Water Vapor Pressure in the Still Air Layer Adhering to Perforated Plastic Plates

Abstract

Although relative humidity and temperature sensors have become smaller and more compact, still some bulk size persists. It is conceivable that the sensor may be im permeable to the water vapor in the zone close to the sample. The water vapor pressure in the zone was investigated using two different kinds of sensors (fiber and flat). The water vapor pressure gradients were straight, and water vapor diffusion occurred ev erywhere in the still air layer. If a flat humidity sensor is used to measure the water vapor pressure close to a sample through which vapor is diffusing, an error will result when the sensor is too close, as described in our previous paper. For a sensor 3 mm wide, a 4 mm distance is too close, but a thinner sensor such as a hair can be used down to about 1 mm.