I had hoped my last newsletter about arterial roads would get you thinking and get some response. I guess you all think I am mad. For those who are not yet quite convinced I am mad, here follows an even more deranged idea!
Now what about our public transport? In Europe they have buses, trams, trains, express trains, underground trains, aeroplanes and taxis. At a transport hub such as large railway stations and airports, all of these facilities converge. You do not need to own a car, at all. In South Africa we have…………...virtually nothing. The Gautrain would work well in Europe, because it would connect with a plethora of complementary systems. Here we have to create its own bus service to try to get it feasible. To fix our public transport system would be an enormous task. The rot set in when we abandoned our trams, which an old toppie like me can scarcely remember. Let us not try to copy the first world, but face the realities of our situation and adapt to them. Gauteng has a long axis from Springs to Randfontein. Fortuitously it just so happens that we have below us a wide, gently sloping cavity which was formerly gold mines. It extends all the way from Springs to Randfontein. This would cost trillions to dig, but it happens to be there already. Now since it is so wide, we could put everything except aeroplanes down there. We could have separate roads for bicycles, motorcycles, cars, taxis, buses, trucks and trains. What absolute bliss!!!
It wouldn’t get all the traffic off Jo’burg’s streets. So let’s think about that. We have basically cars and taxis. How can we get them moving efficiently? I propose a ring rail. This is very wide railway line with very wide flatbed carriages. You drive your car or taxi to the siding, select your destination, and follow the signs to your flatbed railcar. Pay at the toll point, drive onto your flatbed. After 5 minutes it engages with a cable which pulls it from the siding onto the mainline. There it engages with the high speed cable and goes non-stop to your chosen siding. It stops and you drive off and continue what’s left of your journey. I reckon this would cut the average commuter’s travel time in half. There is no locomotive, no exhaust emissions, and just some big electric winches. No broken robots, no stress, no road rage. You pass the short time chatting to fellow commuters who share your destination and time slot.
PRODUCT FEATURE – Detonator Coolers
My colleague Clive Woodford involved me in a project for an explosives manufacturer. He was asked to make detonator coolers to prevent premature explosions in hot blast holes. His solution was too expensive. I did a lot of basic R& D and eventually solved the problem. Our goal was to keep the detonator below 137°C for half an hour with the temperature at 1000°C in the hole.
Sometimes coal seams ignite underground, and smoulder very slowly because it takes very long for oxygen to get down there. If you drill blast holes into such a seam, you suddenly let fresh air in and the temperature goes screaming up to 1000°C. Then they put a detonator down, and pump dynamite down the hole. The detonator overheats and explodes when it reaches about 137°C. If you happen to be pumping dynamite down the hole at the time, the explosion goes up the pipe to the tanker and wipes out everything in the vicinity. I devised a super insulation capsule to delay the heat transfer.
Wide ranges of porous insulating ceramics were tested. Those which started melting at 1000°C were eliminated and those which exploded when placed in a furnace at 1000°C were eliminated. A temperature calibration method was devised to indicate above or below 137°C.
Capsules with 9mm thick walls were placed in a furnace at 1000°C and failed to keep the interior below 137°C for long enough. Increasing the thickness of the walls would solve the problem, but the capsule has to fit down the drill hole.
A method of dissipating the heat was needed.
The solution will be called “endothermic thermal dissipation”. The heat is consumed in an endothermic process.
An insulation material with good strength, very high porosity and ample permeability was selected. The best was Keramicalia’s Kerafire. A capsule cover was made from this material. It was fully impregnated with water, and then frozen. When the capsule is placed in a furnace at 1000°C the temperature stays near 0°C until the ice has melted. After that the heat is consumed at 1 joule per gram for every degree C until the temperature reaches 100°C. The temperature stays close to 100°C until all the water has been boiled off as steam. Only then can the heat start to find its way through the ceramic.
A wall thickness of 9mm kept the interior below 137°C for 20 minutes. One would expect the time to increase in proportion to the wall thickness.
Endothermic thermal dissipation can be taken further by addition of solids in the ceramic structure which decompose endothermically. It can then be taken still further by placing “dry ice”; frozen carbon dioxide inside the interior of the capsule.
TECHNICAL FEATURE – Endothermics
Nearly all chemical reactions are associated with either heat absorption (endothermic) or heat release (exothermic).
Sometimes we use endothermic reactions to stop heat from travelling. Phase changes also involve heat absorption or release. Ice melts at 0°C. It remains at 0°C, absorbing heat, until all the ice has turned to water. Then the water absorbs 1 joule per gram per °C as it heats up to 100°C. Then it remains at 100°C (at sea level) until it has all turned to steam. The most effective way to raise your swimming pools temperature is to cover it with transparent plastic, thereby stopping the heat loss through evaporation.
Insulation is effective as long as heat is extracted at the far end. If you completely enclose something in insulation and place it in a furnace, it will reach the temperature of the furnace. The insulation will only delay the heat flow. Sometimes data loggers are mounted under kiln cars to monitor temperatures as they pass through a tunnel kiln. The ambient temperature under the kiln car is too high for the electronics to work. Since the cycle is several days, insulation alone cannot keep the electronic box cool. Here we have to use endothermic reactions. Three types are used; an ice box enclosing the electronics, a water box, or a salt which absorbs a lot of heat to melt.
A client had a problem with a data logger. I explained the endothermic principle. When I arrived on site, I found the data logger encased in a steel bath. One of the staff said “Oh yes, now I remember; we used to fill that thing with water.”
Many endothermic reactions are associated with the release of gas, most commonly steam. Useful ones are gypsum → calcium sulphate hemihydrates (128°C) → anhydrite (163°C)
Aluminium trihydrate → aluminium oxide + H₂O at 300°C
Calcium Aluminate hydrates → calcium aluminates at 400°C
Clay → metakaolin at 600°C
Calcium carbonate °→ CaO + CO₂ at 825°C
Magnesium Carbonate → MgO + CO₂ at 900°C
When firing a ceramic body, these reactions must be accommodated. Firing must be slowed down at the appropriate temperatures so that gases can escape without the pressure exceeding the tensile strength of the ceramic and causing an explosion. Such explosions are quite violent. I have destroyed a kiln at 600°C with a clay rich refractory; it blew the sides right off. I also blew up a very dense 2.5ton refractory launder at 400°C, 40 hours into its drying cycle. It destroyed the dryer, and bent the bogey, made of railway lines, to the floor. The cops came to investigate the explosion, and it took me hours to convince them it was only a steam explosion.
Endothermic reactions are used in many fireproofing applications.
Have a great 2016!
Dave and staff.