Humidity? Build a Psychrometer!
Using thermometers, cotton balls, string and water, students make simple psychrometers—a tool that measures humidity. They learn the difference between relative humidity (the ratio of water vapor content to water vapor carrying capacity) and dew point (the temperature at which dew forms). Teams collect data using their homemade psychrometers and then calculate relative humidity inside and outside, comparing their results to an off-the-shelf psychrometer (if available). A lab worksheet is provided for data collection and calculation. As a real-world connection, students learn that humidity and air density is taken into consideration by engineers for many design projects. To conclude, they answer and discuss analysis and application questions.
Gaining an understanding of relative humidity has implications for the engineering design of all sorts of technologies.Copyright 2015 Krauss, Wikimedia Commons CC BY-SA 4.0 https://commons.wikimedia.org/wiki/File:Cloud_forest_mount_kinabalu-withHygrom.jpg
Weather can affect many aspects of engineering, from flight dynamics to the efficiency of wind turbines and cooling systems. Humidity is a key concept in understanding weather. Having an understanding of relative humidity and dew point is useful when designing products. Humidity and air density is taken into consideration by engineers for design projects such as wind turbines and kites, and solar panels used for electricity generation.
Many engineers are involved in measuring, collecting, sorting, analyzing and drawing conclusions from real-world data. To correctly interpret data requires an understanding of how engineers consider and account for instrument error (instrument accuracy) and observational error (human misreading or incorrect instrument use).
After this activity, students should be able to:
- Define and explain relative humidity and dew point.
- Use thermometers to calculate relative humidity and dew point.
- Put together a simple device for data collection.
- Collect data, make calculations and analyze experimental results.
- Make the real-world connection that humidity and denser air impact the design of engineered technologies.
- Describe the operation of a psychrometer.