A gas humidifier is a device used to add water vapor to gas flow to create an exact relative humidity (RH). Relative humidity refers to the ratio of partial pressure of water vapor (pH2O) present in the gas to the equilibrium vapor pressure at saturation at a certain temperature.
Gas humidifiers are often used to humidify gases that have no water-soluble components. They also humidify air which needs to be used in other processes, such as gas blending.
Applications of Gas Humidifiers
Gas humidifiers replicate real life environments, in both research and calibration applications. Often, they are used to mimic emissions, human breath, exhaust or ambient conditions and allow users to add exact relative humidity levels to a blend of gases, simulating a broad range of conditions in which gas samples contain humidity.
Water to Gas Humidifiers
At Environics, we use Nafion™ tubing in our water-to-gas humidifiers. These instruments allow water to travel through the Nafion membrane to gain equilibrium of the partial pressure of water vapor on both sides of the membrane.
There is a discrepancy in humidity levels on both sides of the membrane, which means that the incoming dry gas stream is humidified whilst it flows over the tubing and the water travels through in the opposite direction. Gases which are not able to cross this membrane are the only gases which can be humidified using this method.
Gas humidifiers come with a range of lengths and number of Nafion tubes as standard, which means that various surface areas are reachable, depending on the flow rate and RH required, however, ranges are generally between 5-95% relative humidity. The temperature needs to stay consistent in order for repeatable and stable RH to be achieved.
A water circulating pump is often used in combination with humidifier’s water reservoir. As an endothermic process, heat is removed from the water while the gas is being humidified. The pump is needed to keep the water temperature from getting too cold and preventing the production of higher humidity levels.
Bubbler Gas Humidifiers
Bubblers are another type of gas humidification which allows dry gases to bubble through water at room temperature. These gas humidifiers produce small bubbles of gas, enhancing the contact surface, offering maximum humidity for the bubbles to pick up.
Gas to Gas Humidifiers
Gas to gas humidifiers are often used for the humidification of calibration gases, aerosol streams, particle streams and gases that have water soluble components within. Gas to gas humidifiers work using water vapor outside the tubing which is transferred selectively into a gas stream which is traveling through the tubing. To do this, the humid gas needs to be pumped and run in the opposite direction to the current of the gas stream.
Gas Humidifiers and Environics
Environics can design standalone gas humidifiers as well as gas mixing or dilution system which include a gas humidifier. Both units can be designed for a fixed or adjustable relative humidity level.