Finding specific heat C_p coefficients using NIST

In summary, in the conversation, the speaker is trying to find the specific heat (at constant pressure) coefficients for liquid nitrogen using the JANAF model, which assumes that the specific heat is a polynomial function of temperature. Before doing so, they are trying to find the coefficients for water and verify that they are correct. They are looking for the coefficients in the NIST-JANAF table, but they cannot find them. They then question where the coefficients they have found for water come from and how they lead to the expected specific heat value. The speaker also mentions implementing the thermo-physical properties of liquid nitrogen and finding data for density, dynamic viscosity, and thermal conductivity in the temperature range of -193 to -173 Celsius. They point out
  • #1
JD_PM
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TL;DR Summary
I am trying to find the specific heat (at constant pressure) ##C_p## coefficients linked to the JANAF model
I am trying to find the specific heat (at constant pressure) ##C_p## coefficients linked to the JANAF model, which basically assumes that ##C_p## is a polynomic function of ##T##, for liquid nitrogen (at ##\approx## 97 K).

Before doing that, I am trying to find those for water (at ##\approx## 300 K) and verify that they are ##9850.69, -48.6714, 0.13736## and ##-0.000127063##.

I am looking into NIST data for water; I checked both gas and condensed thermochemistry data but the coefficients don't match with the above. I also checked the NIST-JANAF thermo tables, for water, but the coefficients are not there.

How to find the desired coefficients for water (at ##\approx## 300 K)? They should be somewhere in the NIST-JANAF table.

Once I see the above it should be straightforward to find those for liquid nitrogen

Thank you! :biggrin:

PS: Actually, I am implementing the thermo-physical properties of liquid nitrogen.
 
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  • #2
JD_PM said:
Before doing that, I am trying to find those for water (at ##\approx## 300 K) and verify that they are ##9850.69, -48.6714, 0.13736## and ##-0.000127063##.
Where do these come from ? How do they lead to a ##\ c_p=75.349\ ## J/(K.mol) as expected ?

##\ ##
 
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  • #3
Just for the record, here's an explanation of the JANAF model

74897298478ddsd.png


BvU said:
Where do these come from ? How do they lead to a ##\ c_p=75.349\ ## J/(K.mol) as expected ?

##\ ##

Good question, here is the derivation.

I am trying to find the coefficients for liquid nitrogen online. However, I think the best I could do is follow the same procedure to derive them (not only for ##c_p## but for the density, dynamic viscosity and thermal conductivity).

So I am going to take the temperature range ##-193 < T < -173## Celsius (using ##80K < T < 100K## should also work).

First I am trying to find the density, ##c_p##, dynamic viscosity and thermal conductivity data associated to this temperature range (as done for water in the above derivation).
 
  • #4
JD_PM said:
Good question, here is the derivation.

Still think there is a mismatch somewhere. I can find no way to get a reasonable ##c_p## with e.g. formula ##(23)## or ##(24)## with such coefficients $$9850.69*300^4 -48.6714*300^3+ 0.13736*300^2 -0.000127063*300 = 7.979 \times 10^{13}\ \ ?$$

##\ ##
 
  • #5
JD_PM said:
I am looking into NIST data for water; I checked both gas and condensed thermochemistry data but the coefficients don't match with the above.
The NIST data is for the Shomate equation, which is not polynomial (note the ##E/t^2## term).
 
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  • #6
BvU said:
Still think there is a mismatch somewhere. I can find no way to get a reasonable ##c_p## with e.g. formula ##(23)## or ##(24)## with such coefficients $$9850.69*300^4 -48.6714*300^3+ 0.13736*300^2 -0.000127063*300 = 7.979 \times 10^{13}\ \ ?$$

##\ ##

There are no formulas numbered 23 nor 24. Did you mean 7.4 here?
 
  • #7
JD_PM said:
Just for the record, here's an explanation of the JANAF model
https://www.physicsforums.com/attachments/298450
 

Related to Finding specific heat C_p coefficients using NIST

1. What is NIST?

NIST stands for the National Institute of Standards and Technology. It is a non-regulatory federal agency within the United States Department of Commerce that is responsible for promoting innovation and industrial competitiveness by providing measurement and standards infrastructure.

2. Why is NIST used for finding specific heat C_p coefficients?

NIST houses a comprehensive database of thermophysical properties, including specific heat C_p coefficients, for a wide range of materials. This database is widely recognized and used by scientists and engineers for accurate and reliable data.

3. How does NIST determine specific heat C_p coefficients?

NIST determines specific heat C_p coefficients using a variety of experimental techniques, such as differential scanning calorimetry, adiabatic calorimetry, and isothermal calorimetry. These techniques involve measuring the heat capacity of a material under different conditions and using mathematical models to calculate the C_p coefficients.

4. Is NIST the only source for specific heat C_p coefficients?

No, there are other sources for specific heat C_p coefficients, such as published research studies and manufacturer data. However, NIST is widely considered to be the most reliable and accurate source due to its rigorous testing and validation processes.

5. Can NIST be used for all materials when finding specific heat C_p coefficients?

No, NIST's database does not include data for all materials. However, it does cover a wide range of common materials, and the database is regularly updated with new data. If NIST does not have data for a specific material, other sources may need to be consulted.

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