This blog post explores the concept of chilled-mirrors and their role in accurately determining dew point, a crucial parameter in various applications.
Table of contents
Understanding Dew Point:
Phase Transition: Gases transition from vapor (gas) to liquid (dew) upon reaching a specific temperature called the dew point. This point is influenced by the gas composition and pressure.
The Chilled-Mirror Technique:
Core Principle: By forcing condensation onto a cooled surface (the mirror), the chilled-mirror method directly measures dew point. This approach provides a highly accurate and fundamental measurement.
Widespread Applications:
Over a Century of Use: Chilled-mirrors have been employed for over 100 years, primarily for moisture determination.
Beyond Moisture: The principle can also be applied to measure the dew point of any gas or gas mixture.
Chilled-Mirrors in Natural Gas Analysis:
Two Key Dew Points: In natural gas analysis, two dew points hold significance:
Water (Moisture) Dew Point: The temperature at which moisture condenses out.
Hydrocarbon Dew Point (HCDP): The temperature at which heavier hydrocarbon components liquefy.
Chilled-Mirrors for Both Measurements: With the exception of ZEGAZ Instruments CEIRS(™) Technology, there are no other automated chilled-mirrors that are capable of measuring both dew points successfully and accurately.These instruments have been used for a long time to determine both dew points.
Essential Components of a Chilled-Mirror:
Cooled Surface: A mirror that can be precisely chilled.
Temperature Sensor: Measures the mirror's temperature.
Condensation Detection: A mechanism to identify the onset of condensation (dew formation).
Evolution of Chilled-Mirrors:
Early Manual Systems: Early chilled-mirrors relied on an operator visually observing the metal mirror surface for condensation signs during cooling with refrigerant gas.
Limitations: Subjectivity based on the operator's experience impacted the accuracy of this method.
Automated Chilled-Mirrors:
Light Scattering Method (Pre-2009): This method used a light beam directed at the mirror during cooling. A change in the reflected light profile upon dew formation signalled the dew point, allowing for temperature recording.
Issues with Light Scattering:
Inability to Differentiate: It cannot distinguish between water and hydrocarbon dew points, leading to inaccurate readings.
Contamination Sensitivity: Dirt on windows or in the gas can cause false readings.
Mirror Degradation: Metallic mirrors used in these systems tend to corrode over time, requiring replacements.
Introducing CEIRS™ Technology:
Developed by ZEGAZ Instruments: This technology addresses the limitations of the light-scattering method.
Focus of Next Blog: A future blog post will delve deeper into CEIRS™, specifically its infrared aspects, explaining how it overcomes these challenges in dew point measurement.
In essence, chilled-mirrors offer a reliable and direct method for dew point determination. While the light-scattering technique has limitations, advancements like CEIRS™ technology address these issues, providing a more accurate and robust solution for various applications.