1 88 1. *»'^ Trans. N. V. Ac. Scz, 



S. Exterior surface of steam pipes (sq. teet). 



A. Area of cross-section of flue (or flues). 



T^. Absolute temperature of external air (found b\ adding to the 

 thermometric temp. Fahr. the number 459.4). 



Tg. Absolute temperature of air in the flue. 



Ts. Absolute temperature of steam in the pipes. 



D. . Weight in lbs. of a cubic foot of the external air. 



Do. Weight in lbs. of a cubic foot of the flue air. 



v. The theoretical velocity of the air in the flue. 



V. The actual velocity. 



r. The rate in units of heat per hour, per square foot of the surface 

 (S) (and for each degree difference between Tj and TJ at which the 

 air receives heat from the pipes. 



Jt A coefficient of loss of velocity such that /&V — V. 



P The unbalanced pressure (upward) due to the difference of weight 



between the column of air in the flue and a corresponding column of 



external air. 



Then, 



p=H.D-HD, or p=H {0,-0^) (i) 



This pressure may be represented by the weight of a column of flue 



air of a height— 



and the velocity in the flue will be found from the expression 



y' _ //i^a-^c) . . (3) 



2i- A 



Z>„ 



or, y — y - ~^1d ~ ^^ 



But from the Mariotte-Gay-Lussac law we have — 



D T T 



±ls - iji or D, = D^ -" (6) 



substituting this value of D^ in formula (4) there results — 

 V ■= l/^gH.i^^ (7) 



In this expression the theoretical velocity of flow is expressed in 

 terms of the height of the flue and the absolute temperatures of the 

 flue air and the external air. From formula (7) we have — 



The quantity of heat transferred to the air may be represented by 



0= W.c.{T^- T,) . (9) . 



