Elsevier Ltd. All rights reserved.


Costa S.C.,Cs Centro Stirling S Coop | Barrutia H.,University of Mondragon | Esnaola J.A.,University of Mondragon | Tutar M.,University of Mondragon | Tutar M.,Ikerbasque
Energy Conversion and Management | Year: 2014

Nusselt number correlation equations are numerically derived by characterizing the heat transfer phenomena through porous medium of both stacked and wound woven wire matrices of a Stirling engine regenerator over a specified range of Reynolds number, diameter and porosity. A finite volume method (FVM) based numerical approach is proposed and validated against well known experimentally obtained empirical correlations for a random stacking woven wire matrix, the most widely used due to fabrication issues, for Reynolds number up to 400. The results show that the numerically derived correlation equation corresponds well with the experimentally obtained correlations with less than 6% deviation with the exception of low Reynolds numbers. Once the numerical approach is validated, the study is further extended to characterize the heat transfer in a wound woven wire matrix model for a diameter range from 0.08 to 0.11 mm and a porosity range from 0.60 to 0.68 within the same Reynolds number range. Thus, the new correlation equations are numerically derived for different flow configurations of the Stirling engine regenerator. It is believed that the developed correlations can be applied with confidence as a cost effective solution to characterize and hence to optimize stacked and wound woven wire Stirling regenerator in the above specified ranges. © 2013 Elsevier Ltd. All rights reserved.


Gallo A.,University of Mondragon | Arana A.,University of Mondragon | Oyanguren A.,University of Mondragon | Garcia G.,Cs Centro Stirling S Coop | And 3 more authors.
Journal of Electronic Materials | Year: 2013

In this work the properties of thermoelectric modules (TEMs) and their behavior have been numerically modeled. Moreover, their applications very often require modeling not only of the TEM but also of the working environment and the product in which they will be working. A clear example is the fact that TEMs are very often installed with heat-dissipating elements such as fans, heat sinks and heat exchangers; thus, the module will only work according to the heat dissipation conditions that these external sources can provide in a certain environment. In this context, analytic approaches, even though they have been proved to be useful, do not provide enough, accurate information in this regard. Therefore, numerical modeling has been identified as a powerful tool to improve detailed designs of thermoelectric solutions. This paper presents numerical simulations of a TEM in different working conditions, as well as with different commercial dissipation devices. The objective is to obtain the characteristic curve of a TEM using a valid numerical model that can be introduced into larger models of different applications. Also, the numerical model of the module and different cooling devices is provided. Both of them are compared against real tested modules, so that the deviation between them can be measured and discussed. Finally, the TEM is introduced into a manufacturing application and results are discussed to validate the model for further use. © 2013 TMS.


Barreno I.,Cs Centro Stirling S Coop | Costa S.C.,Cs Centro Stirling S Coop | Cordon M.,Cs Centro Stirling S Coop | Urrutibeascoa I.,University of Mondragon | And 2 more authors.
Applied Energy | Year: 2014

In this paper, a promising heat pump based on Stirling technology is examined. Based on the volume variation produced by the oscillating displacement of two pistons, the advantages of this particular system lie in the elimination of a transmission mechanism, as the driving machines are directly coupled to the working pistons, and in the use of environmentally friendly working gases. The system is analysed by coupling the dynamics to an isothermal model of the Stirling cycle. A methodology is proposed to preliminarily size this type of heat pump based on simulations performed on a mathematical model built in MATLAB. The stability of operation is analysed by considering possible changes in working conditions. Actions are proposed to minimize the effect of these changes on the performance of the system. © 2014 Elsevier Ltd.

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