Counterflow geometry

It is well known that in a jet flame blow-out occurs if the air-fuel mixture flow rate is increased beyond a certain limit. Figure 18.3 shows the relationship between the blow-out velocity and the equivalence ratio for a premixed flame. The variation of blow-out velocity is observed for three different cases. First, the suction collar surrounding the burner is removed and the burner baseline performance obtained. Next, the effect of a suction collar itself without suction flow is documented. These experiments show that for the nozzle geometry studied, the free jet flame (without the presence of the collar) blows out at relatively low exit velocities, e.g., 2.15 m/s at T = 1.46, whereas for > 2 flame lift-off occurs. When the collar is present without the counterflow, the flame is anchored to the collar rim and blows out with the velocity of 8.5 m/s at T = 4. Figure 18.4a shows the photograph of the premixed flame anchored to the collar rim. The collar appears to have an effect similar to a bluff-body flame stabilizer. The third... 

Figure 13 also shows the range of liquid and gas velocities corresponding with the operation of industrial trickle-flow reactors. It follows that an internally finned tube of the present geometry with an outlet angle of 70 allows counterflow operation in the... 

From the observable effect of the cutoff angle on the flow regime transition it can be deduced that notwithstanding the favorable results obtained at an angle of 70°, the transition is still determined by the outlet geometry to a large extent. This implies that the limits to counterflow operation in the internally finned tube proper have not yet been reached in the previously discussed experiments. 

A new recycle isotachophoretic process (93) uses a thin-film geometry with the electrical field perpendicular to the principal flow direction. Leading buffer, a marker dye, feed and trailing buffer are introduced into one end of the slit. An isotachophoretic stack develops perpendicular to flow as the liquid moves downstream. A fraction collector at the outlet collects the fractions, which are recycled until the stack sharpens. A computerized feedback control system keeps the stack centered in the apparatus. It regulates the withdrawal of trailing buffer and the addition of leading buffer in counterflow to the migration of the stack, based on the position of the marker dye front. 

The values of and HETS depend on the form of the packing material, the type of packing (or the geometry in general), the operating conditions, and the properties of the two counterflow phases, n, can only be computed in particularly simple cases. The value is usually determined experimentally. 

Maximum gas and liquid throughput rates of packed columns depend on the type of packing and packing geometry, the relative free void fraction and the physical properties of the mixed phases. The column becomes flooded beyond a certain volumetric flux of the vapor at a given flux of the reflux. A controlled counterflow of the phases then does not exist the separation efficiency of the column is reduced drastically. 

Fig. 13 Comparison of the anode and cathode probabilities of failure for the GSK (compressive gaskets), GSKT (compressive gaskets tied at the sealing interfaces) cases and enforced flatness of the MlCs in the co-flow (PR = 0.99 %) and counterflow (PR = 0.25 % or PR = 0.99 %) configuration. The system specific power is 0.21, 0.25 or 0.29 W cm and the MIC thickness is 2 mm. Insetted values refer to the anode probability of failure at 0.29 W cm [86]. Reproduced here with kind permission from Elsevier 2012. The considered SRU geometry is depicted in Fig. 5...

Counterflow flame geometries. Stretched one-dimensional flames... 

Figure 12. Counterflow diffusion flame geometry in forward stagnation region of a porous cylinder.

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