Evacuated Tube Applications

The mother load of evacuated tubes are now manufactured in China. They have become popular because of the high temperatures they produce made possible by  vacuum that separates the outer shell of the tube from the inner shell where sunlight is transformed into heat. Although the heat gain associated with evacuated tubes is less than the heat gain of flat-plate collectors the heat loss is minimized by the vacuum. Heat transfer takes place through a selective coating on the glass that's attached to a conductive material that's attached to a copper heat pipe. A low boiling point liquid such as acetone boils when heated. As the vapor from this low boiling point liquid travels up the heat pipe heat is lost through the bulb and transferred into the domestic hot water heat exchange system through a water/glycol heat transfer liquid that's circulated over the heat exchange bulb. The cooled Acetone then drops to the bottom of the heat pipe where the cycle begins again.

Even though individual evacuated tubes are capable of getting quite hot many are needed to supply sufficient heat for a DHW system and many more are needed to supply heat to a home heating system. The evacuated tube system on the left uses 50 tubes to gather enough heat for a solar heated domestic hot water system.

Light glancing off the curved outer shell of the tube does not contribute to the tube that reflects the light BUT adjacent tubes receive much of this reflected light and additional radiant energy is made available from a reflective plate under the tubes.

I wonder how much heat energy a single tube could handle if it were placed at the focal line of a concentrator???

Let's explore this idea with the help of a simple V concentrator and later build a parabolic or hyper-parabolic trough...








This V trough concentrator is made from a few cardboard boxes glued together and covered with aluminum foil. It's 4' long and has a window 16" across. This means that the surface area that intersects the sun is about 6 sq ft. 

Of course a V concentrator lined with aluminum foil will not concentrate as much light as a hyperbolic trough made from highly polished stainless steel, but it's a start and I am assuming that the V trough will make more light available than a tube without a concentrator.

AND if steam can be generated with this simple low budget project steam power could be generated with a more professional concentrator and the right kind of engine. We know evacuated tubes get hot. Can we use this tube to boil water directly, produce steam and generate power.








On a sunny day the heat collected and transferred through the wet polyester felt is actually much better than expected. I got lucky with such a day on January 22, 2011 when the outside temperature was only 30*F. Here is temperature data I was able to collect from inside the evacuated tube on this day.

 

Sound Tracks

Evacuated_Tube 1
Evacuated_Tube 2

Evacuated_Tube 3

 







The Ambient temperature on January 22 was 30*F. The sky was mostly clear with a few clouds. At first I thought the steady rise in temperature stopped because of clouds, but then I realized that the pocket of water at the bottom of the evacuated tube were going through a transition phase from a liquid to a gas. After all the liquid water became a gas the temperature of the remaining steam continued to climb until 1:05 when the test was terminated.

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Collector Efficiency

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HEAT EXPERIMENTS
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Evacuated Tube Introduction

Evacuated Tube Steam

Modular Heat Storage

GENERAL INFORMATION
What is Energy ?
 

Our Big Sun

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Oil Alternative for a Solar Age

Green Solar Recycling

Green Machine
Green Train

A Green Energy Workshop

about JC


Sun 4 Earth

Oil Alternative Articles

Collector Efficiency

Energy Alternatives 

Green Collar Work

Photovoltaic Discoveries

HEAT EXPERIMENTS
Brick Test

Jug Test

Evacuated Tube Introduction

Evacuated Tube Steam

Modular Heat Storage

GENERAL INFORMATION
What is Energy ?
 

Our Big Sun

Origin of Time

Oil Alternative for a Solar Age

Green Solar Recycling

Green Machine
Green Train

A Green Energy Workshop

about JC

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