We present a numerical investigation of an acoustic sensor based on a cylindrical resonator to monitor the acoustic properties of liquids flowing in a tube. The sensor design consists of a hollow cylindrical washer surrounding the tube, which carries the liquid, and which can be filled during the sensing process. Due to the impedance mismatch between the liquid and the solid washer, we demonstrate the presence of high-quality factor resonances associated with the acoustic properties of the liquid (such as velocity, density, or viscosity) appearing as sharp spectral features in the transmission and detection measurements. An appropriate choice of geometrical parameters allows either to obtain two distinct resonances associated with the liquid and the surrounding washer or to overlap the narrow resonance of the liquid with the broad resonance of the washer and achieve a Fano-type resonance from their interaction. The sensitivity of the resonances to the acoustic properties of the liquid are investigated as a function of the geometrical parameters. We show that for highly viscous fluids, the vanishing of very narrow peaks can be avoided by increasing the thickness of the washer and, therefore, decreasing the quality factors. The calculations are performed in the framework of a finite element method. Our design provides a promising platform for sensing several acoustic characteristics of liquids flowing in tubes.