Hí Drew,

Mettler-Toledo offers high pressure crucibles with thread. Maybe this would be an alternative for you.

https://www.mt.com/hk/en/home/products/Laboratory_Analytics_Browse/TA_Family_Browse/Crucibles/High_Pressure.html

Regards

Markus

Please note that if the sample pan is truly well sealed in air atmosphere, and was not entirely filled with liquid water, it should contain both liquid water and water vapour saturated air. Both phases would contribute for what would be rather more close to a Helmholtz free energy based measurement (constant volume), than to an enthalpy based measurement (constant pressure) ― in spite of some expectable deformation and expansion of the sealed pan. Hence, besides the contribution of the Helmholtz free energy of water vaporization and boiling, such experiment should account for the mass-averaged heat capacity at constant volume of both phases, up to the complete vaporization of the liquid phase, when that phase ceases to contribute. Obviously, it is just for the liquid phase that the constant volume heat capacity approaches that at constant pressure.

The starting point of thermodynamic logic is: 1) opposing perpetual motion. 2) The irreversibility of dynamics. Let's look at how to get Carnot efficiency = 1-T1/T2.

1.1 There are many kinds of type 2 perpetual motors, each of which is a natural phenomenon.

A) Machine A: against the irreversibility of thermodynamics (diffusion, heat conduction, friction, etc) - dynamics;

B) Machine B: Utilizing the Difference of Carnot Efficiency (Reversible Thermodynamics) - Thermodynamics

1.2 A and B belong to different disciplines. There is a parallel relationship between them and there is no logical mutual inevitability.

1.3. Logic of the Second Law of Thermodynamics:

Experience induction, deny that A machine==> B machine can not be manufactured==> All material Kano efficiency: 1-T1/T2.

1.4 The logic of the second law of thermodynamics violates the physical logic that A and B cannot be inferred from each other.

1.5 The second law of thermodynamics elevates the "irreversibility", which is in fact only a kinetic experience.

📷 Detailed discussion can be found in the following figure.

Hi Bo,

what does your contribution have to do with the question? I don't like it when a thread is just boarded like that.

Regards

Markus

Markus Christ , thanks for the suggestion, we will give the 15 MPa pan a shot. Vapor pressure is ~ 100 KPa so we shouldn't even be near the limit. Carlos Araújo Queiroz I understand that the heat capacity would have both liquid and vapor contributions, but we'd expect the vapor contributions to be much smaller than the liquid given the relative mass fractions of the liquid/vapor system. The other thing is that when we measure the mass of the pan before and after running it through the DSC, there's a small mass change, and when we calculate the latent heat of vaporization associated with that mass change and compare it to the extra heat input we see at larger temperatures the story checks out -- meaning there's evaporation and it's leaving the system.

Even if you use high-pressure pans that would not leak, there occurs vaporization in the system and what you finally get is saturation heat capacity, not isobaric heat capacity. These two are almost equal well below the boiling point, but the Cs increases compared to Cp when getting to moderate- and high-pressure region. You would therefore need to make corrections based on vapor space in the pan and vaporization enthalpy and vapor pressure of the water. These are not negligible, while contribution of heat capacity of the vapor phase most probably is.

Another thing is that it doesn't have to be the pressure inside the pan, that wastes your experiments, but a fact, that aluminum (you did not mention material of the pans - so I suggest the most common) reacts with water - and the reaction rate increases with the temperature. I have seen aluminum pans disintegrated after several runs with water or gallium ever around room temperatures (depending on manufacturer of the pans).

Finally, DSC is not a device for accurate heat capacity measurements (except for Tian-Calvet DSC and perhaps Power-Compensation DSC). Why do you actually try to measure heat capacity of so well-known compound with a method with so high uncertainty?

Thank you for the thoughtful response Vojtěch Štejfa . I will see if I can correct the data for the latent heat of vaporization and see if that fixes the issue. We are trying to measure the heat capacity of water as a baseline before we measure the heat capacity of water + added stuff so that we can see how much the added stuff affects things. What other methods would you suggest? I'm a mechanical engineer, so calorimetry isn't my area of expertise but when I asked the chemists I work with they pointed me towards a DSC.

1. The second law of thermodynamics loses the ability of quantitative prediction.

2. Data processing method of law 2 of thermodynamics violates scientific discipline: modifying experimental data to satisfy theory

See the picture for details.

3. The second law of thermodynamics can only be called science if it reaches the same quantitative prediction ability as Newton's second law, otherwise it is pseudoscience.

4.Unfortunately, all the charts of enthalpy and entropy are organized in this way.

Comparison of New and Old Thermodynamics

1. Logic of the Second Law of Thermodynamics: Subjectivism, Logical Jump, Interdisciplinary Argumentation.

2. New thermodynamics pursues universality, two theoretical cornerstones:

2.1 Boltzmann formula: ro=A*exp(-Mgh/RT) - Isotope centrifugal separation experiments show that it is suitable for gases and liquids.

2.2. Hydrostatic equilibrium: applicable to gases and liquids.

3. The second and third sonic virial coefficients of R143a derived from the new thermodynamics are in agreement with the experimental results.

3.1. The third velocity Virial coefficient derived is in agreement with the experimental data, which shows that the theory is still correct when the critical density is reached.

4. See Appendix Pictures and Documents for details.

The corrections for vaporization are as far a I know only performed for adiabatic-calorimeter data. With the uncertainty of DSC heat capacities, it is probably not the critical issue actually.

If I understand well, what you're looking for is excess heat capacity for mixture of water and solute? Otherwise you would measure your solute separately...

The excess heat capacities are typically very small and the uncertainty you can reach with a DSC is not sufficient (you're subtracting two big numbers to get a small one). There are special types of circulation calorimeters, where you measure heating of a mixture with pure water as reference. I don't see many alternative possibilities.