Psychrometric wet elements as a basis for precise physico-chemical measurements

Under appropriate conditions, psychrometric wet elements of simple design can he highly reproducible in behavior. A temperature depression of 10 K can be reproducible from element to element within 2 mK. The properties of a wet element can be determined very accurately by direct comparisons with other wet elements in a common airstream. Comparisons with one specially developed type show the effects of practical water-retaining coverings. Comparisons with another type, which simulates the fully calculable flat-plate system, then give the behavior in absolute terms. A cotton-yarn covering increases the psychrometer coefficient A by only 0.2 percent. The departure of the flow around a cylinder from laminar boundary-layer flow increases it by 0.7 percent. The background and theory are outlined. The detailed behavior of cotton-yarn covered cylinders is deduced from element comparisons; and their absolute value of A obtained as a function of diameter, airspeed, and the temperature, pressure and water content of the airstream. The dependence of A on these parameters is essentially simple. The work leads to a large increase in the accuracy of water vapor measurements and to new methods of measuring some other physico-chemical quantities.