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

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Transcript of Evacuated Tube Solar Collectors - TabSynth Design Works · Liquid inside the tube begins to boil....

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 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.

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 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>.

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