23rd IATP Meeting, July 5th 2025
The meeting was opened by the Chairman, Prof. Sir William Wakeham, who welcomed all present and thanked Dr Bernd Rathke, as the local organiser of the meeting, for the excellent arrangements.
The meeting was divided into the usual scientific session and business session. The proceedings are recorded here in that order.
2. SCIENTIFIC SESSION
Each presentation engendered discussion and a few points of special interest are noted here:
2.1 Magnetic Amplification of Heat Transfer Requires Customised Ferronanofluids
Matthias Buschmann, A. Meyer, A. Potthoff (Germany)
M. Buschmann considered heat transfer in fluids containing solid magnetic particles of nanometer dimensions. He stressed that in any problem of heat transfer involving fluids it was always necessary to understand the fluid flow first recognizing the balance between inertial and viscous forces embodied in the various dimensionless groups, before consider heat transfer, When one considered fluids with suspended magnetic particles it was possible to introduce another, electromagnetic, force to the system which had the potential to enable some influence on heat transfer.
2.2 Intercomparison of the Specific Heat Capacity of Heat Transfer Fluids
Hans-Peter Ebert, Michael Brütting (Germany)
H.-P. Ebert stated that water, or monoethylene-glycol-water, or ethanol-water mixtures are used as heat transfer fluids for geothermal applications. To measure the specific heat capacity of these fluids, 7 institutes coordina-ted their measurements: 1) Acqua concept Gesellshaft fur Wasebehandlung GmbH, 2) Austrian Institute of Technology, 3) Belimo Automation AG, 4) Center for Applied Energy Research e.V., 5) German Aerospace Center, 6) Institute fur Luft- und Kaltetechnik GmbH, and 7) Netzsch-Geratebsu GmbH. The target of uncertainty of 2% was achieved.
2.3 Measurements of the Viscosity and Density of Gaseous Hydrogen + Nitrogen Mixtures with a Combined Vibrating-wire Viscometer/Single-Sinker Densimeter
Ruben Harten, Karsten Meier (Germany)
R. Harten discussed modifications of the combined vibrating wire/single sinker instrument for measurements of gas mixtures containing hydrogen. It is designed to operate between 273-473 K, and up to 30 MPa, with uncertainties of 0.1% for density and 0.25-0.3% for viscosity. The instrument was calibrated with He, and measurements of the viscosity and density of H2/N2 mixtures were presented.
2.4 Diffusivities in Polymer Melts with Dissolved Blowing Agents by Dynamic Light Scattering (DLS) and Equilibrium Molecular Dynamics (EMD) Simulation
Patrick Schmidt, Tobias Klein, Andreas Paul Fröba (Germany)
P. Schmidt presented the current work on the diffusion measurements on polystyrene samples studied (PS10, 20, 500 and 950) with different blowing agents N2, CO2 and R134a. Equilibrium Molecular Dynamic simulations helped in explaining these measurements by predicting trajectories of atoms and molecules.
2.5 Viscosity and Electrical Conductivity of Pure and Mixed Aqueous NaCl and CaCl2 Solutions at 293 K to 353 K and 0.1 MPa
Harald Milsch, Ulrike Hoffert (Germany)
U. Hoffert presented her work in geothermal research in the German Research Centre for Geosciences (GFZ). Reservoirs are usually at temperatures up to 423 K and 50 MPa, so properties up to these ranges are required. Fluids of sedimentary basins are often dominated by aqueous solutions of NaCl and CaCl2. She presented new viscosity measurements with about 2% uncertainty, and electrical-conductivity measurements with about 3% uncertainty and examined the possibility of a correlation between electrical conductivity and viscosity.
2.6 Entropy Scaling Approaches Applied to the Viscosity of Asymmetric Mix
J.P. Martin Trusler, Iusiph Eiubovi (UK)
I. Eiudovi presented his work in the field of safer carbon storage. He attempted to derive a universal viscosity correlation with 2 parameters. On pure components the new correlation predicts the values within 5-10%, while in the case of mixtures, it seems to work much better, depending on the mixing rule. A group-contribution approach based on branching and the total number of carbons, seemed to be promising. There was discussion of other approaches to the same problem and on the underlying physics of Entropy-Scaling. It seemed likely that it was closely connected to models based on repulsive forces which determine structure such as the Enskog theory and its offshoots.)
2.7 Enhancing Low-Temperature Thermal Energy Storage with Next-Generation PCMs
Maria Carolina M. Sequeira, Timur Nikitin, Fernando J.P. Caetano, Hermínio P. Diogo, João M.N.A. Fareleira, Rui Fausto (Portugal)
M.C.M. Sequira presented an overview of the work carried out during her PhD. The main purpose was to find PCMs for low-temperature (-80 to -20’C) thermal energy storage. She employed DSC, HSPM, and Raman spectroscopy to build the solid-liquid phase diagrams and showed measure-ments on n-alkanes and n-alkyl adipates. They now have 8 different systems together cover the range of temperatures encountered in medical and food transport.
2.8 Thermophysical Measurements on Carbonate Molten Salts for Solar Plants Applications
Maria José Lourenço, João Chainho, Valentim Nunes, João Serra, Ivo Costa, Manuel Abreu, Carlos Nieto de Castro, Pedro Celestino (Portugal)
C.A. Nieto de Castro discussed new materials approaches for concentrating solar power, main problem being that molten salts are corrosive. He discussed the problems of (LiNaK)2CO3 as a possible candidate, including nanosalts with SiO2 and MgO nanoparticles. He showed large deviations in the data available for the heat capacity and thermal conductivity. In the case of the viscosity, he described the modification of their viscometer and showed new measurements, while the thermal conductivity instrument is still under construction.
2.9 Definitions and Preferred Symbols for Mass Diffusion Coefficients in Multicomponent Fluid Mixtures Including Electrolytes (Report on the IUPAC Project 2014-010-1-100)
Tobias Klein, Chathura J. Kankanamge, Thomas M. Koller, Michael H. Rausch, Andreas P. Fröba (Germany), Marc J. Assael (Greece), William A. Wakeham (UK), Gabriela Guevara-Carrion, Jadran Vrabec (Germany)
T. Klein presented the successful paper just published on this matter (Pure & Applied Chem. 97:689-713, 2025). He discussed all different types of mass diffusion coefficients employed today. In discussion it was agreed that it would be sensible to ask Journals likely to publish experimental or theoretical treatments of Diffusion in fluid systems to require their authors to adhere to the new recommendations in their papers.
2.10 Towards a definition of “ideal-solution” for transport properties
Gabriela. Guevara Carrion (Germany), Carlos A. Nieto de Castro (Portugal)
G Guevara-Carrion described the work to develop a useful definition of an ideal solution for transport properties as an analogue of the concept familiar in equilibrium properties. The model was likely to be based upon MD modelling for a mixed system of L-J molecules in which all interactions are identical, but the masses of species differ. This model agrees with the Eyring theory for viscosity. There was fundamental discussion and some disagreement with the proposed concept and radically different alternatives proposed such as the Chapman-Enskog equations for a low-density gas mixture, which in the concept of the authors is not applicable for ideal liquid solutions. There is no relation between a model for a perfect gas mixture (or a low-density mixtures) and the ideally liquid solution.
2.11 Kinematic Viscosity of High Saline Waters at Low Temperatures
Yunus Demir, Sabine Wagenfeld, Bernd Rathke (Germany)
B. Rathke discussed the viscosity of H2O/NaCl or H2O/CaCl2 at very low temperatures (-20 to -80’C). These two fluids are potential working fluids space for geo cooling applications although they are highly corrosive. Data, especially viscosity data are missing in this temperature range. He further described an Ubbelohde capillary viscometer employed for this work, and showed viscosity measurements down to -30’C.)
2.12 Association Equilibrium in the Chemical and the Physical Picture
Wolffram Schröer, Bernd Rathke (Germany)
W. Schröer sought to demonstrate the reconciliation of the physical description of association equilibrium through, for example, the virial equation of state and a chemical description through the law of mass action. The equivalence was shown unequivocally.
2.13 Discussion: Are There Areas of Science/industry Where There are Urgent Need for Transport Properties?
William A. Wakeham (UK).
A discussion, initiated by W.A. Wakeham, was carried out aiming to identify areas of science/industry where transport properties are in urgent need. He emphasised that the concentration of efforts of the past on fossil-fuel derived fluids in thermodynamic states that were quite benign were already diminishing to be replaced by those focused on more difficult experimental circumstances with corrosive materials at more extreme conditions. Would this be a continuing trend and should the IATP do anything about is.
M.J. Assael drew attention to the fact that from his perspective as an editor, many investigators are examining the use of nanofluids, but other areas where large number manuscripts are submitted are properties for space materials, biofluids, solar systems, carbon-storage systems, and thin films.
M. Trusler argued that IATP was a forum for a discussion of what individuals were doing in response to their own circumstances and that it was inappropriate to dictate areas of endeavour.
W.A. Wakeham responded that this had not been his intent in raising the discussion but the topics in this meeting already showed that there was a strong move away from the traditional fluids and that this already reflected changes in the wider world. It was agreed that IATP should continue to be responsive and an open forum for discussion without any attempt to be prescriptive.)
3. BUSINESS SESSION
3.1. PROJECTS CONCLUDED
1. IUPAC Project 2014-010-1-100: Definitions and Pre-ferred Symbols for Mass Diffusion Coefficients in Multicomponent Fluid Mixtures Including Electrolytes
CT. Klein, C.J. Kankanamge, T.M. Koller, M.H. Rausch, A.P. Fröba (Germany), M.J. Assael (Greece), W.A. Wakeham (UK), G. Guevara-Carrion, J. Vrabec (Germany)
Paper published in Pure & Applied Chem. 97:689-713 (2025), DOI: 10.1515/pac-2024-0251
A.P. Fröba and particularly T. Klein were congratulated for the excellent work carried out in this manuscript.
The possibility of further promoting this nomenclature was examined WA. Wakeham and M.J. Assael to communicate with editors of relevant journals.C.
3.2. PROJECTS CONTINUED
The following projects were discussed and it was agreed to continue them:
2. Reference Correlations for the Viscosity and Thermal Conductivity of Fluids over Extended Temperature and Pressure Ranges.
M.J. Assael (Greece), M.L. Huber, R.A. Perkins (USA), F. Caetano, J.M.N.A. Fareleira (Portugal)
This is an on-going project on developing new reference correlations of the viscosity and thermal conductivity of fluids. M.J. Assael pointed out that new recent ab-intio calculations carried out by R. Hellmann allow the incorporation of a much more accurate dilute-gas correlation for the transport properties that is capable of excellent prediction at high temperatures. Project continues.
3. High-Temperature High-Pressure Viscosity Standards
J.M.N.A. Fareleira, F. Caetano (Portugal), W.A. Wakeham, J.P.M. Trusler (UK), A.P. Fröba, A. Lei¬pertz, B. Rathke (Germany), K. Harris (Australia), J. Fernandez (Spain), K. Schmidt (Canada), Chr. Boned (France)
The project is concluded, and a summary review will be written by J.M.N.A. Fareleira, and F. Caetano.
4. Thermal Conductivity and Enthalpy of Fusion of n-Alkanes as Practical PCM
L. Fedele (Leader), S. Bobbo (Italy), M.J. Assael (Greece), W.A. Wakeham (U.K.), M.L. Huber, R. Perkins (USA), A.P. Fröba, T.M. Koller, K. Meier, B. Rathke, S.E. Quiñones-Cisneros (Germany), J.M.N.A. Fareleira, F.J.P. Caetano (Portugal), J. Fernandez (Spain), E. May (Australia), V. Shevtsova (Belgium), V. Diky (USA)
Project continues.
5. Further Understanding of the Operation of the Torsional Crystal Viscometer
C.A. Nieto de Castor (Portugal), F.J.V. Santos (Portugal), W.A. Wakeham (UK)
Project continues but awaits more experimental input.
6. Special Issue of the International Journal of Thermophysics titled “Transport Property Measu-rements in Research and Industry: Recommended Techniques and Instrumentation”
W.A. Wakeham (UK), M.J. Assael (Greece).
M.J. Assael reported that 18 articles have so far been published in this Special Issue and thanked particularly the authors present in the meeting (W.A.Wakeham, J.P.M. Trusler, M.C.M. Sequeira, C.A. Nieto de Castro, A.P. Fröba, H.-P. Ebert, and V. Shevtsova). He further pointed out that the SI papers have already gathered a very large number of downloads, and a good number of citations. He also thanked his co-Guest Editor, W.A. Wakeham for the idea and the running of the SI.
7. Transport of Hydrogen in Solids and Liquids
J.M.P. Trusler (UK), T.M. Koller, M.H. Rausch, A.P. Fröba, B. Rathke (Germany), F. Caetano, J.M.N.A. Fareleira (Portugal).
Project continues but it will be narrowed down to only liquids. A review article will be written at some stage.
8. Apparent Thermal Conductivity of Nanofluids
J. Fernandez (Leader, Spain) L. Fedele (Italy), C.A. Nieto de Castro (Portugal), A.P. Fröba, M. Buchmann (Germany), M.J. Assael (Greece), M. Buchmann (Germany)
Project continues.
9. Towards a Definition of “Ideal-Solution” for Transport Properties.
C.A. Nieto de Castro (Portugal), Gabriela Guevara Carrion (Germany)
Project continues.
3.3. NEW COLLABORATIVE PROJECTS
Ideas for new projects were discussed briefly but are awaiting better formulation.
3.4. PROCEDURE FOR IATP ENDORSEMENT
Members were reminded that if they wish to have the endorsement of IATP for their work they should submit it to the Secretary in the first instance to arrange a rapid review. Referees who have agreed to participate in the review process in addition to the Executive Member are M.L. Huber and E. May.
4. MEMBERSHIP
Prof. M.J. Assael reminded everyone that all information about IATP activities, as well as the current list of members, can always be found at
https://ltpep.com/ -> I.A.T.P.
It was also decided that members who had not attended for some time, and where there was evidence that they would probably not have a continuing connection, would be removed form the list.
The criterion to become a Member of IATP is to be present to at least two meetings. Having checked the list of attendees of the last three meetings, the following were approved as Members:
- Dr Hans-Peter Ebert
- Dr Sofia Mylona
- Professor Tatjana Vasyltsova
5. FUTURE MEETINGS
5.1. 24th IATP Meeting, 2026
The 24th IATP Meeting will take place on Sunday, June 21st, 2026, in the Campus Serge Kampf Les Fontaines, 40 km outside Paris prior to the ECTP 2026. Details will be announced in due course.
5.2. 25th IATP Meeting, 2027
The 25th IATP Meeting might take place on Sunday June 20th, 2027, in Boulder, CO, USA, prior to the STP 2027. If it does not take place then, other arrangements will be made. Details will be announced in due course.
6. LIST OF ATTENDEES
List of people that attended the meeting:
1. Professor Sir William A. Wakeham (Chairman)
2. Professor Marc J. Assael (Secretary)
3. Professor Andreas P. Fröba
4. Professor Carlos Nieto de Castro
5. Professor J.P. Martin Trusler
6. Dr Eckard Bich
7. Priv.-Doz. Matthias H. Buschmann
8. Mr Yunus Demir
9. Dr Hans-Peter Ebert
10. Mr Iusiph Eiubovi
11. Dr Gabriela Guevara-Carrion
12. Dr Ulf Hammerschmidt
13. Mr Ruben Harten
14. Dr Robert Hellmann
15. Dr Sebastian Herrmann
16. Ms Ulrike Hoffert
17. Professor Karsten Meier
18. Professor Johannes Kiefer
19. Dr Tobias Klein
20. Dr Sofia Mylona
21. Dr Harald Milsch
22. Professor Akira Nagashima
23. Professor Sergio E. Quiñones Cisneros
24. Dr Bernd Rathke
25. Mr Patrick Schmidt
26. Ms Sabine Wagenfeld
27. Professor Wolffram Schröer
28. Ms Maria Carolina Sequeira
29. Professor Tatjana Vasyltsova
