Parry. — Resistance to Flow of Water through Pipes. 55 



gathered from contemplating them is that their general trend indicates 

 that the law of resistance can be expressed in the form of equation (5). 

 The observations are, however, not consistent enough among themselves, 

 and, if they were, they do not cover a sufficiently wide range to enable a 



curve expressing the relation between - and to be drawn. There is 



V" V 



evidently some disturbing factor at work which seems to have a greater 

 effect at low values of the mean velocity and low friction heads. 



Comparisons. 



Comparing the results as a whole as plotted in figs. 1, 2, and 3, 

 it may be said that their general trend is such as to conform with 

 the law expressed in equation (5), and that they do not disprove the wide 

 application of the principle to comprehend both large and small diameters, 

 provided that the surface characteristics are similar. 



As regards cast iron with clean, asphalted surfaces, the results of the 

 more recent experiments are remarkably consistent and afford strong 

 evidence in support of the theory, and it only requires a few more 

 experiments in the proper region of exploration in order to enable a curve 

 to be drawn for this class of surface. 



As regards wood-stave pipe, the available results are not consistent, 

 and new observations are required throughout the range. 



As regards riveted steel pipes, none of the existing data are of much 

 assistance, because of the wide variations between the readings. It 

 is evident that in all the experiments some disturbing factors were 

 operating in such a way as to vitiate the results, these making their 

 influence felt more at low than at high velocities. More experiments 

 extending over a wider range are required. 



Conclusion. 



The result of this investigation is not very conclusive. A beginning 

 is, however, made in the direction of applying a principle which has been 

 found to be applicable throughout a wide range of values of vd, and for 

 widely different fluids, such as water, air, and steam, and extending it 

 to large pipes in commercial use ; and before further progress can be 

 made more experiments are required on pipes of different diameters and 

 different surface characteristics, selected with a view to extending the 

 range of observations already obtained. 



Whether or not this theory is applicable under all conditions, 

 there is considerable advantage to be derived from plotting the results of 



observations against — , as by this means one is able to exercise a far 



V 



greater degree of judgment in selecting a probable value of c than by 

 studying all the literature on the subject which exists, and the method is 

 to be recommended on this account. 



Eeaders are referred to a previous paper, ;:: printed in the Transactions 

 of the New Zealand Institute, for a diagram representing the coefficient of 

 viscosity and the coefficient of kinematic viscosity of water at different 

 temperatures, and also a diagram showing the relation between the values 



of log. - and vd for water at temperatures 0, 10, 20, and 30 degrees 



V 



centigrade, the use of which will facilitate the manipulation of the 

 diagrams presented in this paper. 



* E. Parry, Resistance to the Flow of Fluids through Pipes, Trans. N.Z. Inst., 

 vol. 48, pp. 487-88, 1916. 



