# Converting watt into temperature (celcius)

Discussion in 'General Electronics Chat' started by rajat1684, Aug 28, 2013.

1. ### rajat1684 Thread Starter New Member

Aug 26, 2013
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0
Thanks you all.

Intersting..I think I can understand now why more power (watt) means more heat (KJ).

Converting watt into temperature (celcius)

Say 70% of 50 watt of Halogen Bulbs converts into heat (hypothetically)
i.e. = 0.7*50 = 35 watt of heat

Bulb is on for 5 minutes = 60*5 = 300 sec

1 watt = 1 joule/ sec, thus 35*300 = 10500 joules = 105 KJ
Specific Heat of Dry Air (Cv) = 0.716 KJ/kg.K
Thus,
105KJ/0.716KJ/kg.K = 146 Kg.K
Density of Air = 1.3 Kg/m3

Thus 146 (Kg.K)/1.3 (Kg/m3) = 112.3 K-m3

This means temperature rise will be 112.3 K per m3 of dry air.

Converting Kelvin to Celsius

Celsius = Kelvin- 273
Celcius = 112.3-273 = -160.7 (taking mode = 160 degree celcius)

Is this correct that temperature rise will be 160 degree celcius?

2. ### rajat1684 Thread Starter New Member

Aug 26, 2013
13
0
Sorry because I'm not an electrical engineer any advice would be good for me

3. ### wayneh Expert

Sep 9, 2010
14,858
5,341
A degree kelvin is the same size as a degree celsius, so no need to go any farther once you have °K.

Your calculation is reasonable although I haven't checked every detail. One problem, though, is that both the density and the heat capacity are not constant, but are functions of temperature themselves. So the precise answer requires integral calculus.

Depending on what happens to the light, it might end up heating the air as well.

4. ### rajat1684 Thread Starter New Member

Aug 26, 2013
13
0
Thanks wayneh

5. ### rajat1684 Thread Starter New Member

Aug 26, 2013
13
0
It just seems lot of rise in temp so just thought to share it in forum

6. ### wayneh Expert

Sep 9, 2010
14,858
5,341
Oh, hey, you slipped a decimal in converting to kJ.

7. ### GopherT AAC Fanatic!

Nov 23, 2012
8,025
6,786
Here...with errors corrected.

8. ### PaulEngineer Member

Dec 21, 2016
159
7
Uuuuum the 10500 J is not 105KJ it is 10,5KJ ! 105KJ = 105000J

9. ### hp1729 Well-Known Member

Nov 23, 2015
2,306
283
Are there other factors? Does the housing for the light provide a heat sink? On a power transistor for example, I can be dissipating 20 Watts but with a large enough heat sink temperature does not rise considerably.

Sep 9, 2010
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