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WFU Physics

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TITLE: Equilibration and heat transfer near the liquid-vapor critical point of a pure fluid

SPEAKER: Professor Horst Meyer,

Most of the properties of a fluid near the critical point diverge when this transition is approached from either the homogeneous phase (T > T_c) or from below (T < T_c) where the liquid and the vapor coexist. The flights with the space shuttle under microgravity conditions permit to measure the critical properties very close to T_c where the results obtained under normal gravity are affected by stratification. This is why it is important to know how the fluid reaches equilibrium after a change of temperature of the container, and in the absence of free convection which is driven by buoyancy. After a short review of the critical phenomena, measurements will be described as well as computer simulations in one dimension describing the road to equilibration in ³He. Near the critical point, T = 3.3 K, ³He behaves like other fluids, but the conditions encountered at low temperatures are particularly advantageous for these studies. In the equilibration experiments, the onset of convection was also observed. We have made a detailed study of this phenomenon in a separate ("Rayleigh Benard") cell, and detected a phenomenon not studied before under laboratory conditions. The diverging compressibility of the fluid near T_c makes this detection possible and the results are discussed and compared with predictions.