From astronomic to gastronomic

While gas prices may dip a little, the trend is likely to continue upwards in the long term. So the incentive is there to come up with a better way to tap into the fuel that feeds us. For one thing, vast amounts of methane exist in the world, in the form of methane hydrates, on the sea floors, in front of river estuaries – while decomposing organic rubbish produces the same gas. Several third world countries have schemes to harness it, with 140,000 biogas digesters in Nepal, and hundreds, if not thousands, in India and Pakistan. These are mostly small units, and an important part of their function is to take cattle excrement and convert it to a sort of fertiliser from which plants can quickly obtain benefit. But it is also possible to extract methane from municipal rubbish dumps in the west. Indeed, most western sewage plants produce the stuff to fuel their equipment, even if they do not presently export a surplus. Hence, there is not going to be any shortage of gas in the long, term, whatever happens in the short term, so the gas cooker is clearly here to stay. The problem is, of course, that the fuel on which it runs is going to get ever more expensive. The Challenge Our challenge this month is to some up with a fundamental redesign of the humble gas cooker to make it more efficient, rather than a licence to burn money. At present, most of the combusted gas and hot air rises around the pans and saucepans, without transferring all its heat content to what has to be cooked. That means there is plenty of scope either to re-design the utensils, improve heat transfer from the gas phase – or to re-design the burners or even the whole cooker. While there are many alternatives, the solution offered below looks particularly simple, inexpensive and ingenious. And yes, it was designed by a practising engineer. Once you see what it is, the light bulb will no doubt come on and it will seem blindingly obvious – except it is innovative enough to be protected by patent. For those without access to the web, the solution will be described fully in our November edition. See if you have the imagination to cook up something equally impressive. Solution Our solution this month comes from Dr André Batako, who describes himself as a researcher engaged in manufacturing engineering, and who lives in Liverpool. What he has done is to devise metal rings that go round the burners, which leave only a small gap between themselves and the utensils. The rings include apertures on their lower parts to accommodate the ironwork of the utensil supports on the cooker top, as well as cut-outs to admit air. Their primary function, he says, is to prevent the heat generated by the burned gas from dissipating into the environment. After heating the pans and saucepans, the hot air and exhaust gases escape through the narrow openings between the rings and the pans, then pass upwards in a thin boundary layer adjacent to the pans. This is probably reinforced by the Coanda effect, in which a flowing gas layer tends to stick to a curved surface. Whatever the mechanism, the end result is a dramatic improvement in heat transfer efficiency. Without a ring, he tells us, a litre of water typically takes 11 to 12 minutes to boil on his cooker. However, with a ring, this is typically reduced to 7 minutes, which amounts to a near doubling of heat transfer effectiveness.