Universal expression for the drag on a fluid sphere

An expression was developed for prediction of drag coefficients for any spherical particle, drop or bubble in an infinite, homogeneous liquid. The formula reproduces the limiting cases for gas bubbles and solid spheres, as well as the exact Hadamard-Rybczynski solution. The accuracy of the expression, which is valid for Reynolds numbers up to a few hundred, is confirmed by comparison with published numerical predictions of the drag coefficient for a range of physical circumstances.