Determination of resistance coefficient and turbulent friction factor in non-circular ducts

Abstract

Static pressures in non-circular ducts and pipe fittings (globe, ball and butterfly valves) have been measured in a closed circuit water channel at the range of Reynolds number from 20 000 to 80 000, which give rise to fully developed turbulent pipe flow, so as to define the friction coefficient (C-f) and resistance coefficients (K). A new proposed equation for friction factor with two new dimensionless parameters as a function of cross sectional area are successfully adopted to fully developed turbulent flow in all cross sections with a precision of better than +/-4%. Measurements showed that friction factors decreased with increasing eccentricity and were in good agreement with the proposed equation. It was also found out that Reynolds number has no effect on resistance coefficients of butterfly, globe and gate valves, but the closing ratio caused K to increase remarkably, and the K value of bends can easily be obtained by an empirical formula based on Moody chart friction factor. Static pressures on front and back sides of the circular disc of butterfly valve decreased with Reynolds number, remained almost constant in the radial direction and increased particularly at closing angles of bigger than 60 degrees, where flow rate starts to decrease sharply.