On the Development and Transmission of Power: From Central Stations

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Longmans, Green, 1894 - Mechanical engineering - 312 pages
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Page 237 - ... is the efficiency with which the motor uses the fluid, the indicated work will be — There is no reason for expecting r)3 to be different in this case from what it was in the previous one, unless hot-air jacketing, or steam injection, is used.
Page 226 - ... practically in most cases heat given to the air in the compressor is in fact wasted before the air is used for motive purposes. A perfect compressor for power distribution would be one in which the air taken in at atmospheric pressure...
Page 241 - In the following calculations it will be assumed that i/i = 0-85. As to the efficiency of the process of compression, this varies greatly with the type of compressor. In some of the older singlestage compressors it is as low as 0-5. But taking the best of those tried by Professor Riedler and slightly rounding off the values — For single-stage compressors . . . i/2 = 0 • 7 „ two-stage „ . . . i/2 = 0-9 The loss in the main must be calculated for each special case.
Page 9 - Its full effect was only gradually felt, and water continued to be economically the better agent during the first quarter of the nineteenth century; but eventually as a consequence of Watt's invention, water-falls became of less value. Instead of carrying the people to the power, employers found it preferable to place the power among the people at the most convenient trading centres.
Page 245 - Here the efficiency of the whole arrangement — calculated on the indicated pow6r, the air being delivered at a distance of 20 miles, and including all losses — is 40 to 50 per cent. if the air is used cold, and 59 to 73 per cent. if the air is reheated. The results are based absolutely on efficiencies already obtained in similar cases, and the sole loss neglected is possible leakage in the mains. Fig. 7 is drawn to scale for Case II e. It is a diagram showing the relation of the work expended...
Page 225 - ... of the steam-cylinder and compression-cylinder. If the compressor is driven by water-power there will also be a corresponding loss in friction of the mechanism, probably not widely different in amount. It will be sufficient here to consider a compressor driven by steam. Let U be the work expended, measured on the steam-cylinder indicator diagram, and U, the corresponding work shown on the compressor-cylinder diagram.
Page 213 - AIR MAINS. Hitherto information as to the resistance of air mains has been scanty. The best experiments were those made by Mr. Stockalper on the pipes of the boring machines at the St. Gothard Tunnel. The new experiments carried out by Professor Riedler and Professor Gutermuth on the air mains in Paris are therefore of great value. The Paris mains are larger than any hitherto tried, and by coupling up different mains at night, a length of 10^ miles could be experimented on. The main for the older...
Page 220 - Eeduced, as shown in the last line, the results are consistent if it is assumed that the leakage was really greater in the sections included in I, II, and IV than in the other sections. Now, with an initial gauge-pressure of 6 atmospheres and an initial velocity of 30 feet per second, the main would deliver about 600,000 cubic feet of air per hour, reckoned at atmospheric pressure. Then the percentage of loss by leakage per mile per hour would be as follows: Per cent~| I.
Page 222 - ... resistance of these is included in the observed results. It appears, however, that the most serious additional resistance was that of the draining-tanks, and as special experiments were made on these, their resistance can be estimated with very approximate accuracy and allowed for. The following table gives the results of the experiments reduced to English measures. The columns marked with an asterisk are those taken directly from Professor Riedler's Tables. The others are deduced from his figures....
Page 54 - He takes a normal midwinter load curve and examines how the necessary current could be supplied during the twenty-four hours (1) with an engine capable of exerting the maximum power required ; (2) with smaller engines. The results, rearranged and a little modified, are given by Unwin in the following table. It is assumed for convenience that the maximum load is 500 electric horse-power and that the engines are non-condensing.

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