Working equation for a capillary viscometer with non-steady compressible flow

A working equation is developed for a capillary viscometer in the case of a compressible flow. This equation is applied on a viscometer that operates with a steadily decreasing large pressure difference over a long vertical capillary. Also, an earlier approximate version of the working equation is given for this viscometer. The impact of the various assumptions in the earlier calculation is evaluated by making a comparison between the results obtained from both equations, starting from the same experimental data on the viscosity of ethylene. The differences between these results are huge, especially in the critical region and reach almost to 100%