58 EGGS IN COLD STORAGE. 



running- fan wheel is very much more economical of 

 dtffertntspe a eds power than a small fan running- at a hig-h rate of speed, 

 both doing- the same amount of work. The loss of 

 ref rig-eration, too, in a rapidly moving- fan, is of conse- 

 quence, because the air is warmed by impact with the 

 blades. The proportion of power saved by the use of 

 a larg-e fan running- at a slow rate of speed, rather than 

 a small fan running- at a hig-h rate of speed, both de- 

 livering- the same amount of air, is almost phenomenal, 

 and does not seem at all reasonable at first view. The 

 volume of air delivered by a fan varies very nearly as 

 the speed, while the power required varies about as 

 the cube of the speed. That is, doubling- the speed 

 doubles the volume of air, while the power required is 

 increased eig-ht times. We will take a specific case. 

 A 45-inch fan wheel, revolving- at a speed of 200 revo- 

 lutions per minute, delivers, say, 5, 000 cubic feet of air 

 per minute, and requires but one-quarter of a horse 

 power to operate it. If the speed is increased to 400 

 revolutions, the volume of air delivered will be only 

 about 10,000 cubic feet, while the power required to 

 drive it will be raised to two horse power. These 

 fig-ures are theoretical, but within certain limits are 

 approximated in practice. 

 LOSS of power p or use [ n co id storage work the objection com- 



from excessive J 



fan weights. mon to nearly all the air moving- machinery found 

 listed by the manufacturers is the seemingly unnec- 

 essary amount of metal used in its construction. 

 The heavy weig-ht of the fan wheels, and the larg-e 

 diameter of shaft necessitated by such weig-ht, causes 

 much friction on the journals, so that when running- 

 at the slow speeds desirable for cold storag-e work, 

 more power is required to overcome the mechanical 

 friction than is actually required to move the air.* 



*Having been unable to find a fan wheel well suited to the requirements of 

 cold storage duty, the writer has designed and constructed a line of fan wheels 

 especially for slow speeds, which are amply strong and capable of moderately 

 high speeds, when necessary, but are very much lighter than most fans on the 

 market, and consume proportionately less power in mechanical friction. 



