Temperature rise as K? 11

[Jakelian]

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!

 

[RRaghunath]

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.

 

[Jakelian]

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..

 

[GTstartup]

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

 

[Jakelian]

Dear GTstartup,

Thanks, but,

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

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..

 

[bashar2008]

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

 

[burnt2x]

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!

 

[GTstartup]

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

 

[rbulsara]

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

 

[Compositepro]

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?

 

[electricpete]

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.

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[burnt2x]

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.

 

[electricpete]

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

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

 

[Skogsgurra]

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

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[rbulsara]

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

 

[Compositepro]

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.

 

[ScottyUK]

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.


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

 

[Skogsgurra]

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

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Jakelian]

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!

 

[Jakelian]

... and here is the jpeg from EN60335-1 !