Science Interviews

Interview

Sun, 9th Oct 2005

A Water Pump For The Developing World

Tom Smith from Cambridge University

Part of the show Stem Cells, Brain Repair and Tricks of the Light

Chris - So what's your pump all about?

Tom - What I've invented is a pump without any moving parts. It uses heat rather than electricity as a power source. Most existing pump use electricity and have moving pistons to move the water along. My pump expands and contracts fluids by heating and cooling them, and this provides a movement of fluids which can be used to pump water. What distinguishes it form other pumps without moving parts is that it can use heat from sources at very low temperatures, for example, waste heat or heat from the sun. It could be useful for pumping water to irrigate fields, particularly in Third World countries, but it also has many here at home. These include pumping water round your domestic central heating system.

Chris - So talk us through a little more precisely exactly how this works and why it's better than what people have got at the moment.

Tom - That depends on the application we're looking at, but let's look at irrigation in developing countries. Farmers in developing countries earning less than a dollar a day typically tend to farm areas of about half a hectare in size. The only way they can get water is to lift it out of the ground by hand or to pump it out with pumps. In many cases, they spend up to four hours a day providing themselves with water. For some time we've had photovoltaic cells, which are solar electricity panels and can be used to produce electricity for water pumps. However, they are very expensive and tend to fail in the middle of nowhere where there's no-one to repair it. What we really need is a system that's very simple, and heat is much easier to work with than electricity.

Chris - So some heat comes out of an exhaust pipe from a boiler, but what does it do to your pump. How does it work?

Tom - Imagine two columns of liquid side by side, and imagine that they're joined at the top and the bottom. This looks a bit like a rectangle if we look at it. If we heat the left hand column at the top end and cool it at the bottom end, then what happens is that as we heat it, the water starts to boil. As it boils, the pressure rises, steam is produced and pushes liquid out of the right hand column at the right hand side of the rectangle. We'll come onto what happens at the right hand corner in a minute. As liquid leaves the system, we get a level difference between the two columns. Gravity then causes the level difference to even out, and we get hot vapours moving down into the cold end. When hot vapours see cold surfaces they condense and the pressure lowers. This sucks the liquid back up in the right hand column.

Chris - So you get an oscillation. It goes up and down.

Tom - That's right. The liquid in the two columns is moving up and down, heat is being added, and heat is being rejected. Down in the right hand corner of this rectangle, there are two non-return valves. These are one - way valves that allow water to move in one direction. As liquid is moving up and down, it's sucking water from below, such as in a hole, and delivering it to a field above.

Chris - So this is going to save these guys hours and hours of back-breaking work and use energy that would otherwise be seen as a waste product.

Tom - Yes, and I've heard the figure that 10% of the energy we use in our homes in winter is for pumping water around heating systems, because these systems are running for several hours a day. If we could use some of the heat that's there anyway to do this job, then the whole system becomes significantly more efficient.

Chris - So it not only ha applications in the Third World, but it could also help the rest of the world to live a cleaner, greener life.

Tom - Absolutely, and so the idea behind my company is that I'll try to commercialise this pump for several of these green-type applications here at home and use the finds from that to help with some of the charitable application sin developing countries.

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