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How to read the Humidity chart & do the operating diagram for Cooling tower of Air-Water at 1 atm. Assume you have air of a definite air- water mixture at dry bulb temp T 1 and wet bulb temp T w1

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T1T1 T w1 (a) 1. Find point (a) which represents this air on the chart

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T1T1 T w1 (a) 2.The moisture content of this air Y 1 is given by point (b) kg of water vapor/kg dry air (b) Y1Y1

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T1T1 T w1 (a) 3.The Dew point of this air is given by point (d) to which this air should cool down at constant Humidity (b) Y1Y1 (d) (e ) (c)

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T1T1 T w1 The Adiabatic Saturated Temp T s and and Saturated humidity Y s of this air is given by points (f&g). To find these points : start from point (a) follow the adiabatic cooling line to 100% line on point (e), then read T s at point (g) and Y s at point (f) Note: for air water system the wet bulb T w1 apparently resembles the adiabatic saturation temp. T s (b) Y1Y1 (d) (c) (e ) (f) TsTs YsYs (g) (a) C s (T-T s ) +Y s = Y s s

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T1T1 (k) (a) To find Enthalpies h 1 of air of point (a) coordinate, follow the enthalpy line through point (a) to its intersection (k) with enthalpy scale line. h1h1

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Equilibrium curve: is a plot of h * vs. T L find Enthalpy h * of a saturated vapor - air mixture in equilibrium with the liquid bulk, j/kg dray air at liquid temp, follow the temp line to its intersection with 100% line and the read h* on enthalpy scale line which given by point m. T1T1 (k) (a) h1h1 T L1 (m) h*h*

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Operating diagram Air-Water at 1 atm This fig. contains the saturated enthalpy carve, and on this plot is point (A) representing the conditions at the bottom of the tower (T L1 & h 1 ). Point (B) represents the conditions at the top of the tower (T L2 & h 2 ). m. G & m. L are the mass follow rates of gas and liquid (H 1 &H 2 are water enthalpies) Equilibrium Curve h * (Sat’d air) vs T L A B Enthalpy of air – water vapor J/kg dry air Water Temperature h1h1 T L2 h2h2 T L1 Slope =(m. L /m. G )C L H1H1 H2H2

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