Water works

Motivated by a burning desire to improve the lives of the world’s poorest people, Cambridge University engineer Dr Tom Smith has reinvented a 200-year-old technology that could both irrigate crops in the developing world and lead to new energy-saving heating systems here in the West.

An enthusiastic young researcher driven by a healthy combination of idealism and commercial nous, Smith believes that low-cost heat-powered engines using expanding and contracting gases or liquids in place of moving parts could be used to heat and pump fluids in a variety of applications. He hopes to tap in to the commercial potential of the idea through his spin-out company Thermofluidics.

Smith explained to The Engineer that his devices are like analogue electronic oscillators but built from fluid components. ‘We aim to build capacitors from tanks of liquid or compressible gases, resistors from throttling valves and inductors from long coils of liquid and we get amplification from temperature differences,’ he said.

Like many of engineering’s more esoteric devices, thermofluidic engines have been around for some time. One of the earliest devices to illustrate the principle was the flame organ, an 18th-century musical curiosity consisting of open-ended glass tubes with a burner at their bottom ends which, when ignited, produced an intense acoustic oscillation. Similar principles are embodied in the so-called ‘putt-putt toy’, a candle-powered toy boat that is popular with children in India.

But while inventions such as these have occasionally captured the imagination, their heavy dependence on the low inertia of the fluid to achieve a useful output has limited application of the principles beyond novelty items.

Smith’s big breakthrough has been the development of a machine that operates independently from the inertia of the operating fluid, meaning that it can sustain oscillation and give a much bigger pressure amplitude than earlier systems.

Over the past three years he has set about proving the science through the development of a system that uses heat as a power source to pump water into the roof of his base at Cambridge University’s Hopkinson laboratory. His experiments with this so-called Non-Inertive Feedback Thermofluidic Engine (NIFTE) have demonstrated that it could achieve bigger pressure amplitudes than the inertia-dependent oscillators from the past.

The small company is now working on developing applications for the technology in two priority areas: central-heating water circulation powered by waste heat and irrigation pumps for farmers in the developing world.

With domestic hot water circulation accounting for 10-15 per cent of domestic electricity consumption, Smith and his colleagues believe that the technology could be used in place of the pumps that circulate water around radiators and hot water tanks. Smith said that by using waste heat from exhaust/flue gases in fossil fuel-fired heating systems, or by tapping some heat from the combustion chamber, his device could perform the role of the circulator, dumping the waste heat in radiators.

The group’s currently working on the development of a lab-based system which they hope to match to the output of a pump on a domestic central heating boiler.

The other big application is the use of the technology to develop low-cost irrigation pumps for the developing world powered by heat from solar water collectors.

Most existing solar pumping systems are based on solar cells, which convert sunlight to electricity before it is converted to hydraulic work by an electric pump. However, as well as being fairly expensive, photovoltaic cells only operate efficiently over a small range of voltages and the current that they can deliver also increases or decreases according to the sunlight.

Smith claimed that solar-powered pumps based on NIFTE devices could be made from far cheaper off-the-shelf solar collectors. He said that he envisages a field of solar collectors feeding a pump that would pressurise water for drip irrigation systems or for use in gravity pumps. The group is currently, therefore, building a solar water pump that it hopes will match the output of a number of existing irrigation pumps.

But these are not the only potential applications. Indeed, the technology could ultimately be applied anywhere where heating and pumping are being done simultaneously, said Smith. ‘These oscillators are never going to be competitively efficient with electric pumps but they consume a power source that is otherwise wasted and much more readily available — wherever you’re heating a fluid and pumping it we can claim to be able to do both of those jobs.’ For instance, another possible developing world use of the pumps could be to provide a refrigerative effect for vaccine storage.

If the current experiments are successful Smith hopes to be able to take some test rigs out into the field within the next 12 months. But while he has already made some industrial contacts in priority areas, Smith told The Engineer that he is keen to keep a reasonably low profile for the moment.

For now he has just enough money to do what he needs to do courtesy of a £100,000 award from The Sunday Times, and is applying for a DTI research grant that should enable him to turn the technology into a proper product.

While he hopes to eventually tap into EU funding, he’s sensibly choosing to spend the bulk of his time on the R&D that will secure the company’s future. ‘The amount of time that it takes to write proposals often isn’t worth the amount of money that you get,’ he said.

While the longer-term commercial plan isn’t exactly set in stone, he said that it’s likely that Thermofluidics will grant worldwide exclusive licences to manufacturers and distributors in each application area, but not to grant one across all the applications, he said. ‘We want to maintain some control over the technology but allow our licensees to operate worldwide. We really want to concentrate our efforts on R&D and would rather invest our revenue into new projects rather than building up manufacturing plants ourselves.’

The manufacturing process itself is likely to be pretty straightforward. ‘In principle it can be produced entirely from extrusion and injection moulding — the heat exchanger components are fairly simple. We might hitch a ride on something like the back of the aluminium can industry using processes that are already very well established.

‘In general our aim is to make the thing as locally manufacturable as possible, so that it could be built largely from off-the-shelf components,’ said Smith.

Clearly, it’s early days for Smith’s fledgling company, but he is hopeful about his technology: ‘I’m very optimistic about the technology and its capabilities, but its success depends on the susceptibility of these markets to this sort of innovation.

For example, the electric pumps in domestic hot water circulators are still quite inefficient, but the extent to which consumers care depends on the cost of the units which isn’t very high as so many of them are produced,’ he said.

So success in the domestic market is likely to depend upon the extent to which consumers prioritise energy and water saving and this, said Smith, is driven by energy prices.

‘It’s certainly a topical subject — and everything does seem to be going in the right direction for us at the moment,’ he said. ‘But only the future will tell.’