ON THE TRANSMISSION OF POWER BT COMPRESSED AIR. 



461 



0-52 



0-845 



^ = 0-61. 



€•845 indicated horse-power in compressors delivers as Efficiency of compressors 



much air as will do 052 indicated horse-power in 



adiabatic expansion after it has fallen in tempera- 

 ture to the normal temperature of the mains. 



The fall of pressure in mains between central station 

 and Paris (say 5 kilometres) reduces the possibility 

 of work from 052 to 051 indicated horse-power. 



Efficiency of transmission 



through mains, 



0-52 



= 0-98. 



The further fall of pressure through the reducing valve Efficiency of reducing valve 

 to 4^ atmospheres (5i atmospheres absolute) reduces 0!jO ^ ' 



the possibility of work from 051 to OoO. qT^j = "■^^• 



The combined efficiency of the mains and reducing valve, between 

 5 and i^ atmospheres, is thus 098 x 0-98 = 0-9(;. If the reduc- 

 tion had been to 4, 3i, or 3 atmospheres tlie corresponding 

 efficiencies would have been 093, 089, and O-So respectively 

 Incomplete expansion, wire-drawing, and other such Indicated efficiency of 

 causes reduce the actual indicated horse-power of 039 



the motor from 050 to 0-39. motor, -_^ = 078. 



Indicated efficiency of 

 whole process with 

 cold air, 0-39. 

 Apparent indicated effici- 

 ency of whole process 

 with heated air, 0-54, 



By heating the air before it enters the motor to about 

 320° Fahr., the actual indicated horse-power at the 

 motor is, however, increased to 0-54. The ratio of 



• gain by heating the air is, therefore, ?^ = 1-38 



0-39 



In this process additional heat is supplied by the com- 

 bustion of about 0-39 lb. coke per indicated horse- 

 power per hour, and if this be taken into account 

 the real indicated efficiency of the whole process 

 becomes 0-47 instead of 0-64. 



"Working with cold air the work spent in driving the 

 motor itself reduces the available horse-power from 

 0-39 to 0-26. 



Working with heated air the work spent in driving the 

 motor itself reduces the available horse-power from 

 0-54 to 0-44. 



Keal indicated efficiency of 

 whole process with 

 heated air, 047. 



Mechanical efficiency of 

 motor, cold, 0-67. 



Mechanical efficiency of 

 motor, hot, 081. 



One particular instance of variety of application which interested me 

 much 1 may mention. At the ' Montagnes Russes ' I found a large 

 horizontal engine placed in a recess driving a dynamo and cells for the 

 electric lighting of the whole building ; a small vertical engine in another 

 place worked the rotary pump, which actuated the ' cascade • ' two or 

 three large air-driven fans in wooden shafts served for ventilation • and 

 lastly, a simple connection on a flexible pipe threw the air pressure into 

 the beer barrels as they were brought in, and transferred their contents 

 to a height from which they could afterwards descend by gravity to the 

 place where they were required. 



As to the rate at which the compressed air is sold, I believe that in 

 mo.st of the larger installations the work is done by contract (at so much 

 per lamp-hour m the case of the electric lighting), but in the smaller ones 

 the air is charged for by meter. The rate of charge is 1-5 centime per 

 cubic metre for air used in motors and 2 centimes per cubic metre for air 

 used directly Air used for raising fluids is charged according to 

 quantity raised. The former rate is equivalent to 4>-2bd. per 1,000 cubic 

 teet (the volume in all cases being measured at atmospheric pressure) 

 In addition to this a fixed charge of from 100 to 250 francs is made for 

 pipes and connections, and a small rent for the motor if it be not bouc»ht 

 outright, or by twenty-four monthly instalments. ° 



