Abstract
Pressure loss for laminar flow in a 90-deg square bend is discussed on the assumption that the friction factor can be expressed as a function of the Dean number. The turbulent viscosity is newly defined so that the product of the friction factor and Reynolds number for turbulent flow has the same value as that for laminar flow in a straight square duct, i.e. 14.2. Using the newly defined turbulent viscosity the friction factor for turbulent flow can be related to Reynolds number Reμ and the dimensionless curvature a/R.
Then the empirical formulae of the friction factor for both laminar and turbulent flows in a 90-deg square bend is obtained by experiments for the dimensionless curvatures 0.0365, 0.0729, 0.146 and 0.292, and Reynolds numbers range from 4.8 × 102 to 2.4 × 104. The difference between the pressure at the outer wall and that at the inner wall in the 45-deg cross-section of a bend can be related to the dimensionless curvature for Reynolds number such as Reμ>5000.
