Posted by Morris Dovey on March 26, 2009, 4:06 pm
Tim Jackson wrote:
> Morris Dovey wrote:
>> Tim Jackson wrote:
>>> Morris Dovey wrote:
>>>>
>>>> Nope. I've already /measured/ that half of that trough width can
>>>> produce 725F. Doubling the trough width while maintaining the same
>>>> "bright line" width will deliver twice the energy to the same area -
>>>> so I expect a temperature at least close to double the 725F, or 1450F.
>>>
>>> That is flawed physics. First you need to be thinking about absolute
>>> temperature not relative, and second, in radiation the temperature
>>> goes as the fourth root of energy.
>>
>> Might work for you, but I'm working with old-fashioned temperature
>> which represents energy density per unit mass.
>>
>> I think of and talk about temperature in units with which the person
>> I'm talking is familiar - and yes, convert (whatever) to Kelvins for
>> calculations.
>>
>> Just out of curiosity, do /you/ have a thermometer graduated in Kelvins?
>>
>> :)
>>
>
>
> No I don;t have a thermometer calibrated in kelvins, nor one that will
> measure 1450F. But nonetheless when you are talking about radiation you
> have to convert to absolute temperature to do any useful calculations.
>
> I'm not criticising your units, but I'm giving you a C- for your physics.
>
> It works like this.
>
> The maximum temperature you can achieve in your target is that
> temperature where the self-radiated power is equal to the incident
> power. This is calculated by Stefan's Law.
> (http://en.wikipedia.org/wiki/Stefan%27s_law )
> which says that the emitted power is proportional to the fourth power of
> the temperature.
>
> So if you double the incident power you will increase the absolute
> temperature by about 20%
>
> If you started with 725F, that's 658K, doubling the power will get you
> 783K, which I make to be 950F.
>
> This of course is the 'ideal' situation, and does not account for any
> power you may be removing to drive an engine, this of course has to be
> subtracted from the incident power before doing the temperature
> calculation.
>
> So for example if you were capturing a kilowatt of sunlight and getting
> 725F at your target without load, then it was radiating a kilowatt back
> into space. If you doubled the power by using a bigger mirror around
> the same target then you could draw off one kilowatt while maintaining
> 725F. Two kilowatts come in, one gets radiated, just the same, the other
> goes into your engine.
My apologies - I think I misunderstood what you were saying. Yes, I
understood that the re-radiation will be a problem - and no, I did not
have an adequate physics background to be able to quantify it.
A full kW into the engine wouldn't really be a bad starting point.
Obviously, more would be better (which is why I'm puzzling over ways to
make the tube [my hot head] both a better absorber and a poorer radiator).
In the real world, I have to work with whatever heat/temperature I get -
and if it's not enough for some particular purpose, scale up until it
/becomes/ adequate. The method isn't physics or engineering at its
finest, but then the overall problem doesn't seem to have captured the
interest of either of those communities.
The most dismaying aspect for me is that sometime in the near future I'm
going to need to shop for a torch and regulators; and learn to weld and
braze sufficiently to cobble this monstrosity together.
Hmm - I just realized that not only did the Stirling engine originate in
the UK, but so has much of the physics help I've gotten. :)
Thanks for posting - and for your patience and persistence!
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by Morris Dovey on March 26, 2009, 4:28 pm
For anyone running MS systems, I just uploaded a pair of quick and dirty
Fahrenheit->Celsius and Celsius->Fahrenheit converter programs to
http://www.iedu.com/DeSoto/Misc/c2f.exe and
http://www.iedu.com/DeSoto/Misc/f2c.exe
Both are intended to run in a command window.
*nix users already the units program, and Google web search will convert
almost any value in any units to the corresponding value in any other
conforming units (try entering "convert c to furlongs per fortnight" for
a test case).
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by Morris Dovey on March 31, 2009, 11:02 am
Morris Dovey wrote:
>
> For anyone running MS systems, I just uploaded a pair of quick and dirty
> Fahrenheit->Celsius and Celsius->Fahrenheit converter programs to
>
> http://www.iedu.com/DeSoto/Misc/c2f.exe and
> http://www.iedu.com/DeSoto/Misc/f2c.exe
There were enough downloads to justify adding
http://www.iedu.com/DeSoto/Misc/c2k.exe
http://www.iedu.com/DeSoto/Misc/f2k.exe
http://www.iedu.com/DeSoto/Misc/k2c.exe
http://www.iedu.com/DeSoto/Misc/k2f.exe
So now we can convert temperatures every which way. :)
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by Jim Wilkins on March 31, 2009, 2:21 pm
> Morris Dovey wrote:
> > For anyone running MS systems, I just uploaded a pair of quick and dirty
> > Fahrenheit->Celsius and Celsius->Fahrenheit converter programs to
> > http://www.iedu.com/DeSoto/Misc/c2f.exeand
> > http://www.iedu.com/DeSoto/Misc/f2c.exe
> There were enough downloads to justify adding
> http://www.iedu.com/DeSoto/Misc/c2k.exe
> http://www.iedu.com/DeSoto/Misc/f2k.exe
> http://www.iedu.com/DeSoto/Misc/k2c.exe
> http://www.iedu.com/DeSoto/Misc/k2f.exe
> So now we can convert temperatures every which way. :)
> --
> Morris Dovey
> DeSoto Solar
> DeSoto, Iowa USAhttp://www.iedu.com/DeSoto/
Spreadsheets are a good simple way to handle problems of this general
nature and they give you considerable flexibility in formatting and
printing the results. Mine lists every degree Celsius from -40 to +100
and separately every 10 degrees C from -273 (0 Kelvin) to +1000C. I
wrote it as a program first and wasted a lot of paper and ink
experimenting with PRINT USING. If you don't have MS Office, this is a
good free substitute:
http://www.openoffice.org/
Jim Wilkins
Posted by sno on March 31, 2009, 5:59 pm
Jim Wilkins wrote:
>> Morris Dovey wrote:
>>
>>> For anyone running MS systems, I just uploaded a pair of quick and dirty
>>> Fahrenheit->Celsius and Celsius->Fahrenheit converter programs to
>>> http://www.iedu.com/DeSoto/Misc/c2f.exeand
>>> http://www.iedu.com/DeSoto/Misc/f2c.exe
>> There were enough downloads to justify adding
>>
>> http://www.iedu.com/DeSoto/Misc/c2k.exe
>> http://www.iedu.com/DeSoto/Misc/f2k.exe
>> http://www.iedu.com/DeSoto/Misc/k2c.exe
>> http://www.iedu.com/DeSoto/Misc/k2f.exe
>>
>> So now we can convert temperatures every which way. :)
>>
>> --
>> Morris Dovey
>> DeSoto Solar
>> DeSoto, Iowa USAhttp://www.iedu.com/DeSoto/
>
> Spreadsheets are a good simple way to handle problems of this general
> nature and they give you considerable flexibility in formatting and
> printing the results. Mine lists every degree Celsius from -40 to +100
> and separately every 10 degrees C from -273 (0 Kelvin) to +1000C. I
> wrote it as a program first and wasted a lot of paper and ink
> experimenting with PRINT USING. If you don't have MS Office, this is a
> good free substitute:
> http://www.openoffice.org/
>
> Jim Wilkins
There is a freeware little program that is used by NASA that will
convert just about anything to anything....and you can make your own
other conversions easily....check it out....
http://joshmadison.com/article/convert-for-windows
have fun....sno
XML site map
>> Tim Jackson wrote:
>>> Morris Dovey wrote:
>>>>
>>>> Nope. I've already /measured/ that half of that trough width can
>>>> produce 725F. Doubling the trough width while maintaining the same
>>>> "bright line" width will deliver twice the energy to the same area -
>>>> so I expect a temperature at least close to double the 725F, or 1450F.
>>>
>>> That is flawed physics. First you need to be thinking about absolute
>>> temperature not relative, and second, in radiation the temperature
>>> goes as the fourth root of energy.
>>
>> Might work for you, but I'm working with old-fashioned temperature
>> which represents energy density per unit mass.
>>
>> I think of and talk about temperature in units with which the person
>> I'm talking is familiar - and yes, convert (whatever) to Kelvins for
>> calculations.
>>
>> Just out of curiosity, do /you/ have a thermometer graduated in Kelvins?
>>
>> :)
>>
>
>
> No I don;t have a thermometer calibrated in kelvins, nor one that will
> measure 1450F. But nonetheless when you are talking about radiation you
> have to convert to absolute temperature to do any useful calculations.
>
> I'm not criticising your units, but I'm giving you a C- for your physics.
>
> It works like this.
>
> The maximum temperature you can achieve in your target is that
> temperature where the self-radiated power is equal to the incident
> power. This is calculated by Stefan's Law.
> (http://en.wikipedia.org/wiki/Stefan%27s_law )
> which says that the emitted power is proportional to the fourth power of
> the temperature.
>
> So if you double the incident power you will increase the absolute
> temperature by about 20%
>
> If you started with 725F, that's 658K, doubling the power will get you
> 783K, which I make to be 950F.
>
> This of course is the 'ideal' situation, and does not account for any
> power you may be removing to drive an engine, this of course has to be
> subtracted from the incident power before doing the temperature
> calculation.
>
> So for example if you were capturing a kilowatt of sunlight and getting
> 725F at your target without load, then it was radiating a kilowatt back
> into space. If you doubled the power by using a bigger mirror around
> the same target then you could draw off one kilowatt while maintaining
> 725F. Two kilowatts come in, one gets radiated, just the same, the other
> goes into your engine.