Miniaturized Acoustic Sensing Platform for Spatial Mapping of Ultrasonic Fields in Small-Diameter Tube Bundles

Shell-and-tube heat exchangers often operate under harsh conditions that induce fouling, leading to loss of thermal efficiency, production downtime, and increased maintenance costs. Conventional cleaning procedures generally require scheduled or unscheduled shutdowns, with direct operational and financial impacts. In this context, ultrasonic cavitation has been investigated as a strategy for fouling prevention and equipment cleaning, with the potential to reduce cleaning downtime or support in-service mitigation strategies. This work presents the development of an acquisition platform based on a miniaturized, waterproof acoustic probe designed for operation inside 8 mm tubes under cavitating ultrasonic fields, with the goal of experimentally mapping the relative acoustic response amplitude and dominant frequency in U-tube heat exchangers. The system integrates a piezoelectric sensing element embedded in protective encapsulation, signal-conditioning electronics, and a high-sampling-rate acquisition module. Experiments were conducted in a reduced-scale exchanger comprising 90 access ports and measurement depths up to 775 mm, using 28 kHz ultrasonic transducers. The probe successfully captured both the spectral content and the spatial variation of the voltage-based acoustic response along the tube bundle, revealing position-dependent amplitude variations and dominant-frequency measurements concentrated around the imposed excitation frequency. The analysis supported the definition of a reduced set of representative sampling locations, decreasing acquisition time while preserving the main spatial trends relevant to the objectives of this study. The procedures established here provide an experimental basis for future studies on the application of ultrasound to fouling-mitigation strategies in industrial thermal systems.