Experimental Research On The Influence Of Inner Plug On Resistance Characteristics Of Pipe Flow

For the very wide applications in energy dissipation,heat transfer,expansion of animal blood vessel stenosis,enhancing of heat exchange of drag reducing flow with additives,turbulent flow control,and in other fields,researching the minor loss characteristic of a plug in tube flows has a great significance for the fluid dynamics and applications in industrial engineering.In this paper,the minor loss characteristic of plugs with different geometrical sizes has been measured both in a water and a surfactant solution flow at different Reynolds numbers in a 10 mm inner diameter tubeThe drag measurement system of tubes with plugs has been built according to the principles of hydraulics,firstly.In the system,pressure taps are set at the tube wall whose flow pattern is a fully developed turbulent flow.The characteristics of minor loss induced by the plugs both in a water and a surfactant solution flow are clarified by measuring the pressure drop flowing through the plugs with different sizes at different Reynolds numbers.The Experimental results for the water flow show that the minor loss coefficient of the plug with different ?(the plug length to the tube inner diameter ratio)and ?(the plug inner diameter to the tube inner diameter ratio)is independent of Reynolds numbers.The minor loss coefficient increases with a decrease of ? and an increase of ?.However,when ? is smaller than a certain critical value,the minor loss coefficient is larger than the critical one's.The influence distance of the minor loss between two plugs increases with the decrease of ? but is not affected by ?.Experimental results for the surfactant solution flow show that the drag reduction increases with concentration at Reynolds numbers before of the critical Reynolds number,but decreases gradually until vanishing after the critical Reynolds number.The minor loss characteristics induced by a plug with different ? and ? are qualitatively the same as the water flow at a constant concentration,and the minor loss coefficient increases with the decrease of concentration.At lower Reynolds numbers in theupstream flow,the minor loss coefficient of the plug in the surfactant solution flow is higher than that for water flow,but lower at bigger Reynolds number numbers flow with high drag-reducing rate.The maximum reduction rate of the minor loss is 50%.The drag reduction rate of th plug is gradually reduced with a increase in Reynolds number,exceeding the critical Reynolds number.To again form a fully developed turbulent flow,a much longer downstream length from the plug is needed in a surfactant drag-reducing flow than in a water flow,and the length decreases with an increase of ?.