alluminum block

E

elahetal

Guest
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.

Thanks
 
"elahetal" <elahetale@yahoo.com> wrote in message
news:1cednUIyaMjf5dLWRVn_vwA@giganews.com...
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.

Thanks
Click to expand...
You need to start with more specific information.
 
elahetal wrote:
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.
Click to expand...
What parameters are fixed besides the material of the block?
Or at least, what are their reasonable ranges?

Some things you haven't specified:

1. How is the block heated? Is heat applied to one side, the
inside? All sides? What's its efficiency in getting its
consumed power into the block as heat?
2. What medium is the block in? What is the size of the
ambient region?
3. Is the block in contact with anything else?
4. Is the block coated with anything?
5. What temperature scale are you using?
6. How long should it take to heat the block to 60 (C? F?)
7. How much heating power is available?

Is the block supposed to remain at 60 (C? F?) for as long
as heat is being applied, or is there a temperature controller?
 
elahetal wrote:
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.

Thanks


Check wirewound or power resistors. They come already sealed in an
Click to expand...
aluminium block. Problem solved.
 
elahetal wrote in message <1cednUIyaMjf5dLWRVn_vwA@giganews.com>...
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.

Thanks


Materials have a thermal resistance which is simply stated as watts per
Click to expand...
degree. For example if your block has a thermal resistance of 1 watt per
degree, then 40 watts input will raise the temperature 40 degrees over
ambient. As you can see there are watts, degrees and thermal resistance so
any one of those quantities can be juggled to get the desired results.
Thermal resistance will depend on several things such as the size and shape.
It would be much easier to take
a block of suitable dimmensions, dump power into it and measure the
temperature rise.
 
"elahetal" <elahetale@yahoo.com> wrote in message
news:1cednUIyaMjf5dLWRVn_vwA@giganews.com...
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.
Click to expand...
Do you have a practical application you're trying to work out?
 
"elahetal" <elahetale@yahoo.com> wrote in message
news:1cednUIyaMjf5dLWRVn_vwA@giganews.com...
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.

Thanks
Click to expand...
Start as simply as possible. Al has a specific heat capacity of 0.9 joules
per gram.
If your aluminum weighs 1 gram it will take 0.9 joules to raise the temp 1
degree C.
To raise the temp 40 degrees then you need 40*0.9 = 36 Joules

A Watt is a Joule per second. So it will take 36 seconds at the rate of 1
watt to heat your one gram by 40 degrees using one watt of power.

If you want to heat 1 gram in 3.6 seconds then you will need 10 watts.
 
bw wrote:
"elahetal" <elahetale@yahoo.com> wrote in message
news:1cednUIyaMjf5dLWRVn_vwA@giganews.com...
Hello all,

If I need an Al Block to heat up and I need the least possible
dimensions but I need to increase its temperature from ambient
temp(20 degree) to 60 degree. how many watts I need and what
the
dimensions should be? I do not know from which point I should
start.

Thanks

Start as simply as possible. Al has a specific heat capacity of
0.9
joules per gram.
If your aluminum weighs 1 gram it will take 0.9 joules to raise
the
temp 1 degree C.
To raise the temp 40 degrees then you need 40*0.9 = 36 Joules

A Watt is a Joule per second. So it will take 36 seconds at the
rate
of 1 watt to heat your one gram by 40 degrees using one watt of
power.

If you want to heat 1 gram in 3.6 seconds then you will need 10
watts.
Click to expand...
That's a good starting point. However, it assumes that there's no
loss. In practice, there will be loss of heat from conduction,
convection, radiation and imperfect transfer from the heat
source. The extent of the loss depends on the environment. The
temperature will stabilize when the rate of loss balances the
rate of heating energy supplied. If heat loss is zero (impossible
in practice but can be approximated), the temperature will
continue to rise indefinitely as long as power is applied.
 
On Fri, 15 Jan 2010 00:37:38 -0600, "bw" <bwegher@hotmail.com> wrote:

"elahetal" <elahetale@yahoo.com> wrote in message
news:1cednUIyaMjf5dLWRVn_vwA@giganews.com...
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.

Thanks

Start as simply as possible. Al has a specific heat capacity of 0.9 joules
per gram.
If your aluminum weighs 1 gram it will take 0.9 joules to raise the temp 1
degree C.
To raise the temp 40 degrees then you need 40*0.9 = 36 Joules

A Watt is a Joule per second. So it will take 36 seconds at the rate of 1
watt to heat your one gram by 40 degrees using one watt of power.

If you want to heat 1 gram in 3.6 seconds then you will need 10 watts.
Click to expand...
The numbers work out, pretty close, that you can use Spice to model
thermal systems, using 1 gram of aluminum to be one farad, 1 K/W as
one ohm, 1 K becoming 1 volt. You can approximate thermal diffusion
with a string of R-Cs, sorta.

John
 
On Jan 15, 5:58 am, "pimpom" <pim...@invalid.invalid> wrote:
bw wrote:
"elahetal" <elahet...@yahoo.com> wrote in message
news:1cednUIyaMjf5dLWRVn_vwA@giganews.com...
Hello all,

If I need an Al Block to heat up and I need the least possible
dimensions but I need to increase its temperature from ambient
temp(20 degree) to 60 degree. how many watts I need and what
the
dimensions should be? I do not know from which point I should
start.

Thanks

Start as simply as possible. Al has a specific heat capacity of
0.9
joules per gram.
If your aluminum weighs 1 gram it will take 0.9 joules to raise
the
temp 1 degree C.
To raise the temp 40 degrees then you need 40*0.9 = 36 Joules

A Watt is a Joule per second. So it will take 36 seconds at the
rate
of 1 watt to heat your one gram by 40 degrees using one watt of
power.

If you want to heat 1 gram in 3.6 seconds then you will need 10
watts.

That's a good starting point. However, it assumes that there's no
loss. In practice, there will be loss of heat from conduction,
convection, radiation and imperfect transfer from the heat
source. The extent of the loss depends on the environment. The
temperature will stabilize when the rate of loss balances the
rate of heating energy supplied. If heat loss is zero (impossible
in practice but can be approximated), the temperature will
continue to rise indefinitely as long as power is applied.- Hide quoted text -

- Show quoted text -
Click to expand...
Yup, Is the block floating in space or attached to something? The
smaller the block the faster you can rasie it's temperature. (As long
as it's not attached to some other heat sink.) I always seem to end
up with heaters in the 10 Watt range. Can you give us more details?

George H.
 
On Jan 15, 6:42 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 15 Jan 2010 00:37:38 -0600, "bw" <bweg...@hotmail.com> wrote:

"elahetal" <elahet...@yahoo.com> wrote in message
news:1cednUIyaMjf5dLWRVn_vwA@giganews.com...
Hello all,

If I need an Al Block to heat up and I need the least possible dimensions
but I need to increase its temperature from ambient temp(20 degree) to 60
degree. how many watts I need and what the dimensions should be? I do not
know from which point I should start.

Thanks

Start as simply as possible. Al has a specific heat capacity of 0.9 joules
per gram.
If your aluminum weighs 1 gram it will take 0.9 joules to raise the temp 1
degree C.
To raise the temp 40 degrees then you need 40*0.9 = 36 Joules

A Watt is a Joule per second. So it will take 36 seconds at the rate of 1
watt to heat your one gram by 40 degrees using one watt of power.

If you want to heat 1 gram in 3.6 seconds then you will need 10 watts.

The numbers work out, pretty close, that you can use Spice to model
thermal systems, using 1 gram of aluminum to be one farad, 1 K/W as
one ohm, 1 K becoming 1 volt. You can approximate thermal diffusion
with a string of R-Cs, sorta.

John- Hide quoted text -

- Show quoted text -
Click to expand...
Yeah, and your heater is a current source 1 Watt of heat is an amp of
current.

George H.
 
Thanks a lot for your comments. They gave me good starting point at least
but let me provide you with more detailed info to see if the suggestion
you have written before is applicable to my case or not. In advance, you
help is appreciated.

I am going to design a closed loop temperature controller .

The Al block is attached to a power transistor( from uppers face) and on
power resistor on one of the lateral sides( may be two power resistors o
two of the lateral sides)is/are placed. The Al block is placed in a roo
(consider 3*4m )and in ambient temperature of 25C. It will be heated up b
a power resistor which is/are placed on the block. the temperature of th
block is measured by a thermocouple and is reported to a temperatur
controller.The output of the temperature controller activate the heate
circuit including voltage supply and power resistor.The Al block is use
as a reference temperature so should be kept constant from the temperatur
setting until the end of the measurement.The measurement process is ver
fast and takes maybe less than 1 second even about 1 ms.As the powe
resistor is heated up by a voltage supply( by current through th
resistor)then I need an estimation about the size of the Al block to se
which power resistor and voltage supply I need.

Please, if you have any suggestion regarding my previous question or th
set up that I described above, let me know. I appreciate your help.

Ela


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