Water is evaporating from the placid surface of a lake and the vapour(A) diffuses through a stagnant film of air(B) of estimated thickness 3 mm. The water temperature is 23°C and the air temperature is 27°C. The relative humidity of air is 65%. If the diffusivity of water vapour through air is 0.257 cm²/s at 23°C and 0.262 cm²/s at 27°C, calculate the rate of evaporation. The vapour pressure of water can be calculated using the Antoine equation, Pv (in bar), of water is given by: In Pv = 13.8573 - 5160.2/T where T is the temperature in K. V-humid volume, m³/kg dry air 1.4 280 260 1.3 240 220 200 180 €. 1.1 160 1.2 2140 1.0 120 100 80 60 40 20 0 0.9 0.8 0.7 0 Specific volume dry air 10 20 Saturated humid volume Enthalpy of saturated air 30 40 50 60 70 Temperature, °C 80 90 Adiabatic saturation curve 100 Enthalpy of dry air 110 120 10.15 78000 -6000 0.14 0.13- 5000 4000 0.12 3000 0.11 2000 0.10 0.09 0.08 0.07 Y'-absolute humidity, kg water vapour/kg dry air 130 1000 4800 500 400 -300 H'= enthalpy, kJ/kg dry air 0.05 200 0.04 0.03 0.02 0.01
Water is evaporating from the placid surface of a lake and the vapour(A) diffuses through a stagnant film of air(B) of estimated thickness 3 mm. The water temperature is 23°C and the air temperature is 27°C. The relative humidity of air is 65%. If the diffusivity of water vapour through air is 0.257 cm²/s at 23°C and 0.262 cm²/s at 27°C, calculate the rate of evaporation. The vapour pressure of water can be calculated using the Antoine equation, Pv (in bar), of water is given by: In Pv = 13.8573 - 5160.2/T where T is the temperature in K. V-humid volume, m³/kg dry air 1.4 280 260 1.3 240 220 200 180 €. 1.1 160 1.2 2140 1.0 120 100 80 60 40 20 0 0.9 0.8 0.7 0 Specific volume dry air 10 20 Saturated humid volume Enthalpy of saturated air 30 40 50 60 70 Temperature, °C 80 90 Adiabatic saturation curve 100 Enthalpy of dry air 110 120 10.15 78000 -6000 0.14 0.13- 5000 4000 0.12 3000 0.11 2000 0.10 0.09 0.08 0.07 Y'-absolute humidity, kg water vapour/kg dry air 130 1000 4800 500 400 -300 H'= enthalpy, kJ/kg dry air 0.05 200 0.04 0.03 0.02 0.01
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Transcribed Image Text:Water is evaporating from the placid surface of a lake and the vapour(A) diffuses
through a stagnant film of air(B) of estimated thickness 3 mm. The water temperature
is 23°C and the air temperature is 27°C. The relative humidity of air is 65%. If the
diffusivity of water vapour through air is 0.257 cm²/s at 23°C and 0.262 cm²/s at
27°C, calculate the rate of evaporation. The vapour pressure of water can be calculated
using the Antoine equation, Pv (in bar), of water is given by:
In PV = 13.8573 - 5160.2/T
where T is the temperature in K.
VH-humid volume, m³/kg dry air
1.4
280
260
1.3 240
220
1.2 200
180
1.1160
140
1.0 120
100
80
60
40
20
0
0.9
0.8
0.7
0
10
Specific volume
dry air
20
Saturated humid
volume
Enthalpy of saturated air
30
40
50
60
70
Temperature, °C
80
saturated air
90
Adiabatic saturation curve
100
Enthalpy of dry air
110
120
0.15
0.14
0.13-4000
'-absolute humidity, kg water vapour/kg dry air
0.07
78000
-6000
5000
0.12 3000
0.11
0.10
0.09
0.08
130
2000
1000
800
400
-300
H' enthalpy, kJ/kg dry air
0.05
200
0.04
0.03
0.02
0.01
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