Frictional Resistance in Artificially Roughened Pipes

The flow of fluids in smooth pipes is so well understood that the losses due to friction may be predicted to within 5 per cent. The problem of estimating friction losses in old pipes, or in those roughened by use, however, has been inadequately solved. In order to clarify the problem completely much study and experimentation are necessary. This paper, which is an effort in that direction, presents the results of an experimental investigation of frictional resistance in artificially roughened pipes. It has been undertaken in an effort to show, qualitatively, the effect on the friction factor of certain artificial irregularities-varying in shape and size-that were introduced in pipes used for the tests. With water as the fluid, loss of head was investigated for roughened, 2-in., brass pipe, the Reynolds numbers ranging from 20 000 to 1 250 000. The roughness elements consisted of grooves cut spirally into the pipe. The degree of roughness was varied by changing the depth, shape, and number of grooves per inch.

The loss of head due to friction was found to increase with an increase in the depth of the grooves, provided the same general shape was maintained. The shape of the grooves, however, seems to have almost as much affect on the loss of head as the depth. The experiments also indicate that the roughness elements may be placed so close together that the loss of head is reduced. The work of previous investigators is summarized briefly; the apparatus, preliminary experiments, experiments for obtaining data, and computations are described; and the results of this investigation are discussed.