Numerical study of the thermo-hydraulic characteristics in a circular tube with ball turbulators. Part 1: PIV experiments and a pressure drop

In the paper, being the first part out of two (the second one is focused on processes of heat transfer), results of the computer simulations of the flow in a circular pipe with a ball inserts turbulising the flow are presented. An influence of the diameter of balls and their longitudinal distance on a pressure drop in the turbulent flow as a function of the Reynolds number (for Re = 10,000 / 300,000) was analyzed. The investigations were carried out for different diameters of the balls (Db = 7,10,13,16 and 19 mm) and different distances between them (L = 20, 24, 28, 32, 36, 40, 48, 60 and 85 mm) at a constant inner diameter of the tube (Dp = 26 mm). The results indicate that for the whole tested range of ball diameters and their longitudinal arrangements, there is an analytical dependency which allows for expressing a friction factor by the relationship: f = A.Re-B. The constants A and B were functions of two variables: a dimensionless diameter of the ball (X = Db/Dp) and a dimensionless longitudinal distance between balls (Y = L/Dp). These two constants are closely related. They can be calculated analytically for the entire range of X and Y using a formula of the fourth order surface polynomial (15 coefficients of that polynomial are presented in the paper). The paper presents also experimental investigations carried out using a PIV (Particle Image Velocimetry) apparatus. A comparative analysis of selected inserts and numerical calculations was the goal. The obtained results show a good correlation between the experiment and computer modelling. (C) 2014 Elsevier Ltd. All rights reserved.