Abstract
We present a new method of chemical quantification utilizing thermal analysis for the detection of relative humidity. By measuring the temperature change of a hydrophilically-modified temperature sensing element vs. a hydrophobically-modified reference element, the total heat from chemical interactions in the sensing element can be measured and used to calculate a change in relative humidity. We have probed the concept by assuming constant temperature streams, and having constant reference humidity (~0% in this case). The concept has been probed with the two methods presented here: (1) a thermistor-based method and (2) a thermographic method. For the first method, a hydrophilically-modified thermistor was used, and a detection range of 0–75% relative humidity was demonstrated. For the second method, a hydrophilically-modified disposable surface (sensing element) and thermal camera were used, and thermal signatures for different relative humidity were demonstrated. These new methods offer opportunities in either chemically harsh environments or in rapidly changing environments. For sensing humidity in a chemically harsh environment, a hydrophilically-modified thermistor can provide a sensing method, eliminating the exposure of metallic contacts, which can be easily corroded by the environment. On the other hand, the thermographic method can be applied with a disposable non-contact sensing element, which is a low-cost upkeep option in environments where damage or fouling is inevitable. In addition, for environments that are rapidly changing, the thermographic method could potentially provide a very rapid humidity measurement as the chemical interactions are rapid and their changes are easily quantified.
Highlights
Humidity sensing is a well-established field with a range of sensors available at low-cost, high accuracy, or other special applications, humidity sensing in harsh or complex environments is still a challenge
We have developed disposable humidity sensors based on color change detection for product monitoring [17]
We demonstrate the utility of the humidity detection via thermal analysis
Summary
Humidity sensing is a well-established field with a range of sensors available at low-cost, high accuracy, or other special applications, humidity sensing in harsh or complex environments is still a challenge. Some examples of harsh environments are sewers and equipment for drying prepared foods. In both of these cases, monitoring humidity may be needed for improved outcomes. Relative humidity is an important factor in predicting corrosion rates in sewers. In the United States alone, it was estimated that sewer corrosion incurs a cost of 14 billion dollars annually [1]. Work has gone into building predictive models for service life in order to avoid costly sewer collapse [2,3,4]; as seen in the work of generating predictive models, humidity is an important factor and is beneficial for predicting corrosion rates. It has been found that in the Sensors 2017, 17, 1196; doi:10.3390/s17061196 www.mdpi.com/journal/sensors
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