We study the response of a fluid in near-critical conditions to a heat pulse, in the absence of gravity effects. The fluid under investigation is CO 2 at critical density. It is enclosed in a thermostated sample cell. We apply a theory that accounts for hydrodynamics and a real equation of state. Comparison with experiments performed under reduced gravity on board the MIR orbital station show quantitative agreement and demonstrate that the dynamics of relaxation is ruled by two typical times, a diffusion time t D and a time t c associated to adiabatic heat transport, the so-called ''Piston effect'' ͑PE͒. Three regions are observed in the fluid. First, a hot boundary layer, developing at the heat source, which shows large coupled density-temperature inhomogeneities. This part relaxes by a diffusive process, whose density and temperature relaxations are slowed down close to the critical point. Second, the bulk fluid, which remains uniform in temperature and density and whose dynamics is accelerated near the critical point and governed by the PE time. At the thermostated walls a slightly cooler boundary layer forms that cools the bulk also by a PE mechanism. The final equilibration in temperature and density of the fluid is governed by the diffusion time t D , which corresponds to the slowest mechanism. Comparison with a one-dimensional model for temperature relaxation is performed showing good agreement with experimental temperature measurements. A brief comparison is given with the situation in the presence of gravity.

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One of the most important preoccupation of car manufacturers is to reduce emissions and hence to reduce weight of cars. One of the outstanding materials able to reduce weight while at the same time keeping the same crash absorption and hence safety, is austenitic steel. Austenitic stainless steels are used in crash relevant parts of cars. Moreover, designers can use their very good corrosion resistance and their well known surface aspect for structural visible parts like wheels, cross members, roof panels or tailgates. In this paper, stainless steels for automotive use are presented in detail. First, their chemical composition and tensile properties are explained. Then, a model for forming and crash behaviour is described. Using this model, stainless steels can be engineered into automotive parts and thus stainless steel can be considered as a workable and predictable material for the automotive industry.