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The piston effect as a means to measure near-critical bulk viscosity

Carles, P. and Dadzie, K. and Zhong, F. (2003) The piston effect as a means to measure near-critical bulk viscosity. In: UNSPECIFIED.

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Fluids close to their liquid-vapour critical point exhibit peculiar properties which have strong consequences on their hydrodynamics. Considerable experimental work has been conducted to measure the divergence of near-critical fluid’s properties close to the critical point. But owing to their peculiar hydrodynamics, some of these quantities have proved difficult to access. One way out of this limitation has been the use of microgravity experiments, in which the effects of gravity could be suppressed. But even in the absence of gravity, near-critical fluids are subjected to very strong dynamical phenomena. In particular, it has been observed that the heat transfer in fluids near the liquid-vapour critical point is governed not only by diffusion, convection and radiation, but also by a thermo-mechanical coupling called the Piston Effect, discovered in the early 90s. Among the least known properties close to the critical point is the bulk viscosity, which is expected to exhibit a very strong critical divergence. Despite this divergence, most existing theoretical models of the Piston Effect are based on non-viscous equations. Using equations recently developed for the hydrodynamics of viscous nearcritical fluids, we propose a new indirect way of measuring bulk viscosity close to the critical point. This method is based on the use of a carefully monitored Piston Effect, acting as a probe and triggering a dynamic response in which the signature of bulk viscosity can be measured.