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| impakshi |
 Posted: Thu Jan 31, 2008 5:26 am Post subject: Should heater coil length be more or less for better heating |
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Forum Freshman
Joined: 29 Jan 2008
Posts: 5
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| Distribution voltage is a constant voltage a.c. supply voltage.A heater being connected to the supply mains,heat developed should be more if the resistance of the wire of the heater is less( since P=V*V/R, where R is the resistance).In other words the heating capacity of a heater with lesser length of the heating coil should be more.But is this not erroneous??!! |
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| Harold14370 |
| Posted: Thu Jan 31, 2008 6:42 am Post subject: |
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Forum Professor
Joined: 13 Apr 2007
Posts: 1560
Location: Pennsylvania
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| The power will increase as you decrease the resistance. What will happen as you shorten the heater coil is that the power density will increase and the temperature will go up. There is a practical limit because you will eventually burn out the heater. |
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| impakshi |
| Posted: Fri Feb 01, 2008 4:03 am Post subject: |
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Joined: 29 Jan 2008
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| But Sir,heat is developed due to electrons collision.More the resistance, more the collisions and more is the heat.Then how come a wire of less resistance will develop more heat?Wherfrom will this heat be developed? |
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| Harold14370 |
| Posted: Fri Feb 01, 2008 4:43 am Post subject: |
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Forum Professor
Joined: 13 Apr 2007
Posts: 1560
Location: Pennsylvania
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| impakshi wrote: |
| But Sir,heat is developed due to electrons collision.More the resistance, more the collisions and more is the heat.Then how come a wire of less resistance will develop more heat?Wherfrom will this heat be developed? |
Yes, you are correct, for a given current, more resistance means more heat. But the current is not constant, it increases when you decrease the resistance.
If you have one heater plugged in, let's say 1000 watts, and then you plug in another 1000 watt heater you get 2000 watts, right? The current is doubled and total resistance in the system is 1/2 the resistance of one heater because you have two resistors in parallel. R=R1R2/(R1+R2). If you halved the resistance by making the heating element shorter, you would get the same heat output as if you had plugged in two heaters. You would also probably burn out the heating element because you have 4 times the heat per unit length of heating element. |
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| VTMechEng |
| Posted: Sun Feb 03, 2008 3:13 pm Post subject: |
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Joined: 03 Feb 2008
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Hmmm... Thinking about convection in heat transfer, a shorter heating coil using the same power will heat the immediate area around the coil faster than if that power was spread out over a larger surface area, would it not?
It could be a half-baked explanation, though. |
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