Sciencemadness Discussion Board - Electrical hot plate

Electrical hot plate

chyke - 11-9-2015 at 14:13

This sounds simple but i need some clarifications. I am using a hot plate to heat a solution in an oil bath. The power rating and maximum temperature of the hot plate is 1520 W and 500 oC respectively. I set the hot plate temperature to 140 oC based on my experiment. How can i determine the exact/near exact power output (W) of the hot plate at 140 oC?

Many thanks for your expected assistance.

aga - 11-9-2015 at 14:23

Well, with no exact data, you may as well assume that it's linear.

1530W / 500 C = X / 140 C

X = (140 x 1530) / 500 = 428 W

blogfast25 - 11-9-2015 at 15:18

Quote: Originally posted by aga

Well, with no exact data, you may as well assume that it's linear.

1530W / 500 C = X / 140 C

X = (140 x 1530) / 500 = 428 W

That would work quite well if only the oil bath lost heat (power loss is directly proportional to T<sub>bath</sub> - T<sub>surroundings</sub>, Newton's cooling law)) but there are other losses. So 428 W is probably an underestimate.

[Edited on 11-9-2015 by blogfast25]

chyke - 11-9-2015 at 22:15

@Aga, thanks for your reply. I have attached an image of my experimental set-up for your view.
From my experience just now, i discovered that when i set the hot plate temperature at 140 oC (after 1 hour), the oil bath temperature is about 95 oC while the temperature of my solution in the three necked flask (immersed in oil bath)is 85 oC. I intend to heat my solution (in the three necked flask) for 1 hour at constant temperature (85 oC). What i require is to get a rough estimate of the heat input (watt).

Sulaiman - 11-9-2015 at 22:41

you could use something like this http://www.ebay.co.uk/itm/Plug-in-Electricity-Power-Consumpt...

blogfast25 - 12-9-2015 at 07:01

Quote: Originally posted by chyke

@Aga, thanks for your reply. I have attached an image of my experimental set-up for your view.
From my experience just now, i discovered that when i set the hot plate temperature at 140 oC (after 1 hour), the oil bath temperature is about 95 oC while the temperature of my solution in the three necked flask (immersed in oil bath)is 85 oC.

It's obvious from the oil bath temperature that you haven't reached thermal equilibrium yet: the bath is still heating up. During heating up you'll consume more power.

BTW, I was that second member that answered your question at physics.stackexchange.

chyke - 12-9-2015 at 08:58

@blogfast25, thanks! The temperature in the oil bath might not hit equilibrium because its not insulated. I noticed that after 1 hour of heating, the temperature of the oil in the bath is increased and maintained at 95 oC, while the temperature in the flask (immersed in the oil bath) is maintained at 85 oC. At this constant temperature, i allowed the solution in the flask to heat for an extra 1 hour (at constant 85 oC). So, what i want to determine is the equivalent power supplied by the hot plate in the 1 hour of heat (when the temperature was constant).