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Heat Transfer Calculation in Lab Furnace

  1. Jan 15, 2010 #1
    Greetings All,

    I am a PhD student in a physical chemistry department. Our research group would like to build our own high termperature ovens for preparing samples. Nothing fancy, just a controled rise in temperature to a given setpoint, hold it there for a designated amount of time and the cool down. The controllers that will do this are inexpensive and also the relays and thermocouples...that is not a problem. The question is about heat transfer and power.

    We will be using Kantahl resistance heating wire. It is serviceable to 1350°C and we have a 230V, 16 Amp service to the normal labortory outlet. The question is how much power input to heating chamber should we design to reach temperature "X" in a heating chamber of volume "Y". The volume we have in mind is about 2700 Cubic Centimeters (15cm X 15cm X 12cm). This can all be calculated through the heat transfer equaitons and knowing the R factor of the insulation, surface area...etc.
    Does anyone know of some softwear that can simplify this process?

    Thank You,
  2. jcsd
  3. Jan 15, 2010 #2
  4. Jan 15, 2010 #3
    I will admit that I am not an electrician. That is why I work closely with the department electrician and he advises me as to what is safe with our system. Also I get advice form the technical support department at the heating element and insulation manufactures.

    The way I usually work it is to design the furnace around the experiments I want to run. Then make a CAD drawing and send my idea to the heating element company to see if there elements will perform in this configuration. If they suggest changes then I change the design with their suggestion in mind. But they are not furnace builders and do not tell me how much power and insulation I will need to reach a certain temperature and what the surface temperature of the furnace shell will be when the heating chamber is at temperature “X”. That I have to figure out for myself.

    So I have the safety issues well covered with technical advice from the manufactures and also by our electrician. Also, my actual training is as a machinist. I did not start studying science until I was 27.

    One may ask “Why go through all this trouble…there are furnace companies that will sell you one.” Sure there are companies that will sell me one…as long as you have the money to pay for it, they can supply it. But you have to have the money to pay their price. High temperature furnaces are something that our research group does not have in the budget.

    Also, most people would be surprised at how inexpensive the parts are that go into making a furnace compared with the finished product. For instance, the temperature control system (controller, thermocouple and solid state relay) can be put together for under 200 dollars. But you have to buy the parts separately and put it together yourself.

    Next year I hope to be done with my PhD and I intend to open my own lab. I already talked to the technology transfer office about what I intend to produce there and after considering my proposal they are have indicated that they are willing to support the venture. The ability to not only build my own equipment but also fix it myself if it needs repair will be a tremendous business advantage.

    But back to the original problem of this post…
    I am not sure how to calculate how much power I need to maintain a certain temperature with a given amount of insulation. I already built two furnaces but I think I have designed them with more power than was necessary. This is not especially bad but by designing it to use less power I can save space in the heating chamber and on heating element costs.

    Any suggestions as to where I can find additional information… webpages, softwear or other resources … to better refine my design would be very helpful.

    Thank you,
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