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Research Papers

Numerical Analysis of Thermal Stratification in Large Horizontal Thermal Energy Storage Tanks

[+] Author and Article Information
Maikel Shaarawy

Department of Mechanical Engineering,
McMaster University,
Hamilton, ON L8S 4L8, Canada
e-mail: shaaramm@mcmaster.ca

Marilyn Lightstone

Professor and Chair
Department of Mechanical Engineering,
McMaster University,
Hamilton, ON L8S 4L8, Canada
e-mail: lightsm@mcmaster.ca

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received April 17, 2015; final manuscript received October 27, 2015; published online February 5, 2016. Assoc. Editor: Jorge E. Gonzalez.

J. Sol. Energy Eng 138(2), 021009 (Feb 05, 2016) (13 pages) Paper No: SOL-15-1098; doi: 10.1115/1.4032451 History: Received April 17, 2015; Revised October 27, 2015

This paper presents the results of a numerical study on the thermal performance of large horizontal thermal energy storage tanks. The numerical model was validated using measurements obtained from Drake Landing Solar Community (DLSC), which is located in Alberta, Canada. A total of seven different baffle configurations were assessed for a range of operating conditions. Characterization of the tank performance was done by monitoring the tank outlet temperature and computing the Huhn efficiency, which is a characterization index based on the second law of thermodynamics. Results show that the current tanks at DLSC experience excessive mixing due to fluid entrainment from the inlet jet. A newly introduced design that confines the inlet jet mixing shows the potential to enhance the level of stratification during charging or discharging at a constant temperature. In addition, most designs tested have a relatively high level of stratification during charging, discharging, and simultaneous charging and discharging, but fail to sustain the level of stratification when a positive buoyant jet is introduced.

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References

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Figures

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Fig. 1

Simplified illustration of the current system in use at DLSC [2]

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Fig. 2

Transient profile of inlet temperature (a) and velocity (b)during charging (data for Oct. 23, 2007)

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Fig. 3

Location of temperature sensors in STTS tanks at DLSC (not to scale)

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Fig. 4

Transient simulated and actual temperature at the top (a), middle (b), and bottom (c) sensor of the hot tank showing the predictions using the SST and k−ω turbulence models

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Fig. 5

Existing and alternative designs investigated (not to scale). Note: the direction of the arrows depicts the flow direction during discharging.

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Fig. 6

Temperature contour plot of seven different designs 15 min (a) and 3.5 hrs (b) into simulation of case 1

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Fig. 7

Transient temperature of fluid leaving the top of the tank (a) and Huhn efficiency (b) for seven different designs during simulation of case 1

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Fig. 8

Transient temperature of (a) base tank and (b) vertical inlet tank during simulation of case 1

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Fig. 9

Temperature contour plot of six different designs 5 min (a) and 2 hrs (b) into simulation of case 3

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Fig. 10

Transient top (a) and bottom (b) outlet temperatures and Huhn efficiency (c) for six different designs during simulation of case 3

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Fig. 11

Temperature contour plot of six different designs 15 min (a), 1 hr (b), and 5 hrs (c) into simulation of case 4

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Fig. 12

Transient temperature of fluid leaving top (a) and bottom (b) of the tank and Huhn efficiency (c) for six different designs during simulation of case 4

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Fig. 13

Transient temperature of (a) base tank and (b) vertical inlet tank during simulation of case 4

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