Annulus eccentricity optimisation of a phase-change material (PCM) horizontal double-pipe thermal energy store
File(s)
Accepted version
Author(s)
Kadivar, MR
Moghimi, MA
Sapin, P
Markides, CN
Type
Journal Article
Abstract
The application of phase-change materials (PCMs) has received significant interest for use in thermal energy storage (TES) systems that can adjust the mismatch between the energy availability and demand. In the building sector, for example, PCMs can be used to reduce air-conditioning energy consumption by increasing the thermal capacity of the walls. However, as promising this technology may be, the poor thermal conductivity of PCMs has acted as a barrier to its commercialization, with many heat-transfer enhancement solutions proposed in the literature, such as microencapsulation or metal foam inserts, being either too costly and/or complex. The present study focuses on a low-cost and highly practical solution, in which natural-convective heat transfer is enhanced by placing the PCM in an eccentric annulus within a horizontal double-pipe TES heat exchanger. This paper presents an annulus-eccentricity optimisation study, whereby the optimal radial and tangential eccentricities are determined to minimize the charging time of a PCM thermal energy store. The storage performance of several geometrical configurations is predicted using a computational fluid dynamics (CFD) model based on the enthalpy-porosity formulation. The optimal geometrical configuration is then determined with response surface methods. The horizontal double-pipe heat exchanger studied considered here is an annulus filled with N-eicosane as the PCM for initial studies. In presence of N-eicosane, for the concentric configuration (which is the baseline case), the charging is completed at Fo = 0.64, while the charging of optimum eccentric geometries with the quickest and slowest charging is completed at Fo = 0.09 and Fo = 2.31, respectively. In addition, an investigation on the discharging performance of the studied configurations with N-eicosane shows the quickest discharge occurs with the concentric annulus case at Fo = 0.99, while the discharge time of the proposed optimum annuli is about three times this value. In other words, the proposed optimum geometry with the quickest charging time charges ~7.1 times faster but also discharges ~3 times slower, which is ideal for a TES, especially when used as passive thermal storage systems in nearly zero-emission buildings. Complementary studies demonstrate that the proposed optimum configuration improves the TES performance also when employing other PCM types as well as various shell-to-tube diameter ratios.
Date Issued
2019-12-01
Date Acceptance
2019-10-24
Citation
Journal of Energy Storage, 2019, 26
ISSN
2352-152X
Publisher
Elsevier
Journal / Book Title
Journal of Energy Storage
Volume
26
Copyright Statement
© 2019 Elsevier Ltd. All rights reserved. . This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000501787200005&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
EP/P004709/1
EP/R045518/1
Subjects
Science & Technology
Technology
Energy & Fuels
CFD
Phase change material
Thermal energy storage
Optimization
Charging
Discharging
Eccentric
POROUS METAL FOAM
HEAT-TRANSFER
CONDUCTIVITY ENHANCEMENT
OPERATIONAL PARAMETERS
NATURAL-CONVECTION
NUMERICAL-ANALYSIS
SHELL
SYSTEM
PERFORMANCE
SOLIDIFICATION
Publication Status
Published
Article Number
ARTN 101030
Date Publish Online
2019-10-31