alluminum block
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From: George Herold on 15 Jan 2010 12:11 On Jan 15, 6:42 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Fri, 15 Jan 2010 00:37:38 -0600, "bw" <bweg...(a)hotmail.com> wrote: > > >"elahetal" <elahet...(a)yahoo.com> wrote in message > >news:1cednUIyaMjf5dLWRVn_vwA(a)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 - Yeah, and your heater is a current source 1 Watt of heat is an amp of current. George H.
From: elahetal on 15 Jan 2010 15:39
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 suggestions you have written before is applicable to my case or not. In advance, your 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 one power resistor on one of the lateral sides( may be two power resistors on two of the lateral sides)is/are placed. The Al block is placed in a room (consider 3*4m )and in ambient temperature of 25C. It will be heated up by a power resistor which is/are placed on the block. the temperature of the block is measured by a thermocouple and is reported to a temperature controller.The output of the temperature controller activate the heater circuit including voltage supply and power resistor.The Al block is used as a reference temperature so should be kept constant from the temperature setting until the end of the measurement.The measurement process is very fast and takes maybe less than 1 second even about 1 ms.As the power resistor is heated up by a voltage supply( by current through the resistor)then I need an estimation about the size of the Al block to see which power resistor and voltage supply I need. Please, if you have any suggestion regarding my previous question or the set up that I described above, let me know. I appreciate your help. Ela --------------------------------------- This message was sent using the sci.electronics.basics web interface on http://www.Electronics-Related.com |