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Research Papers

# Experimental and Numerical Study of Mixing in a Hot-Water Storage Tank

[+] Author and Article Information
A. Aviv, Y. Blyakhman, O. Beeri, G. Ziskind, R. Letan

Heat Transfer Laboratory, Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

J. Sol. Energy Eng 131(1), 011011 (Jan 08, 2009) (8 pages) doi:10.1115/1.3028043 History: Received June 29, 2007; Revised December 11, 2007; Published January 08, 2009

## Abstract

Thermal mixing and stratification are explored numerically and experimentally in a cylindrical tank, which simulates a storage of water heated by a solar collector. The tank is $70cm$ in height and $24cm$ in diameter. The inlet and outlet are vertical and located off the centerline of the tank. The study is conducted in a transient mode, namely, the tank is filled with hot water, and as the hot water is being withdrawn, the tap water replaces it in a stratified way or by mixing. The flowrates of $2l∕min$, $3l∕min$, $5l∕min$ and $7l∕min$, which correspond to superficial velocities of $4.35cm∕min$, $6.52cm∕min$, $10.87cm∕min$, and $15.2cm∕min$, are explored. Temperature of hot water ranges within $40–50°C$, while the tap water is about $25–27°C$. Installation of one and two horizontal baffles above the inlet is examined. Simultaneous experimental and numerical investigations are performed. In the experiment, both flow visualization and temperature measurements are used. Three-dimensional transient numerical simulations are done using the FLUENT 6 software. Validation of the numerical model is achieved by comparison with the experimental results. Then, the numerical model is applied to a study of various possible changes in the system. The results show that at low flowrates, up to a superficial velocity of about $11cm∕min$ through the tank, the baffles have no effect on tap water mixing with the stored hot water. At higher flowrates, a single horizontal baffle prevents the mixing and preserves the desired stratified temperature distribution in the storage tank.

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## Figures

Figure 1

Experimental setup: (a) overall view, (b) the tank and the baffle, and (c) schematics

Figure 2

Validation of the numerical model versus experiments reported in literature: (a) Zachár (4) and (b) Lavan and Thompson (2)

Figure 3

Visualization for the flowrate of 2l∕min, without and with a baffle

Figure 4

Visualization for the flowrate of 7l∕min, without and with a baffle

Figure 5

Comparison of the visualized and simulated patterns for the flowrate of 5l∕min: (a) without a baffle and (b) with a baffle

Figure 6

Measured and simulated outlet water temperature for various flowrates (8): (a) without a baffle and (b) with a baffle

Figure 7

Effect of baffles: (a) simulated outlet water temperature and (b) simulated temperature distributions at same instants

Figure 8

Effect of temperature difference: (a) simulated outlet water temperature and (b) temperature field evolution for ΔT=10°C

Figure 9

Effect of baffle parameters: (a) baffle size and (b) baffle installation height

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