Mon 2:04:28 PM. Introduction

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Amanda Logan
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1 Mon 2:04:28 PM Slide Nr. 0 of 18 Slide Introduction Air in the tmohere normlly contin ome wter vor (or moiture) nd i referred to tmoheric ir. By contrt, ir tht contin no wter vor i clled dry ir. It i often convenient to tret ir mixture of wter vor nd dry ir ince the comoition of dry ir remin reltively contnt. The mount of wter vor chnge reult of condention nd evortion from ocen, lke, river, hower, nd even the humn body.

2 Mon 2:04:28 PM Slide Nr. 1 of 18 Slide Sturtion Temerture nd Sturtion Preure At given reure, the temerture t which ure ubtnce chnge he i clled the turtion temerture T t. t At given temerture, the reure t which ure ubtnce chnge he i clled the turtion reure P t.

3 Slide Nr. 2 of 18 Slide Pychrometric Mixture Pychrometric or Pychrometry re term ued to decribe the field of engineering concerned with the determintion of hyicl nd thermodynmic roertie of g-vor mixture. Conider tmoheric ir t br nd 15 C. The turtion reure of wter vor correonding to 15 C i br. Unle the wter vor i in contct with it liquid it will not be turted, nd it reure will be below the turtion vlue of br. In norml liction the tmohere i well removed from the turted condition. At uch low vor reure the vor cn be conidered to ct erfect g, nd the roertie of the mixture cn be found uing the Gibb-Dlton lw.

4 Slide Nr. 3 of 18 Slide Pychrometric Mixture Aume tht in quntity of tmoheric ir the vour reure i 0.01 br t 15 C nd the totl reure i br = + = = br The turtion temerture correonding to 0.01 br i 7 C, hence the vor in tmoheric ir under thee condition h degree of uerhet of ( 15-7) = 8 K. (oint 1) 288 K 280 K

5 Slide Nr. 4 of 18 Slide Pychrometric Mixture The dew-oint temerture T d i defined the temerture t which condention begin when the ir i cooled t contnt reure. In other word, T d i the turtion temerture of wter correonding to the vor reure. Cooling

6 Slide Nr. 5 of 18 Slide Secific humidity, reltive humidity, nd ercentge turtion The ecific humidity (or moiture content or humidity rtio) i the rtio of the m of wter vour to the m of dry ir in given volume of the mixture ω = m m ω = V nd m R ~ m~ m = = T V R ~ m~ T R ~ T V m ~ = m ~ m ~ = V R ~ m~ T = 0.622

7 Slide Nr. 6 of 18 Slide Secific humidity, reltive humidity, nd ercentge turtion ω = m m ω = = (the totl reure i uully the brometric reure).

8 Slide Nr. 7 of 18 Slide Secific humidity, reltive humidity, nd ercentge turtion The reltive humidity of the tmohere i the rtio of the ctul m of the wter vour in given volume to tht which it would hve if it were turted t the me temerture (mximum mount of moiture the ir cn hold t the me temerture) φ = m ( m ) t V m = nd ( m ) = t R T g R V T where g i the turtion reure t the temerture of the mixture.

9 Slide Nr. 8 of 18 Slide Secific humidity, reltive humidity, nd ercentge turtion V m = nd ( m ) = t R T g R V T φ = g

10 Slide Nr. 9 of 18 Slide Secific humidity, reltive humidity, nd ercentge turtion The term ercentge turtion i lo ued, defined the rtio of the ecific humidity of mixture to the ecific humidity of the mixture when turted t the me temerture, exreed ercentge ψ = ω ω g ψ = 100 φ g where g i the turtion reure t the temerture of the mixture.

11 Thu 8:40:02 AM Slide Nr. 10 of 18 Slide Exmle Exmle

12 Thu 8:40:02 AM Slide Nr. 11 of 18 Slide Exmle Exmle

13 Thu 8:40:02 AM Slide Nr. 12 of 18 Slide Exmle Exmle

14 Slide Nr. 13 of 18 Slide Wet Bulb Temerture The temerture meured by thermometer whoe bulb i covered with cotton wick turted with wter nd ir i moved over the wick

15 Slide Nr. 14 of 18 Slide Meurement of reltive humidity An intrument ued to meure reltive humidity i clled ychrometer, or hygrometer ling ychrometer Some of the wter evorte nd thi roduce cooling effect t the bulb. the wet bulb indicte lower temerture thn the dry bulb. If the reltive humidity i low, then the rte of evortion t the wick i high, nd hence the wet bulb dereion i high.

16 Slide Nr. 15 of 18 Slide THE PSYCHROMETRIC CHART The tte of the tmoheric ir t ecified reure i comletely ecified by two indeendent intenive roertie.

17 Slide Nr. 16 of 18 Slide

18 Slide Nr. 17 of 18 Slide m 3 /kg 73.5 kj/kg 24.2 C 19.8 C kg H2o/kg dry ir

19 Thu 8:46:56 AM Slide Nr. 18 of 18 Slide

UNIT 6 PROPERTIES OF MOIST AIR

UNIT 6 PROPERTIES OF MOIST AIR Proertie of Moit Air Structure 6.1 Introduction Objectie 6.2 Working Subtnce in Air Conditioning 6.2.1 Gibb-Dlton Lw 6.2.2 Mole Frction of Comonent Ge 6.2.3 Moleculr Weight