Turbulent temperature fluctuations in liquid sodium

The axial transport of temperature fluctuations in vertical slug flow is investigated. The behavior of the temperature fluctuations in the high-frequency range is only correctly described if axial conduction is taken into account as a dissipation mechanism. In the case of high thermal conductivity of the fluid, a simple approximation is found for the transfer function of temperature fluctuations. Its form explains why the fluid velocity may be derived from the peak of the cross-correlation function. Numerical results for the transfer function are given for liquid sodium. Experiments were performed in a sodium loop in order to obtain the following statistical characteristics for turbulent temperature fluctuations in flow through a circular pipe (constant wall heat flux 6 W/cm2, Re = 20,000 - 120,000, frequency range 0.25 to 100 cps, Pr approx. = 0.007): autocorrelation functions, spectral power densities, variances, third and fourth moments and microscales