Unit conversion of "Thermal Conductivity" & "Specific Heat Capacity"

Unless I'm somehow mistaken....

1. If you mulply (or divide) by 1 you will have the exact answer...a degree C is the same a a degree Kelvin!

2. It follows from 1. that the conversion factor for #2 will be 1000 (I'll let you decide wether to multiply or divide)

Del

"Unless I'm somehow mistaken...." - you are mistaken !!

What exactly is the unit "Degree Kelvin" , surely you mean "Kelvin".

'Kelvin' is someone's name ..
'Degree Kelvin' is a unit of temperature measurement.

I'm strugging to guess...are you trying to appear witty or intelligent?
I fear the result is neither .

Del

Del,

Before you get upset you really need to understand what was being pointed out here (I believe you do not actually understand the issue).

The unit is not "Degree Kelvin" the unit is "Kelvin". To add more weight to my point TVP45 wrote "The difficulty is in the temperature portion where conversion from "degCelsius" to "Kelvin" ..." - Do you now see where you made the error.

Perhaps if you would consider the fact that you made an error and not just jump in with your big mouth trying to defend your macho image then this response would not be necessary.

I do appreciate your input and your comments on this site but in this case you are incorrect and I just thought that I would point it out to you before you made a complete bafoon of yourself.

"I'm strugging to guess...are you trying to appear witty or intelligent?
I fear the result is neither" - well it looks like your comment has come back to bite you on the ass.

We will just have to agree to differ. AS we each obviously believe the other to be wrong.

BTW a quick search shows sites referring to both degrees K and just K.

I will concede I was curmudgeonly if you will concede you were pedantic.
I don't think the inclusion or omission of 'degree' effects it a jot.

If I really want to be pedantic I could say the expression 'degree Kelvin' doesn't actually state that the unit is considered to be a 'degree kelvin' it could be interpreted as being the same as stating a 'unit of kelvin' or an 'increment of kelvin' etc merely showing the singular as opposed to some other interval.

Also I may be a 'buffoon' but my sinature allows for that.

Del

PS Can a Cat be accused of trying to be macho?

Del,

This is not a matter of opinion. It is a matter of fact. For example there is not unit (that I am aware of) that is "Degree bar" or "Degree meter". It is a very minor point but you will often see persons referring to "Degree Kelvin" but in fact what they mean is "Kelvin" - everyone understands what they are talking about so I suppose it is not that important.

Perhaps some other persons could clarify this issue and if I am incorrect then I will be more than happy to apologise as I will have learned something new, which is the reason I sometimes check out this site.

I do take you point, but it is one of semantics. I suggest you look at the dictionary definition of 'degree'.

Del

One problem is that as a 'guest' I have no idea of your native language.
I am a native English speaker.

Consider the following..

" The cat crept up on the mouse by degrees"

" By degrees the attack pressed home it's advantage"

Neither implies units of attack or creep called 'degrees'

The Oxford English Dictionary says a degree is a

'Thing placed like step in series…. Stage in intensity or amount' etc

Thus it has meaning other than as the title of a unit, indeed it describes the stepwise nature of something… e.g The Kelvin temperature scale.

So while a increment of the Kelvin scale is not per se a 'degree' the scale does progress 'by degrees'!

Del

You are both correct, and incorrect, at the same time...

"kelvin" is a physical phenomena that occurs at a certain point on the Celsius temperature scale. How many Kelvin? this will be expressed by °C. Therefore it is not a quantitative value. The "degrees" Kelvin is merely an extrapolation.

• You can say that "Zero Kelvin " is -273°C or -459°F and it will be correct.
• Or you can also say, Today's temperature is boiling minus 75°C. it will also be correct (if this is the case)
• Actually some scientists define Kelvin and NOT 0-Kelvin as absolute zero for the Celsius or the Farenheit scales.

You see my point? So if you are in agreement let's wrap it up. If you do not, Shoot me also...

Wangito.

BTW Guest, why not register? looks as if you could contribute a good knowledge...Many of us never reply to a guest as it is considered lack of respect...

Ok..

If I'm allowed to continue this semantic discussion in a non acrimonious way.
My original (and highly contentious) statement was.

'a degree C is the same as a degree Kelvin!'

Maybe I should re-phrase it as.

'a degree C is the same as a degree on the Kelvin scale?'

This would be a perfectly acceptable use of degree, but is it really an improvement?

I would ask you to consider the alternative.

'A degree C is the same as a Kelvin'
This is demonstrably wrong as 'A Kelvin' can be construed as 1K which is about
-272^oC.
Also consider the purpose of language, which surely, is understanding.

I still believe my original heinous statement fulfills that criterion.

Del

Del,

When I questioned this issue originally I was doing so out of curosity as I was taught to use Kelvin and not Degree Kelvin. Yes it is a very minor point and it did not make the statement that you made totally senseless - everyone knew what you meant.

I did like the "Degree bar" and the "Degree meter" example put forward by Guest - I thought it was quite funny .

I look forward to reading more of your replies on many different matters and I am sure we will agree on some and disagree on others, but our disagreements shall never be taken personally.

Kind Regards

Mr. W.A Snow

I am coming around to your way of thinking by degrees...

Guest,

I don't disagree with you, but beg your patience. What is now Kelvin was once called Absolute Degrees, then degrees Kelvin, now Kelvin. OFs like me who went to school before electricity (we had to backlight our laptops with candles) often forget to change over to the new (read that as a Bonapartist conspiracy) system. I am frequently corrected on this point. I just forgets to remember.

The difficulty is in the temperature portion where conversion from "degCelsius" to "Kelvin" is not linear. Please advice me. Thanks in advance.

Huh? Why do you say this? Did someone tell you about something like this?

Hello c j chng

Conversion from "degCelsius" to "Kelvin" is linear but has a different zero. So an actual temperature is a different figure in the two systems.

But your 2 definitions involve a temperature difference, and a change in temp is same in "degCelsius" and "Kelvin", as Del has said.

Cheers......Codey

You wrote: "...but have different zero..."

Wrong sir. One zero comes with "°" , the other without. Hence, they can NOT the same...

Zero Kelvin , 0K (it doesn't use the "°" symbol and is -273°C approx) is the temp. where a perfect gas has lost all of it's energy. 0°C is the freezing temp. of water at ISA. 1°C, is 1/100 of the difference between icing temp. and boiling temp. of water at ISA....Not only different "0", different definitions also...

Sorry for being so pickey...

Wangito.

In my openion, Thermal conductivity of a material is the property of the material determined by the specific heat capacity of the material.

Both are proportional.

Thermal conductivity can be refered to the body as a whole while specific heat capacity is the themal conductivity for a mass of 1 kg of the same material.

Hence the units of thermal conductivity is J/oC or J/oK and

units for the Specific heat capacity is J/kg/oC or J/kg/o'K

The change in temperature of 1o'C = (is the same as) 1o'K

Rate of change of energy / sec.(measured in J/s) = Power (measured in W Watts).

J/s = W (watts),; J = Ws

If you replace 'W' with J/s or 'J' with Ws, the units for

Thermal Conductivity become Ws/o'C or Ws/o'K

and units of Specific heat capacity will become Ws/kg/o'C

I hope I'm right, but I stand to be corrected.

Thank you.

Sorry Mr. Chng,

I forgot to define the two quantities in my last reply.

Please read this reply before you read my privious reply. Thanks.

Specific heat capacity can be defined as "The quantity of heat energy (measured in Joules) required to raise the temperature od 1 kg of a substance through 1 o'C (or o'K) This will be measured in J/kg

Thermal conductivity is that property of the body which needs a quantity of heat energy required to raise its temperature.

Hence Thermal conductivity of a body is the quantity of heat required to raise the temperature of the whole body through 1 o'C. This will be measured in Joules.

Hope I'm right but stand to be corrected.

Thank you.

Hello Prayman

You're OK on specific heat but not on thermal conductivity. In any case you go into far too much detail. I'm pretty sure from the post that c j chng knows what these properties are, it's just that he was confused by the difference between an actual temperature (different in °C and K) and a ΔT. Hopefully this has been cleared up now.

Cheers......Codey

Thanks for your explaination, its really helpful and give me a better understanding of the property.

I concure with you, that be it that the property is stated as "/K" or "/degC", they actually mean the same thing which is a change in 1degC (in this case is equivalent to change in 1Kelvin). Thanks again...

Mr chang ,

1 w/cm deg c =100 w/m deg k .

2 1 joule/gram/°C = 1000 joule/kilogram/K

Hope this will solve ur problems .

i feel the confusion is because K=273+C

so 1/k = 1/(273+C) does not give a linear equation.

But thinking on practical terms what is /deg C ? it is increase/ decrease as the temp is increased by 1 deg C , (say from 27 deg C to 28 deg c) it will be same as that from 300 degK (=27 degC) to 301 deg K (=28 Deg C) so that in 1 Deg C and 1 Deg K it is same.

On Mathematics it is / (t2-t1) so if the variables are linearly related with unit coefficient, Y=1*X+c,

y2-y1= x2-x1

hope it is lucid

There's a little confusion. Thermal conductivity and specific heat are two different properties of a material. Thermal conductance and heat capacity are properties of a finite body.

Coarsely speaking, the thermal conductivity is the ratio between the conductive heat flux (expressed in Watt) through a unit cross-sectional area of material and the temperature gradient through the same section. Its dimensions are therefore (power/area)/(temperature/length) = Power/(length*temperature). Specific heat is the energy (expressed in Joule) required to increase the temperature of a unit mass of material of a unit temperature. It is therefore expressed as (energy/mass)/temperature = energy/(mass*temperature)

Therefore, thermal conductivity is referred to a dynamic phenomenon (heat transport), heat capacity is referred to a static phenomenon (energy accumulation).

When these definitions apply to a real finite body (e.g. we calculate the energy accumulated or the heat transferred through a real system), we introduce the concepts of thermal conductance and heat capacity. These items are not material properties, but properties of the real system, and are defined as follows:

• K = thermal conductance = thermal conductivity *cross-sectional flow area (expressed as power/temperature)
• C = heat capacity = specific heat * mass = specific heat * volume * density (expressed as energy/temperature)

Therefore, thermal conductance is the ratio between the transferred heat flux by conduction and the delta temperature through the body, originated by the same flow. Heat capacity is the ratio between the absorbed energy and the temperature increase of the body. Although expressed as constants, these parameters are actually depending on the temperature of the system.

These concepts can better understood with the electric similarity, where thermal conductance is the equivalent of electric conductance, heat capacity corresponds to electrical capacity, temperature is the equivalent of voltage and heat flow is the equivalent of current.

Although electrical and thermal phenomena are quite different by nature, they are perfectly analogue as regards their mathematical expressions. Now, the transferred current in a circuit is a function of the voltage deltas along its branches, rather than the absolute nodal voltages measured wrt a zero point, such as ground. In the same way, the heat transfer phenomena are depending on temperature differences, rather than absolute temperatures.

That's the reason why the thermal conductivities expressed in Celsius degrees or Kelvin have the same values, despite the different nature of the employed units: that's just because a temperature delta expressed in Kelvin or Celsius degrees has the same numerical value. Instead, if you want to convert, for example, a thermal conductivity from W/mK to W/m°F, following the same reasoning, you should divide the first value by 1.8, in such to get the second one.

"There's a little confusion. Thermal conductivity and specific heat are two different properties of a material. Thermal conductance and heat capacity are properties of a finite body."

couldnt put it any more clear myself

Hi,

Download the Uconeer (Units conversion for engineers), from this website http://www.katmarsoftware.com/uconeer.htm

I guess it will help you.

Regards

When using conversion factors the main operations are product and division, we must use the equivalent increment of temperature in each scale. Both Celcius and Kelvin have the same increment, this means 1 C = 1 K, in the english unit 1 F = 1 R. Therefore

Question 1: Thermal conductivity 1 Watt/m.C = 1 Watt/m.K

Question 2: Specific heat capacity: 1 joule/g.C = 1000 joule/Kg.C since 1 Kg = 1000 g

The equations K = C + 273 and R = F + 460 are not applicable in conversion factors.