Due to its fluid properties, cryogenic nitrogen can be used to study flows at high Reynolds and Rayleigh numbers in a compact apparatus compared to standard test fluids. We present the design of a new convection experiment with rotation that uses cryogenic nitrogen, and discuss a few scientific problems that can be addressed with it.

The apparatus consists of a 0.5m diameter 1m tall pressure vessel that can hold a pressure up to 35bar, enclosed in a vacuum jacket to improve insulation, and mounted on a rotating table. Several ports on the vessel provide space for different diagnostics and/or optical access to visualize the flow. By using cryogenic nitrogen from its freezing point up to the critical point, we can greatly vary its fluid properties and tune them for different experiment.

Liquid nitrogen below 77K is particularly useful to study highly convective flows where the effect of rotation is important, i.e. at high Rayleigh numbers and low Rossby numbers. In particular with a 20cm diameter liquid nitrogen cell of aspect ratio 1/2 we plan to study the heat transfer scalings in the geostrophic regime at Rayleigh numbers of order 1011 and to test different theories [1, 2, 3].

Nitrogen close to its critical point would yield the highest Rayleigh numbers flows, allowing us to inves- tigate highly turbulent convective cells with large aspect ratios. In such region of the parameter space very limited data is available and several outstanding questions are still open. In particular, we are interested in the large scale structures of the flow and in studying the existence of polygonal convective cells observed in simulations [4]. With a 37cm diameter cell with top and bottom sapphire plates, and aspect ratio 8, we plan to visualize the flow at Rayleigh number as high as 1011 − 1012.

By using both liquid and gaseous nitrogen along the saturated vapor curve, these experiments can be done also in the case of two phase convection.

References

- [1] E. M. King, S. Stellmach, J. Noir, U. Hansen, and J. M. Aurnou, “Boundary layer control of rotating convection systems.,” Nature, vol. 457, pp. 301–4, Jan. 2009.
- [2] E. M. King, S. Stellmach, and J. M. Aurnou, “Heat transfer by rapidly rotating Rayleigh–B ́enard con- vection,” Journal of Fluid Mechanics, vol. 691, pp. 568–582, Jan. 2012.
- [3] K. Julien, E. Knobloch, A. M. Rubio, and G. M. Vasil, “Heat Transport in Low-Rossby-Number Rayleigh- B ́enard Convection,” Physical Review Letters, vol. 109, p. 254503, Dec. 2012.
- [4] J. Bailon-Cuba, M. S. Emran, and J. Schumacher, “Aspect ratio dependence of heat transfer and large- scale flow in turbulent convection,” Journal of Fluid Mechanics, vol. 655, pp. 152–173, May 2010.