The Waste of Heat

Typography
No system is 100% effective. There is always some energy wasted. One of the more common examples is the automobile engine which gets quite hot. Some of the waste is recovered by heating the car for example. With the completion of a successful prototype, engineers at Oregon State University have made a major step toward addressing one of the leading problems in energy use around the world today – the waste of half or more of the energy produced by cars, factories and power plants. New technology is being developed at the university to capture and use the low-to-medium grade waste heat that’s now going out the exhaust pipe of millions of automobiles, diesel generators, or being wasted by factories and electrical utilities. The new systems now being perfected at the university should be able to use much of that waste heat either in cooling or the production of electricity.

No system is 100% effective. There is always some energy wasted. One of the more common examples is the automobile engine which gets quite hot. Some of the waste is recovered by heating the car for example. With the completion of a successful prototype, engineers at Oregon State University have made a major step toward addressing one of the leading problems in energy use around the world today – the waste of half or more of the energy produced by cars, factories and power plants. New technology is being developed at the university to capture and use the low-to-medium grade waste heat that’s now going out the exhaust pipe of millions of automobiles, diesel generators, or being wasted by factories and electrical utilities. The new systems now being perfected at the university should be able to use much of that waste heat either in cooling or the production of electricity.

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Waste heat sometimes called secondary heat or low-grade heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found. Energy is often produced by a heat engine, running on a source of high-temperature heat. A heat engine can never have perfect efficiency, according to the second law of thermodynamics, waste heat is regarded as a waste by-product of this process.More than half of the heat generated by industrial activities is now wasted and even very advanced electrical power plants only convert about 40 percent of the energy produced into electricity. For example it is common practice to estimate in engineering that only 70% of the usable fuel energy is applied to the industrial engine.  The internal combustion engines of automobiles are even worse – they generally operate around 25-40 percent conversion efficiency. The very function of an automobile radiator is to dissipate wasted heat.Various approaches have been attempted, and are sometimes used, to capture and use at least some of that waste heat to produce cooling.

The new system being developed at OSU may do that as, or more efficiently than past approaches, be more portable, and also have one major advantage – the ability to also produce electricity.It’s called a thermally activated cooling system that gains much of its efficiency by using extraordinarily small microchannels which help to better meet the performance, size and weight challenges. It effectively combines a vapor compression cycle with an organic Rankine cycle.  The Rankine cycle is a cycle that converts heat into work.

The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 80% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants.The new prototype completed at OSU succeeded in turning 80 percent of every kilowatt of waste heat into a kilowatt of cooling capability. Researchers say the conversion efficiency would not be nearly as high if the goal is to produce electricity – about 15-20 percent – but it’s still much better than the current approach, which is to waste the energy potential of all of the heat.

However, the OSU scientists said that may be just the beginning. Factories often produce enormous amounts of wasted heat in their operations. The systems could also be incorporated into alternative energy technologies such as solar or geothermal, scientists say, in addition to fossil fuel use.Conceptually, it should also be possible for such systems to be used in hybrid automotive technology, taking waste heat from the gasoline engine and using it not only for air conditioning but also to help recharge the battery that powers the vehicle.

 "There continues to be significant potential for reducing energy consumption and greenhouse gas emission by improving overall energy efficiency for various energy systems.  One route toward satisfying both paths is to develop technology able to recover waste heat that would be otherwise rejected to the atmosphere without usage."  the scientists said in their study. 

The study this story is based on is available in ScholarsArchive@OSU: http://bit.ly/ljOJZh

For further information:    http://oregonstate.edu/ua/ncs/archives/2011/jun/prototype-demonstrates-success-advanced-new-energy-technology

Photo:   http://farm3.static.flickr.com/2466/3740036450_9bf9e41504_z.jpg