Measurement
of
adiabatic
saturated temperature (tas)
Because the contact is between
Air
large
amount of water and small
Make up
water
I
amount of air, the water
temperature is almost unchanged.
•Because adiabatic with ambience,
Air
heat loss Ql=0. Vaporization of
I
Make up
water
water
will lead to the decrease of
temperature of air.
2
1
Airt
Airt
Make up water
Make up water
Circulation Pump
as
as
1
I1  C H t  Hr0  (1.01 1.88
II1 
C
Hr
 (1.01 1.88H
))tt  Hr

H tt 
0  (1.01 1I.88
0

C

Hr
H
Hr

 C H t  Hr
 (1.01 1.88H )
1
H
0
0
1 I
0  H

C
t
 r0  (1.0
2 1.88HH
, as )ast  Has r
II 2 
C
t

H

r

(
1
.
01
 1.88H
 asHr
..01

88
Has
))tt
 (Hr
as tC
as Ht H
as
as r
tC11..88
Hr
.0r01
0

tH
H
(1.01 1
 CIH1 ,
 r00I ((11IC
01
1H


1
2 H



1.01
IC
(t1,C.H
tasHr
(1.01
 1H.
88
H
)Hr
t r

Hr

(
1
1
.
88
)
t

1H
H
I 2as
C H1, as t as  IH as
I1rC
01
1
.
88
H
)
t
H

H
,
H
0
H
as
as
as
H
,
H

1
0
0
0
0
 H , H as  1
2
H , as tasas  H as  r0   (1.01
,as(C

H
H
r
(1.
.01
01
11H..88
, Has1.Air

I 2Hr
I1C
t.
t.asH
88
r,H
88
.01
01
11.88

1
01

1
.
H
.

2C
H
, as
as )
 CH 
 1H.01
88
H1t.01

.
88
H
C
C
1
.
01

1
.
1

8
I1H1
C


1
01
1
.
88
t
Hr
0(1
H
as
as
a
H
H
0
as
H
as
0
0
 C H  1.01 1.Make
88H

1
.
01

1
.
88
H

C
H
,
H

1
as
H , as
as
up
water
 C H  1.01

1
.
88
H

1
.
01

1
.
88
H

C

H
,
H

1
as
H , as

H
,
H

1
as
近似等焓：
I

I
I

C
t


r

(
1
.
01

1
.
88
as
I
近似等焓：I 2  I21 HC
2 I
1 I H as )t as  H a
, as as 近似等焓：
as

0
1 1.01 1
 1.01 1.882 H 
近似等焓：
I

I
H
2
1
近似等焓：I 2  Nearly
I
C
Hr
1.01
 1C
Has.01
1H
.01

.88
H
constant
enthalpy
: r1H
t 1H


CC1
.01
1.88
H.88
1.as88

1
H
Ht1
H
as
H
,
H
0
0
 C H t  Hr0  C
t

H
r

as
H as
as 0 C t  Hr   C t
 CH
t CHr
C
t

H
r
H as  H as r0
近似等焓：
I

I
 Hr
 HH r
t

C
t

0
H
as
as
2
1
0
0
H
H 近似等焓：
as 近似等焓：
as 0 Ir II2  I1
0 C


1
.
01

1
.
88

1 1.88H as  C H , as
H
r0 Air
 t as  tH  120 .01
(H
as  H )  (5 

C
t

Hr

C
t

H
r
r
r0 ( H ras0 I H ) 
)Hr

t C
C

C
t


t

H
r
 t as 
t

(
5

14
H
H
as
as

C
t

Hr

C

H
r
0
0
H
H
H
as
as
0
0
0
H
H
as
as
H)as

H
)

(5  14()H 
近似等焓：
I 2(t5
0t)
0 H ) 
 t as 
 ttas CHt (H
(H
I1
14
Make
up
water

as
as
as
H
CH t C
rr0 Hr0CrH
 C
t

Hr

C
t
Air
H t
(0HasasH
) 
H
)
5 ) 1(5
(asH
H
)(

0
t astt
tHast0 ( H
5(14
as
as
as 
C
C HH C H
Air t
Make up water r
2
H , as as
as
0
H , as as0as
as as




0as
0






2




Circulation Pump
as
Make up water t as  t 
as

0
CH
2



1





( H as  H )  (5  14)

as
 C H  1.01 1.88H  1.01 1.88H as  C H ,as
N  kG ( pw  p) S  k H ( H s ,tw  H ) S
•Comparing
with Eq.(5-12)
近似等焓：
I 2  I1
k H rtw
HHs ,ttwas HH)as
(5  12)
t wCH tt  Hr  (C
r

0
0
r0
k
—
以湿度差
H
)为推动力的传质系
tw 
 tHas  t 
( H (asHs ,H
)
(5  14)
CH
tas  t wtas;  t w ;
1)For air-water system,
Other
systems,tast  t
w;t
as
t as  t w
tas  t w
 CH  
w
 1.09, rtW  r
Why？
kH

  1.09

C
,1rt.09

C

 ,r0rtW
H
H
For air-water system,
kH k
H
W
Question: Are tw and tas affected by the initial
temperature of water？
3

 r0
2)tw and tas are two different concepts, but they are
all functions of air state（t, H）.
•tw is the result of heat transfer and mass transfer
between liquid phase and gas phase under steady
state. It is a dynamic state.
•tas is the temperature of gas which is humidified,
cooled and saturated under adiabatic condition. It is a
state of thermodynamic property. tas是大量水与空气接
触，最终达到两相平衡时的温度，过程中气体的温度和湿度
都是变化的；tas由热平衡得出的，是空气的热力学性质
4
(8)Dew point td
•Dew point is the temperature to which a vapor-gas
mixture must be cooled (at constant humidity H) to
become saturated.
Let

H
,
p

p
H

H
,
p
LetLet
HH

H
,
p

p
s
,
t
s
,
t
d
d
s , t d s ,t d
s ,t d  p
s ,t d
令：
H=saturation
H , pstemperature
s
,t d 
,t d  p
at dew point
H
露点时的饱和湿度


露点时的饱和湿度
H ss,H
,t t ds ,t 露点时的饱和湿度
d
d
H sp,t d ——
露点时的饱和湿度
露点时的水饱和蒸汽压
=saturated
vapor pressure at dew point
—
露点时的水饱和蒸汽压
pss,,tdtpd—
s ,t d露点时的水饱和蒸汽压
p s ,t d —
露点时的水饱和蒸汽压
We have,
ps ,td ps ,tpd s ,td
得：

0
.
622


(
5

16
)
得：
H

0
.
622

(
5

16)
得：
HH

0
.
622


(
5

16
)
s
,
t
d
s ,t d
s ,t d
p
,tP
Ps 
d p
s ,
P

p
tp
d s ,(
t d5  16)
s
,
t
得：H s ,t d  0.622 d
P  p s ,t d
H
P
H s ,td P sH
,t d s ,t P
d
ppss,,ttpd s 


(
5

17
)


(
5

17
)


(
5

17
)
,t d H
P
d
s .,H
t622
0.622
d  H
5
0
.
622

0
,
t d s ,
t d (5  17)
s ,t d  sH
p s ,t d 
d
—
露点时的水饱和蒸汽压
时的水饱和蒸汽压
psp,tpds ,t—
露点时的水饱和蒸汽压
d
—
露点时的水饱和蒸汽压
s ,t d
p s ,t d
psp,tdps ,td
(8)Dew
point
td
s ,t d
得：
H

0
.
622


5(16
 16
))
.622 得：


(
5

16
)
H

0
.
622

(
5(
)16
s
,
t
s
,
t
d d
得：
H

0
.
622

5

P  p s ,t d s ,t d
P PPpsp,tdp
s ,t d
s ,t d
P
HH
t d PP
sH
,t ds ,P
d
5 17
 17

p
 (5  17) s ,td 

(5(
))
sp
,tp
ds ,t d


(
5

17
)
.622
 H s ,td s ,td 0.0622
 HH
t ds ,t d
0.622s ,H
s ,t d
(from tables of properties
of saturated steam and water)
查饱和水蒸汽表

t
由由
psp,tds
查饱和水蒸汽表

t
水蒸汽表
t
d d
d
由p,std,td 查饱和水蒸汽表

td
反之，由
HH
HH

psp,tds ,t
 ps ,t反之，由
 H s ,td td tH
d 
s ,t ds ,t
d
d
d
Reversed, t d  ps ,t  H s ,t  H
反之，由
d
d
(测量湿度的另一方法
(测量湿度的另一方法
))
另一方法
)
Dew-point
methods of measurement
of humidity.
(测量湿度的另一方法)
小结：
小结：
小结：
t d  1:1t:t tWtW(t as(t)as ) t d t d
as )  
  1 : t  tW (t as )  t d
6
 t as ) 
 td 1:1t:t tWtW((t ast)as ) t d t d
  1 : t  t ( t )  t
(8)Dew point td
Unsaturated air： t＞t =t ＞t ；
w as
d
Saturated air： t= tas = tw = td。
7
2.Humidity Chart of Air-Water System (H-I) Diagram
[Figure 5-3][p.252]
(1)Characteristics of H-I diagram
I (Ordinate)纵坐标
P=101.3kPa
135°
H(Auxiliary axis)
Projected value
H(Abscissa)横坐标
8
(2)The groups of lines in H-I diagram
The H-I diagram consists of five groups of lines
1)Constant humidity lines (Constant H lines)
H1
H2
H3
I
H1
H2
H3
H
Auxiliary axis
H
9
2)Constant enthalpy lines (Constant I lines)
[Adiabatic cooling/ saturation lines
H1
H2
H3
I
I1
I4
I3
I2
H1
H2
H3
H
Auxiliary axis
H
10
I
I1
I2 I
HI
1
I2
H 1I temperature lines (Constant t
3)Constant
dry-bulb
I2
IH1
H 2H
lines)
I1
H
II2 1
t1 H
I  1.01t  (1.88t  2490) H
I 12
I 12
H
t2 H
H2
I 21 I I
tH
1
t
Slope , every constant
t3 t
I
1H
H
tH
t line is not parallel with
I1
1
2 2 I I1
I1
t 2H
each other.
I
t1H
I
I
I
2
3 1I 1 2
2
I2
t 3t
I1
H
H
tH
1
2 2 II12
B
H
A
t2
I2
tt31 IHH 1 H 1
H1 2
t3
H
t2 H
HH
1 2 H2
H2
H1
t3 H
Ht112 t1
t1
H2
t1 t22 t 2
H
t2
t1 11
t12t 3 t 3
t
t
t2
H1
t1
H2
H
A
4)Constant relative humidity lines (Constant
 I
H
3
H1
BI
line )
t3

H
II
tt3
H2
Constant
lines
Ct3
t2
A
ps
H3
t 2线
H  0.622
t3 等
I
t1

p
3

p
s
s
B
0.622 P  ps
H H0.622
tt 2 t H t
t1
H1
3
2
2
P P
psps
C
tt1 t A t
P
一定，


f
(
H
,
p
)
H1
s
H2
For
certain
P,
2
1
1
P
一定，


f
(
H
,
p
)
P一定，  f ( H , ps ) s
等线
B
H
H2
1 t
而
p

f
(
t
),



f
(
H
,
t
)
H
H
H3
s
1
1
1
而
p

f
(
t
),



f
(
H
,
t
)
 ps  sf (t ),  f ( H , t )
C
H
2
H 2 H1 H 2 H 3
H
Fixing a  value, an H~t line is determined.
等线 H
H
3
H
H3 2 H3
A
H
A
H H3 H
B
A
B
A H A
C
There are 11 lines of constantBin figure 5-3. From the
C
B A B
等线
figure, we know that, if H is unchanged, t
 i.e.,
C
C B C . 等线
air capacity of absorbing vapor/moisture
等线
12等  线
C 等线
I
Function of preheater:
1)t I , this is favorable to heat transfer;
2)t  , this is favorable to mass transfer.
I
Undersaturated zone(drying
zone)（干燥区）
 =100%
(Saturation line)
Supersaturated zone（过饱和区）
H
13
p1
p1
H1
5)Partial pressure line of water vapor
H1
PH
p
0.622  H
H
H
 1
  1 p  f (H )
p  f (H )
p1
p1
H1
p1
H1
H
H1
H
 1
H
 1
p  f (H
 1
p  f (H
p  f (H )
I
•Because total pressure P
is constant, and
H<<0.622, relation
between p and H is
almost linear. [Figure5-3]
14
(3)Applications of H-I diagram
1)Independent parameters: Only two Independent
parameters can determine the air state in the H-I
diagram.
•
Non-independent parameters:
td ~ H ; p ~ H ; td ~ p; t w ~ I ; tas ~ I .
各在同一等
I线或等
线上。
Above
couples are
on theHsame
constant I line or constant
H line respectively.
15
I
I
t
t
I
I
tW
t state by two independent
t
tW
2)Determining
the air
H conditions:
tW
H
parameters
from thetWcommon known
 1
I
II A
tt
t
tWW
ttW
H
H
H
 11
 1
A
AA
(a)Given t, tw
H
 1
A
II
tt
I
H
A
 1
A
tttWW
t
 1
Constant H line
d
H
H
 11
tW
H
 1
H
H
 1
(b)Given t, td
16
t
tW
AA
A
I
A
tW
I
H
t
(3)Applications
 of
 1H-I diagram
tW
A Constant  line
II
H
tt
  1I
ttWW
A t
H
H
tW

 11
H
A
A
 1
A
(c)Given t, 
17
t
I
t
tW
p1
tW p1
p1 the
3) Determining
the
air
state
parameters
from
H p1
H1
H H1
H1
given air H
state:
p1
  11 H
  1H
H
 1
 1
AH
A
  1 H1
I
p  f (H ) H
  1 p  f (H ) t
p  f (H )
 1
p  f ( H ) p1 (tas )tttwW
p1
H
H
Hp  f (
I
I
d
1
H
Question:
1
 1
A
H
 1
 tf (H65
) C ,   20%.
Givenp：
t w , tas , td , I , H , p  ?
18
H
 1
p  f (H
Question:
Determining:
Given：t  65C,   20%.
tw , tas , td , I , H , p  ?
t as  t w  37C; td  33C;
I  158[kJ / kg Dry air]
H  0.034[kg Water vapor/ kg Dry air]
p  5.2[kPa]
19
•Supplementary: Influence of total pressure P on
H-I diagram：
ps
H  0.622
P  ps
1
•WhenP1P changed,
p line,  lines will change

too. P2  2
ps
H

0
.
622
When H and t unchanged, (ps is also
from the
P unchanged),
 ps
above equation,
P1 1

P2  2
20
Assignment: Problem
5-2.
Problem 5-2. Fill in the blanks from given conditions by
using the H-I diagram of air-water system, and plot the
illustrative diagram of the solution of question No.4.
Attached Table of Problem 5-2
Dry-bulb
temperatur
No.
e
˚C
1
(60)
2
(40)
3
(20)
4
(30)
Wet-bulb
temp.
˚C
Humidity Relative Enthalpy
kg/kg dry humidity kJ/kg dry
air
air
%
Partial
pressure of
water
vapor
kPa
Dewpoint
˚C
(35)
(25)
(75)
(4)
21
•Exercises：
1.Under total pressure 101.325kPa, temperature of
undersaturated moist air is 40℃, and relative
humidity 60%,
(1)What are the changes of the following air
parameters if air is heated to 80 ℃?
Humidity H________，relative humidity 
________，wet-bulb temperature tw________，
dew-point td_________，enthalpy I_________.
(unchanged, decrease, increase, unchanged, increase)
22
[1.Under total pressure 101.325kPa, temperature of
undersaturated moist air is 40℃, and relative
humidity 60%,]
(2)If the total pressure of air is decreased to
50.6625kPa without changing temperature, what
changes will happen of the followingparameters？
ps
H  0.622humidity
Humidity H________，relative
P  ps
________，
(increases, decreases, P1 ) 1
P2

2
23
2.Under constant total pressure and dry-bulb
temperature of some moist air, if the dew-point td
increases, what changes of the following parameters
will happen？
pwater vapor_______, H________, _______,
tw________, I______ . (increases, increases,
increases, increases, increases)
3.Under constant total pressure and dry-bulb
temperature of some moist air, if the wet-bulb
temperature tw increases, what changes of the
following parameters will happen？
pwater vapor _______,H________,  _______, td________,
I______ . (increases, increases, increases, increases,
increases)
24
4.The order of magnitude among dry-bulb
temperature t, wet-bulb temperature tw, dew-point
td of undersaturated moist air is
_____________________.
25
26
27