Sciencemadness Discussion Board

A cheap oil bath

Sulaiman - 14-6-2015 at 03:47

I bought a solder pot via eBay http://www.ebay.co.uk/itm/371013321371?_trksid=p2057872.m274...
to use as an oil bath.

Unfortunately I received a smaller 38mm 100W version ... (I got a 50% discount)

nevertheless I have tested it and I think it may be of use to those operating on a semi-micro scale
this 38mm pot accommodates a 5ml or 25 ml pear shaped flask
... buy the 50mm as it should give a little extra versatility.



here is a photo' of its first test, to check that at low power it is not too high power
... success, gentle boiling of water,
power control knob needed to be above minimum so I expect even lower temperatures suitable for solvents etc. will be no problem



Solder_pot.jpg - 1MB

j_sum1 - 14-6-2015 at 04:57

Cool idea. I might get one for making Bismuth crystals.
I am not sure that I am going to work at scales small enough to make it functional as an oil bath. OTOH, if I have it then what is to stop me.

smaerd - 14-6-2015 at 05:41

Way cool thanks for sharing! I had no idea this item existed

Deathunter88 - 14-6-2015 at 06:01

Another idea would be one of those hot glue melting pots. The ones where you melt hot glue in the pot and dip whatever you want to glue in it.

Sulaiman - 14-6-2015 at 13:12

I tried a 'hot wax' (wax for depilation) pot, http://www.ebay.co.uk/itm/221778618190?_trksid=p2057872.m274...
mine can not even bring water to the boil
ok for keeping several test tubes/samples at a near constant temperature.


side note; I calculated that a 100W heater can only distil about one drop of water (2260 J/g) per second if negligible heat loss and no reflux !
For my B10 distillation kit, the 150W heater with reflux should have resulted in about two to three minutes per ml of product ...
water of course has a very high enthalpy of vaporization,
ethanol for example would give 2.7 times more 'drops per second per watt'



j_sum1 - 14-6-2015 at 15:00

Ok, I just bought an 80mm version of the desolder pot. It cranks up to 250W. i figured it could hold a small RBF. I can put a crucible in it. I can use it for evaporating dishes. I can keep test tubes and small beakers at a constant temperature. And I can work comfortably with low MP metals. I think that is enough reasons to get one.

Loptr - 15-6-2015 at 05:53

Very nice! I was looking at one of these for casting lead a while back, and it never occurred to me that it could be used as hot bath.

So what is the maximum temperature attainable by this model.

Also, side question, how can you determine the maximum temperature that could theoretically be reached given a certain wattage?

EDIT: I found something that might help here. https://www.physicsforums.com/threads/conversion-of-dissipat...

[Edited on 15-6-2015 by Loptr]

Sulaiman - 15-6-2015 at 10:14

maximum temperature would be dependant upon how the wind blows :P

in still air an approximation (sorry, memory only, no reference) is

dT = (mW/cm2)^0.833

dT = increase in Celcius above ambient
mW = milli-Watts dissipated
cm2 = surface area available for convection cooling

this approximation is used for electronic devices etc. up to about 125C
I have no idea what the errors would be at say 400C
or in the case of the solder pot with restricted airflow

Loptr - 15-6-2015 at 10:36

Quote: Originally posted by Sulaiman  
maximum temperature would be dependant upon how the wind blows :P

in still air an approximation (sorry, memory only, no reference) is

dT = (mW/cm2)^0.833

dT = increase in Celcius above ambient
mW = milli-Watts dissipated
cm2 = surface area available for convection cooling

this approximation is used for electronic devices etc. up to about 125C
I have no idea what the errors would be at say 400C
or in the case of the solder pot with restricted airflow


I was wondering about the theoretical amount of heat that could be attained by the coils given an isolated environment. i will take a look your formula. Thank you!

Sulaiman - 15-6-2015 at 12:58

temperature will rise until equilibrium between electrical power input and heat loss is established
OR the heating wire melts.
heat loss is by conduction, convection and radiation
e.g. the temperature of a filament lamp element is almost entirely determined by Stefan-Boltzman law https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

so if you could have a truly isolated heater,
the temperature would rise to about 1400C,
the m.p. of the (presumed) nichrome heating element