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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

EFFECT OF INLET TUBE SPACING ON FRICTION FACTORS IN MULTIPLE CIRCULAR TUBES IN THE TRANSITIONAL FLOW REGIME

Get access (open in a dialog) DOI: 10.1615/IHTC16.cov.023024
pages 3541-3548

Abstract

The purpose of this study was to investigate the effect of inlet tube spacing on the fully developed friction factors in multiple circular tubes in the transitional flow regime. An experimental set-up was designed, built and validated. Three circular tubes, with an inner diameter and length of 3.97 mm and 6 m respectively, were investigated at pitch ratios of 1.25 and 1.5 using water as the test fluid. Isothermal and diabatic pressure drop measurements were taken for Reynolds numbers between 1 000 and 7 000. It was found that the maldistribution effects from the adjacent tubes were negligible in the laminar, quasi-turbulent and turbulent flow regimes, while the transitional flow regime was significantly affected. The adjacent tubes dampened the inlet disturbances in the centre tube, which caused a delay in transition compared to a single tube with a square-edged inlet. Furthermore, the asymmetric velocity profile in the side tubes led to increased critical Reynolds numbers and transition gradients, therefore the transitional flow regime decreased. An increased pitch ratio increased the dampening effect of the inlet disturbances in the centre tube and reduced the flow asymmetry in the side tubes. Therefore, the differences in the critical Reynolds numbers and transition gradients of the three tubes decreased. For mixed convection conditions, the inlet disturbances caused by adjacent tubes were dampened by free convection effects, therefore the difference in the results of the three tubes became negligible.