Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Air temperature
- Thread starter StefanoBr
- Start date
LittleInch
Petroleum
Sorry, makes no sense.
You're asking a question which is about energy ( heat capacity difference of air from 1 temp to another), but don't provide any energy data.
A temperature is not energy.
E.g. if you blew in air of 30C at 1m3/sec it would take a second
If you had an item with a surface area of 1cm2 at 30C it would take an eternity.
An item with a surface area of 10m2 (e.g. with loads of fins) it would take 10 seconds.
See what I mean?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
You're asking a question which is about energy ( heat capacity difference of air from 1 temp to another), but don't provide any energy data.
A temperature is not energy.
E.g. if you blew in air of 30C at 1m3/sec it would take a second
If you had an item with a surface area of 1cm2 at 30C it would take an eternity.
An item with a surface area of 10m2 (e.g. with loads of fins) it would take 10 seconds.
See what I mean?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
- Thread starter
- #3
LittleInch
Petroleum
Ok that's starting to get an idea of the issues.
So what you need to do is:
figure out a surface area around your cold store which is surrounded by your 30C heat.
If it is literally a 1m cube, then this is 6 m2
Find out what is the thermal conductivity of your insulation and thickness.
From that you can work out a heat transfer quantity per m2.
That will give you an energy value going into your cube
From the web find out the heat capacity of air per degree at 5 C.
Do a simple calculation.
Of course this goes astray as soon as you include within your cold storage area anything which is also at 5C which is not air ((e.g. food or a cold ice block or whatever). the much larger mass of the other things will take a lot longer to heat up than air. And it also goes completely astray as soon as you open the cold store and let in air at 30C.
SO I suggest you go away, think about what it is you're trying to work out, get all the required information, give it a go as described above and then come back to us.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
So what you need to do is:
figure out a surface area around your cold store which is surrounded by your 30C heat.
If it is literally a 1m cube, then this is 6 m2
Find out what is the thermal conductivity of your insulation and thickness.
From that you can work out a heat transfer quantity per m2.
That will give you an energy value going into your cube
From the web find out the heat capacity of air per degree at 5 C.
Do a simple calculation.
Of course this goes astray as soon as you include within your cold storage area anything which is also at 5C which is not air ((e.g. food or a cold ice block or whatever). the much larger mass of the other things will take a lot longer to heat up than air. And it also goes completely astray as soon as you open the cold store and let in air at 30C.
SO I suggest you go away, think about what it is you're trying to work out, get all the required information, give it a go as described above and then come back to us.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
- Thread starter
- #6
To add to LI is to determine the inside and outside convective heat transfer coefficients which are based on air movement (speed) inside and outside the box. You may also have heat sources such as lightings, blower motors inside the box and sunlight inside the box which may have to be considered. Lastly, you are involved in transient calculations meaning that the temperature of the wall will increase, therefore, you'll need to do time step calculations. It is not as simple as first believed but if you had heat transfer in a college course, it is doable with a spread sheet.
- Status
Similar threads
- Locked
- Question