12 research outputs found
Monitoring surface crystal growth using an intrinsic exposed-core optical fiber sensor (IECOFS)
An unclad section of silica optical fiber has been used to detect, and measure heterogeneous (surface) crystal growth in a solution of calcium carbonate. Surface crystal growth is found to attenuate radiation transmitted along the fiber core via the refraction of guided modes out of the core. Optical power output was found to be linearly correlated with crystal size (R² = 0.97, n = 9) and the optical signal was found to be restored following chemical removal of deposited crystals (without physical intervention). Sensitivity to crystal growth was found to be proportional to the length of the unclad (exposed) core and inversely-proportional to fiber diameter. These results suggest a simple skip-length ray model, coupled with refraction of guided modes out of the fiber core can be invoked to explain the mechanism of optical power attenuation
Using an intrinsic, exposed core, optical fibre sensor to quantify chemical scale formation
An intrinsic exposed core, optical fibre sensor has been used for directly monitoring surface crystal growth 'in-situ'. A negative, linear relationship (R²=0.98, n=8) was also observed between measured crystal thickness (on the surface of the fibre core) and attenuation of radiation guided within the fibre. An empirical geometric ray-model, based on the refraction of guided modes out of the exposed fibre core into the crystals of higher refractive index supported the experimental observations. Results point to the potential of using an optical fibre as a fully recoverable, quantitative sensor of crystal growth
Intrinsic Exposed Core Optical Fibre Sensors for Monitoring Heterogeneous Crystal Growth
Unwanted surface (heterogeneous) crystallization, known as scale formation, can often be found in industrial processes that make use of water or oil and can cost the industries involved millions of dollars. Chemicals, known as scale inhibitors, can be added to process solutions in order to prevent or retard the formation of scale, however an accurate determination of the onset and growth of the scale is required to optimise the use of inhibitors. Current methods for monitoring scale are compromised due to inability of the techniques to discriminate between heterogeneous (surface) and homogeneous (bulk) crystallization. These two crystallization types propagate via different crystallization pathways and an ability to distinguish between the two crystal types is critical if the amount of the scale formed on a surface is to be determined. An intrinsic exposed core optical fibre sensor (IECOFS) has been tested for the detection and monitoring of heterogeneous crystallization. The exposed core of the optical fibre provides a surface for heterogeneous crystallization. The sensor works by the refraction of radiation out of the fibre by the presence of a medium of higher refractive index on the optical fibre core. A model describing the refraction of the radiation out of the fibre and out of the crystals has shown to accurately describe the IECOFS measurements. The sensor is capable of monitoring the average crystal growth process on the optical fibre sensor by the increase in interactions that accompanies the growth of the crystals. The IECOFS has shown to be insensitive to the homogeneous crystallization and is therefore able to distinguish between the two crystallization types. Furthermore, it was shown that the crystal growth kinetics between two different surface types under similar crystallization conditions do not differ significantly. Heterogeneous growth kinetic measurements have shown that the IECOFS can accurately monitor the heterogeneous process on a surface of interest, either in the presence, or not, of chemical scale inhibitors. The results obtained are important in the evaluation of the IECOFS as either an industrial or a lab based sensor for heterogeneous crystallization
An intrinsic exposed core optical fiber sensor as a quantitative surface crystallization monitoring sensor
An intrinsic exposed core optical fiber sensors has been described that is capable of monitoring surface crystallization, also known as scale formation. The optical fiber sensor is a more reliable sensor of scale growth than other scale sensing methods, such as turbidity measurement, due to its ability to discriminate between bulk and surface crystallization. When the sensor was subjected to the same crystal growth conditions as a stainless steel surface, the optical fiber sensor showed the capability to follow the scale formation on the scale affected stainless steel surface
Determining crystal growth kinetic parameters using optical fibre sensors
The capability of an 'intrinsic exposed core optical fibre sensor' (IECOFS) as a monitoring device of scale formation has been evaluated. The IECOFS has been used to measure kinetics parameters of calcium carbonate heterogeneous crystal growth such as the activation energy, the crystal growth rate and the induction time. The IECOFS was able to evaluate crystal growth inhibition through the use of chemical inhibitors
Guided-mode refraction model for optical fiber sensing of surface crystal growth
An empirical "guided-mode refraction model" has been invoked to explain the optical attenuation of radiation in an exposed core optical fiber sensor subject to heterogeneous (surface) crystal growth. Based on Fresnel reflectance values at the internal fiber–crystal and crystal–solution interfaces, the model predictions agree with experimental observations of radial loss of radiation from the fiber core through the crystals as well as attenuation of guided radiation as a function of the radiation launch angle into the fiber
Investigating surface crystal growth using an intrinsic exposed core optical fibre sensor
Surface, or heterogeneous crystallisation processes, also known as scale formation, has been monitored directly using an intrinsic, exposed core optical fibre sensor (IECOFS). Optical attenuation was found to be linearly correlated with scale layer height and average crystal contact area and the optical signal was found to be restored following chemical removal of deposited crystals (without physical intervention). The IECOFS was found to be insensitive to bulk-solution (homogenous) crystallisation processes, making it a potentially powerful tool for the study of heterogeneous-only crystallisation processes. Kinetic parameters extracted from the obtained crystallisation measurements showed that the IECOFS is capable of providing a reliable means of monitoring surface crystal growth
Progress in the application of exposed core, optical fibre sensors for detecting and monitoring surface crystallization processes
Intrinsic Exposed Core Optical Fibre Sensors (IECOFS) based on step-index, silica fibres have been used to monitor surface crystallization processes. When applied to scale (CaCO₃) detection, the sensor is fully recoverable; requiring only immersion in a solution of dilute HCl. Unlike conventional scale sensors, the IECOFS responds only to heterogenous (surface) crystal growth and the optical response correlates to several crystal growth processes, offering a tool for monitoring surface crystal growth kinetics. Kinetic parameters extracted from the IECOFS response profiles are similar to those obtained from surface crystal growth on stainless steel surfaces indicating the potential for IECOFS as a sensor of scale formation in industrial processes
Monitoring the kinetics of heterogeneous crystal growth using an Intrinsic Exposed Core Optical Fiber Sensor
The prevention of unwanted heterogeneous crystal growth, known as scale formation, requires accurate detection of the rate and amount of scale deposition on surfaces. An Intrinsic Exposed Core Optical Fibre Sensor (IECOFS) has been used to measure heterogeneous crystal growth kinetic parameters, such as the rate of crystal growth and the induction time. Measurements at different temperatures allowed the activation energy to be determined for three crystal types, with excellent agreement with literature values. Crystal growth kinetic parameters were determined for calcium carbonate with the IECOFS and were found to compare well with kinetic parameters extracted from crystal growth measurements on a stainless steel surface. Crystal growth kinetic measurements were also performed in the presence of a poly-acrylic-acid (PAA) crystal growth inhibitor. The IECOFS monitored a reduction in the crystal growth rate and an increase in the induction time, matching well with the expected behaviour of the PAA inhibitor and agreeing with a literature model of crystal growth