"Thermodynamic" temperature relates to an "ideal heat engine" a Carnot Cycle for the inflow and outflow of heat and the production of work.
John has explained the practical temperature scales tied to the properties of melting and freezing substances. ---- Original message ---- >Date: Tue, 31 Aug 2010 04:45:00 -0700 (PDT) >From: "John M. Steele" <[email protected]> >Subject: [USMA:48436] Re: kelvin >To: "U.S. Metric Association" <[email protected]> > > Stan, Bill > > Metrology is all about splitting hairs (and in this > case, hairs I don't entirely grasp). > > As to what other temperature scales, measurement on > the thermodynamic scale is somewhat impractical, and > there have been a succession of international > practical scales, based on multiple fixed points, > and official means of interpolating between them, > the latest being ITS-90. Google throws a "may harm > your computer" warning on the official ITS-90 site, > but I believe this is a faithful copy of the text: > http://www.omega.com/techref/intltemp.html > > A brief quote from its priciples > > 2. Principles of the International Temperature Scale > of 1990 (ITS-90) > > The ITS-90 extends upwards from 0.65 K to the > highest temperature practicably measurable in terms > of the Planck radiation law using monochromatic > radiation. The ITS-90 comprises a number of ranges > and sub-ranges throughout each of which temperatures > T90 are defined. Several of these ranges or > sub-ranges overlap, and where such overlapping > occurs, differing definitions of T90 exist: these > differing definitions have equal status. > > --------------------------------------------- > > > > This scale differs from previous scales attempting > the same thing, differences are around ±0.02 K at > ambient temperature ranges increasing to about -0.1 > K at 600 K, and +0.4 K at 800 K. > > > > At one time freezing and boiling points of water at > std. pressure may have precisely defined the > Centigrade scale; however, under the modern ITS-90 > scale, the melting point of water at standard > pressure is around +0.0025 °C, not 0 °C. (The > above link includes a table of pressure > depressions). > > > > A more precise measure is given in a reference in > this Wikipedia article (I don't have access to the > reference itself): > http://en.wikipedia.org/wiki/Melting_point > > ^ The melting point of purified water has been > measured to be 0.002519 +/- 0.000002 degrees Celsius > - see R. Feistel and W. Wagner (2006). "A New > Equation of State for H2O Ice Ih". J. Phys. Chem. > Ref. Data 35: 1021–1047. doi:10.1063/1.2183324. > > > > I would further point out, although irrelevant to > this discussion, that the boiling point of water at > standard pressure is around 99.98 °C. > > > > Your proposed explanation of the Celsius scale would > have to become more convoluted, the elevation of > temperature above the point which is 0.01 K below > the triple point of water. Lets just leave it as an > offset of precisely 273.15 K. The 0 °C and 100 °C > explanations commonly used have fallen to the status > of the quarter-meridian being precisely 10 Mm, > useful approximations, but not definitions. > > ------------------------------------------------ > > From: Bill Hooper <[email protected]> > To: U.S. Metric Association <[email protected]> > Sent: Mon, August 30, 2010 10:27:49 PM > Subject: [USMA:48435] Re: kelvin > > On Aug 27 , at 10:27 AM, Stanislav Jakuba wrote: > > ... BIPM is neither infallible nor keen on > removing its own contradictions. Several of those > concern temperature and Celsius, particularly the > thermodynamic temperature. > > Why the adjective thermodynamic with the > temperature in the main table? What are the other > temperatures and what are their units? Some > justify the adjective on the basis of the > existence of the “Celsius temperature” (see > SI10). But it is not in any table. > For decades I have been fighting for the simple > statement: > “Temperature – its unit is the kelvin in SI, > symbol K.” > > Some (SI10 included) claim that degree Celsius is > a derived unit. This cannot be true if one > believes the definition of SI derived units and > how they are formed. One or the other must be > incorrect. > > Stan, > I agree that there is something wrong ith the logic > here and I think I have a reasonable alternative > view of the situation that may be helpful. > My view is that kelvins and degrees Celsius are NOT > two different units for measuring the same thing. > They are two IDENTICAL units used to measure > DIFFERENT things. > The two different things are > (1) the elevation of temperature above absolute > zero > and > (2) the elevation of temperature above (or below) > freezing. > (Throughout this note, when I write "freezing" I > mean the freezing point of water with all the usual > conditions that are normally prescribed.) > Using the terminology "the temperature is 30 kelvins > above freezing" is identical to the practice of > measuring altitudes of geographic features or things > in the Earth's atmosphere (or even above). One > commonly measures the elevation above (or below) > mean sea level. It would certainly be possible in > this day and age to measure "absolute" elevations, > meaning distance from the center of the Earth. No > one would consider measuring both of these in metres > but calling the unit by one name if the elevation is > from the center of the planet while calling it by a > DIFFERENT name when it is measured above sea level. > The measures, both in metres, are measures of two > different things (height above sea level vs. > distance form Earth's center). > My suggestion would be to emphasize that the phrase > "degree Celsius" MEANS "kelvins above freezing". The > proper usage would be to state "Today's high > temperature was 30 kelvins above freezing" or > writing "Today's high temperature was 30 K afw". I > just invented the abbreviation "afw" to mean "above > freezing water". This would be similar to using ASL > to mean "above sea level" as in "The height of that > mountain is 2224 m ASL", as is already done in some > places. > I would be the first to point out that it is > improper (by SI rules) to combine the metre symbol > with the sea level abbreviation (as it indeed is > done in some places) so that it should not be > written "The height of that mountain is 2224 > mASL". So also it would be improper to write "The > temperature is 30 Kafw"; it must be "The temperature > is 30 K afw". > > Bill Hooper > Temperature 37 K apf > Fernandina Beach, Florida, USA > ========================== > SImplification Begins With SI. > ==========================
