Humidity

About: Humidity is a research topic. Over the lifetime, 13614 publications have been published within this topic receiving 192720 citations.

Humidity fixed points of binary saturated aqueous solutions

Abstract: An evaluated compilation of equilibrium relative humidities in air versus temperature from pure phase to approximately 105 pascal (1 atm) in pressure is presented for 28 binary saturated aqueous solutions. The relative humidities of the solutions range from about 3 to 98 percent. Using a data base from 21 separate investigations comprising 1106 individual measurements, fits were made by the method of least squares to regular polynomial equations with two through four coefficients. Equations and tables are presented along with the estimated uncertainties in the correlated results. Research, hygrometer calibration, testing and material conditioning often require the accurate control of humidity in a working space. The common methods of controlling the humidity accurately use either a humidity generator (1A)1 or the equilibration of a closed space with a chemical system (IB) which produces the desired equilibrium vapor pressure. Humidity generators tend to be expensive and complex whereas equilibration with chemical systems that provide fixed points is a relatively inexpensive and simple method of humidity control. Among the chemical systems used for this purpose are aqueous sulphuric acid solutions, glycerine and water solutions and single and binary salt solutions. Each such solution offers a degree of humidity adjustment that can be achieved by changing its concentration. On the other hand, special problems are associated with the use of solu- tions because their concentrations must be measured and controlled. Not only must the concentration of the solution be determined initially but the presence of any humidity sources or sinks in the controlled space and even the initial equilibra- tion process of the space can alter the solution concentration. An especially useful method of humidity control by chemi- cal system involves the use of binary saturated aqueous solutions (primarily of single salts) in which the solute is highly non-volatile. At any temperature, the concentration of a saturated solu- tion is fixed and does not have to be determined. By provid- ing excess solute, the solution will remain saturated even in the presence of modest sources or sinks. Where the solute is a solid in the pure phase, it is easy to determine that there is indeed saturation. Due to the ease of its use, this is a popular method of humidity control. Since a given saturated salt solution provides only one relative humidity (RH) at any desired temperature, a different relative humidity must be achieved by selecting another appropriate salt. Though much data on saturated salt solu-

Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity

Abstract: Radiative convective equilibrium of the atmosphere with a given distribution of relative humidity is computed as the asymptotic state of an initial value problem. The results show that it takes almost twice as long to reach the state of radiative convective equilibrium for the atmosphere with a given distribution of relative humidity than for the atmosphere with a given distribution of absolute humidity. Also, the surface equilibrium temperature of the former is almost twice as sensitive to change of various factors such as solar constant, CO2 content, O3 content, and cloudiness, than that of the latter, due to the adjustment of water vapor content to the temperature variation of the atmosphere. According to our estimate, a doubling of the CO2 content in the atmosphere has the effect of raising the temperature of the atmosphere (whose relative humidity is fixed) by about 2C. Our model does not have the extreme sensitivity of atmospheric temperature to changes of CO2 content which was adduced by M...

Moisture Absorption and Desorption of Composite Materials

Abstract: Expressions are presented for the moisture distribution and the mois ture content as a function of time of one dimensional homogeneous and composite materials exposed either on one side or on both sides to humid air or to water. The results apply during both moisture absorption and desorption when the moisture content and the temperature of the environ ment are constant. Test procedures are described for determining experi mentally the values of the moisture content and the diffusivity of com posite materials. A series of tests using unidirectional and π/4 Graphite T-300 Fiberite 1034 composites were performed in the temperature range 300—425 K with the material submerged both in moist air (humidity 0 to 100%) and in water. The test data support the analytical results and pro vide the moisture absorption and desorption characteristics of such com posites. Extension of the results to materials exposed to time varying envi ronmental conditions is indicated.

Water harvesting from air with metal-organic frameworks powered by natural sunlight

Abstract: Atmospheric water is a resource equivalent to ~10% of all fresh water in lakes on Earth. However, an efficient process for capturing and delivering water from air, especially at low humidity levels (down to 20%), has not been developed. We report the design and demonstration of a device based on a porous metal-organic framework {MOF-801, [Zr6O4(OH)4(fumarate)6]} that captures water from the atmosphere at ambient conditions by using low-grade heat from natural sunlight at a flux of less than 1 sun (1 kilowatt per square meter). This device is capable of harvesting 2.8 liters of water per kilogram of MOF daily at relative humidity levels as low as 20% and requires no additional input of energy.