Pipe Contraction Research Articles

The effects of inlet sharpness on the pipe contraction pressure loss coefficient

Pipe contractions occur in heat exchangers at the entrance to tube bundles and in conjunction with enlargements, as ferrules which are often used for the close control of the flow distribution within the tube bundles. These contractions are normally sharp at the commencement of service but suffer erosion or corrosion over the lifetime of the plant. This significantly affects their pressure loss characteristics and upsets the flow distribution. Thus it is important to be able to predict the variation of contraction pressure loss coefficient with variations in the small-bore pipe inlet geometry, referred to as inlet sharpness. There are no known experimental data for the effects of inlet sharpness on the pipe contraction pressure loss coefficient, but there are data for intakes set flush in a plane wall which are used as approximations. Experimental data showing the variation of pressure loss coefficient with the inlet sharpness are presented and compared with the approximate data. The comparison shows significant differences.

The determination of pipe contraction pressure loss coefficients for incompressible turbulent flow

The accurate prediction of pipe contraction presure loss is important in the design of pipe systems, such as heat exchangers, particularly when close control of the flow distribution in a network of pipes is required. The prediction of the contraction pressure loss depends heavily on experimental data. Large discrepancies in these predictions are evident in the literature. New experimental results giving pressure loss coefficients for range of Reynolds numbers of 4×10 4 to 2×10 5 and area ratios 0.13 to 0.7 are presented and compared with those of other workers and with predictions from a method that allows for velocity profile variation through the contraction. The results show a Reynolds number dependence. The effects of small-bore pipe inlet geometry on the loss coefficients are also examined.

Erosion of Metallic Plate by Solid Particles Entrained in a Liquid Jet

An experimental and theoretical study on erosion of a metallic plate by solid particles entrained in a liquid jet has been performed. The test section involved a two-phase flow jet of liquid water and silica-sand impinging on a metallic plate upon which erosion occurred. In combining the fluid mechanics of particle suspension in a liquid and a model of weight removal from the plate (by a single abrasive particle), an analytical approach is developed to determine the distribution and amount of erosion along a metallic plate. This model of erosion distribution along the metallic plate can be used as a tool to predict erosive damage in industrial equipment such as pipe bends, elbows, subsurface safety valves, and pipe contractions.

Unsteady flows in a semi-infinite contracting or expanding pipe

Physiological pumps produce flows by alternate contraction and expansion of the vessel. When muscles start to squeeze its wall the valve at the upstream end is closed and that at the downstream end is opened, and the fluid is pumped out in the downstream direction. These systems can be modelled by a semi-infinite pipe with one end closed by a compliant membrane which prevents only axial motion of the fluid, leaving radial motion completely unrestricted. In the present paper an exact similar solution of the Navier–Stokes equation for unsteady flow is a semi-infinite contracting or expanding circular pipe is calculated and reveals the following characteristics of this type of flow. In a contracting pipe the effects of viscosity are limited to a thin boundary layer attached to the wall, which becomes thinner for higher Reynolds numbers. In an expanding pipe the flow adjacent to the wall is highly retarded and eventually reverses at Reynolds numbers above a critical value. The pressure gradient along the axis of pipe is favourable for a contracting wall, while it is adverse for an expanding wall in most cases. These solutions are valid down to the state of a completely collapsed pipe, since the nonlinearity is retained in full. The results of the present theory may be applied to the unsteady flow produced by a certain class of forced contractions and expansions of a valved vein or a thin bronchial tube.