**4.2.2 Results**

Before studying the phenomenon of fouling, the metrological variation of the measurement system was taken into account according to the main technological parameters:


This phase is essential in order to separate the interferences of acoustic values generated by the fouling phenomenon from those linked to the technological conditions of the exchanger and its environment.

The curves in figure 21 show the evolution of the energy of the acoustic signals as well as the pressure drop in the system as a function of the process time.

The "Power" curve shows the damping effect linked to the load on the plate caused by fouling.

Fig. 21. Evolution of the power of the acoustic signal received during the fouling test and cleaning

In conclusion, this work concerned the monitoring of fouling using acoustics. By adopting a multi-stage experimental protocol we have been able to show that the variation in the acoustic signal can be used to predict variations in the pressure drop as well as the state of fouling in the plate heat exchanger under very specific operating conditions.

Finally, this study illustrates an example of a non-intrusive acoustic technique for the local monitoring in real time of the fouling of plate heat exchangers. The results show that it is possible to follow the relative kinetics of the state of fouling in each zone of the exchanger with the right choice and positioning of the sensors.
