Abstract
A new method is proposed for measuring fluid density using the equation of motion. Since the pressure gradient along a pipe is proportional to the density and the axial acceleration of fluid in the pipe, the density of fluid can be calculated from the pressure gradient and the acceleration. An exciter is mounted to a sensing pipe and is driven at a constant acceleration amplitude. Two pressure taps are made on the sensing pipe spaced a small distance apart along the pipe axis. The pressure difference between these taps, which is a finite difference approximation for the axial pressure gradient, is picked up by a manometer. A phase-sensitive detector being employed, the output of the manometer is converted to two DC voltages; these outputs are proportional respectively to the fluid acceleration and to the fluid velocity. The fluid density can be known from the output proportional to the acceleration, while the voltage proportional to the velocity can be used to eliminate the error due to the fluid viscosity. A trial device was built which employed a flat diaphragm speaker for the exciter, and several experiments were performed for gases with this device. The experimental results were in good agreement with theoretical predictions.
