Induced circulation

Internal-loop airlift reactors (ALRs) are widely used for their self-induced circulation, improved mixing, and excellent heat transfer [1], This work reports on the design of an ALR with a novel gas-liquid separator and novel gas distributor. In this ALR, the gas was sparged into the annulus. The special designed gas-liquid separator, at the head of the reactor, can almost completely separate the gas and liquid even at high gas velocities. 

If pnliL is large, Q approaches unity. If ////// is small, Q approaches a value of 1.5. Thus the effect of circulation is small when a liquid drop falls in a gas although is large when a gas bubble rises in a liquid. If the fluid within the drop is very viscous, the amount of energy which has to be transferred in order to induce circulation is large and circulation effects are therefore small. 

Figure 15.1—Inductively coupled plasma torch. A radiofrequency current (between 27 and 50 MHz) that induces circulation of the electrons in the inert gas drives the torch. The argon serves as an auxiliary gas, a cooling gas and the nebulisation gas. In the upper right is shown an optic device used to collect emitted light in the longitudinal axis of the plasma. Lower down, plasma generated by microwave.

In the emulsion phase/packet model, it is perceived that the resistance to heat transfer lies in a relatively thick emulsion layer adjacent to the heating surface. This approach employs an analogy between a fluidized bed and a liquid medium, which considers the emulsion phase/packets to be the continuous phase. Differences in the various emulsion phase models primarily depend on the way the packet is defined. The presence of the maxima in the h-U curve is attributed to the simultaneous effect of an increase in the frequency of packet replacement and an increase in the fraction of time for which the heat transfer surface is covered by bubbles/voids. This unsteady-state model reaches its limit when the particle thermal time constant is smaller than the particle contact time determined by the replacement rate for small particles. In this case, the heat transfer process can be approximated by a steady-state process. Mickley and Fairbanks (1955) treated the packet as a continuum phase and first recognized the significant role of particle heat transfer since the volumetric heat capacity of the particle is 1,000-fold that of the gas at atmospheric conditions. The transient heat conduction equations are solved for a packet of emulsion swept up to the wall by bubble-induced circulation. The model of Mickley and Fairbanks (1955) is introduced in the following discussion. 

To prevent stratification in an initially homogeneous tank which is known to be already in jet induced circulation, assume 0.5F of the values computed from the above expressions. 

Bioreactors come in many different designs and shapes. The stirred tank reactors are common. They comprise a cylindrical tank, a mechanical stirrer, and a guidance system for the liquid to reduce stress and enhance mixing. Pneumatic reactors use air or oxygen to mix the fermentation broth. The gas is introduced near the bottom of the reactor and induces circulation of the liquid. 

Experiments were performed at boiling induced circulation of saturated liquid and forced boiling condition. The description of measurement procedure was done at [21] and [23]. 

E. Demedde, E. L. Cambridge, Gas induced circulation in an aluminum reduction cell, Paper presented at the AIME Annual Meeting, New York, 1975. 

The extreme range of chemical shifts is to be found in the tin(II) compounds, R Sn . When R is an alkyl or aryl group, the doubly occupied and the vacant orbital on tin appear to be close in energy, and the induced circulation of electrons between these two orbitals deshields the tin. When R is cyclopentadienyl, the HOMO is close to an sp2 hybrid, and the LUMO has almost pure p character the energy separation is too large to permit efficient circulation of charge, and the tin is highly shielded. 

Elliott, A. J. (1978). Observations of the meteorologically induced circulation in the Potomac estuary. Estuarine Coastal Mar. Sci. 6, 285-299. 

Pool boiling. Here, boiling occurs by the generation of vapor from a heated surface in a pool of liquid. Though the liquid may circulate within the pool due to natural convection, mechanically induced circulation of the liquid does not take place. 

FIGURE 15.79 Induced circulation in a kettle reboiler (from Hewitt et al. [13], with permission. Copyright CRC Press, Boca Raton, FL). 

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