**4.1.1 Sensor excitation mode**

In order to monitor the evolution of the damping of the plate modes due to fouling of the exchanger, it is necessary to excite these modes with enough energy to preserve the signalnoise ratio (of the signal received) after going through the exchanger.

A mechanical shock is the only way of producing enough energy for local excitation.

The frequency response obtained by modal analysis in the absence of structural constraints is given in the first column in table 7. This column gathers the different modes specific to the structure studied. Some correspond to simple, longitudinal or transversal displacements, others to more complex displacements (flexions, torsions...).


Table 7. The first 6 modes specific to the sensor

modes remain the same as the previous case (disc sensor). The principle of the measurement is to excite a vibration mode in one or several plate exchangers and to analyse the evolution

A bivariate system-sensor study enabled the geometry of the latter to be defined over the

reference sensor

**Exchanger plate** 

In order to monitor the evolution of the damping of the plate modes due to fouling of the exchanger, it is necessary to excite these modes with enough energy to preserve the signal-

The frequency response obtained by modal analysis in the absence of structural constraints is given in the first column in table 7. This column gathers the different modes specific to the structure studied. Some correspond to simple, longitudinal or transversal displacements,

A mechanical shock is the only way of producing enough energy for local excitation.

Mode Frequency (Hz) - numerical Frequency (Hz) - experimental

Receiver

Electromagnet soliciting a

under the effect of fouling by measuring the response of the plates using a receiver.

same vibration frequency range as the system (exchanger).

Fig. 19. Positioning of the sensors on an exchanger plate

noise ratio (of the signal received) after going through the exchanger.

others to more complex displacements (flexions, torsions...).

1 1683 1586 2 2387 2894 3 3557 3639 4 5422 5330 5 5734 6639 6 7417 7390

Table 7. The first 6 modes specific to the sensor

**4.1.1 Sensor excitation mode** 

Sensor

The second column shows the modal frequencies obtained from the analysis of the impedance of the sensor mounted on a heat exchanger.

The mean standard deviation between the frequencies obtained by modal analysis and those obtained experimentally is 5 %. The good correlation between these results indicates that the numerical modelling provides a good estimation of the resonance frequencies of the sensor.
