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14/11/2007
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When extreme heat kicks in, how do you insulate electronics against the potential consequences? Tom Shelley reports
How do you record images of the insides of chimneys at temperatures of up to 400ºC? One means, it seems, is to use a camera housed within a container that has two layers of insulation.
Delta International has come up with such a solution whereby four cameras gather digital images horizontally – three images per second – while a fifth camera is aimed straight down the chimney.
The novel approach emerged out of a request the company received from a client some years ago to inspect one of its chimneys at a plant that could not be shut down.
“So we designed a camera and a wall mounted davit to suspend it from,” says the company’s Nigel Matthews.
The maximum it has been up to is 400ºC for 25 minutes. The temperature of the inside of the case only increased by 3ºC during this period – but the maximum operating temperature of the digital electronics is 40ºC.
According to Matthews, Delta International researched the market to find the best possible thermal insulating materials and came up with ‘Microtherm’, a microporous material made by the Microtherm Group, an offshoot of Morgan Ceramics. Described as, Pyrogenic silica with a mineral oxide opacifier and E-glass filament reinforcement, it is capable of being used at up to 1000 deg C, is non combustible, and said to be environmentally safe and free of respirable fibres. Thermal conductivity is 0.0221W/m deg K at 100 deg C and 0.0244 W/m deg K at 400 deg K. Among other applications, the material, which is machinable, is used to protect aircraft flight recorders. Matthews describes it as a specialist product that “costs us a small fortune”.
Between the Microtherm and the steel, outer containment is a layer of another insulating material, Foamglas, a ferrous aluminium silicate cellular glass with closed cells and no binders, made by Pittsburgh Corning. Temperature limits are –268 to +485ºC, although it does not soften until 730ºC. The material, which Matthews states has a better initial thermal gradient, is derived from 66% post-consumer waste glass, and is quite widely used in the building and process industries.
The outer steel containment – 1m high and 600mm in diameter – is equipped with, what Matthews described as special double glazed panels filled with argon that go up to 1000ºC. “A conventional air filling would allow the glass to steam up when cold,” he points out. “We keep the openings down to minimal size, because the double glazing does not offer insulation as good as the insulated steel.”
The only hot environment electronic camera systems that might possibly have worked in a more demanding environment were the cameras of the Venera Russian space probes that were landed on the surface of the planet Venus in the 1970s and early 1980s. These devices had to survive temperatures of 480ºC and atmospheric pressures of 90 bar. The atmosphere of Venus is mostly made up of carbon dioxide and none of the devices was able to continue functioning for more than an hour.
Pointers
* The camera system has been used at up to 400ºC for 25 minutes although it could probably survive hotter conditions than this and for longer
* Dustbin sized, it employs four horizontal cameras and one vertical downward-looking camera to inspect the inside of chimneys while they are still in use
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Author
Tom Shelley
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