Development and calibration of a fluorescence and fiber-optics based real-time thickness sensor for dynamic liquid films

A condenser's performance can be better understood and better heat transfer correlation for flows in a particular flow regime can be obtained through consideration of real-time measurements of film thickness in the annular regime. Various existing film thickness measuring devices or techniques, viz. conductance probes, ultrasound sensors, reflectance based fiber-optics probes, capacitance probes, etc. were not suitable for measuring dynamic and local film thickness under the conditions of interest (e.g. wavy liquid film) and thickness ranges of interest (typically from 0.5mm to 3mm).; This dissertation presents design, development and calibration of a fiber-optics and fluorescence principles based real-time sensor for measuring a dynamic liquid film's time varying thickness. FC-72 liquid, which is commonly used for electronic cooling purposes, has been doped in small concentration by fluorescent bi-acetyl and selected as the working fluid for film thickness measurements.; This dissertation also presents an important paired set of calibration experiments that highlight the developed calibration principle that is based on one-to-one correspondence among various collected signals and the desired film thickness measurements. This novel calibration technique does not require complete elimination of the detected noise light. However, in order for the sensor to work for wavy films, effects arising from reflections of fluorescent and noise-lights from the liquid-vapor interface are addressed in a way that these effects become nearly independent of the interface angles that are likely to be present.; The effects of doped solution's concentration and temperature variations on the detected amount of light signals have also been reported. By minimizing the errors associated with the variations in concentration and temperature, the total error of the sensed signal D can be minimized to within +/- 5.1%. This, in turn, leads to a thickness measurement whose resolution varies from +/- 0.09 mm (over 0.5 to 1.5 mm) and +/- 0.18 mm (over 1.5 to 3.0 mm).; The functionality of the invented sensor has been verified with the help of a separate dynamic test involving time-varying film thickness of independently ascertained frequency and amplitude. Details and guidelines for further improvements and adaptation of this sensor is also presented.