Waste low grade heat
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To drive any heat engine, you need a temperature difference. Usually the hot end vaporises a liquid increasing it's volume, and the cold end condenses it again. However, the laws of thermodynamics are very clear. The greater the temperature difference, the more energy can be converted. A low temperature difference will have a very low efficiency and very little of the heat can be used to make electricity, movement, etc. |
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The Carnot Theorum give the formula: Maximum efficiency = 1- T cold/T hot. Temperature of hot and cold sides are expressed in degrees Kelvin. In practice the efficiencies in industry is usually about half the theoretical. For a power station producing steam at 650 deg C, the maximum theoretical efficiency is 66%. The average around the world is 31%. With more expensive materials the steam can be heated more and the efficiency can reach 43%. |
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Sources of low grade heat are: Ocean thermal Geothermal Waste heat can be recovered in the following: Recovered Waste Heat (RWH), in the following industries: |
Source Granex |