Still-heads, comparison

Still head must always be smaller in its capacity in comparison to the still pot in order to avoid the possibility of the still pot boiling dry. 

Comparison of Improved with Plain Vertical Still-Head.—The relative efficiency of the different s ill-heads is well shown by the following comparison of the number of fractional distillations with a plain vertical tube of 30 cm. height, which give the same result as a single distillation with the improved apparatus. 

One of the main benefits of a premixed head in comparison with a diffusive head is the low noise emission at the stack. A premixed burner is generally quieter than a diffusive burner because of the lower combustion turbulence, on the condition there is no instability in the combustion, an instability that is possible with diffusive flames too. Figure 25.7 shows the comparison between the noise at the stack of the configurations previously examined. Like gas emissions, noise measurements are influenced by the combustion chamber type. Regarding sound emissions at the stack, the mat head still exhibits lower emissions in comparison with the metal sheet head as seen in Figure 25.8. 

Bethe at twenty-seven was sturdy, indefatigable, a skier and mountain climber, exceptionally self-confident in physics if still socially diffident. His eyes were blue, his features Germanic his thick, dark-brown hair, cut short, stood up on his head like a brush. His custom of plowing through difficulties eventually won Bethe comparison with a battleship, except that this particularly equable vessel usually boomed with laughter. He had already published important work. 

Hot entrainer at the temperature of the column top should be fed continuously at the column head, while a conventional batch distillation takes place. Product, inevitably containing some entrainer, should be withdrawn at the column top and the batch should be continued until there is no further component 1 in the system. The still should be very large in comparison with normal laboratory batch distillation practice, since it will have to hold almost all the entrainer fed into the column head during the course of the batch. 

The 2001 recall has not, however, dampened the general enthusiasm for ceramic materials in orthopedics. Alumina is currently the ceramic material of choice for orthopedic applications, either for articulations with UHMWPE or for use in COC alternate bearings. Starting at the end of 2002, a new alumina composite material (BIOLOX Forte CeramTec, Plochingen, Germany) has been available as a femoral head material (Merkert 2003). This ceramic composite, consisting of 75% alumina matrix, is reinforced by 25% zirconia. The improved strength of this new ceramic composite, in comparison with alumina and zirconia, is summarized in Table 6.2. Clinical studies are still needed to determine the effectiveness and reliability of this new biomaterial. 

Stilling et al. (2009) undertook a clinical comparison of penetration rates for femoral heads made from CoCrMo alloy and zirconia when articulated against UHMWPE, with a mean patient follow-up of 65 months. They found similar penetration rates for the femoral heads made from CoCrMo alloy (0.25 mm year ) and zirconia (0.23 mm year" ). 

Stilling M, Nielsen KA, Soballe K, Rahbek O (2009), Clinical comparison of polyethylene wear with zirconia or cobalt-chromium femoral heads , Clin Orthop Relat Res, 467, 2644-2650, DOl 10.1007/sl 1999-009-0799-5. 

This aqueous suspension of fibers is formed into a mat in the next step, called formation. Here the slurry is fed to a head box that evenly disperses a layer on a porous belt where the fibers are collected. At the same time the water is allowed to drain off or is drained via vacuum assist. The speed of the belt, in comparison to the feed rate of the liquid from the head box, will determine the basis weight of the material. The various types of equipment used include fourdriniers, rotoformers, and inclined wires. As the mat leaves the formation step, the web is still 60 to 80 wt% water and has limited strength [24]. 

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