Date of Graduation


Document Type


Degree Name

Bachelor of Science in Civil Engineering

Degree Level



Civil Engineering


Coffman, Richard


A series of tests were conducted to control relative humidity (RH) using a bubbler system that contained a series of glass jars and glass vials filled with different concentrations of glycerin. The relative humidity within the glass jars was measured. The total time interval for each laboratory test was 48 hours. During the first 24 hours a pump was used to bubble air through the glycerin solution. During the second 24 hours, the pump was turned off, and the RH within the system was monitored within the closed system. Target RH measurements from 100% to a 0% were obtained. The factors that affected the RH measurements included the glycerin concentration and the air temperature within the bubbler system. Even subtle changes, such as going from 23° C to 22.8° C, resulted in a RH measurement increase between 5% to 10%. For example, when the target of RH was 100, the measured values stabilized at 95%. Likewise, when the target RH was 40%, the measured values stabilized at 33%. These changes occurred at a different rate over time. For example, at the 2 hours mark the target 100% RH was at 92% whereas at the 13 hours mark the target 100% RH was at 95%. Thus, a method was implemented to correct measurements of RH to 20° C, so these measurements could be more accurate to what the target values of RH (from 100% to 0%). This method included the back calculation of RH by using the absolute humidity (A) which is the ratio of the mass of water contained per volume of moist air. However, this method failed to correct the values as it increased the RH measurements by approximately 20%. Instead of correcting the values to 20° C, a new system was developed to control the system to 20° C ± 0.1° C.


RH, relative humidity, soil suction, glass jars, vials, service learning