Mixing loss

In addition, one other feature of the prefractionator arrangement is important in reducing mixing effects. Losses occur in distillation operations due to mismatches between the composition of the column feed and the composition on the feed tray. Because the prefractionator distributes component B top and bottom, this allows greater freedom to match the feed composition with one of the trays in the column to reduce mixing losses at the feed tray. 

The elimination of mixing losses in a prefractionator arrangement means that it is inherently more efficient than an arrangement using simple columns. 

Both the side-rectifier and side-stripper arrangements have been shown to reduce the energy consumption compared with simple two-column arrangements. This results from reduced mixing losses in the first (main) column. As with the first column of the simple sequence, a peak in composition occurs with the middle product. Now, however, advantage of the peak is taken by transferring material to the side-rectifier or side-stripper. 

Wake-mixing loss. This loss is from the impeller blades, and it causes a wake in the vaneless space behind the rotor. It is minimized in a diffuser, which is symmetric around the axis of rotation. 

Stewart, W.L., Investigation of Compressible Flow Mixing Losses Obtained Downstream of a Blade Row, NACA RM E54120 (1954). 

The primary cause of efficiency losses in an axial-flow turbine is the buildup of boundary layer on the blade and end walls. The losses associated with a boundary layer are viscous losses, mixing losses, and trailing edge losses. To calculate these losses, the growth of the boundary layer on a blade must be known so that the displacement thickness and momentum thickness can be computed. A typical distribution of the displacement and momentum thickness is shown in Figure 9-26. The profile loss from this type of bound-ary-layer build-up is due to a loss of stagnation pressure, which in turn is... 

The casing losses are due to friction and mixing. The frictional losses and their reasons are the same as those in the impeller channel. The mixing losses develop because the velocity of the impeller exit is not the same at every point as in the spiral casing it is an average velocity. Mixing of two different flow velocities leads to acceleration and deceleration and pressure difference, whose equalizing increases the entropy. 

Iversen, H. W., Rolling, R. E., Carlson, J. J. Volute pressure distribution, radial force on the impeller and volute mixing losses of a radial flow centrifugal pump. Trans. ASME, journal of Engineering for Tower 82 (1.960), pp. 136-144. 

A COOLED - ONE STEP, WITH MIXING LOSSES -t-UNCOOLED ... 

The elimination of mixing losses in the prefractionator arrangement means that it is inherently more efficient than an arrangement using simple columns. The same basic arguments apply to both distributed distillation and prefractionator arrangements, with the additional degree of... 

Mixing Too much mixing Not enough mixing Loss of agitation Reverse mixing Phases Extra phase Phase missing... 

A mixing loss as the fuels are mixed. Separative work would be required to undo the mixing. 

One way to remove this inefficiency is done where the side draw from the main column is split first and returned as sub-cooled stream while the other stream is stripped in the side stripper. Therefore, the required stripping steam is reduced tremendously as the feed is reduced. The total savings in operating cost are 40,000/ for this simple modification in the piping connections. Another example of inefficiency is mixing two vapour streams with a big difference in their composition causes this inefficiency. The returned vapour from the KE side stripper is mixed with the vapour inside the main column which resulting in mixing losses. 

Analysis of the increased deuterium production made possible through use of supplementary hot water feed will be made by reference to Fig. 13.35. Here it is assumed that the flow rate of supplementary feed F to the top of stage number of the hot tower and the product rate P are so adjusted that the deuterium content of water flowing from stage rtg -I-1 to stage ng equals that of natural water feed Xp, to prevent mixing loss at the supplementary... 

To avoid mixing losses at the feed point, the solution for which... 

A gas centrifuge 300 cm long and 40 cm in diameter is to be run at 300 K and 500 m/s peripheral speed. It is fed at the midplane with UFs at a rate of 0.03 g UFe/s. The longitudinally uniform heavy-stream flow rate is 0.20 g UF /s. Heads and tails flow rates are set so that there is no mixing loss at the point of feed injection. Find the heads separation factor, tails separation factor, and separative capacity. Note /], I3 and /(/ i/a) are given in Table... 

If the factice is added in the early stages of a mix with the polymer, incorporation of the fillers is facilitated and certainly in the days when much of rubber compounding took place on open mills, the ability of the factice to ease incorporation of Mlers and prevent bagging of the mix (loss of adhesion of the mix to the mixing rolls) was a bonus point for its use. Factice also helps to prevent heavily filled stocks being internally mixed from crumbling and not forming a coherent mass. 

Retentate recycling is attractive for membranes which show to too low selectivity. This option can lead to the highest efficiency, especially when the composition of the retentate corresponds to the composition of the respective feed stream. Otherwise, mixing losses decrease the overall efficiency of the process. 

The two-step system design shown in Figure 21.5c is used when 90% recovery of hydrocarbons from the vent gas is not enough, and a higher recovery of hydrocarbons is desired. In the example calculation shown, the recovery is 99%. Two membrane units are used in series. The permeate from the first membrane step is recycled to the reactor, and the permeate from the second membrane step is recycled to the front of the first step. To minimize mixing losses, it is desirable to size each membrane unit so that the second-step permeate... 

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