Definition blend time

Figure 18-21 gives some data on the circulation time of the hehcal impeller. It has oeen observed that it takes about three circulation times to get one blend time being the visual uniformity of a dye added to the material. This is a macro-scale blending definition. 

Compute blend time. Blend time can be computed directly from rearrangement of the definition and the values for dimensionless blend time, for D/T, and for agitator speed ... 

There is a lot of common usage of the terms blend time, mixing time, and circulation time. There are differences in concept and interpretation of these different "times. For any given experiment, one must pick a definition of blend time to be used. As an example, if one is measuring the fluctuation of concentration after an addition of material to the tank, then one can pick an arbitrary definition of blending such as reducing the fluctuations below a certain level. This often is chosen as a fluctuation equal to 5% of the original fluctuation when the feed material is added. This obviously is a function of the size of the probe used to measure these fluctuations, which often is on the order of 500 to 1000 pm. 

The manufacture of fuel oils at one time largely involved using what was left after removing the desired products from crude petroleum. Now fuel oil manufacture is a complex matter of selecting and blending various petroleum fractions to meet definite specifications. 

Polymer alloys and blends constitute over 30 wt% of polymer consumption, and with an annual growth rate of about 9.3% that has remained constant for the last ten years (i.e., four times the growth rate of the plastics industry as a whole), their role can only increase. In the text, the following standard definitions will be used [Utracki, 1989 1991 see also Nomenclature in Chapter 1 of this Handbook],... 

From all these data analyses, we can definitely say that the D and H chain stems are distributed statistically randomly in the crystalline lamellae of the D/H cocrystallized blend. This conclusion is quite important in relation with the chain-folding problem, a controversial research theme that had been discussed for a long time (30). The random distribution of the D and H chain stems naturally supports the idea that the D and H chains reenter randomly into and out of the crystalline lamellae as shown in Fig. 5.7. The regular adjacent reentry model is impossible to apply at all as for as the melt-crystallized sample is concerned. 

---