Optimizing the Temperature Profile of the Nafion Dryer
Black Line = Sample Gas Temperature
Red Line – Sample Gas Dew Point
For this example, the sample gas enters the dryer hot and wet on the left and exits cool and dry on the right.
For consistent and repeatable performance, condensation must be prevented from forming at any point along the sample gas pathway. As shown in the graph, the dew point of the gas must never reach the gas temperature. The pathway “A” might require heating to prevent condensation if the heat energy is the sample gas is not enough to keep the temperature above the dew point. We recommend that this area be heated to a temperature of at least 10 C above the dew point to prevent condensation. It normally represents 1/3-1/2 of the dryer length.
The exit temperature of the gas in portion B affects the dryer performance in as much as the membrane operating temperature affects the performance – the lower the better. See the graph above for more information. A portion of the dryer might need to be routed away from hot areas in the analyzer (like next to the furnace) or cooled to a lower temperature in order to facilitate this. If the purge gas can provide a cooling effect, it might be advantageous to increase the purge flow from 2-3x to 4-10x of sample flow.