Abstract
The specific heat at constant volume cv shows a weak singularity at the critical point. Renormalization group techniques have been applied, predicting a universal critical behavior which has to be experimentally confirmed for different systems. In this paper an experiment is presented to measure the specific heat of SF6 along the critical isochore (ρc=0.737 g·cm−3), applying a continuous heating method. The results cover a temperature span of −1.5×10−2< τ<1.70×10−2 [τ=(T−T c)/T c] and were strongly affected by gravity effects that emerge in the sample of 1-mm hydrostatic height near the critical point. Using regression analysis, data were fitted with functions of the form c v/R=A × ¦τ¦−α + B for the one-phase state and c v/R=A″ × ¦τ¦−α″ + B″ for the twophase state. Within their error bounds the critical values (α=α″=0.098, A″/A=1.83) represent the measurements for the temperature span 3.5×10−5< ¦τ¦<2.0×10 −3, in good agreement with theoretical predictions. In order to exclude density profiles in the specimen, which are unavoidable in terrestrial experiments due to the high compressibility of fluids at the critical point and the gravity force, a space-qualified scanning ratio calorimeter has been constructed, which will permit long-term cv measurements under microgravity (μ-g) conditions. The experiment will be part of the German Spacelab mission in October 1985. The significant features of the apparatus are briefly sketched.
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Straub, J., Lange, R., Nitsche, K. et al. Isochoric specific heat of sulfur hexafluoride at the critical point: Laboratory results and outline of a spacelab experiment for the d1-mission in 1985. Int J Thermophys 7, 343–356 (1986). https://doi.org/10.1007/BF00500160
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DOI: https://doi.org/10.1007/BF00500160