Evacuated Tube Solar Collectors - TabSynth Design Works Liquid inside the tube begins to boil. 3. Water

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  • http://antwrp.gsfc.nasa.gov/apod /image/0511/sunflame_soho.jpg

  • Research Objective:  Test out evacuated tube s solar

    collectors to learn:  How they work  How their efficiencies can be

    improved  Why they should be used for

    heating water.

    http://www.eliotsolar.com/heat_tube.jpghttp://www.spec-net.com.au/press/0906/images/elc270906_img01.jpg

  • What is an Evacuated Tube Solar Collector (ETC)? •A type of solar collector mainly used for heating water. •Distinguished by their cylindrical design. •Used in arrays of 10 to 30 tubes.

  • Components of ETC:

    Evacuated Tube Absorbing Layer Copper Heating Rod Heating Rod Exterior Tip Interior Liquid Support Clips

    http://www.apricus.com.au/images/tube.gif

  • How do ETC work? 1. The sun’s radiating heat is

    absorbed by the collector . 2. Liquid inside the tube begins

    to boil. 3. Water vapor is distributed

    throughout the interior of the tube.

    4. By means of convection, the copper rod is heated.

    5. Hot water vapor accumulates at the top of the tube and then drips to the bottom.

    6. Heating rod tip transfers heat through conduction to flowing water in manifold.

    http://www.hillssolar.com.au/arbitrage/pages/79/evac_tube_500.jpg

  • Constructing the Calorimeter: Constructed out of 2 inch PVC pipe. Had a hollow copper tube for inserting the heating rod’s tip. Was insulated with foam insulator Contained 3 thermocouples to measure specific temperatures.

  • Position of Thermocouple Wires:

    Steel Wool

    Water

    Top View Side View

    ETC

    Hollow copper tube

  • Precision Solar Pyranometer (PSP): Is a device used for measuring solar radiation. Measures in mV but is converted to W/m^2 using calibration number.

    http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Pyranometer_sr11_hukseflux.gif/400px-Pyranometer_sr11_hukseflux.gif

  • Single Tube Data Collection: Single tube was placed on a vertical mount during experimentation. Data was recorded every minute. Data was collected throughout 2 hour periods or until water in calorimeter reached boiling point. PSP was placed on above the solar collector .

  • Analysis:  Excel was used for recording the

    data and preliminary calculations.  ESS is an equation solving

    program that can solve simultaneous equations using interpolations and parametric tables.

    Thermodynamic Energy Balance and Equations:

    Solar Collector Heat Loss Eq.

    Beckman, William A., and John A. Duffie. Solar Engineering of Thermal Processes. Maryland: American Association of Physics Teachers, 1985.

  • Single Tube Array Results:

    0 1000 2000 3000 4000 5000 6000 10

    15

    20

    25

    30

    35

    Time [sec]

    W [W

    at ts

    ]

    Power Over Time

     Wdot d(Time) = 137323

  • Single Tube Array Results:

    0 0.05 0.1 0.15

    0.3

    0.4

    0.5

    Xdir [(C*m^2)/W]

    Ef fic

    ie nc

    y

    Efficiency Curve

    Efficiency=0.423604 - 0.460323·XdirEfficiency=0.423604 - 0.460323·Xdir

  • 20 Tube Array Components  Cooling/Heating Station.  Battery powered steering

    mechanism.  Tracking Mount

    (Elevation/Azimuth)

  • Tracking The Sun:

    Heating/Cooling Station Steering Mechanism

    Tracking Mount

    ETC Array

    Tracking The Sun:

  • 20Tube Array Testing Array was inclined to 53 degrees for maximum amount of solar irradiance. Sun was tracked using the azimuth directions on the array mount. Water was heated before entering the array for proper testing specifications. Measurements of mass flow were taken when steady state was reached.

  • 20 Tube Array Results:

    0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.39

    0.4

    0.41

    0.42

    0.43

    0.44

    0.45

    0.46

    0.47

    0.48

    Xdir [(C*m 2)/W]

    Ef fic

    ie nc

    y [-

    ]

    Efficiency=0.487717 - 1.62365·XdirEfficiency=0.487717 - 1.62365·Xdir

    Efficiency Curve

  • 20 Tube Array Averaged Results:

    0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.39

    0.4

    0.41

    0.42

    0.43

    0.44

    0.45

    0.46

    0.47

    0.48

    X [(C*m2)/W]

    Ef f [

    Ef fic

    ie nc

    y C

    or re

    ct io

    n]

    Eff=0.487861 - 1.62892·XEff=0.487861 - 1.62892·X

    Efficiency Curve

  • SRCC Ratings:

    Solar Ratings and Certification Corporation.2008. Solar Ratings and Certification Corporation. 20 Jul. 2008.< http://www.adobe.com/products/acrobat/readstep2.html>.

  • Experimental Results vs. SRCC: Experimental Result SRCC Ratings  Efficiency Curve:

     Intercept = 0.488  Slope = -1.624

     Efficiency Curve:  Intercept = 0.345  Slope = -1.153

  • Solar Irradiance During Testing:

    0 5 10 15 20 25 30 35 40 45 890

    900

    910

    920

    930

    940

    950

    960

    970

    Point [-]

    S [W

    /m 2 ]

  • Conclusion: Results obtained from mainly sunny days compared reasonably well to the actual SRCC ratings for this type of evacuated solar collector. ETV offer efficient ways to heat up water that ultimately pay for themselves.

    http://www.sciencedaily.com/images/2007/10/071030105347-large.jpg

  • Future Work:

     Further testing on tube/array efficiencies.

     Find other uses to heating fluids with ETC’s other than conventional ones.

     Use ETC area as a cylinder instead of plate.

    http://flickr.com/photos/wuerzi/303621860/

  • References: Photos and Models: http://antwrp.gsfc.nasa.gov/apod/image/0511/sunflame_soho.jpg http://www.eliotsolar.com/heat_tube.jpg http://www.spec-net.com.au/press/0906/images/elc270906_img01.jpg http://www.apricus.com.au/images/tube.gif http://www.hillssolar.com.au/arbitrage/pages/79/evac_tube_500.jpg http://www.sciencedaily.com/images/2007/10/071030105347-large.jpg

    Other References: Beckman, William A., and John A. Duffie. Solar Engineering of Thermal Processes. Maryland: American Association of Physics Teachers, 1985. Solar Ratings and Certification Corporation.2008. Solar Ratings and Certification Corporation. 20 Jul. 2008.< http://www.adobe.com/products/acrobat/readstep2. html>.

  • Acknowledgements:  Prof. Sanford Klein  Prof. Thomas Kaminski  Prof. Greg Nellis  Kelly Burton  Don Gilbertson  Mike Wagner

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