CouchHatter
Hazard to Others
Posts: 152
Registered: 28-10-2017
Location: Oklahoma
Member Is Offline
Mood: 76 elements taken!
|
|
fume hood airflow is cooling off hotplate
I have a good hot plate and whenever I use it inside my fume hood, it takes FOREVER to heat up. Whenever I start the blower after my oil bath is
heated up, it cools everything down. The face velocity is right around 100ft/min (measured with a Vaneometer) so decreasing it substantially isn't
really an option, otherwise it defeats the entire point of a hood.
Is this a common problem? All I can find when searching is 'malfunctioning hot plate'. Should I just accept that I'll have to run it +25°-50° hotter
and dial in the 'actual' temperature (like calibrating a thermometer at non-sea level by boiling water) than I would normally, or is there something
in my setup that I can change? My hotplate is on a scissor lift about 5 inches off the bottom of the hood.
|
|
|
NZniceguy
Harmless
Posts: 48
Registered: 16-9-2017
Member Is Offline
Mood: No Mood
|
|
Maybe put a shroud around the hotplate?
|
|
|
draculic acid69
International Hazard
Posts: 1371
Registered: 2-8-2018
Member Is Offline
|
|
Definitely try the shroud idea.its the simplest fixed
|
|
|
Ubya
International Hazard
Posts: 1247
Registered: 23-11-2017
Location: Rome-Italy
Member Is Offline
Mood: I'm a maddo scientisto!!!
|
|
100ft/min is around 50cm/s, if i remember correctly tge minimum was 10cm/s and a good value was 30cm/s, so maybe you could dial down a bit your hood
blower.
at uni i always worked under hood, and i don't remember to have ever had a problem with a hotplate being cooled too much by the air flow
---------------------------------------------------------------------
feel free to correct my grammar, or any mistakes i make
---------------------------------------------------------------------
|
|
|
CouchHatter
Hazard to Others
Posts: 152
Registered: 28-10-2017
Location: Oklahoma
Member Is Offline
Mood: 76 elements taken!
|
|
Valuable information, all of the above. I guess I'll have to retrofit a belt pulley system for my motor to slow it down. It's a 4-speed motor on speed
1. I'll try the shroud first, but was planning a pulley anyways for explosion-proofing the blower.
|
|
|
DavidJR
National Hazard
Posts: 908
Registered: 1-1-2018
Location: Scotland
Member Is Offline
Mood: Tired
|
|
Face velocity is a terrible performance metric for fume hoods. It has very little correlation to the ability of a hood to actually contain
internally-generated fumes. In fact, increased turbulence resulting from too high a face velocity very often results in much poorer fume containment
than would be achieved with the same hood if the flow rate was decreased.
|
|
|
Dr.Bob
International Hazard
Posts: 2759
Registered: 26-1-2011
Location: USA - NC
Member Is Offline
Mood: Mildly disgruntled scientist
|
|
I have seen the same issue when running reactions without good temperature control, when the hood is one full, the reaction stay at a one temp, but if
it is on standby mode (very low flow), the temp can climb quite higher. That can actually boil reactions dry at night when the hood go to low mode.
|
|
|
Tsjerk
International Hazard
Posts: 3032
Registered: 20-4-2005
Location: Netherlands
Member Is Offline
Mood: Mood
|
|
I use aluminium foil for high boilers, works great.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
