Characterization of film condensation: a review of experimental methods and emerging technologies

Abstract Liquid‐film condensation underpins heat‐transfer efficiency and safety in nuclear‐reactor cooling loops, industrial heat exchangers, and spacecraft thermal‐control systems; yet accurately characterizing film thickness and dynamics remains challenging: although a wide range of diagnostic methods is available, each occupies a distinct and often non-overlapping window in spatial and temporal resolution, accuracy, intrusiveness, cost, and adaptability, which complicates the choice of technique and the comparison and synthesis of data across studies. In this review, we apply a unified six‐criteria framework to benchmark ten leading techniques; classical calorimetric and thermal‐probe approaches, thin‐film interferometry, infrared thermography, pulse‐echo ultrasound, acoustic‐emission monitoring, chromatic‐confocal sensing, total‐internal‐reflection imaging, particle‐based velocimetry, laser‐induced fluorescence, x-ray tomography, and high‐speed particle tracking, and introduce two decision‐support schematics: a multi‐axis radar chart that maps each method’s performance envelope and a decision‐tree flowchart that aligns experimental requirements with optimal approaches. Our analysis reveals four critical gaps: noninvasive nanometer‐scale mapping over large areas; real‐time capture of microsecond‐scale transients; co‐located measurement of thickness, temperature, and heat flux; and robust deployment in harsh environments. Finally, we survey emerging solutions; fiber‐optic fiber-optic Bragg grating arrays, MEMS‐based capacitive and piezoelectric sensors, terahertz time‐domain spectroscopy, benchtop x-ray phase-contrast imaging, and digital holographic interferometry, and discuss their integration with machine-learning–driven data fusion and CFD, laying out a roadmap for next‐generation, high‐fidelity condensation modeling in both terrestrial and microgravity applications.