﻿Air Velocity by means of Hot Wire Anemometer. 5G5 

 Fig. 4. 



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Teat of Anemometer Readings at High Velocities : S-mil Wire No. 7. 



The distribution of velocity illustrated in fig. 4 was measured by 

 setting- the anemometer-wire in various positions by means of a 

 micrometer-screw in a plane at a distance g=3 mm. from the upper 

 extremity of the channel described under fig. 3. The dimensions of 

 the channel were :— width, 2b = 0'75 mm. ; breadth, d = 5-08 cm. ; 

 length, 1= 5-06 cm. Integrating this velocity-distribution between the 

 limits .i~ 4-0-92 mm., the total flow per unit breadth of channel is 

 182 cm.ysec. under a pressure -difference of 11*5 cm. water. From a 

 series of observations on the rate of fall of the gasometer for various 

 pressure-differences, the total flow for breadth d was obtained, and 

 hence the flow per^ unit breadth, assuming approximately uniform 

 distribution of conditions over the breadth. From the curve connecting 

 this flow with the pressure, the value per unit breadth corresponding to 

 a pressure-difference of 11*5 cm. water came out to be 190 cm.'Vsec. in 

 fair agreement with the value obtained from the anemometer measure- 

 ments ; the latter is probably an underestimate, owing to the destruction 

 ot momentum of flow as the jet travels through the stagnant air in 

 this region. The low velocities beyond the edges of the "channel are 

 due partly to a " diffusion '' of the jet owing to its dragging action on 

 the quiescent air through which it is flowing, and at a greater distance 

 to an indraught of air from the surroundings into the moving air of the 

 jet. The distribution of velocity over the channel approximates fairly 

 well to a parabola. 



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