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Natural convection in high temperature flat plate latent heat thermal energy storage systems

Vogel, Julian and Felbinger, Jonina and Johnson, Maike (2016) Natural convection in high temperature flat plate latent heat thermal energy storage systems. Applied Energy, 184, pp. 184-196. Elsevier. DOI: 10.1016/j.apenergy.2016.10.001 ISSN 0306-2619

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Official URL: http://dx.doi.org/10.1016/j.apenergy.2016.10.001

Abstract

The impact of natural convection on melting in high temperature flat plate latent heat thermal energy storage systems is studied with an experimentally validated numerical model in a parameter study with various widths and heights of enclosure dimensions. The storage material is the eutectic mixture of sodium nitrate and potassium nitrate (KNO3-NaNO3). The investigated half widths of the rectangular enclosures between two heated vertical flat plates are 5, 10 and 25 mm; their heights are 25, 50, 100, 200, 500 and 1000 mm. These parameters result in low to very high aspect ratios between 0.5 and 40 and Rayleigh numbers between 1.2 · 10^4 and 1.6 · 10^6. The results are evaluated by dimensional analysis to find general dependencies between enclosure dimensions and natural convection occurrence and strength. To assess the influence of natural convection on the heat transfer enhancement, the convective enhancement factor is introduced. This non-dimensional number is defined as the ratio of actual heat flux by natural convection to a hypothetical heat flux by conduction only. The central findings of the present work are correlations for the mean convective enhancement factor and the critical liquid phase fraction for natural convection onset that are valid for a wide parameter range. The results indicate that heat transfer enhancement due to natural convection increases with greater widths and smaller heights of storage material enclosures. Hence, the vertical segmentation of high enclosures into smaller ones should be considered to enhance heat transfer during charging.

Item URL in elib:https://elib.dlr.de/106581/
Document Type:Article
Title:Natural convection in high temperature flat plate latent heat thermal energy storage systems
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Vogel, Julianjulian.vogel (at) dlr.dehttps://orcid.org/0000-0001-9792-2332
Felbinger, JoninaUNSPECIFIEDUNSPECIFIED
Johnson, Maikemaike.johnson (at) dlr.deUNSPECIFIED
Date:15 December 2016
Journal or Publication Title:Applied Energy
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:184
DOI :10.1016/j.apenergy.2016.10.001
Page Range:pp. 184-196
Publisher:Elsevier
ISSN:0306-2619
Status:Published
Keywords:High temperature flat plate latent heat storage; Phase change material (PCM); Melting and solidification; Natural convection; Parameter study of rectangular enclosure dimensions; Numerical simulation (CFD)
HGF - Research field:Energy
HGF - Program:Storage and Cross-linked Infrastructures
HGF - Program Themes:Thermal Energy Storage
DLR - Research area:Energy
DLR - Program:E EV - Energy process technology
DLR - Research theme (Project):E - Thermochemical Processes (Storage) (old)
Location: Stuttgart
Institutes and Institutions:Institute of Engineering Thermodynamics > Thermal Process Technology
Deposited By: Vogel, Julian
Deposited On:13 Oct 2016 10:15
Last Modified:06 Sep 2019 15:21

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