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We consider the flow induced in a spherical shell by fixing the outer sphere and rotating the inner one, with the aspect ratio = (r o − r i )/r i ranging from 0.1 to 10. The basic state consists of a jet in the equatorial plane, carrying fluid from the inner sphere to the outer, and involving also an azimuthal component. The azimuthal component dominates for 1, the radial component for 1. The basic state is otherwise much the same over the entire range 0.1 10. We next linearize the Navier-Stokes equation about this basic state, and compute the linear onset of non-axisymmetric instabilities. For 0.1 3.8 the instabilities have the opposite equatorial symmetry as the basic state, and consist of a series of waves on the initially flat radial-azimuthal jet. The azimuthal wavenumber decreases monotonically from m = 12 at = 0.1 to m = 2 at = 3.8, but with a puzzling transition between = 0.27 and 0.28, where one m = 6 mode is replaced by another, very similar one. For 3.8 10 we obtain an m = 2 mode having the same equatorial symmetry as the basic state. This instability is further differentiated from the previous ones in that it consists of a modulation in the strength of the return flow after the jet has reached the outer sphere, rather than an instability of the jet itself. Finally, we solve the fully three-dimensional Navier-Stokes equation, and consider the equilibration of some of these modes in the supercritical regime. For = 0.5 we can achieve Re = 1.15 Re c , and obtain results in excellent agreement with experiments. For = 0.8, 1.5 and 2.5 we can achieve up to 1.9 Re c , and

Carbon capture with subsequent compression and storage is a promising possibility for the reduction of CO2 emissions from coal‐fired power generation. A very efficient post‐combustion CO2 capture technology is the carbonate looping process. To further increase the process efficiency, a new concept is considered where the heat for calcination is transferred from an external combustor to the calciner by means of heat pipes. Some thermodynamic evaluations for a retrofit of a coal‐fired host plant with the indirectly heated carbonate looping process and cold flow model tests of a 300‐kWth test facility that will be erected in 2013 in Darmstadt are presented.

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