SUMMARY

1. Mixing can be characterized by analysis of sample compositions and then calculation of the standard deviation, s, of these from the mean composition of the whole mixture,
where
s2 = 1/n [(x1 - [IMG]file:///C:/DOCUME%7E1/BERKIN/LOCALS%7E1/Temp/msohtml1/03/clip_image001.gif[/IMG])2 + (x2 - [IMG]file:///C:/DOCUME%7E1/BERKIN/LOCALS%7E1/Temp/msohtml1/03/clip_image001.gif[/IMG])2 + (xn - [IMG]file:///C:/DOCUME%7E1/BERKIN/LOCALS%7E1/Temp/msohtml1/03/clip_image001.gif[/IMG])2]
2. An index of mixing is given by:
(M) = (s02 - s2)/(s02 - sr2)
3. A mixing index M can often be related to the time of mixing by
[1 - (M)] = e-Kt
4. The power consumed in liquid mixing can be expressed by a relationship of the form
Po = K(Re)n(Fr)m




PROBLEMS
1. Analysis of the fat content of samples from a chopped-meat mixture in which the overall fat content was 15% gave the following results, expressed as percentages:
23.4 10.4 16.4 19.6 30.4 7.6
For this mixture, estimate the value of s2, s02, and sr2, if the samples are 5 g and the fat and meat are in 0.1 g particles in the mixture.
[0.68 x 10-2 ; 12.8 x 10-2 ; 0.256 x 10-2 ]
2. If it is found that the mixture in Problem 1 is formed from the initial separate ingredients of fat and lean meat after mixing for 10 min, estimate the value of the mixing index after a further 5 min of mixing.
[ 0.966 ; 0.994 ]
3. For a liquid mixer in which a propeller stirrer, 0.3 m in diameter, is rotating at 300 rev/min in water estimate the power required to operate the stirrer. The tank is 0.6 m in diameter.
4. If the same assembly as in Problem 3 is to be used to stir olive oil estimate the power needed.
5. A blended infant feed powder is to include a nutrient supplement, supplied as a powder similar to the bulk feed, incorporated at 15 parts per million. The plant is to produce 50 tonnes per day and has powder mixers with capacities of 3, 0.5 and 0.05 tonnes, which will mix efficiently down to one-sixth of their nominal capacity. Suggest a mixing schedule that should lead to the required dispersion of the supplement.