Fuel Cell Testing Products and Services

Types of Humidification

Contact Saturation

A humidification method in which gases come to an equilibrium vapor pressure based on the temperature of a body of water. Changes in the set dew point will control the relative humidity of the sample under test. Changes in back pressure do not effect relative humidity in this method, except when these changes create boiling in the saturator.

Liquid Injection

A humidification method in which a constant flow of water is injected into the gas stream. Back pressure is used in this method to control the relative humidity of the sample under test.

Effect of Pressure on Relative Humidity When Using Contact Saturation

When using Contact Saturation for your tests, setting back pressure assists you in preventing the water in your Saturator/Humidifier from boiling. If the water in your system is boiling, water will condensate in your cell and you will be creating an environment of 100% Relative Humidity in your cell.

Use back pressure to prevent boiling. The following information will assist you in determining the appropriate amount of pressure to set for your tests:

• Determine the Relative Humidity desired for your test.
• Use the BekkTech RH Calculator to assist you in determining the appropriate dew point to achieve your desired Relative Humidity.
• Use the BekkTech RH Calculation Spreadsheet to calculate the Vapor Pressure associated with this dew point.
• Set your back pressure (pressure of the cell hardware) to a pressure greater than the Vapor Pressure calculated.
• If your Cell Pressure falls below the Vapor Pressure, that water in your saturator will boil and you will not be achieving an accurate dew point.