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TECHNICAL PAPERS

Natural Convection from a Horizontal Tube Heat Exchanger Immersed in a Tilted Enclosure

[+] Author and Article Information
Wei Liu, Jane H. Davidson, F. A. Kulacki, Susan C. Mantell

Department of Mechanical Engineering, University of Minnesota, 111 Church St. S.E., Minneapolis, MN 55455

J. Sol. Energy Eng 125(1), 67-75 (Jan 27, 2003) (9 pages) doi:10.1115/1.1531146 History: Received January 01, 2002; Revised April 01, 2002; Online January 27, 2003
Copyright © 2003 by ASME
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References

Figures

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Proposed integral collector storage solar water heater with an immersed heat exchanger
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Flow in the collector is envisioned as the interaction of small-scale negatively buoyant plumes developed in the heat exchanger boundary layer and a large-scale circulating flow in the core of the storage fluid
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a) Drawing of the enclosure and immersed tube: thermocouples are indicated by solid circles and identified by numbers, dimensions are shown in cm, dimensions for the enclosure are inside dimensions; b) Drawing of the immersed tube that shows the location of the tube within the enclosure and placement of thermocouples along the tube wall: dimensions are in cm; c) Expanded drawing that shows the locations of the thermocouples Nos. 19–25 that measure water temperatures near the tube in the mid y-z plane (x=0), thermocouples Nos. 26 and 27 are located in the tube wall: Dimensions are in cm.
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Water temperatures in the enclosure during discharge in experiment No. 2. Cooling proceeds generally uniformly over the entire enclosure with less than 3.2°C variation over all measurement locations.
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Water temperatures in the top portion of the enclosure over a 30-min interval during experiment No. 2. The points labeled “Enclosure” are the average of the seven thermocouples at x=0,y=5.1 cm, and 25.4 cm≤z≤87.6 cm. These data indicate a cold plume is formed in the boundary layer of the tube.
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Water temperature distributions along the horizontal line in the mid y-z plane (x=0) over a 30-min interval in experiment No. 2. These data indicate that cold water sinking from the tube flows along the rear surface of the enclosure.
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Hourly water temperature distributions in the enclosure during charging in experiment No. 13. The initial state indicated at ‘0 hr’ is isothermal. As energy is added to the enclosure, the storage fluid becomes increasingly stratified.
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Hourly water temperature distributions in discharging experiment No. 4. The mixing in the enclosure decreases stratification as energy is removed.
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Hourly water temperature distributions in discharging experiment No. 5. The initially stratified enclosure is nearly isothermal after 1 hr.
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Water temperatures near the tube over a 30-min interval in the charge/discharge experiment No. 9. Water in the vicinity of the tube becomes stratified very quickly when a heat flux is applied, even with discharging.
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Water temperature distributions in the mid y-z plane (x=0) in the charge/discharge experiment No. 12.
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Nusselt and Rayleigh number data for experiments Nos. 1–12. The dashed lines show the ±15% band of the correlation. Correlations developed by Churchill and Chu 5, Lienhard 6 and Morgan 4 for a horizontal tube in an infinite medium are shown for comparison.

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