In the design of the dew point instrument, it is important to consider various factors that directly affect the heat and mass exchange in the dew point process. This principle is also applicable to the selection of operating conditions for dew point instruments that are not highly automated. Here we mainly discuss the cooling rate of the mirror surface and the sample gas flow rate.
The temperature of the measured gas is usually room temperature. Therefore, when the airflow passes through the dew point chamber, the heat and mass transfer process of the system must be affected. When other conditions are fixed, increasing the flow rate will facilitate mass transfer between the airflow and the mirror surface. Especially when measuring the low frost point, the flow rate should be appropriately increased to speed up the formation of the dew layer, but the flow rate should not be too large, otherwise it will cause overheating problems. This is especially obvious for thermoelectric refrigeration dew point meters with relatively low cooling power. If the flow rate is too high, the pressure in the dew point chamber will decrease, and the change in flow rate will affect the heat balance of the system. Therefore, it is necessary to select an appropriate flow rate in the dew point measurement. The selection of the flow rate should depend on the cooling method and the structure of the dew point chamber. The general flow rate range is 0.4~0.7L. Between min-1. In order to reduce the effect of heat transfer, consider pre-cooling the measured gas before entering the dew point chamber.