Post on 03-Jul-2020
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 TubeAbsorbing LayerCopper Heating RodHeating Rod Exterior TipInterior LiquidSupport 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 insulatorContained 3 thermocouples to measure specific temperatures.
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 600010
15
20
25
30
35
Time [sec]
W [W
atts
]
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]
Effic
ienc
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 TestingArray 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 0.050.39
0.4
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
Xdir [(C*m2)/W]
Effic
ienc
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 0.050.39
0.4
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
X [(C*m2)/W]
Eff [
Effic
ienc
y C
orre
ctio
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 45890
900
910
920
930
940
950
960
970
Point [-]
S [W
/m2 ]
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.jpghttp://www.eliotsolar.com/heat_tube.jpghttp://www.spec-net.com.au/press/0906/images/elc270906_img01.jpghttp://www.apricus.com.au/images/tube.gifhttp://www.hillssolar.com.au/arbitrage/pages/79/evac_tube_500.jpghttp://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>.