Mixing work input

Van Buskirk et al. claimed that the flow behaviour of SBR-black compounds was a function of mixing work input. Flow behaviour was independent of mixer size, speed and mixing time as long as the temperature-time profiles were identical. From this they introduced the unit work concept. In a later paper Turetzky et al. suggested that rather than using the second peak of the torque-time curve as in the BIT test described above, it would be more appropriate to take a later point on the torque-time curve, the so-called t point. The position of this t point is illustrated in Fig. 1. 

The number of rotor revolutions per mix cycle relates directly to unit work input and to temperature rise. This variable can be employed when checking between mixed batches for changes in feeding operations, materials and mixer conditions. Power/work input measures the energy consumed by the mixer. A greater compensation for variations in feed stocks and mixer temperatures is provided by power control. 

Chin, N.L., and Campbell, G.M. (2005). Dough aeration and rheology. II. Effects of flour type, mixing speed and total work input on aeration and rheology of bread dough, J. Sci. Food Agriculture 85 2194-2202. 

I. Effect of mixing intensity and work input, Cereal Chem. 49, 4 7. 

Kilborn, R. H., and K. H. Tipples. 1972. Factors affecting mechanical dough development. 1. Effect of mixing intensity and work input. Cereal Chemistry 49 34-47. 

In real (fine) chemical processes, concentrated materials are mixed at great ex-ergy loss in huge quantities of water and other solvents. The problems created here have to be solved in the downstream processing. The recovery and purification of the desired product demands a further work input in the sense of mixing the feed with (pure) solvents (precipitation and extraction), salts (ion exchange), heat (evaporation and solvent recovery), electrical power (electrodialysis), pressure (filtration and membrane separations) or just extra water (gel filtration). 

Crumb structure is the culmination of many aspects of dough control, including the choice of raw materials, mixing machine, work input, level of oxidation, processing conditions and time sequence. Under normal... 

By starve feeding of a twin screw mixer, ttie amount of mechanical work input to the material can be varied. The materiab to be mixed have to enter the twin screw mixer continuously in their proper proportions because the twin screw mixer, owing to the fact that the material passes through in almost a plug flow fashion, does not intermix in the axied direction. Since the material in this extruder is transported by positive displacement and not by hictional and viscous forces, the melt temperatures do not rise and, in fact, generally heat has to be applied externally. 

It is possible to make a special extruding screw to mix and extrude rubber compounds continuously. A problem is that ideally the design of the screw, both in shape and length, should be changed to suit each compound to be processed, as different compounds require different work inputs and processing temperatures. 

Tadmor and Manas-Zloczower" conclude that the two most successful criteria in practice have been the unit work input, and the total shear strain conceptespecially when temperature profiles and volume loading for different machines are closely matched. They propose a new scale-up criterion, derived from their theoretical model of the dispersive mixing process mentioned earlier. ... 

The last of these methods has been applied particularly to chemical reaction vessels. It is covered in detail in Chapter 17. In most cases, however, the RTDs have not been correlated with impeller characteristics or other mixing parameters. Largely this also is true of most mixing investigations, but Figure 10.3 is an uncommon example of correlation of blend time in terms of Reynolds number for the popular pitched blade turbine impeller. As expected, the blend time levels off beyond a certain mixing intensity, in this case beyond Reynolds numbers of 30,000 or so. The acid-base indicator technique was used. Other details of the test work and the scatter of the data are not revealed in the published information. Another practical solution of the problem is typified by Table 10.1 which relates blend time to power input to... 

In this paper, we extend the work of [10] by simultaneously considering minimization of the total utility consumption, maximization of operational flexibility to source-stream temperatures, and even minimum number of matches as multiple design objectives. The flexible HEN synthesis problem is thus formulated as the one of multi-objective mixed-integer linear programming (MO-MILP). This formulation also assumes that the feasible region in the space of uncertain input parameters is convex, so that the optimal solution can thus be explored on the basis of the vertices... 

The second difference is the dynamic response to disturbances or changes in manipulated variables. In a perfectly mixed CSTR, a change in an input variable has an immediate effect on variables in the reactor. In a tubular reactor it takes time for the disturbance to work its way through the reactor to the exit. Therefore there are very significant dynamic lags and deadtimes between changes made at the inlet of the reactor and... 

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