Design Article
Turning waste heat into electrical energy
Josh Moczygemba, Marlow Industries
9/18/2012 10:29 AM EDT
Test setup
Figure 1 shows a photograph of a 10-inch diameter EverGen PowerStrap. The unit was designed for outdoor use, 120°C operation in a vertical orientation for an industrial exhaust pipe. Twelve identical TEG and heat sink assembly sections were spaced evenly around the perimeter of the strap base. Each thermoelectric generator module was held in compression between the heat sink and the strap base with two stainless steel bolts fitted with insulating phenolic washers. Thermal pads on both sides of the TEG were used to improve thermal resistance at the hot (strap) and cold (heat sink) interfaces. The clamping strap base was divided into three identical sections that form a compression fit around the pipe when bolted together. A series of lab tests were conducted with this design that mimicked varying operating conditions throughout the year. The test assembly was made from a section of 10” diameter steel pipe that was capped at one end and filled with oil. Submersible heaters, attached to an electronic temperature controller, were used to control test assembly wall temperature. The PowerStrap was clamped to the exterior of the test assembly, with non-setting thermal mastic applied between the pipe wall and the strap base to aid in heat transfer. During testing, ambient temperature around the test assembly was altered to reflect seasonal changes.
Both natural convection and forced convection up to 6.5 mph were studied. Omega OM-420 data acquisition equipment was used to collect temperature, voltage and current measurements during testing. Figure 4 is an expanded view sketch that depicts thermocouple placement on the test assembly. Readings were collected and recorded in two second intervals.
Test results
The results of this testing, compared against model predictions, are shown in Figure 5 for two different pipe temperatures covering a wide range in ambient conditions. From the data, it is obvious that the EverGen PowerStrap performance is maximized when ambient temperatures are the coldest. This is to be expected since thermoelectric efficiency is greater for larger temperature differentials. In real world operation, this means that the PowerStrap performance will be maximized during the colder months of the year. Such performance makes this product a natural complement to solar cells, which usually perform poorly during the winter months. Another key point is that there is significant performance increase, by as much as 40 percent, when typical outdoor wind conditions are accounted for. For applications requiring higher power levels, multiple units can be employed. The data also shows that the model predictions close well with experimental data. By expanding the model to include different pipe temperatures and diameters, performance under different operating scenarios can be predicted.
About the author:
Josh Moczygemba is Power Generation Product Engineering Manager at Marlow Industries - www.marlow.com
See related links:
Energy harvesting from thermoelectric sources gets a boost
Green power to the people everywhere
Power-management functions for energy harvesting
Energy harvesting module suits thermoelectric, vibrational, photovoltaic sources
Ambient energy stands ready to serve
Courtesy of EETimes Europe
------------------------
If you found this article to be of interest, visit SmartEnergy Designline where you will find the latest and greatest design, technology, product, and news articles with regard to all aspects of clean technologies. And, to register to our weekly newsletter, click here.
Figure 1 shows a photograph of a 10-inch diameter EverGen PowerStrap. The unit was designed for outdoor use, 120°C operation in a vertical orientation for an industrial exhaust pipe. Twelve identical TEG and heat sink assembly sections were spaced evenly around the perimeter of the strap base. Each thermoelectric generator module was held in compression between the heat sink and the strap base with two stainless steel bolts fitted with insulating phenolic washers. Thermal pads on both sides of the TEG were used to improve thermal resistance at the hot (strap) and cold (heat sink) interfaces. The clamping strap base was divided into three identical sections that form a compression fit around the pipe when bolted together. A series of lab tests were conducted with this design that mimicked varying operating conditions throughout the year. The test assembly was made from a section of 10” diameter steel pipe that was capped at one end and filled with oil. Submersible heaters, attached to an electronic temperature controller, were used to control test assembly wall temperature. The PowerStrap was clamped to the exterior of the test assembly, with non-setting thermal mastic applied between the pipe wall and the strap base to aid in heat transfer. During testing, ambient temperature around the test assembly was altered to reflect seasonal changes.
Both natural convection and forced convection up to 6.5 mph were studied. Omega OM-420 data acquisition equipment was used to collect temperature, voltage and current measurements during testing. Figure 4 is an expanded view sketch that depicts thermocouple placement on the test assembly. Readings were collected and recorded in two second intervals.
Figure 4: Expanded view sketch of the thermocouple placement on the test assembly.
Test results
The results of this testing, compared against model predictions, are shown in Figure 5 for two different pipe temperatures covering a wide range in ambient conditions. From the data, it is obvious that the EverGen PowerStrap performance is maximized when ambient temperatures are the coldest. This is to be expected since thermoelectric efficiency is greater for larger temperature differentials. In real world operation, this means that the PowerStrap performance will be maximized during the colder months of the year. Such performance makes this product a natural complement to solar cells, which usually perform poorly during the winter months. Another key point is that there is significant performance increase, by as much as 40 percent, when typical outdoor wind conditions are accounted for. For applications requiring higher power levels, multiple units can be employed. The data also shows that the model predictions close well with experimental data. By expanding the model to include different pipe temperatures and diameters, performance under different operating scenarios can be predicted.
Figure 5: The EverGen PowerStrap test results.
About the author:
Josh Moczygemba is Power Generation Product Engineering Manager at Marlow Industries - www.marlow.com
See related links:
Energy harvesting from thermoelectric sources gets a boost
Green power to the people everywhere
Power-management functions for energy harvesting
Energy harvesting module suits thermoelectric, vibrational, photovoltaic sources
Ambient energy stands ready to serve
Courtesy of EETimes Europe
------------------------
If you found this article to be of interest, visit SmartEnergy Designline where you will find the latest and greatest design, technology, product, and news articles with regard to all aspects of clean technologies. And, to register to our weekly newsletter, click here.
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Brakeshoe
9/20/2012 11:14 AM EDT
FALSE:
Electrical efficiency η ≠ R(load)/R(source ("TEG"))
η = R(load)/[R(load) + R(source)]
It's unbelieveable such a fundamental error could make it past the editors and be published in EETimes: A cursory glance would show that if the source resistance is less than or equal the load resistance, the efficiency η would be ≥1.0
Dan Schwartz
Editor, The Hearing Blog
http://www.TheHearingBlog.com
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Brakeshoe
9/20/2012 11:24 AM EDT
For the record, when the source resistance is zero, the efficiency η is 100%; while when in maximum power transfer conditions, the source resistance = the load resistance, the efficiency η = 50% i.e. the voltage drop and hence the i²R power dissipation is equal across the source and load.
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DaveR1234
9/26/2012 5:46 AM EDT
Bill Schweber would have caught this. Where is he?
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Brakeshoe
9/26/2012 9:29 AM EDT
I posted this six days ago; and it's been nothing but crickets chirping.
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I_B_GREEN
9/27/2012 11:11 AM EDT
Also this must use true waste heat as a source.
if not then increasing thermal conductivity will lower the mother ships efficiency. This would negate any power produced by the parasitc system running of the exaust heat.
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DadOf3TeenieBoppers
9/28/2012 9:12 AM EDT
This is great for legacy systems, but given the cost of energy, it is a poorly planned new design that could effectively utilize this technology.
Real energy savings can be had with heat pump water heaters (cool the house, create hot water simultaneously), or the University of Michigan using the Great Lakes for a heat sink and cutting their air conditioning bills by about $500K per month.
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PlumbArena for Heating & Plumbing
2/25/2013 6:42 AM EST
Solar electric energy is electric power generation from sunlight. It could be direct to PV - Photovoltaic, or it could be indirect. An instance of the indirect type is concentration of solar power, where the energy of the sun is concentrated to boil water used to generate power.
http://www.plumbarena.co.uk
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