Hi all, I need to heat a steel rod 12inches long and half and inch in diameter up to around 40 degrees centigrade and keep it within 2degrees. It will need to be kept constantly at this temperature. it can only be heated at one end, the other end needs to be un cluttered.
Any suggestions how I can do this?
Cheers!
Steve
Get an electronic aquarium heater/stat and set it to 40C in a gallon or two of water. Put the end of the bar in it.. wrap the rest in a couple of inches of insulation.. job done.. or is it?
You don't actually supply enough info to be sure what can be done or even if its possible.
You need to provide more information...
I assume that the rod is solid?
I assume that the rod is suspended in free air?
I assume that there is no dynamic thermal load bearing? (i.e. nothing randomly comes into contact)
I assume the environment is reasonably controlled? (i.e. not placed in a draught)
I assume there's no limitation on the heating technology?
I assume that the environment is cooler than the rod - that we're talking heating and not cooling!
If my assumptions are broadly correct, then I'd suggest machining two bore holes , connected at the far end, and pump water or oil through these channels, pre-heated to 40c. (pro: with an adequate sump of pre-heated water/oil) this would provide good stability under differing thermal loads and a good (flat) temperature gradient across the length of the bar)
Another option is to machine a single hole, and insert a straight heating element down the length of the hole. If temperature control is vital, then make this a multi-stage element, each stage with some thermal control to modulate power to each stage of the element (con: difficult to maintain a stable temperature gradient across the length)
Another option, again requiring the machining of a single hole, is to run a conductor to the far end of the rod (internally) and use the rod itself as a heating element, passing a current through the internal conductor to the far end and have the supply return at the near end. Would also need an embedded temperature monitor (con: likely to be slow to heat and have poor response to thermal loading)
The easiest option, of course, is to change the environment to present a constant 40c around the bar, however, I'm guessing that this is not a solution for your problem.
More info please!!!
Mike
it can be solid or hollow.
i want it to sit on a base of some sort that acts as a heater and so that the rod protrudes from it and the rod stands upright.
no, but the temperature must be stable so will need some kind of automatic and manual adjustment of temperature.
the item will be kept indoors, away from draughts.
no, but i dont want hight running costs and a big bulky item.
yes, rod will need to be heated from room temperature and held at 40 degrees.
many thanks for your help Mike! Can you suggest any actual components that I could use for the heating/monitoring?
Cheers
Steve
Besides all the comments here about how to go about this, it might be an idea to say what you are using this for - someone might have an easy suggestion for you to achieve your aim.
Paul
Don't know what sort of temp this thing gets up to but it may be possible to cannibalize this :o)
I'd love to tell you, but if i told you, i'd have to kill you!
I'm a bit of an inventor, this only one part of the gadget i am currently working on. Any help to solve this problem as simply and as cheaply as possible is most helpful!
Cheers
Steve
R.P.McMurphy said the following on 04/02/2006 23:21:
How about trace heating cable?
See here:
You will need some kind of PID temperature controller to maintain closed-loop feedback of the temperature.
Heating at one end means the other end may be significantly cooler unless it's insulated, amd presumably insulation counts as clutter. Copper would be a better choice as it would heat more evenly because of its better thermal conductivity. But you haven't given many clues, such as what's happening at the other end.
I would hope you'll be sharing out the royalties from the production of the gadget...
:-)
well if it makes any money, I will remember my friends!
Steve
Rough calcs suggest that you need about 2-3 Watts to raise that sized bar (20 sq inches) about 20C above ambient. It looks rather low, so my calcs could be wrong (probably are).
Might be worth looking at a tube, filled with oil, heating resistor(s) and temperature sensor (diode?) mounted at the bottom. Four wires coming out of the bottom of the tube, which is to be solidly plugged, and the top of the tube lightly plugged... enough to hold the oil in, but something that allows air in and out as the oil expands/contracts.
Temperature control circuitry mounted in the base.
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