How to make a resistance heater?

  1. How do i make a resistance heater for heating a liquid?
    DC or AC both are acceptable.
    But i need to know the power of the heater - (P = VI)
     
  2. jcsd
  3. berkeman

    Staff: Mentor

    Do you mean you want to make something like a stovetop from scratch? Or is this a dip-in-the-liquid heater? Does it need to be food quality? What kinds of liquids? How hot?
     
  4. actually, this heater is needed to find the specific heat of a liquid.
    since we are finding the specific heat, we need to the power (P = VI), so that we can know the energy by ( E = VIT).
    So it needs to be a dip-in-the-liquid heater....
     
  5. berkeman

    Staff: Mentor

    Can you use a simple commercially-available dip heater, or is there a requirement that you make your own?
     
  6. hmm
    i tried searching but i could not find...
    any suggestions?
     
  7. Q_Goest

    Q_Goest 2,950
    Science Advisor
    Homework Helper
    Gold Member

    Warning: stupid story ensues...
    My wife and I had a 3 month old daughter when we moved from San Diego to Denver. We took a few days to do it, driving a truck and checking out the sights. On the way, we would need to heat baby bottles though, so I took an old hair dryer apart and used the wire heating elements to make a baby bottle warmer. The wire got wrapped around a cup and was glued in place with a filled epoxy (to increase thermal conductivity). The cup was put inside a larger insulated cup and potted there with more filled epoxy. The only other part was an electric cord that plugged into a cigarette lighter. I'd put the baby bottle in the cup with some water and we'd have a warm bottle in about 30 minutes. Wasn't the best, but it worked.
     
  8. sophiecentaur

    sophiecentaur 13,297
    Science Advisor
    Gold Member

    I believe that many 'modern' parents use room temperature milk for their sprats these days. My three grandchildren have thrived on it although I would never have considered such a spartan regime for our own kids. (I think the modern formula milk mixes better in cold water than the old stuff)

    In answer to the OP, I should say that a coil of bare wire dipped in the liquid would be suitable and cheap (low thermal mass and good contact with the liquid).
     
  9. 12 V DC this one plugs into a car's lighter socket, available on E-Bay.
     
  10. sophiecentaur

    sophiecentaur 13,297
    Science Advisor
    Gold Member

    You are planning a particular experiment, expecting a certain temperature rise in your liquid (water?). The mass of liquid and the proposed time will give an indication of power needed for your heater. I imagine you will want some tens of Watts. AC or DC is not relevant but DC measurements may be more accurate. A large 12V battery would provide a good source. Resistance will be
    Vsquared over Power required. You can get resistance wire from Electtonics supply shops. Maplin, I expect. But an old mains convector heater will have something to suit you FREE! inside it. Cut a suitable length and see it get hot when connected to the battery. Mind your fingers, though, when it's not under water. You will get branded if you touch the wire when it's not cooled by the liquid.
    You just need to experiment with a pair of good multimeters til you get the power you need.
    The other solution is to BUY something Arrrgh!!
     
  11. Consider making a safety precaution checklist. If you put the liquid into a closed container and heat it up, it might explode violently. If you are using high voltage, especially around water, you will have an electrocution hazard. Sparks from loose connections could ignite a flammable liquid. Liquids that may not very flammable will burn violently when heated near their boiling point.

    Heating elements that I know of off hand:
    Water heater replacement elements 500-1000's of watts.
    Water heaters (a small water heater will hold a few gallons / 10s of liters)
    Light bulbs can be encased in a test tube.
    Electronic axial leaded resistors. can be sealed with electrical grade RTV (non-corrosive room temperature vulcanizing silicone rubber)
    Nichrome wire sealed in RTV
    Heat tape, cartridges. Check McMaster-Carr Omega

    To start, you should consider the quantity of liquid to test, the precision of the test, speed of the test, and what can go wrong and the consequences.

    You would probably want your container insulated and characterized to know how much energy went into the fluid, the container, the insulation, and the surrounding environment.

    Did I mention safety?

    Try to preserve yourself intact.
     
  12. Making a resistance heater should be pretty easy but here are some things to consider.

    P=IV, so you need to measure (or otherwise know) both the IV simultaneously. Remember that the resistance of a wire increases as it heats up, so you can't use the wire's resistance unless you measure it when it is at operational temperatures.

    Many liquids are conductive. DI water is not, but tap water is. Before you use a dip heater you should know if you need to insulate the wire to protect against a short. Many wires come coated in thin enamel which will be enough to insulate (especially low voltages) but make sure that your liquid doesn't remove the enamel and cause a short. (If your using a strong acid or something)

    You should pick a gauge of wire that is appropriate for your heating needs. Thinner wires will have lower current & higher voltage compared to thinner ones. If you are going to use a wall socket you should ensure the current will be low enough so you don't blow any fuses or cause any damage.

    Don't forget about safety.
     
  13. we finally used a kettle for our project =)
    thanks for help everyone.
     
  14. which one is best for water to steam?

    hi friends..........
    which heater is best for water to steam?





    all glory to god
    sakthikumar.r.c,
     
  15. Re: which one is best for water to steam?

    Again,that really depends on the intended use. If it is for a short experiment it really doesn't matter. If on the other hand you are trying to make a device that will need to last for many hours and heating/cooling cycles you will need to build more robust heating unit. What is your intended application?
     
  16. which one is best for water to steam?

    my work is steam rocket...........
     
  17. How much power do you want to use? It probably would be best to use an external heater so that the heater is not launched with the rocket. One or more halogen lamps inside of a stainless steel reflector might do the trick. Paint the rocket black with high-temperature paint. Be able to remove the heater so it does not get damaged by the exhaust. Avoid heating the top of the tank where there is no water. It would likely get very hot, soften the tank, and fail. Could use a propane torch with a can / baffle to keep the heat swirling around the tank.

    Probably best not to have an electrical penetration on the tank.

    Hot metal is not as strong as cold metal. Take that into account. Make sure you don't blow yourself up or get peppered with shrapnel from an exploding rocket! Don't electrocute yourself. Use a GFCI. Have a method for aborting the launch such as releasing the steam without releasing the rocket. Things will be hot after the launch.
     
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