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Research Papers

Liquid Calcium Chloride Solar Storage: Concept and Analysis

[+] Author and Article Information
Josh A. Quinnell, Jane H. Davidson

 University of Minnesota, Minneapolis, MN 55455quinnell@me.umn.edu

Jay Burch

 National Renewable Energy Laboratory, Golden, CO 80401-3305jay_burch@nrel.gov

The units of kWh/m3 are selected to be consistent with those used in the International Energy Agency Task 32 to compare energy densities of storage materials and systems (2).

J. Sol. Energy Eng 133(1), 011010 (Feb 03, 2011) (8 pages) doi:10.1115/1.4003292 History: Received April 09, 2010; Revised December 14, 2010; Published February 03, 2011; Online February 03, 2011

Aqueous calcium chloride has a number of potential advantages as a compact and long-term solar storage medium compared with sensibly heated water. The combination of sensible and chemical binding energy of the liquid desiccant provides higher energy densities and lower thermal losses, as well as a temperature lift during discharge via an absorption heat pump. Calcium chloride is an excellent choice among desiccant materials because it is relatively inexpensive, nontoxic, and environmentally safe. This paper provides an overview of its application for solar storage and presents a novel concept for storing the liquid desiccant in a single storage vessel. The storage system uses an internal heat exchanger to add and discharge thermal energy and to help manage the mass, momentum, and energy transfer in the tank. The feasibility of the proposed concept is demonstrated via a computational fluid dynamic study of heat and mass transfer in the system over a range of Rayleigh, Lewis, Prandtl, and buoyancy ratio numbers expected in practice.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 3

Conceptual sketch of a solar heating system with sensible and absorption energy storage: (a) collector loop (charge) and (b) load loop (discharge)

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Figure 4

The density of CaCl2–H2O solution as a function of S at 296 K and 356 K (12)

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Figure 1

The heat of dilution of CaCl2 as a function of the solute mass fraction at 298 K and 356 K (12)

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Figure 2

Material energy storage density as a function of ΔS; ΔT=60 K. λCaCl2 (—), λLiCl (–), and λH2O(-∙-)

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Figure 10

Transient Sh for cases 2–5: 3×105<Ra<3×108, N=131, Pr=3.3, and Le=158

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Figure 11

Transient Sh for cases 2, 6–8: Ra=3×108, 13<N<131, Pr=3.3, and Le=158

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Figure 5

(a) Novel concept to manage temperature and mass fraction distribution in a liquid desiccant storage tank during charge and discharge (shown in the charge configuration) and (b) cross-sectional view (without manifold) indicating convection cells as the tank is heated

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Figure 6

Convection develops (a) from the boundary layers, (b) to form quasi-steady convection cells, (c) which merge when there is no longer a density gradient between them.

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Figure 7

Computational domain for (a) case 1 and (b) cases 2–8

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Figure 8

Dimensionless velocity magnitude, temperature, and mass fraction contours for case 2 with Ra=3×108, N=131, Pr=3.3, and Le=158 at (a) τ=0, (b) τ=9.8×10−5, (c) τ=3.1×10−3, (d) τ=7.4×10−3, and (e) τ=1.5×10−2

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Figure 9

Shear layer velocity profiles throughout heating for case 2: Ra=3×108, N=131, Pr=3.3, and Le=158

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