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LXXX VI. The Discharge of Air through Small Orifices, and 

 the Entrainment of Air by the Issuing Jet. By J. S. G. 

 Thomas, D.Sc. (London and Wales), A.R.C.Sc, A.I.C., 



Senior Physicist, Soatlt Metropolitan Gas Company, 

 London "*. 



[Plate VI.] 



Introduction. 



THE present paper details some of the results obtained 

 in a preliminary investigation of the conditions deter- 

 mining the entrainment of air by jets of various gases. As 

 there exists considerable uncertainty as to the representation 

 by means of a formula of results for the discharge of gases 

 through fine orifices |, it has been considered desirable to 

 include also a short discussion of results, under this head, 

 obtained during the work. 



In the case of the entrainment of air by a jet of gas either 

 lighter or heavier than air, the volume of air entrained per 

 unit volume of gas in the jet is different according as the jet 

 is directed in an upward or downward direction. With a 

 jet of air, such an effect, if present at all, is small. As the 

 great majority of the practical applications of air-entrainment 

 by gas jets issuing from small orifices with which the author 

 is concerned refer to downwardly directed jets, it was decided 

 to confine the preliminary experiments with air to such 

 direction. 



Experimental. 



(a) The Discharge Tube. — The flow systems employed in 

 the present investigations are shown in fig. 1. Air was 

 delivered under constant pressure to the brass tube A, the 

 interior surface of which was carefully smoothed, and issued 

 as a jet from the orifice in the disk B, situate at the lower 

 end of the tube. Particulars of the preparation and mount- 

 ing of the disks and orifices are given later. The tube A was 

 provided with a water jacket through which tempered water 

 flowed, so that throughout the whole series of experiments 

 the temperature of the water in the jacket was maintained 

 constant at 13° C, with a possible variation of *5° C, the 

 temperature being taken by thermometers placed at the inlet 



* Communicated by the Author. 



t See, e. </., Buckingham & Edwards, Sci. Papers, Bureau of 

 Standards, vol. xv. pp. 574 et seq. (1919-20) ; Walker, Phil. Mag. 

 vol. xliii. p. 589 (1922). 



Phil. Mag. S. 6. Vol. 44. No. 263. Nov. 1922. 3 R 



