(226a) Thermal Conductivity of Fluids near Critical Points – a Saga of Principle, Precision, Persistence and Practical Application

This presentation in honor of the 80^th birthday of Jan Sengers begins with a fundamental experiment on the thermal conductivity of carbon dioxide near its critical point.  He performed this experiment in the 1950s as a graduate student at the Van der Waals Laboratory at the University of Amsterdam, the Netherlands.  At that time, the scant experiments that existed revealed a strong anomaly at the critical point.  The prevalent theory was based on assuming regular behavior of the Onsager coefficients, and it predicted no critical anomaly.  It took Sengers a decade to eliminate the artifacts that had plagued previous experiments and show that nevertheless a critical divergence remained, thus dooming the theoretical expectation of that time.  

The development of the critical region scaling laws and of the mode-mode coupling theory for the behavior of transport coefficients that began in the 1960s formed the basis for a fundamental, non-classical description of transport coefficients in fluids; a task that, in its turn, required persistent attention to details of approximations used, and subsequent generalizations to take into account the asymmetry between coexisting phases that characterize fluids. Sengers and collaborators were avid players in applying and testing the new theory by delicate and definitive light scattering experiments in binary liquid mixtures. 

The last part of this talk focuses on a feature that has distinguished the Sengers School from most other fundamentally oriented groups, namely the emphasis on practical applications to fluids of interest in mechanical and chemical engineering applications. The thermal conductivity of water in the critical region is the most striking example of incorporating rigorous fundamental theory into the international formulations (“steam tables”) used by the electric power industry for design of steam power cycles.  Sengers began with this task in the early 1970s, and persisted.  In the year that he celebrates his 80^th birthday, the new formulation for the thermal conductivity of steam by an international team that he led, and which includes a group of collaborators at NIST, Boulder, has been proposed for adoption by the International Association for the Properties of Water and Steam – an prime example of his principled approach, his persistent striving for precision, and his conviction that his theoretical work needs to cross the bridge to practical engineering applications.