Laminar flow and pressure loss in planar Tee joints: Pressure loss coefficients

Abstract

We present new correlations for the pressure loss coefficients in two-dimensional Tee joints and 90∘ sharp elbows as a function of the geometric and hydrodynamic governing parameters. These are the Reynolds number of the flow (defined in the straight duct with common flow for the Tee joints), the width ratio of the perpendicular ducts and, only for the Tee joints, the mass split ratio. The analysis assumes low-to-moderate values of the Reynolds number, for which the flow remains laminar and steady. This regime is of relevance for the cooling oil flow in oil-immersed power transformer windings operated in the natural cooling mode. The new correlations have been obtained by performing a multiple regression analysis on the numerical results for combining and dividing Tee joints presented in a companion paper, and on new simulations of the flow in 90∘ sharp elbows following the same methodology used for the joints. As main new feature, the correlations for the pressure drop in the elements considered include an explicit dependence on the width ratio between the straight duct and the lateral branch, which is found to have a great influence on the static pressure losses and is not explicitly available from previous studies. When used for the thermal-hydraulic modeling of oil-immersed power transformer windings, the new correlations are expected to give better estimates than those currently available in the literature.