The Optimum Concentration of Electrolytes for an Electrode Humidifier

 Ted Yeh

Classen SAS

Oklahoma City

March 25, 1999

Abstract

The main purpose of this project was to determine what concentration of salt or baking soda would promote the most efficient use of an electrode humidifier.  This type of humidifier passes an electric current between two carbon electrodes to heat the water and produce vapor.  In order for conduction to occur, there needs to be an electrolyte that ionizes in water.  The most common household electrolytes are salt and baking soda.  I tested these two compounds in one to four gram amounts.  At every hour, the height of the water inside the humidifier was measured to monitor the humidifier’s water consumption rate.  Based on research concerning ionization, I predicted that a moderate amount of salt would support a stream of vapor that remained constant for seven hours and would also last that long.  The results supported my hypothesis.  Overall, the salt allowed the humidifier to use the most amount of water.  However, there was significantly more noise than the baking soda units.   The conclusion was that 2 grams (1/4 teaspoon) of salt was the optimum amount to dissolve in 1.5 gallons (5.678 liters) of water.

Introduction

  Humidity plays a very important part in indoor air quality.  The intention of this experiment was to determine what concentration of mineral  (electrolyte) could promote the most efficient use of an electrode humidifier. I chose a Kaz Electrode Vaporizer for this project because of personal usage. The included manual suggests that adding a “pinch” of salt would aid the humidifier’s efficiency. However, a “pinch” is not scientifically accurate enough to describe the amount needed, so I wanted to find a more exact measurement.  I also wanted to test baking soda because it is a good electrolyte.

This particular humidifier functions by passing an electrical current between two carbon electrodes in the water.  In order for it to function, there must be minerals, or electrolytes, in the water to provide a path of current.  Electrolytes, such as sodium chloride (salt) and sodium bicarbonate (baking soda), separate into ions when dissolved in water.  The ions form a channel between two electrodes to allow the passage of electricity.  The electricity then heats the water to the boiling point for steam production (1,2). According to my research on ionization and conductivity (3), a large amount of electrolyte will promote the most evaporation of water, but for purposes of home use, such quantities are not practical.  From personal experience, a humidifier with too much compound will operate with background noise that proves very bothersome.  Also, if the humidifier vaporizes the water too fast, it will not last for the period of operation needed.  Furthermore, this excessive use reduces the life of the humidifier.

Based on the literature search (3,4,5,6,7) and personal experience, I believed that a moderate amount of salt, about 2 grams dissolved in 1.5 gallons of water, would allow the humidifier to use the most water, have the most constant vapor, and last the longest.  In this experiment, one, two, three, and four grams of the substances (salt / baking soda) were dissolved in 5.678 liters (1.5 gallons) of tap water producing .018%, .035%, .053%, and .07%, concentrations, respectively.  The experiment proceeded for seven hours, since this is the average duration of a night’s sleep.

Materials and Methods

The materials required for this experiment were: 5 Kaz electrode vaporizers, table salt (NaCl), baking soda (NaCO₃), balance, metric ruler, stopwatch/clock, humidity meter, one gallon milk jug, one half gallon milk jug, tap water, and graduated cylinders (10, 25, 50, and 500 mL). 

First, each vaporizer was filled with 1.5 gallons of water and labeled 1, 2, 3, 4, and 5.  Unit #5 was the control; no substance was added.  In #1, one gram of salt was added; in #2, two grams, and so forth.  Then I measured the initial height of the water by inserting the ruler perpendicularly into the water until it reached the bottom.  Next, unit #1 was plugged and the time started.  The time was noted when vapor was visibly rising from the unit.  When the watch read 10 minutes, #2 was plugged and the time for vapor was also noted.  Numbers 3, 4, and 5 were continued in the same manner, giving a ten-minute increment before the start of each unit.  At one hour, the top of #1 was quickly removed, the height measured, and the top replaced.  Ten minutes later, the top of #2 was removed and the height was also measured.  Numbers 3, 4, and 5 were continued in the same way in ten-minute increments to insure that each unit had been running for exactly one hour before the reading was taken.  This procedure was repeated for six more hours.  After the seven hour reading, each unit was unplugged consecutively in ten-minute increments after measuring the height with the intention that each has been active for a total of seven hours exactly.  After all the units were unplugged, the volume of the water was measured.  The units were then thoroughly rinsed, and the whole process was repeated with baking soda, except the tops of #1 and #5, and #2 and #4 were switched to balance the strain on the electrodes.

One of the difficulties encountered was the fact that the units were disturbed hourly, and so it took a few minutes for the steam to reappear.  This would cause the humidifier to use slightly less water than if it had run continuously for seven hours.

Results

Based on the collected data, the units containing salt visibly consumed more water than baking soda for every concentration tested (Figure 1, Figure 2).  Although all of the concentrations of baking soda showed a much less variation in the amount of water used in each hour, its total output of steam was much less than that of salt (Table 1, Table 2).  Recording the time for steam to appear is important because it would be unpractical to wait a long time for steam.  The two and three gram amounts of baking soda produced steam quicker than that of salt, but the difference can be ignored (Table1, Table2). 

Discussion

Following the experiment, I proceeded to run the units for 15 hours, desiring to know if each unit would really endure, as marked on the brochure.  Only the one-gram unit of salt lasted for this duration, along with the one, two, and four-gram units of baking soda.

Also, even though the body of the humidifier is not an exact rectangular prism, a one-millimeter change in height was measured to be corresponding to 100 milliliters of water.   As a result, the height change is an accurate measurement of the change in the volume of water. 

Since the purpose of a humidifier is to increase humidity, the relative humidity raised by humidifier was also measured.  Relative humidity is the ratio of the amount of water in the air compared to the amount of water that the air can hold at that temperature.  The results indicated that the humidity increased about 10 percent after seven hours in an 1890 ft³ room at 21^o C.  The increases were similar for both two and three grams of salt because the ventilation system removed excess moisture from the air. 

The amount of salt used in this experiment (1,2,3,4 g) was converted to more familiar unit – the teaspoon (tsp). The correspondent units for these amounts are closed to 1/8 tsp, 1/4 tsp, 1/2 tsp, and 5/8 tsp, respectively.

Conclusion

A concentration of 2 grams of salt in 1.5 gallons of water (0.035%) was concluded to be the best because it gave the most constant vapor output, had a reasonable amount of water used, needed short time for the appearance of vapor, and had the longest vapor duration.   It consumed at a rate of 0.47 liters per hour (Table 1).  The unit that had 3 grams of salt actually used the most water (0.53 liters per hour), but it showed more fluctuations in the production of vapor from hour to hour (Table 1) and was the first unit to stop the production of steam; it only lasted for 9 hours. 

The effectiveness of the humidifier can be altered by other factors such as ventilation and room size.  The duration of operation needed, water hardness, and room temperature can eliminate or enhance the amount of the electrolyte needed in the humidifier.

Acknowledgements

This project was done with the assistance of my mother, Fawn Yeh.  She supervised my work and gave ideas that improved my project greatly. 

Also, Dr. John Testa assisted in my first OJAS competition.

Table 1:  Salt Water Table