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We study time evolution of rotating, axisymmetric, two dimensional inviscid accretion flows around black holes using a grid based finite difference method. We do not use reflection symmetry on the equatorial plane in order to inspect if the disk along with the centrifugal barrier oscillated vertically. In the inviscid limit, we find that the CENtrifugal pressure supported BOundary Layer (CENBOL) is oscillating vertically, more so, when the specific angular momentum is higher. As a result, the rate of outflow produced from the CENBOL, also oscillates. Indeed, the outflow rates in the upper half and the lower half are found to be anti-correlated. We repeat the exercise for a series of specific angular momentum λ of the flow in order to demonstrate effects of the centrifugal force on this interesting behaviour. We find that, as predicted in theoretical models of disks in vertical equilibrium, the CENBOL is produced only when the centrifugal force is significant and more specifically, when λ > 1.5. Outflow rate itself is found to increase with λ as well and so is the oscillation amplitude. The cause of oscillation appears to be due to the interaction among the back flow from the centrifugal barrier, the outflowing winds and the inflow. For low angular momentum, the back flow as well as the oscillation are missing. To our knowledge, this is the first time that such an oscillating solution is found with an well-tested grid based finite difference code and such a solution could be yet another reason of why Quasi-Periodic Oscillations should be observed in black hole candidates which are accreting low angular momentum transonic flows.

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Photooxygenations allow for the incorporation of molecular oxygen into substrates under mild and sustainable conditions. They only use light, oxygen and catalytic amounts of an organic dye to generate singlet oxygen (1O2), a short-lived reactive species, which can subsequently react with a multitude of functional groups within a substrate. Photooxygenations have found applications in fine chemical and pharmaceutical industries, for example in the manufacture of fragrances, building block chemicals and pharmaceuticals. Unlike batch processes, photooxygenations under flow conditions avoid accumulation of potentially explosive intermediates or products by continuously producing small amounts of materials, which can be subsequently quenched or converted safely. Continuous-flow reactors also allow for precise temperature control and the utilization of low-power light sources such as LEDs or OLEDs. The combination of flow operation, miniaturized dimensions and photooxygenations enables an environmentally friendly and safe adaptation to green organic synthesis. This chapter highlights various flow photoreactor technologies and successful examples of photooxygenations in flow.

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