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FROM MAN TO MACHINERY
Since the dawn of civilization, the human race has found it necessary to move and reshape the earth. Great construction projects, such as the pyramids of Egypt, the Great Wall of China, and the Roman network of highways across Europe involved vast amounts of earthworks. In 1681, the Languedoc Canal in Europe required massive amounts of earth to be moved, which demonstrated the need for earthmoving equipment. These and other early earthmoving projects used manual labor. Thousands of men, sometimes assisted by animals, but without the help of machines of any sort, completed these immense undertakings.
As centuries passed, the need for moving material by mechanized equipment increased. Just as todays science-fiction writers create future gadgetry and automation far beyond current technology, in the fifteenth and sixteenth centuries, such creative thinkers as Leonardo da Vinci sketched many types of earth-moving machines and other mechanical contrivances. Still, it would be several centuries before technology allowed them to be constructed.
Mechanized earthmoving equipment is largely a twentieth-century phenomenon. The Industrial Revolution and the steam age of the eighteenth century produced a greater need to move large quantities of material. The desire to move people and materials from place to place spawned the earliest forms of mechanized equipment. Ships were one of the first means of transportation over long distances.
Next the railways developed, and the land excavator was born. The 1835 steam shovel designed by William S. Otis is the earliest known single-bucket excavator used on land. Otis was a partner in a firm of contractors that used its own machines for railroad construction. Just after Otis received a patent for his machine in 1839, he unfortunately died of typhoid fever at the age of 26. Although Otis did not live to see the fruits of his invention, his familys contracting business maintained the steam shovel patent for over 40 years and benefited from its advantage. Due to Otis patents and inexpensive labor, mechanized excavation evolved very slowly. In fact, few Otis shovels were ever built. Manufacture of the Otis shovels was continued by John Souther & Company until about 1913, surprisingly without major design changes.
While mechanized excavation slowly progressed, most of the worlds railways were built using hand labor, even after the invention of the steam excavator. Probably the earliest major mechanized earthmoving project was the Manchester Ship Canal in England, starting in 1887. Here, 58 steam shovels, 18 clamshell excavators, and numerous other excavators worked with 173 steam locomotives and 6,300 rail wagons to move material at rates up to 1.2 million cubic yards per month. In all, 54 million yards were excavated over a six-year period.
As the twentieth-century projects got steadily larger, so did the machines. But at the other end, smaller and smaller machines also became as economical as hand labor. Machines were made in ever increasing varieties, and the distinctive types, such as draglines, graders, scrapers, loaders, and bulldozers, evolved.
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The characteristic of syngas from food waste pyrolysis and gasification have been investigated. Food waste is a char-based sample. Results from char-based samples (samples containing volatile matter and char, such as paper [13], cardboard [14,15], woodchips and food waste) follow, qualitatively similar trend. Syngas is characterized by a high flow rate initially, due to pyrolysis, and then followed by a small flow rate which lasts for longer period, which is due to char gasification. The progress of the food waste sample through pyrolysis and gasification processes is shown in Fig. 2. Syngas characteristics may differ from a quantitative point of view. The differences and similarities between food waste and previously investigated samples is presented in the firstsection of the discussion. The second part is concerned about the kinetics of char gasification from food waste with specific focus on the catalytic effect of ash.
Syngas characteristics. Fig. 3 shows the evolution of syngas flow rate with time at two distinctly different high temperatures of 800 and 900oC. Syngas flow rate starts with a high value which is attributed to the rapid devolatilization of volatile components from the sample. This is then followed by sudden decrease in flow rate, and finally followed by a long period of low flow rate. The low flow rate period is attributed to the char gasification. Syngas flow rate due to char gasification decreases monotonically until char is consumed and only ash is left over. The area confined between the pyrolysis curve and gasification curve represents the syngas yield from the char gasification. The increase in reactor temperature increased syngas flow rate and decreased the gasification period. The syngas flow rate from paper at the same temperatures was higher in terms of maximum value of flow rate. The maximum flow rate from paper gasification [13] was 5.5 g/min and 10 g/min at temperatures of 800 and 900oC, respectively. However the maximum flow rate from food waste gasification was found to be 4 and 7.6 g/min at temperature of 800 and 900oC, respectively. (Ahmed I.I., Gupta A.K. Pyrolysis and gasification of food waste: Syngas characteristics and char gasification kinetics // Applied Energy 87 (2010), Pp. 101108)
Text II
Only a few rotations of the vortex could be computed so far, because of the large amount of computing time required. It is interesting to note that the computed variation of pressure did not contain the high frequency components which were measured. Also, one can see that the development in time so far did not converge to a periodic behavior but appears somewhat chaotic; this is also the case with the measured pressure fluctuation. The evaluation and comparison of the unsteady runner forces is not an easy task. Firstly, the fluctuation in partial load is not as regular, i.e. periodic, as in many Francis turbines; the quasiperiodic contribution from the vortex is only part of the sub synchronous forces observed.
Secondly, the CFD model yields only the part of the runner force created inside of the runner, yet pressure fluctuations are also present at the outward side of the runner crown and band. It is necessary to account for this fraction of force also. For reasons of symmetry, however, the unsteady external forces and moments from the runner crown and band are approximately canceling out, and their influence may be neglected.
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While the time delay for synchronization between the computed and measured time histories in the Fig. 7 has been chosen arbitrarily, the relative phase between the 6 diagrams in Figures 7 through 9 is not; hence the comparison shows fair agreement in the phase angles between the 6 variables between the calculation and measurement. (P. Dörfler1, A. Lohmberg2, W. Michler1, M. Sick. Investigation of pressure pulsation and runner forces in a single-stage reversible pump turbine model).
