1881. 69 Trans. N, ¥. Ae. Sez, 
S. Exterior surface of steam pipes (sq. feet), 
A. Area of cross-section of flue (or flues). 
T,. Absolute temperature of external air (found by adding to the 
thermometric temp. Fahr. the number 459.4). 
T,. Absolute temperature of air in the flue. 
T,. Absolute temperature of steam in the pipes. 
D,. Weight in lbs. of a cubic foot of the external air, 
D,. 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 T, and T,) at which the 
air receives heat from the pipes. 
k A coefficient of loss of velocity such that AV=V’. 
é 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,—H D, or p=H (D,—-D,) (1) 
This pressure may be represented by the weight of a column of flue 
air of a height— 
By DT Ds) gah C) 
Dy D, 
and the velocity in the flue will be found from the expression 
a FA DS 
ao Dz yee’ (3) 
or, Fy Ome ig 
Dz 
But from the Mariotte-Gay-Lussac law we have— 
1B ath ie 87 ae is Ta 
Diya ad oe or mo Ore (6) 
substituting this value of D, nm formula (4) there results— 
ee V og 1, (2S (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— 
V 
—-7,= - Te ‘ 
Fete (8) 
The quantity of heat transferred to the air may be represented by 
P= Wee (7, — FD 2 (9) 
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