ASTM_D_4023_-_82a_1996.pdf

Designation:D 4023 82a(Reapproved 1996)An American National StandardStandard Terminology Relating toHumidity Measurements1This standard is issued under the fixed designation D 4023;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.absolute humidity,vapor concentration,vapor density,dvthe ratio of the mass of water vapor mvto the total volumeof the moist air v:dv5mvv(1)dew cell,dew probean instrument that measures the tem-perature at which a saturated salt solution(usually of lithiumchloride)is in equilibrium with the water vapor in moist air.dew-/frost-point hygrometeran instrument that measuresthe surface temperature at which ambient water vaporcondenses.dry-bulb temperature,tthe temperature of the ambient air,for example,the temperature that is measured by the drybulbthermometer of a psychrometer.electric hygrometeran instrument that determines the watervapor content of an atmosphere by measuring the change inresistance or capacitance of hygroscopic material.enhancement factorthe correction for the departure of themixture of air and water vapor from ideal gas laws.ice-bulb temperature,tithe temperature that a thermometerindicates when its bulb is surrounded by a thin film of ice(ora frozen moistened covering),and allowed to cool bysublimation of the ice into the surrounding air.mechanical hygrometeran instrument for determining thewater vapor content of an atmosphere by measuring thedimensional change produced in an hygroscopic material.mixing ratio,r the ratio of the mass of water vapor mvto themass of dry air mapresent in the moist air;r 5mvma(2)mole fraction of water vapor,xvthe ratio of the number ofmoles of water vapor nvto the total number of moles ofwater and dry air;xv5nvnv1 na(3)where:nv5mvMv(4)na5maMa(5)and where Mvand Maare the molecular weights ofwatervapor and air,respectively.psychrometer,aspiratedan hygrometer comprising wet-and dry-bulb thermometers that are mounted in a housing towhich is attached a motordriven fan or blower that draws airover the thermometer bulbs at a rate which produces themimimum wet-bulb reading.psychrometer,sling(whirling)an hygrometer comprisingwet-and dry-bulb thermometers that are mounted on a framethat can be rotated or whirled.relative humidity with respect to ice,Uithe ratio in percentof the mole fraction of water vapor xvin moist air to themole fraction of water vapor xvithat moist air would have ifit were saturated with respect to ice at the same pressure pand temperature t;Ui5xvxvi3 100(6)If the water vapor and air assumed to behave as ideal gases,thenUi5eei3 100(7)where e is the partial pressure of the water vapor in themoist air and eiis the saturation vapor pressure with respect toice at the same temperature t.relative humidity with respect to water,Uwthe ratio inpercent of mole fraction of water vapor xvin moist air to themole fraction of water vapor xvwthat the moist air wouldhave if it were saturated with respect to water at the samepressure p and temperature t:Uw5xvxvw3 100(8)If water vapor and air are assumed to behave as ideal gases,thenUw5eew3 100(9)where e is the partial pressure of the water vapor in the moistair and ewis the saturation vapor pressure with respect to waterat the same temperature t.saturationthe condition existing when a vapor is in equilib-rium with the plane surface of a condensed phase of the same1This terminology is under the jurisdiction of ASTM Committee D22 onSampling and Analysis of Atmospheresand are the direct responsibility of Subcom-mittee D22.11on Meteorology.Current edition approved Aug.27,1982.Published December 1982.Originallypublished as D 4023 81.Last previous edition D 4023 82.1Copyright ASTM,100 Barr Harbor Drive,West Conshohocken,PA 19428-2959,United States.NOTICE:This standard has either been superseded and replaced by a new version or discontinued.Contact ASTM International(www.astm.org)for the latest information.substance(liquid or solid).saturation mixing ratiothe ratio of the mass of water vapormvto the mass of dry air mapresent in saturated air.Thesaturation mixing ratio is designated by rwwhen saturation iswith respect to the plane surface of liquid water,and by riwhen saturation is with respect to the plane surface of ice.saturation vapor pressure of waterthe pressure of watervapor in equilibrium with plane surface of a condensedphase.When the condensed phase is liquid,the saturationvapor pressure is designated by ew,and when the condensedphase is solid,the saturation vapor pressure is designated byei.The saturation vapor pressure is a function of tempera-ture.specific humidity,qthe ratio of the mass of water vapor mvto the total mass mv+maof the moist air:q 5mvmv1 ma(10)thermodynamic dew-point temperature,Tdthe tempera-ture at which moist air with mixing ratio