ADIABATIC CHANGES OF MOIST AIR NEUHOFF 



473 



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s s 



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N 



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V 



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x 



X 



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10° 



20" 



600 



70O 



760 



it can not be expressed graphically, therefore the construction of 

 one single diagram is sufficient. 



In the snow stage m = 3.44 is to be adopted since here in general 

 only a slight quantity of. moisture can occur. 



The curves given in fig. 2 present the changes of condition for 

 pseudoadiabatic expan- 

 sion under the assump- 

 tion that none of the 

 water that is present at 

 the freezing temperature 

 = o° C. has frozen ; these 

 adiabats of the snow 

 stage therefore join di- 

 rectly on to those of the 

 rain stage. . In conse- 

 quence of the sudden in- 

 troduction of the latent 

 heat of liquefaction (r) 

 at + o° C. the curves do 

 not proceed continuously but have a small nick at the o° line. 



If at temperature o° C. in consequence of the freezing of water 

 there should occur an isothermal fall of pressure, for instance, 

 of io mm , then this would be graphically indicated by a parallel 

 change in the adiabat of the snow stage, as is indicated by the fine 

 line in fig. 2 drawn above the adiabat for 20 and , j6o mm . 



The adiabats of the condensation stage are more steeply inclined 

 than those of the dry stage but at low temperatures closely approxi- 

 mate to the latter. 



In the determination of the adiabatic changes of condition for 

 moist air the determination of the point of saturation or the transition 

 from the adiabats of the dry stage, to those for the condensation stage, 

 is important. 



The point of saturation depends upon the mixing ratio (x) : this 

 is determined in grams for saturated air from the equation 



FIG. 2. CONDENSATION STAGE 



x m - 622 



In this equation e m is a function of the temperature and therefore 

 the quantity of moisture for saturation x m is a function of the 

 pressure and temperature. 



If x is constant we obtain from the preceding equation the curve 



