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Research Papers: Evaporation, Boiling, and Condensation

Computational Studies on Metal Foam and Heat Pipe Enhanced Latent Thermal Energy Storage

[+] Author and Article Information
K. Nithyanandam

Advanced Materials
and Technologies Laboratory,
Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061-0238

R. Pitchumani

Fellow ASME
Advanced Materials
and Technologies Laboratory,
Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061-0238
e-mail: pitchu@vt.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 4, 2013; final manuscript received November 9, 2013; published online February 26, 2014. Assoc. Editor: Bruce L. Drolen.

J. Heat Transfer 136(5), 051503 (Feb 26, 2014) (10 pages) Paper No: HT-13-1278; doi: 10.1115/1.4026040 History: Received June 04, 2013; Revised November 09, 2013

Thermal energy storage is a distinguishing component of a concentrating solar power (CSP) system, which enables uninterrupted operation of plant during periods of cloudy or intermittent solar availability. Latent thermal energy storage (LTES) which utilizes phase change material (PCM) as a heat storage medium is attractive due to its high energy storage density and low capital cost. However, the low thermal conductivity of the PCM restricts its solidification rate, leading to inefficient heat transfer between the PCM and the heat transfer fluid which carries thermal energy to the power block. To address this limitation, LTES embedded with heat pipes and PCM's stored within the framework of porous metal foam that have one to two orders of magnitude higher thermal conductivity than the PCM are considered in the present study. A transient, computational analysis of the metal foam enhanced LTES system with embedded heat pipes is performed to investigate the enhancement in the thermal performance of the system for different arrangements of heat pipes and design parameters of metal foam, during both charging and discharging operation.

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Figures

Grahic Jump Location
Fig. 1

(a) Schematic illustration of metal foam enhanced LTES with embedded heat pipes, (b) unit cell used in the numerical analysis, (c) 2 horizontal heat pipe arrangement, and (d) 2 vertical heat pipe arrangement

Grahic Jump Location
Fig. 2

Contours of PCM melt volume fraction (dark-gray area denotes solid PCM) and streamlines of flow within the molten PCM at time instant of 6 h during charging for LTES with (a) NHP, (b) NHP-MF of pore density 10 PPI and porosity 0.85, (c) NHP-MF of pore density 10 PPI and porosity 0.95, (d) 2HHP-MF of pore density 10 PPI and porosity 0.9, (e) 2HHP-MF of pore density 40 PPI and porosity 0.9, and (f) 2VHP-MF of pore density 10 PPI and porosity 0.9, for HTF flow velocity of 0.00161 m/s.

Grahic Jump Location
Fig. 3

Effect of the arrangement of heat pipes, pore density and porosity of metal foams on the energy charged as a function of time for HTF flow velocities of (a, c, e) Uin = 0.00161 m/s and (b, d, f) Uin = 0.00322 m/s. NMF refers to LTES with no metal foam

Grahic Jump Location
Fig. 4

Contours of PCM melt volume fraction (dark-gray area denotes solid PCM) at time instant of 3 h during discharging for LTES with metal foam of pore density 10 PPI and porosity 0.95 embedded with (a) NHP-MF, (b) 2HHP-MF, and (c) 2VHP-MF for HTF flow velocity of 0.00161 m/s. Variation of surface heat transfer coefficient around the tube circumference for (d) 2HHP and (e) 2VHP arrangement at time instant of 3 h. The inset plots show the streamlines of the HTF flow pattern and contours of HTF temperature

Grahic Jump Location
Fig. 5

Effect of the pore density and porosity of metal foams on the energy discharged as a function of time for HTF flow velocity of 0.00322 m/s for (a) NHP, (b) 2HHP, and (c) 2VHP. NMF refers to LTES with no metal foam

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