×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Temperature rise as K?
11

Temperature rise as K?

Temperature rise as K?

(OP)
Dear users,

In several places of the heating sections of Euro (EN) standards, there are several tables showing 'temperature rise as K'. For example: "During normal operation, the temperature rise of the applience's walls shall not exceed 140 K". What does 'temperature rise as 140 K' mean?

Thanks!  

RE: Temperature rise as K?

sunchallenger,
K-stands for Kelvin.
Degrees Kelvin is same as Degrees Centigrade (hope you are familiar with).
This is intended as a mark of paying respect to the great scientist Dr. Kelvin.

RE: Temperature rise as K?

(OP)
Dear Raghun,

Thanks but 140 K means -133 (minus!!) C !

What I dont understand is: I need to find out the change in the surface temp of the appliance (starting the test at 20C room temp) and a value as -133 C doesnt make a sense...

I need to know how to use those values (140 K is applied as how)?

Thanks again..

 

RE: Temperature rise as K?

You're missing the rise part- it's 140K rise or, in other words, delta

RE: Temperature rise as K?

(OP)

Dear GTstartup,

Thanks, but,

So, in simple words (so a non-engineer naive like myself (just the designer) can understand smile   :

If the limit rise is 140 K on that wall, and if we are starting from room temp of lets say 20 C, what is the max F or C allowed on that part?

Thanks..

RE: Temperature rise as K?

starting temp=20 degree C
temp. rise = 140 degree Kelvin
Final temp limit of appliance = 20+140 = 160 degree C
thanks

RE: Temperature rise as K?

Let me try:
T1 = 20 degrees C = 20 + 273 = 293 degrees K
delta K = 140 degrees K
T2 = 293 + 140 = 433 degrees K = 433 - 273 = 160 degrees C
Crystal!

RE: Temperature rise as K?

Or

20 C =  20 + 273.15 = 293.15K
140K rise allowed = 293.15 + 140K =  433.15K
433.15K= 160C

So in terms of rise or differential 140 K = 140 C

(more or less the same as Burnt's but I had typed it already

;)

RE: Temperature rise as K?

Regardless of it being techncially correct on "delta" basis it is still confusing and senseless.

I have news for technical geeks, you don't really impress people by confusing them with your technical jargons.

The rise should be mentioned in the same units as the normal temperature is being specified or implied. If you want to honor someone, there are other means. If anything, we need   fewer temperature indicating symbols and baselines, not more.

 

Rafiq Bulsara
http://www.srengineersct.com

RE: Temperature rise as K?

Many technical organizations have established rules which require that "standardized" units be used in all of their publications. Thus many dimensions are odd, like 25.4 mm. Pressure and stress must usually be in Pascal. Who uses Pascals in real life?

RE: Temperature rise as K?

2
A similar confusion is possible when converting rises between C and F.  Let's say the rise was specified as 10C rise and my measurements are in F.  Go to your computer program or chart and convert 10C to F and you'll get 50F.  Is 10C rise the same as a 50F rise?  Nope - a 10C rise is an 18F rise.  

I think the answer is not to demand of the world that all temperature rises to be specified in your own personal preferred system of units, but to apply a small degree of critical thinking before you plug and chug.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

sunchallenger,
When computing ideal gas law-related formulas, the Kelvin temperature scale is used. You have to convert all temperatures to degrees K and then proceed in the calculation.
epete,
It's not a matter of demanding things out of preferrence, it's required by the formula you are using.
If others believe the answer offered is wrong, just say it is so, and offer a better answer! No problem here.

RE: Temperature rise as K?

burnt2x -  I have no disagreement whatsoever with your comments.  I was responding to rbulsara's post.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

There is no confusion at all.

K has nothing to do with the absolute zero. It is a measure just like feet or pounds. It is without a fixed reference while C and F both have fixed references.

The reason K is used is to avoid expressing differences in a unit that has a fixed reference. Difference and absolute value only make sense if the reference is zero. If it isn't, like the example mentioned by the OP, then confusion pops up.

It is unfortunate that the misconception that K is referenced to absolute zero has gained such popularity. It was never intended to be like that.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Temperature rise as K?

People can relate to C or F, not to K.

Try forecasting weather in K. If that is not acceptable than why use it where it is really not necessary? Does using K in temp rise clarifies anything more than if it were in C or F?

It anything, it raises a few eyebrows.  

Rafiq Bulsara
http://www.srengineersct.com

RE: Temperature rise as K?

Kelvin is referenced to absolute zero just as C is referenced to zero being the freezing point of water. When discussing temperature differences, however, the zero point of the temperature scale is irrelevant. 0C=273K but 1K delta=1C delta.

Pete, I wasn't quite sure what you were trying say. I can read your post in two different ways.

RE: Temperature rise as K?

Rafiq,

I hold the opposite view regarding Celcius: the Kelvin unit is one of the seven base units of the SI system, and should be the preferred unit of temperature used in technical descriptions. I accept the use of Celcius where the public are involved, but the public appear relate everything to the weight of a jumbo jet these days (at least on Discovery Channel) so they're probably not the best place to make the decision. smile
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Temperature rise as K?

Sorry guys, you didn't get it. K is NOT referenced to the absolute zero at all. K is a unit without a zero point. That is why it is used for delta temperature use.

It is true that the lowest possible temperature is 0 K above absolute zero. But, unfortunately, the three last words are often dropped. Hence the misconception that absolute zero is 0 K.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Temperature rise as K?

(OP)

Dear Users!

Thanks a lot for all the attention! Anyway, I am attaching 2 jpegs; first one is from CSA. Then I will post onother message with the jpeg from EN60335-1.

It is very easy to find the answer in CSA's doc: Item 1 says: "At any point on or within a supply terminal box, the max temp is 60C." Thats it!

What is the answer for the EN 60335-1??? "xxx K?" What is the max temp allowed as C?

Thanks!

RE: Temperature rise as K?

Most IEC standards use a maximum ambient temperature of 40C as the basis for calculating the permissible temperature rises, thus (for example) a Class B insulation system permits a 90K rise on a 40C ambient giving a maximum service temperature of 130C.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Temperature rise as K?

I do not see any point in using K, however correct it could be on techncial basis not relevant to day to day life.

If the ambient temperature is indicated in C (or F) there is not sense in indicating the rise in K. There was no confusion over using C or F for decades, why mess with it.

Keep the K for scientific journals and conversion tables. Normal applications do not need it.


Perhaps there would be no issues, if we say the floor to floor to height is 15 feet and the building should be 50 meters tall, the tile sizes 12"X 30 cm....



 

Rafiq Bulsara
http://www.srengineersct.com

RE: Temperature rise as K?

IEEE 1 – 2000 refers to temperature rises in degrees C (not degrees K).

That is just a datapoint to counter the IEC reference.  As I said above, it seems to me somewhat pointless to argue about which unit someone happens to think is better... with a very small amount of thinking we should be able to cope with whatever units the temperature rise is specified in.  
 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

ePete,

I would give that reference much greater credibility if it was published by a nation which doesn't stubbornly cling to a modified Imperial measurement system... smile
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Temperature rise as K?

LOL.    I can't argue that point.  I will forgo the usual furlongs per fortnight joke.   

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

There is a reason, most engineers are happily invited to meetings in job trailers but are carefully avoided in upper management level meetings with CEOs, VPs or board rooms or even at important marketing presentations!!

 

Rafiq Bulsara
http://www.srengineersct.com

RE: Temperature rise as K?

(OP)
Dear bashar2008, burnt2x, and GTstartup

Thanks a lot for all the valuable effort and data.

Best regards...

RE: Temperature rise as K?

2
Skogsgurra:

I am pretty sure that 0 K is absolute zero.  That is how we define what absolute zero is.

RE: Temperature rise as K?

Ya, I always though 0 K was defined as absolute zero. This also corresponds to −273.15° Celsius or −459.67° Fahrenheit. If that's not true then there are a lot of people doing it wrong.

I like ElectricPete's answer. Since we can't all agree on common units then we need to be able to deal with what is given.
 

RE: Temperature rise as K?

No marks1080. You put the chart before the horse. The strict definition of the degree kelvin is: "the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The definition was taken by the CGPM in 1967.

The definition says nothing about a reference temperature. It is exactly the same thing as the definition of the metre - it is defined as a fraction of the earth's quadrant. But that does not mean that is neccessarily has to start at the North Pole (or Equator).

Re: "If that's not true then there are a lot of people doing it wrong"  Yes. But most people think it is right - remember the saying "Ten thousand flies cant be wrong - eat sh-t" Same thing here.

 

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Temperature rise as K?

skogs,

Why would they pick a rather inconvenient number like 273.16 if it was for some purpose other than to place the zero point of the Kelvin scale at absolute zero?
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Temperature rise as K?

You still do not get it!

It is a unit. Not part of a scale.

I do not say that it isn't based on the absolute zero - it just doesn't start there. It starts nowhere. That is why it has been chosen for temperature deltas. C and F are for temperatures as such. But not for differences. It is about scientific prnciples.

Why is this so dificult to understand?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Temperature rise as K?

They picked 1/273.16 so that the delta T associated with 1K would be exactly the same as the delta T associated with 1C.

RE: Temperature rise as K?

Scogscurra,
I do believe you are mistaken.  In my thermodynamics and aerospace classes way back when, it was defined as 0degK=absolute zero.  See:

http://en.wikipedia.org/wiki/Kelvin

I don't think that has changed since the mid-seventies.

EEJaime

RE: Temperature rise as K?

Quote (skogsgurra):

You still do not get it!

It is a unit. Not part of a scale.

I think we understand perfectly well the difference between a unit and a scale.  Kelvin can be used in both ways as you say:  as a unit/increment (the first sentence below) and as a temperature scale (the third sentence below):
http://en.wikipedia.org/wiki/Kelvin

Quote (Wiki):

The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units.   The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero (0 K).

But it should be noted that Celcius can be used in the same way as either a scale (first sentence below) or an increment (second sentence below)
http://en.wikipedia.org/wiki/Celcius

Quote (Wiki):

Celsius (also known as centigrade) is a temperature scale that is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale two years before his death. The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as serve as a unit increment to indicate a temperature interval (a difference between two temperatures or an uncertainty).
If Wikipedia is not a solid reference, please consider this reference: "Applied Dimensional Analysis and Modeling" by Thomas Szirtes and P. Rózsa
It is a book that delves into the restructuring of problems into dimensionless variables, guessing the solution to an analytic problem by unit analysis, etc.  Chapter 3 is a detailed discussion of unit systems in use.   The authors presumably know just a little bit about units.  (*)

On Page 287 they analyze a thermal growth problem using a difference in temperatures.   And what unit is used for the delta-T?  Degrees C.    See for yourself.
http://books.google.com/books?id=G_KuA5V8JsUC&pg=PA287&dq=A+prismatic+bar+of+uniform+cross-section+is+placed+between+two+unyielding+surfaces#v=onepage&q=&f=false

(* they are Canadian – does that make a difference?)
 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

The OP asked what the temperature difference expressed in K. He got a valid answer and then protested that 140 K = -133 C.

That is where the confusion started. It is important to understand the difference between a measure with a reference and a delta measurement. The former has a zero point, be it center of Paris or the triple point of water. The latter does not have a zero point. It just says how long or how long time something takes - or how big a temperature rise is.

That is all there is to it. I do not deny at all that K is sometimes used to express temperature. But then, it should be used with words saying what reference is used. Common usage is absolute zero. But absolute zero is NOT defined as 0 K. The definition is that all molecular movement has stopped. Thermal energy is zero.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Temperature rise as K?

I agree that on a "scale" the increment K=C, and hence there is no benefit or additional technical accuracy added by expressing ambient in C and the rise in K.  

Unless it changed in last 30 years, we were taught the absolute zero happens at 0 K.

Oh and that brilliant definition of meter being some fraction of the earth's quadrant is another example of going overboard with "technical" definitions. For some reason the earth contracts or expands, which it certainly can, all the distance measurement in meters will be wrong!!  Don't they have a master meter stick in Paris? or is that the mass of a kg?

Rafiq Bulsara
http://www.srengineersct.com

RE: Temperature rise as K?

Well if "absolute zero is NOT defined as 0 K" then 0 K is defined to be absolute zero.

I think everyone had the point about delta temperatures being differences in temperature before anyone bothered to point that obvious fact out.

I am not getting your point about zero K not being absolute zero...  I will have to go back to my graduate studies prof and correct him on this.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Temperature rise as K?

I think is a matter of cause and effect.  Absolute zero is defined as that point at which there is no thermal motion.  Doesn't matter what temperature scale you might use, absolute zero doesn't care.  The Kelvin scale happened to be set up such that the increment from one degree to the next was the same as the Celsius (probably centigrade scale at the time) degree increment and that the zero point would be at absolute zero.

Absolute zero defines 0K, 0K does not define absolute zero.

On the other hand this all way too much ado about nothing.  Anybody who can't recognize that a 140K rise is exactly the same thing as a 140C rise needs to go back and brush up on basic units and anybody that would write a standard that has ambient in C and rise in K needs to get their head back into somewhere that the sun might shine.

RE: Temperature rise as K?

I think we should all change to °Rankine

RE: Temperature rise as K?

Quote (davidbeach):

anybody that would write a standard that has ambient in C and rise in K needs to get their head back into somewhere that the sun might shine.
LOL.   But as you point out (and I agree) it is not an irrecoverable error:

Quote (davidbeach):

anyone who can't recognize that a 140K rise is exactly the same thing as a 140C rise needs to go back and brush up on basic units
And then there's

Quote (davidbeach):

way too much ado about nothing.
Which I cannot particularly argue with.  But what remains unresolved is the mantra that there is only one "right" unit and anyone who doesn't agree doesn't "get it:"

Quote (skogsgurra):

You still do not get it!

It (K) is a unit. Not part of a scale.  I do not say that it isn't based on the absolute zero - it just doesn't start there. It starts nowhere. That is why it (K) has been chosen for temperature deltas. C and F are for temperatures as such. But not for differences. It is about scientific prnciples.

Why is this so dificult to understand?  
The bolded portions in the quote directly above are incorrect.  I have established above that  K, degrees C, and degrees F  can ALL be used as EITHER an element of a temperature scale OR as a unit for differential temperatures.    Check out the references I have provided 10 Aug 09 16:37 along with IEEE 1-2000 which references temperature rises in degrees C along with wiki entry for Fahrenheit which states under the heading "Temperatures and intervals" the following:
http://en.wikipedia.org/wiki/Fahrenheit

Quote (wiki):

As with the Celsius scale, the same symbol, "°", is used to denote both a point on the temperature scale, with a letter (C, F) indicating which scale is being used (e.g. "Gallium melts at 85.5763 °F"), and to denote a difference between temperatures or an uncertainty of temperature (e.g. "The output of the heat exchanger is hotter by 72 °F" and "Our standard uncertainty is ±5.4 °F").

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

Quote (skogsgurra):

The strict definition of the degree kelvin is: "the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The definition was taken by the CGPM in 1967.

The definition says nothing about a reference temperature.

If you look at the following link (by those Canadian authors of dimensional analysis book) you will see almost identical discussion to what you have quoted... but KEEP READING and it is clear  (allowing for typographical error 271.16K vs 273.16K) that they are using K as a temperature scale since they say that temperature of the triple point of water  (which is 0C) is "defined as 271.16K."
http://books.google.com/books?id=G_KuA5V8JsUC&pg=PA48&dq=The+definition+of+kelvin+for+thermodynamic+temperature+was+adopted+at+the+16th#v=onepage&q=&f=false

Quote (Canadians):

The definition of kelvin for thermodynamic temperature was adopted at the 16th
CGMP (in 1967) as follows: The kelvin is the fraction 1/273.16 of the thermodynamic
temperature of the triple point of water. The triple point of water is, by definition,
that single point in the temperature-versus-pressure coordinate plane at which ice,
water, and steam can coexist in equilibrium (see Fig. 3-5). This point is called a triple
point
because at this location (and only at this location) the three curves separating
the three phases (ice, liquid, and vapor) intersect. The curves are the fusion curve A,
the vaporization curve B, and the sublimation curve C (Fig. 3-5). The temperature
at the intersect is defined as 271.16 K
(exactly), and the pressure at this point is
measured to be 610.483 pascal.
I think it's pretty clear they are using K as a temperature scale.

Quote (skogsgurra):

The OP asked what the temperature difference expressed in K. He got a valid answer and then protested that 140 K = -133 C.

That is where the confusion started. It is important to understand the difference between a measure with a reference and a delta measurement. The former has a zero point, be it center of Paris or the triple point of water. The latter does not have a zero point. It just says how long or how long time something takes - or how big a temperature rise is.

That is all there is to it..
I guess we could take your word for it.  Or we could look some more for ourselves:
http://books.google.com/books?id=mn-ky51ZwJ4C&pg=PA38&dq=kelvin+temperature+scale&lr=&as_brr=3#v=onepage&q=kelvin%20temperature%20scale&f=false

Quote:

absolute zero is the basis for the kelvin temperature scale

http://books.google.com/books?id=WwKjznJ9Kq0C&pg=PA99&dq=kelvin+temperature+scale&lr=&as_brr=3#v=onepage&q=kelvin%20temperature%20scale&f=false

Quote:

The commonly used temperature scale in science is the Kelvin scale; its zero point corresponds to the lowest temperature possible (absolute zero), about –273C

http://books.google.com/books?id=kwf8baR1ow4C&pg=PA296&dq=kelvin+temperature+scale&lr=&as_brr=3#v=onepage&q=kelvin%20temperature%20scale&f=false

Quote:

In the S.I. System, Kelvin is the standard unit for temperature..... The scale is based on the average kinetic energy per moleducle of  a perfect gas.  Zero is equal to –273.16C.

http://books.google.com/books?id=FsKyEE8dJAgC&pg=PA37&dq=kelvin+temperature+scale&lr=&as_brr=3#v=onepage&q=kelvin%20temperature%20scale&f=false

Quote:

The Kelvin temperature scale uses the theoretical absolute zero as its zero point

http://books.google.com/books?id=oS50J3-IfZsC&pg=PA104&dq=kelvin+temperature+scale&lr=&as_brr=3#v=onepage&q=kelvin%20temperature%20scale&f=false

Quote:

The most common absolute temperature scale used by scientists is the Kelvin temperautre scale... (next page).  The Kelving temperature scale has an absolute zero.  True comparsions can be made sing the Kelvin scale.  A substance at a temeprature of 400 Kelvins contains particles with twice as much kinetic energy as a substance at 200 Kelvins

There seem to be a whole lot of references that have it wrong.  I couldn't find a single reference that said anyting resembling the fact that K was exclusively to be used as a unit and NOT as a temprature scale (which happens to be absolute).   But in the bolded section of the very last quote above, there is something resembling your statement that K can be used for comparsion while C and F cannot, but the context is energy comparison, not temperature comparison.   Is it possible you have mixed up the concept of energy comparsion with temperature comparison to come up with your conclusion that K can be used for temperature comparsion while C and F cannot?    
  
 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?


sunchallenger:

Are you still with us? Is your question answered satisfactorily?

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Temperature rise as K?

Pete,

"much ado..."

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Temperature rise as K?

(OP)
Yes Wolf39, I am still around and reading the discussion...

I am just a designer for my own project and all those heavy techical arguments do not help me too much. I was just looking for a simple answer, what is the max temp allowed as C?

Therefore, I am basing my decision on the 'direct-to-my-question' answers of dear bashar2008, burnt2x, and GEstartup.

Bottomline:

I will kindly ask my friend who is with me in this project (who actually happens to be one of you guys here) to use the best&fully certified equipment for all areas, and I will also make 'extreme design related changes in cooling', to keep the subject areas in 'basic room temperature'!

This way I will cover myself.

Thanks for your attention!

RE: Temperature rise as K?

sunchallanger:

I gave you a star for saying what matters most:

Quote:

I am just a designer for my own project and all those heavy techical arguments do not help me too much. I was just looking for a simple answer, what is the max temp allowed as C?

Trying to get fancy with K is no betterment over C, which most people understand. The specifier could have done a great service had he/she used C instead of K.

Rafiq Bulsara
http://www.srengineersct.com

RE: Temperature rise as K?

I don't think there is any doubt the original question was answered three times on the first day it was posted.    

If Kelvin is for some reason an unfamiliar concept to you – by all means follow the links.  But don't  bother to read this thread.  There is repeated misinformation that was never acknowledged even after proven wrong.   

Time to move on to more productive things...

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

There is nothing wrong with a side tracked discussion!  Thats part of why this forum is here.

I never looked at the kelvin scale from the point of view Skogsgurra has provided.  Thanks for the insight!  

 

RE: Temperature rise as K?


sunchallenger:

With trying the Google webside first and typing in "Kelvin" and "Wikipedia" you would have saved us a lot of effort and time. Especially as you still seem to be puzzled over this subject.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

RE: Temperature rise as K?

I suggest that IEEE 100 is a better reference for our purpose than Wikipedia:

kelvin (metric practice) Unit of thermodynamic temperature,
it is the fraction 1/273.16 of the thermodynamic temperature
of the triple point of water (adopted by 13th General Conference on Weights and Measures). (QUL) 268-1982s


degree Celsius (metric practice) It is equal to the kelvin and is used in place of the kelvin for expressing Celsius temperature(symbol t) defined by the equation t = T – T0 where T is the thermodynamic temperature and T0 = 273.15 K by definition. (QUL) 268-1982s

RE: Temperature rise as K?

Like I said, it's not a problem at all!

RE: Temperature rise as K?

IEEE 100 appears to be a retrofit definition.

Centigrade was always there and was nicely divided in 100 between water's freezing and boiling temperatures. It was changed to Celsius in 1948.  K's scale of 1/273.15 was selected to fit C scale.

K was adopted in 1967, and to say that C is used in place of K in 1982 is quite interesting.

From US Metric Association:
 The degree Celsius (°C) scale was devised by dividing the range of temperature between the freezing and boiling temperatures of pure water at standard atmospheric conditions (sea level pressure) into 100 equal parts. Temperatures on this scale were at one time known as  degrees centigrade, however it is no longer correct to use that terminology. [The official name was changed from "centigrade degree" to "Celsius degree" by the 9th General Conference on Weights and Measures (CGPM) in 1948.]

The kelvin (K) temperature scale is an extension of the degree Celsius scale down to absolute zero, a hypothetical temperature characterized by a complete absence of heat energy. Temperatures on this scale are called kelvins, NOT degrees kelvin, kelvin is not capitalized, and the symbol (capital K) stands alone with no degree symbol. [The official name was changed to "kelvin" and symbol "K" by the 13th General Conference on Weights and Measures (CGPM) in 1967.]  

Rafiq Bulsara
http://www.srengineersct.com

RE: Temperature rise as K?

To summarize my position (as prelude to a long discussion):   K, degrees C, and degrees F  can ALL be used as EITHER an element of a temperature scale OR as a unit of differential temperature.   This stands in contrast to another forum member's position that C and F are only scales (not units) and therefore cannot be used for differential temperatures .... and that K is only a unit and not a temperature scale.

Great link above by Rafiq confirms that according the US metric association, K can be used as a scale.

I also think it was good for stevenal to post some excerpts from IEEE 100 and I would like to spend some time (the bulk of this post) talking abouut that.  I suspect the reason the IEEE100  definitions were posted is because they don't explicitly state that C can be used as unit or scale and K can be used as unit or scale.   But considering there is only one or two sentences per definition, that omission is certainly not a contradiction to my position.   And closer inspection will in fact reveal that IEEE100 supports my position (that either K or C can be used as a unit or a scale) based on examination of the definitions themselves and also by examination of  useage of those terms in other parts of the document.

First look at the IEEE100 definition for C

Quote (IEEE100):

degree Celsius (metric practice) It is equal to the kelvin and is used in place of the kelvin for expressing Celsius temperature(symbol t) defined by the equation t = T – T0 where T is the thermodynamic temperature and T0 = 273.15 K by definition. (QUL) 268-1982s
Now look at the phrase "It [degree Celsius] is equal to the Kelvin" and ask yourself whether "it" [degree Celsius] is being used as an element of a scale (to indicate temperature) or a unit (such as to indicate differential).    It is clearly not being used as a scale because a temperature expressed in Celsius is not the same as a temperature expressed in Kelvin.  So it is being used as a unit in the same way we can use C as a unit to express a differential temperature.  It is perfect and complete agreement with my position.

Now look at the IEEE100 definition of C and work backward to understand the terminology used in the standard.   How is it that we know that the "T" in the above equation "t=T-TO" is an absolute temperature (we already know from our prior knowledge of these relationships, but what word in this particular definition tells us that T is absolute) ?   It must be by the use of the phrase "thermodynamic temperature".     Thus in the usage of IEEE100, the phrase "thermodynamic temperature" denotes absolute temperature.   And where else is that phrase used within IEEE100?  In the definition of Kelvin ("unit of thermodynamic temperature" ).  But that distinction between absolute and relative temperature would not be important if K were used soley as a unit,  and so there is no reason to use the phrase "unit of thermodynamic temperature" if K were used soley as a unit.  It is thus clear the authors anticipated K would be used as a scale (in addition to a unit) and they are defining for us that the K scale is a thermodynamic temperature.

Now this last point I will certainly agree is more convoluted than the first, but such is the nature of trying to draw conclusions from a document that does not explicitly address the question. More importantly we don't have to stop with the definitions, we can look at how the terms C and K are used elsewhere in the IEEE100 standard and we find as expected that it is 100% consistent with my position.

There are many IEEE100 usages of Kelvin as a temperature scale.  I will quote just one but you can look for yourself to find many others:

Quote (ieee100):

"chromaticity....(4) (electric power systems in commercial buildings) The measure of the warmth or coolness of a light source, which is expressed in the Kelvin (K) temperature scale."
Note also the works "Kelvin temperature scale"... that's what I have been saying... Kelvin can be used as a unit or a scale.

And now more directly related to the question at hand:

Quote (ieee100):

"insulation class .... NEMA Class B. An insulation system (130 C temperature limit including a 40_C ambient or 90C rise)"
Above we are using C as a unit for a rise (not as a temperature scale).  Again, that's exactly what I've been saying since my very first post.

I notice wikipedia was singled out for comment, but wikipedia was certainly not the only reference that was quoted.   There was IEEE-1-2000, there was the dimensional analysis book by those Canadian authors, and there were  many other textbook links provided.   And now add to that the link by Rafiq.

I think my point is very well supported,  but it occurs to me that for someone reading casually this appears to be a question of "dualing standards":    The IEC gives rise in K and the IEEE gives rise in C..... so which one do we believe?   Well.... that is certainly a contradiction to the position of others who stated K is the only unit for rise.  But it is 100% consistent with my position that either C or K (or F) can be used as either a unit (such as for rise) or a scale (for temperature measurement).

 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

I say this jokingly (and also as an engineer)...

... this thread is why engineers get a bad rap sometimes.
 
Do we really need this much information to tell us what temperature is?  Did we not all learn this is grade 8 science class?  My girlfriend is a physicist and if she read this she would make fun of me.  

Its a much simplier than any standard will ever make it out to be.  Keep in mind standard agencies often compete against each other when they try to redefine the wheel in order to seem more relavent.  

RE: Temperature rise as K?

Hi Mark.  In my very first post, I stated anyone can figure out the temperature rise with a little bit of critical thinking regardless of the units.

Then came comments from another forum member suggesting there was only one way to approach the problem (K is the only unit for temperature rise)  and that K is not a temperature scale, but only a unit.      Those comments have still not been retracted.

That is the context in which my most recent posts appears.   Perhaps I have a naive expectation that this may lead others to acknowledge their misinformation.   If you thought the purpose of my comments was to explain in simple terms the  concepts of K and C scales, then you are mistaken.  You will note I have previously directed the original post AWAY from this thread and TO Wikipedia for that very purpose.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

This will be my last post unless someone else chooses to continue the discussion.

Who is the definitive source for the SI system? The CGPM and CIPM
http://physics.nist.gov/cuu/Units/acronyms.html

Quote:

CGPM General Conference on Weights and Measures (CGPM, Conférence Générale des Poids et Mesures).
The CGPM is the primary intergovernmental treaty organization responsible for the SI, representing nearly 50 countries. It has the responsibility of ensuring that the SI is widely disseminated and modifying it as necessary so that it reflects the latest advances in science and technology.

CIPM International Committee for Weights and Measures (CIPM, Comité International des Poids et Mesures).
The CIPM comes under the authority of the CGPM. It suggests modifications to the SI to the CGPM for formal adoption. The CIPM may also on its own authority pass clarifying resolutions and recommendations regarding the SI.
 

Here is a paper on the ITS-90 (International Temperature Scale of 1990) which was proposed by CIPM and approved by CGPM.  Note this paper is published by the CIPM:
http://www.bipm.org/utils/common/pdf/its-90/ITS-90.pdf

Take a look at the last sentence on the first page:

Quote (CIPM):

A difference of temperautre may be expressed in kelvins or degrees Celsius
That completely debunks the claim that Celsius is not a "unit" (i.e. not suitable for temperature differences).

Now take a look at the first paragraph on the 2nd page:

Quote (CIPM):

The International Temperautre Scale of 1990 (ITS-90) defines both International Kelvin Temperatures, symbol T90, and International Celsius Temperatures, symbol t90.  The relationship between T90 and t90 is the same as that between T and t, i.e.

t90/C = T90/K – 273.15  (2)

The unit of the physical quantity T90 is the kelvin, symbol K, and the unit of the physical quanitty t90 is the degreee Celsius, symbol degC, as is the case for the thermodynamic temperature T and the Celsius temperature t.

So International Kelvin temperatures are reported in units of kelvin, and conversion between Kelvin temperature and Celsius temperature is accomplished by equation 2.  Review of the remainder of the document and other references makes it clear that ITS-90 is simply a calibration standard to allow calibration of devices reading out in degrees K or degrees C (the triple point of water is only one of many calibration points).

This completely debunks the claim that K is not a temperature scale.

Personally I would really think that at this point the person who created all the confusion in this thread would want to acknowledge his errors.  But maybe that's just me.

My case has been proven beyond doubt.   I will not make any more posts unless responding to further posts by others in this thread.

Btw Mark I reread your post and realized I misinterpretted it.  Sorry for that.  I guess you were only suggesting a humorous introspective look at ourselves as engineers on the forum.   Not a bad idea.  Sorry to all if I have created any negative tone on the forum.  I could offer the excuse "he started it".  But that doesn't work for my 11 year-old, so I guess it doesn't work here!   

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

Thanks Rafiq.  After all that work, now we all (except one) know exactly what we already knew when we started.    

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Temperature rise as K?

A good and enlightening ending for a hearty discussion. Thanks, electricpete.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources