Pressure Characteristics in Upstream and Downstream Areas of Straight Pipe Enlargement with Re-Entrant Pipe Length Variation

Abstract

A reentrant pipe is a pipe structure designed to allow fluid flow in a more efficient manner and reduce turbulence. A distinctive feature of reentrant pipes is the presence of a narrowed or curved section before widening again, which allows fluid to flow back in the direction of the main stream. The purpose of this study is to determine the effect of the length of the reentrant pipe on the pressure characteristics and the difference in pressure caused on the upstream side to the downstream pressure side when passing through the reentrant pipe. In this study, a variation in the length of the reentrant pipe was used, with values of 0, 0.5, and 1 cm. With this ratio, the diameter (d/D) used was 0.5625 at a water flow discharge of 10 LPM to 21 LPM. This research was carried out by the Center for Technology Research and Development Laboratory, Department of Mechanical Engineering, Faculty of Engineering, Muslim University of Indonesia, Makassar. Based on the results of the research, it was found that the effect of the length of the reentrant pipe significantly affects the pressure reduction that occurs. The difference between upstream pressure and the highest downstream pressure in reentrant L=0 is 107207 N/m with ΔP of −156.331 Pa, the highest downstream pressure in reentrant L=0.5 is 106914 N/m2 with ΔP of −117.249 Pa, while the highest downstream pressure in reentrant L=1 is 106894 N/m2 with ΔP of −273.581 Pa. The pressure drop that occurs is 141.901 N/m2 to 625.785 N/m2. In contrast, the loss that occurs is 0.0052 m to 0.0228 m while the pressure difference generated in the geometry of the reentrant pipe ratio  L= 0: The upstream pressure can be higher due to the accumulation of pressure before the fluid undergoes a sharp change in direction and whereas L = 0.5 and L = 1:  With a smoother geometry, the pressure drop occurs more evenly, so that the upstream pressure does not accumulate the same as at L = 0.