Low grade heat conversion

Some forms of energy, such as electricity and high grade fuels, are intrinsically more valuable than others, such as heat at temperatures close to ambient. This is because all energy eventually ends up as ambient heat, but higher grade forms have the potential to do something useful along the way. Engineers quantify the usefulness of a given form of energy as its 'exergy'. Unlike energy, exergy is 'used up' in performing a given function. For example: when a 100W light bulb illuminates a room, 100W of electrical energy is converted into 100W of heat energy, whereas 100W of exergy is destroyed.

In order to become an energy efficient society, we must also become an 'exergy efficient' society: one which destroys as little exergy as possible in performing any given task. Here at CUED, we are working on a number of different machines known as low grade heat converters, which use heat at near ambient temperatures as an energy input.

With the majority of energy technologies, once basic functional performance criteria have been met, the engineer's role is to save fuel by improving efficiency. However, low grade heat converters rely on an energy source which would otherwise be wasted. Therefore, efficiency is only of secondary importance. Indeed, thermodynamics dictates that low grade heat converters will always be inefficient in comparison with technologies that use high grade fuels. Instead, it is the engineer's role to minimise costs. This relies on the use of low cost materials such as plastics and polymer foams, low cost production techniques such as injection moulding and extrusion, and a minimum number of precision moving parts.

We are working in collaboration with a recent spin-off company, Thermofluidics Ltd., to develop a low cost thermally powered pump, for a number of energy saving, water saving and humanitarian applications. These include solar powered water pumps, for sanitation and irrigation, and embedded pumps such as central heating water circulators which use waste heat as an energy source. To read more about this work, click here.

Doctor Thomas Smith

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Doctor Christos Markides

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Telephone: +44 1223 7 61503
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