paxpax
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question about hot plate stirrer wattage
i apologize if this question was already answered, i didn't find any info
im looking to buy a hot plate stirrer, but there is something
that i don't understand
what is the difference between hot plate with a higher wattage and one with lower wattage
for example, 2 hot plates stirrer from the same brand that reach the same temperature and with the same heating surface can have different wattage,
one at 500w another at 550w
what im supposed to understand ?
[Edited on 15-3-2016 by paxpax]
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gdflp
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A watt is a measure of power, specifically 1 Joule/Second, thus it is energy divided by time. Two hot plates of different power, even if they have
the same max temperature, will reach this temperature in different amounts of time. Other factors play into this as well, for example aluminum hot
plates will heat up quicker than ceramic ones because aluminum has a lower capacity for thermal energy than ceramic does. In general though, to
otherwise equivalent plates will simply have different rates at which the speed up if they use different amounts of power, the higher the power, the
faster they reach their max temp.
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PHILOU Zrealone
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There is also maybe a motor under the plate for the magnetic agitator--> extra energy
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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DJF90
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Note that the maximum surface temperature is not the same as the maximum working temperature with a load in place (e.g. heating bath). I've had
difficulties reaching 200 *C (sand bath temperature) on a hot plate with a 300 *C max (surface) temp because the power output (wattage) was
insufficient.
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Maker
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You would barely notice the difference between a 500 and 550 watt plate.
As has been said, a higher wattage will heat up faster, but it can also heat things to a higher temperature (Even though the surface temperature is
the same). If you're working with very large volumes, a higher wattage will be ideal.
Don't base your choice off wattage alone.
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paxpax
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thank you for the responses guys!
Quote: Originally posted by DJF90  | | Note that the maximum surface temperature is not the same as the maximum working temperature with a load in place (e.g. heating bath). I've had
difficulties reaching 200 *C (sand bath temperature) on a hot plate with a 300 *C max (surface) temp because the power output (wattage) was
insufficient. |
Please can you explain why you couldn't reach 200°c because of the power output ? if i understood gdflp post correctly it is just a question of
time, is there something else i should know ?
| Quote: Originally posted by Maker | You would barely notice the difference between a 500 and 550 watt plate.
As has been said, a higher wattage will heat up faster, but it can also heat things to a higher temperature (Even though the surface temperature is
the same). If you're working with very large volumes, a higher wattage will be ideal.
Don't base your choice off wattage alone. |
What other factors should i take into consideration beside wattage, the power and speed of the magnetic stirrer, the surface length and type
(ceramic...), a LCD with temp and stirrer speed diplay ?
Also i have another question for you guys
what do you think of chinese hot plates stirrer?
Brand names with LCD display a very expensive (200+ $ )
im looking for one that have an LCD with magnetic and temp dislay and Separate Temp and magnetic speed control, with enough surface to heat from 100mL
to 1L flat bottom flask
and enough power to heat sand bath, heating block, round bottom flask stand etc... to atleast 200°C
[Edited on 15-3-2016 by paxpax]
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Herr Haber
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IMO the usual price difference for an LCD display would make me go for a normal analog one.
First, because what you'll be measuring is the temperature of the plate: useless. I'm more interested in the temperature Inside the reaction zone or
at the top of my distillation apparatus and I have a collection of thermometers for that...
BUT, these high tech stirrers usually come with a port where you can plug in a probe and even sometimes plug them to a computer to gather data or
program them (big bucks here!). Then it becomes interesting for obvious reasons.
And yes, some of these probes are Teflon coated 
I might be tempted by one of these when I have 600 to 1000 Euros to spend. So far, I'd rather make due with what I was given for free by a friend
working in a school.
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gdflp
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When you place large items on a hot plate, they will lose heat to their surroundings by both convection and radiation at a certain rate. At
equilibrium, this rate is equal to the rate at which energy is being added to the item by the hot plate, which is dependent on the power rating of the
hot plate. Greater temperatures will lead to a greater rate of heat loss due to a greater delta T to the surroundings, so the hot plates which are
rated at a higher power will reach thermal equilibrium with objects at a higher temperature.
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careysub
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| Quote: Originally posted by gdflp | | ... Other factors play into this as well, for example aluminum hot plates will heat up quicker than ceramic ones because aluminum has a lower capacity
for thermal energy than ceramic does. ... |
Aluminum's specific heat (capacity for thermal energy) is in the same range as ceramics. It does however conduct heat much faster.
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