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concerning resistive heater charecteristics

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When we supply a constant dc voltage to a resistive heater for a time 't',

1. May i know how much temparature will be produced by the heater ?(mathematical equation)

2. Does the resistance of the heater change with time?

3. Does the produced temparature goes on increasing with respect to time or is constant?

Please mail me immediately as i need this information to continue my project work.

Thanking u,
Ramesh Babu


Active Member
The power input is equal to the heat output minus any losses. One example of a loss is the slight heating of the conductors that carry the power to the heater - if the conductors are outside of the space of concern then you can't count that heat. Without a clear understanding of the problem at hand it's impossible to be more specific than that. The equation depends on the information you have to begin with.

The resistance of many materials changes with temperature. Over the long haul (weeks, months) heater materials can degrade so that there is a small change in resistance. Whether or not this is significant depends on the situation. In most cases the change in resistance with temperature is of significance. The change because of time is less significant and ignored in most situations.

The temperature will rise until equillibrium is reached - where the heat input to the system equals the heat output. In some situations equillibrium is reached quickly - or the conditions are considered acceptable quickly. In other situations this can be very tricky to model and predict. If the voltage is constant the heater is changing as it warms or cools so the power input is actually changing. If the power input is controlled then the heater output is actually changing - because the losses are changing. The conductivity of any insulating material changes with temperature.

Heat transfer can be very simple in some situations however it is actually quite the complex process. Share some more specifics and maybe we can help. As with other areas of science and engineering practitioners have developed methods to simply calculations where it's appropriate.
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