THIẾT BỊ NGƯNG TỤ - DÀN NGƯNG GIẢI NHIỆT BẰNG KHÔNG KHÍ potx

-

 Page 1


A. :
 
Q
k
=50kW.
 
B.  
                
    
   

 
               
 
   

C. 
1.            - 
 - 
2.  --

3. -
-
4.         - 
 
D. :


th  
1. 
 
 
-

 Page 2

  
k
2. 
  
 
 
E. :

1.  
2. 
3.              
:
4. 

I. 
1. 
a. 
Môi cht là cht môi gii s dng trong chu trình nhic chi
hp thu nhit cng cn làm lnh và ti nhing có nhit
 t cht tun hoàn trong h thng lnh).
Môi cht làm nhim v mang nhit t  th th

nhi  n không th thiu ca máy l
HCFC (hydro-clo-flo-cacbon) là các cht ít nguy hiNgoài thành phn
Clo, Flo chúng có cha 1 hoc nhiu nguyên t Chính thành ph
làm cho chúng b phân hy nhanh và kh y tng ozon gim.Tuy
nhiên các cht này vn gây hiu ng nhà kính cao.Tùy theo tính cht c th ca
tng môi cht, chúng có th c la chn là môi ch -
2i din tiêu biu là R22 và R123
b. 
Là cht khí trong sut không màu st nhc và d
cháy
-

 Page 3

Công thc hóa hc: CHClF
2

c. 
• Nhi sôi  áp sut khí quyn là: -40,8
0
C
• Nhi c: -160
0
C
• Nhi ti hn: 96,2
0
C
• Áp sut ti hn: 4,99MPa
- (0
0

C) =1,285kg/dm
3

- (40
0
C) =1,13kg/dm
3

• Phân hy  nhi 550
0
C
• ODP= 0,05; GWP= 0.35
d. 
– Bn vng trong khong nhi và áp sut công tác
– i, và phi kim ch t
ng cao su, cht do
– c
– Hòa tan hn ch d -40 ÷ -20
0
C)
– R22 có tính ty ra h thng
e. 
o
C




-

 Page 4



Lng

Áp sut
Mpa
0,50
0,50
Th tích riêng
dm
3
/kg
0,78
47,11
Nhit dung
riêng
- ng áp
- ng tích


kJ/(kg.K)
kJ/(kg.K)


1,17
0,67

0,74
0,57
 nht
10
-6
Pa.s
218,22
11,50
H s dn
nhit

W/(m.K)
0,095
0,009
S  
mt
N/m
0,012
Nhi
kJ/kg
205,1

f. 
R22 không dn  th n
n  th lng, tuy lng lt v máy nén.
g. 
c s dng trong h thng l lp cho các
kho bo qun nguyên liu, máy sn xut, h thng máy
lnh ghép nc bit R22 s dng u hòa không khí.
2. 

c chia ra làm 02 lo 
ng bc.

-

 Page 5

a) 
Lo nhiên ch s dng trong các h thng rt nh, ví d
 l t lp. Các dàn này có cu t
dng.
 Dng ng xon có cánh là các si dây thép hàn vuông góc vi các ng xon.
Môi cht chuyng trong ng xoi nhit vi không khí bên
ngoài. Loi này hiu qu không cao và hay s dng trong các t lnh gia

 Dng tm: Gm tm kim loi s dng làm cánh tn nhi
ng xon bng .
 Dng panel: Nó gm 02 tm nhôm dày khoc to rãnh cho
môi cht chuyng tun hoàn. Khi ch ti ta cán nóng hai tm
li vi nhau,  khong ti ta bôi môi chc bi 02 tm
c hoc không khí áp lc cao (khong
c bit, hai tm s phng lên thành rãnh.
H s truyn nhit ca thit b       nhiên khong 6÷7
W/m
2
.K.
b) 
 ng bc s dng rt rng rãi trong
i sng và công nghip.Cu to gm mt dàn i nhit bng ng
thép hoc ng có cánh nhôm hoc cánh sc cánh nm

trong kho    c qut thi, chuy ng ngang bên
ngoài qua dàn ng vi t  khá ln.Qu   ng là qut kiu
ng trc. Mt  dòng nhit ct khong 180 ÷ 340
W/m
2
, h s truyn nhit k = 30 ÷ 35 W/m
2
.K, hiu nhi 
0
C
Trong quá trình s dng cng bi bám bi bn, gim
hiu qu i nhing xuyên v sinh bng chi hoc. Khi
khí không ngt vào bên trong dàn s . Cn che
chn nt v trí chu nhiu bc x mt tri nh
n hiu qu i nhit.
-

 Page 6

3. 

 


-

 Page 7

4. 
a) 

 Không s dc nên chi phí vn hành giu này rt phù hp 
nhc thành ph 
 Không s dng h thi nhit, va tn kém li gây t
khu v           n xung
quanh và có th lt  nhiu v t
trên nóc nhà vv . . .
 H thng s dt b 
s dng.
 So vi các thit b  gii nhit bc, dàn 
hng và ít b 
b) 
 M dòng nhit thp, nên kt cu khá cng knh và ch thích hp cho h
thng công sut nh và trung bình.
 Hiu qu gii nhit ph thuc nhiu kin khí hu. Nhng ngày
nhi cao áp su lên rt cao Ví d, h thng s dng R22, 
min Trung, nhng ngày hè nhi không khí ngoài tri có th t 40
o
C,
ng nhi  có th t 48
0
C, áp su ng
là 18,5 bar, bng giá tr t ct cao. Nu trong nhng ngày này
không có nhng bic bit thì h thng không th hoc
i vi nhi nhiên hiu
qu còn thp na.
II. 
  

1.  
N

=25
0
C
2. 
K
=42
0
C
3.   
4.  
1
=0,021m
5.   
0
=0,028m
6.  
c
=0,049m
7.  
c
=0,0035m
-

 Page 8

8.  
0
=1,1mm
9.  
d

=0,6mm
    
10.  
1
=0,052m
11.  
2
=0,045m
III. 

    
 
1. 
 
 

2. 
 
     
môi
   
 
k


1. 
 
               
t=610
0

  t=8
0

t
2

t =25+8=33
0
C
 
2
=0,5.(25+33)=29
0
C

2
=29
0


2
=2,67.10
-2
W/m.K ; 
2
=16.10
-6
m
2


2
=1,165 kg/m
3
; Pr
2
=0,701
-

 Page 9


2
=9m/s
33,0
2
375,0
0
625,0
2
0
2
3
6
2
02
2
Pr Re
10.94,15
10.16
028,0.9

.
Re












F
F
d
C
v
d




  C=0,45
  
F
0

0

.L=3,14.0,028.1=0,088 m
2

  
  
mm
S
Sd
F
c
cc
oc
/06,0
10.5,3
10).1,15,3.(028,0.14,3
)(.
2
3
3
0









F = F

c
+ F
oc
=0,752 + 0,06=0,812 m
2
/m
KmW ./2,69)701,0.(
088,0
812,0
.)10.94,15.(
10.28
10.67,2
.45,0
233,0
375,0
625,03
3
2
2














  

mm
D
S
dD
S
F
dc
c
c
c
c
/752,0
10.6,0.049,0.14,3.
0035,0
1
)028,0049,0.(
4
14,3.2
.
0035,0
1

1
).(
4
.2

.
1
2
322
2
0
2







-

 Page 10

2
'
2
.




KmW ./8,582,69.85,0
2'
2




2. 
   
    
 
   
KmW
dtt
B
iWK
a
./,
).(
.555,0
2
25,0











KmW
dq

B
i
a
./,
.
.455,0
2
3
1
















rgrgrg
B

3323


    
  
m
=0,5.(t
k
+t
w

k
.
d
i
-  
t
k
-
-

 Page 11

t
w
-
   
a
10002500
W/m
2


2
5080 W/m
2

 /
a>>

2
 

t= t
k
-t
w
=2
o
C
t
w
=t
k
-t=42-3=40
o
C
 
t
m
=0,5.( t
k
+t

w
) =0,5.(42+40)=41
o
C
 
m
=41
o
 

a
=0,0786 W/m.K ; 
a
=0,196.10
-6
m
2

a
=1127 kg/m
3
;

a
=2,19.10
-4
Pa.s
t
k
= 42

0
C => r
a
=163,92 kJ/kg
12
4
322
2
3
10.878,2
10.19,2
10.91,163.81,9.1127.0786,0



f
aff
rg
B




12
12
10.137
021,0
10.878,2

i

d
B

 
3
25,0
12
25,0
10.42,310.137 








i
d
B

0,555.
25,0









i
d
B
=1899
 
a
=1899. t
a
-0,25

3. 
-

 Page 12


F
1

1
.l=3,14.0,021.1=0,066 m
2
/m
 
F
2
=0,812 m
2
/m


3,12
2
2

F
F



Q
1
=Q
a
=
a.
t
a
. F
1

2
F



2
F
Q
q

a
ang
1899. t
a
-0,25
. t
a
.
2
2
F
F
=154,39. t
a
0,75

   
 

kk


Q
a
=Q
kk
=Q

    
   

w

 
qua:
 
i

Q=k
2
.F
2
.(t
k
-t
2
) W
q
2
=Q/F
2
=k
2
.(t
k
-t
2
)
-

 Page 13


2

1
2
'
'
2
2
.
11
1
F
F
k
ai
i
i
i




























i
i


-  

'
'
i
i


-  


 
   
c
=0,0005 m
2


  
b
=0,0003 m
2
.K/W
  
        R
d
   
th
  
nhôm 
Al
=203,5W/m.K.
  t
a
2
o
C

a
=1899. t

a
-0,25
=1597 W/m
2
.K
 k
2
=33,3 W/m
2
.K
  

q
2
=k
2
(t
k
-t
2
)=33,3.(42-29)=433,3 W/m
2


2
:
q
ang
= 154,39. t
a

0,75
=259,7 W/m
2

-

 Page 14

Do q
2

ang
 t
a


 t
a
=3,5
o
 
   



a
=1899. t
a
-0,25
=1396 W/m

2
.K
 k
2
=31,5 W/m
2
.K
 
  

 q
2
=k
2
(t
k
-t
2
)=31,5.(42-29)=409 W/m
2


2
:
 q
ang
= 154,39. t
a
0,75
=395 W/m

2


2
 q
ang

tb
=402 W/m
2

:
F
2

=Q
k
/q
tb
=50000/402=124,38

L= F
2

/ F
2
=124,38/0,812=153,18 m
      
1
        



n=L/L
1

 
-

 Page 15

Diên t  
 
f=s
1
-d
o
+(D
c
- d
o
).
c
.1/s
c
.1
=0,052-0,028+(0,049- 0,028 ).0,0085.1/0,0035
=0,0189 m
2

 

td
:
F
td
=n
1
.L
1
.f=.
 
2
:
sKg
ttc
Q
G
p
kk
/25,6
)2533.(1
50
).(
'
1
"
2
2
2








2
=29
o

2
=1,165 kg/m
3
 
V
2
=G
2

2
= 5,36 m
3
/s

1,2
36,5
2
2max2

Ftd
V



 

IV. 
 
Q
kk
=G
2
.c
p2.
(t
2

- t
2

)
 t
2

- t
2

= Q
kk
/ G
2
.c

p2
=50/6,25.1=8
t
2

= t
2

+8=25+8=33
0
C
-

 Page 16

    
 
V
2
=5,36m
3
/s=19,30.10
3
m
3
/h