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 229 - The reason of this is that the heat supplied to the air is used nearly five times as efficiently as an equal amount of heat employed in generating steam. In certain cases the air-motor cylinder has been jacketed by hot air. This increases again the amount of work obtained per pound of air used. It can hardly be considered a thermodynamically advantageous process, but it may have advantages practically in raising the exhaust-temperature.
Page 235 - If the air is used oold the power obtained will be as follows : — If the air is reheated to 300 Fahrenheit as assumed in the previous case — Here the efficiency of the whole arrangement— calculated on the indicated power, 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...
Page 218 - Loss of Pressure per Mile of Pipe. — In order to indicate what kind of results this formula leads to, the following cases have been calculated. 1. Given the diameter of the pipe, and the initial pressure and velocity of the air entering the main, it is required to find the loss of pressure in 1 mile of transmission. By simple transposition, putting L = 5,280...
Page 235 - 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 3 - 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 229 - It was using about 31,000 cubic feet (reckoned at atmospheric pressure) or about 2,376 pounds of air per hour. This air was heated to a temperature of about 300 Fahrenheit by the expenditure of only 15 pounds of coke per hour. On a favourable assumption a steam-engine working to the same power would have required ten times this consumption of fuel at least.
Page 229 - Prof. Riedler tried an old 80 horse-power steam engine in Paris which had been adapted to work as an air motor, and which was actually giving 72 indicated horse-power with compressed air at 5% atmospheres.
Page 228 - Eiedler has given some other figures, not based as the above are on the measurement of single diagrams, from which the efficiency of the Paris compressors can be calculated in a more trustworthy way. The following data are given as the result of a series of experiments with each compressor : For each Indicated Steam HP Pressure in Main.
Page 235 - HP Now, let the air be compressed to 4, 8, and 12 atmospheres on the gauge, then the weight of air compressed will be as follows : To ascertain suitable diameters for the main, let initial velocities of 30, 50, and 75 feet per second be assumed. For these velocities, and in the cases described, the diameters required will be as follows: None of these mains are impracticable in size, and for the higher pressures and velocities they are surprisingly small, Case I.

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