低湿度測定に及ぼす脱着水分の影響

抄録

The desorbed water vapour from walls of conduit pipe has a large effect on measurement of very low humidity below -40°C in terms of dew-point temperature. This effect is investigated by the use of a vinyl tube and a copper pipe as the conduit pipe and the following are concluded to be important for the reduction of the effect. 1) The conduit pipe must be as thin and short as possible. 2) The pipe wall temperature must be kept below 30°C. 3) The flow rate of gas must be above 10l/min. Furthermore, the relation between the Reynold's number, Re, and the relative error of indicated dew-point temperature, (p-p_i)/p_i, is obtained, where p is the water vapour pressure corresponding to the indicated dew-point temperature at the outlet of the conduit pipe and pi is the water vapour pressure corresponding to the dew-point temperature of gas entering the conduit pipe, therefore (p-p_i)/p_i means the relative error of indicated dew-point temperature.