Optimum speed increase

The discussion of the specific drive power in the previous section clearly shows that improved quality does not necessarily come at the expense of increased energy input. This is due to improved design of each zone for the task at hand. With the optimum speed at each stage, only the energy required for the process is introduced into the product. 

While very little information is available on gas-phase backmixing in a mechanically agitated CSTR, the extent of mixing increases with the impeller speed. If the reaction depends on the partial pressure of gas, an increased backmixing decreases the driving force for the absorption rate. An increase in impeller speed also increases fcLaL, kgaL, etc. As a consequence, it is likely that an optimum impeller speed exists that gives maximum space-time yield (kmol/m3 s) and this optimum speed probably lies in the vicinity of critical impeller speed. 

A larger mill reaches its critical speed at a slower revolution rate than a smaller mill. Ball mills are operated at from 60 to 85% of the critical speed. Over this range, the output increases with the speed however, the lower speeds are for finer grinding. An empiric rule for the optimum speed of a ball mill is... 

In chiral separations, there is often both a major increase in optimum speed and a simultaneous increase in column efficiency. It is a common occurrence to increase throughput on chiral columns by 10 25 times compared to nHPLC (28,29). 

The optimum heavy-stream flow rate N increases with increasing speed. The separative capacity at optimum N increases as... 

The optimum speeds reported for spinning band columns vary between 1000 and 3500 r.p.m. the shape of the strip here seems to exert an appreciable influence as well as the width. Murray [75], for example, found an optimum speed of 1400 r.p.m. with a star shaped band at a load of 150 ml/h the efficiency remained constant if the speed was increased beyond this figure (Fig. 287b). 

As shown in Fig. 11, at higher cutting speeds, the workpiece temperature and the specific cutting force decrease, the removal rate and productivity increase, and surface quality improves. Tool life has an optimum speed range due to a combination of various wear phenomena, cost, and energy considerations. 

Different zone lengths were tested. The optimum amplitude reduction was obtained when the speed reduction zone started 45 meters before and the speed increased back to set value 255 m... 

Initial die gaps are set to about 20 percent greater than the final film thickness, and then adjusted to accommodate changes in polymer flow which are resin and rate sensitive. Higher screw speeds increase extruder output, overall film thickness, the tendency toward melt fracture, and may alter the flow pattern. Thus, extruder speed is not a recommended control. In contrast, increased chill-roll speeds decrease film thickness, reduce film width due to increased neck in, increase uniaxial orientation, and alter the optimum air gap or drawdown distance. The optimum air gap, which produces the best orientation, crystallization, and surface properties, depends on the material and chill-roll speed. At 23 to 30 m/min (75 to 100 ft/min), the air gap for low-density polyethylene is about 100 mm (4 in), but when the line speed increases, the air gap is found by trial and error, Since the chill-roll speed controls film stretching, the take-off speed has little effect on the film dimensions. 

The use of low levels of water in the HLAS (2-5%) speeds up the rate of neutralization dramatically. Levels of water >10% cause the HLAS to gel. A level of 2-3% gives an optimum of increased neutralization without affecting physical properties negatively. 

Lactic acid bacteria growth is optimum at a pH between 4.2 and 4.5. In the pH range of wine (3.0-4.0), malolactic fermentation speed increases with the pH. The pH limit for growth is 2.9 but even at 3.2 bacterial growth is very limited. Malolactic fermentation becomes possible at a pH of 3.3 or higher. 

The increase in optimum speed, a leads to proportional growth of a gas rate and, hence, to decrease of duration of stay of corpuscles of dust in rotor channels. However, thus it is proportional to cu and centrifugal force grows. As a result, separation of firm corpuscles improves. Thus, the increase in angular speed of a rotor raises the efficiency of clearing of gas. However, thus increases the power demand by the apparatus drive (approximately proportionally co ) and mechanical loadings on a rotor. 

---