18000Nm3h热管式余热回收系统的设计
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18000Nm 3/h 热管式余热回收系统设计
一、设计条件
空气进口温度 20℃ 烟气进口温度 280℃ 空气出口温度 200℃ 烟气出口温度
150℃ 空气流量 18000Nm 3/h
二、设计流程
(1)热管原件的基本选择
管壳选择:20号无缝钢管,钝化处理 翅片选择:10号钢,高频焊翅片管内工质:水 热管形式:重力热管 热管的几何尺寸:
光管外径 d 0 = 32 ㎜ ; 壁厚 0δ= 3.5 ㎜ ;
翅片型式:螺旋式翅片,冷热流体侧的翅片几何、结构相同 翅片长度 f l = 15 ㎜ ; 翅片外径 f d = 62 ㎜ ; 翅片厚度 f δ= 1.4㎜ ; 翅片间距 Y = 4 ㎜ ; 翅片节距 f δ'= f δ+ Y = 5.4 ㎜ ; 每米管长的翅片数 f n =
f 1δ'
= 10001585.4= m 片;
热管换热器管子排列形式为等边三角形,如图: 横向管子中心距 81T S mm =;81L T S S mm ==
(2)计算传热量Q
① 烟气的定性温度h f t
h
f t
=
2
21h h t t +
= 2501502152
+=℃
查得定性温度下烟气的参数为:
定压比热容 h
p C =1.1008 kJ/c kg ︒⋅;
密度 h f ρ =0.7284 kg/m 3;
导热系数 h f λ=4.1345210-⨯ W/(m C ⋅︒)
; 黏度
h f μ=25.0576
10-⨯ kg/(m ⋅s);
普朗特数 Pr h
= 0.667
② 空气侧定性温度及参数
定压比热容c
p C =1.009 kJ/kg C ⋅︒;
密度 c f
ρ=0.922 kg/m 3; 导热系数 c f
λ=3.2752
10-⨯ W/(m C ⋅︒); 黏度
c f μ=22.356
10-⨯ kg/(m ⋅s);
普朗特数 Pr c
= 0.687
③ 冷空气侧实际获得的热量Q c
c'21()c c c c c
f p Q V C t t ρ=-=18000 1.293 1.009200203600=1174.2kW ⨯⨯⨯
-÷() (假设标况下,c f ρ取为1.293kg/m 3。
) 考虑冷侧3%的热损,故:
1174.213%1210.49c Q =÷-=()kW
④ 烟气放出热量h
Q
考虑冷侧3%的热损,故:
h Q =1210.49(13%)=1248kW ÷-
⑤ 烟气的流量
12()
h
h
h h h h
f p Q V C t t ρ=
=
-312483600
24246Nm /h
1.295 1.1008(280150)
⨯=⨯⨯- ⑥ 对数平均温差∆t m ∆t m =
1212t t t ln t ∆-∆∆⎛⎫ ⎪∆⎝⎭=
()()1502028020015020ln 280200----⎛⎫ ⎪-⎝⎭
= 103℃
(3)确定迎风面积ex A 及迎风面管排数B
选取烟气侧和空气侧迎面风速为2.5m/s (在2-3m/s 之间选取)。
① 烟气侧迎风面积1h ex A 以及空气侧迎风面积1c ex A
1
h h ex
h N
V A w =='224246
2.694m 2.53600=⨯
1
c c ex
c N
V A w =='218000
2m 2.53600=⨯
② 迎风面宽度E
取热侧长l h =1.8m
则h ex
h A E l '==2.694 1.8 1.4966m ÷=
可得冷侧长c c
ex
A l E =='
2/1.4966 1.33m = 迎风面管排数T E B S '==1.496618.470.081
= 取B 为19根
实际迎风面宽度 T E B S =⋅=
190.081 1.539
⨯= ③ 两侧实际迎风面积
h h
ex A E l =⋅=21.539 1.8 2.77m ⨯= c c
ex A E l =⋅=21.539 1.33 2.067m
⨯
= ④ 两侧实际迎面风速
h
h N
h ex V w A ==
24246 2.43m /s 2.773600
=⨯ c
c
N
c ex
V w A ==
18000 2.44m /s 2.0673600=⨯ 中间隔板厚 l a = 30 mm ,预留安装段 l s = 35 mm 热管元件总长度 =l l h + l c + l a + 2l s = 3.23m
(4)求总传热系数 H U ①、管束最小流通截面积NFA
NF A h = ()()h 02T f f f S d l n B l δ--⋅⋅⋅⋅⎡⎤⎣⎦
=()()2
0.080.03220.0150.001418519 1.8 1.41m --⨯⨯⨯⨯⨯=⎡⎤⎣⎦
NF A c = ()()c 02T f f f S d l n B l δ--⋅⋅⋅⋅⎡⎤⎣⎦
()()2
0.080.03220.0150.001418519 1.33 1.042m =--⨯⨯⨯⨯⨯=⎡⎤⎣⎦
②、流体最大质量流速 G max
热侧 :max
h h f f h
h
V G
NFA ρ⋅=
=
224246 1.29522267.4kg /m h 1.41
⨯=⋅()
冷侧 :c c f c f c NFA
V G ρ⋅=max 218000 1.29322338.4kg /m h 1.042⨯==⋅() ③、求Re f
热侧 :max 0
Re h h
f
h f
G d μ⋅=
=
6
22267.40.032
789925.057103600
-⨯=⨯⨯ 冷侧 :c f
c c
f
d G μ
0max Re ⋅=622338.40.032888422.35103600-⨯==⨯⨯
④、求流体的换热系数f h
由 3
16338.0Pr Re 137.0⋅⋅=f
f Nu 计算换热系数
热侧:()
()
1
120.6338
0.6338
33
4.1345100.137
Re Pr 0.13778990.6670.032
h
f h h h f
f
h d λ-⨯==⨯⨯⨯
= 45.67 2
W /m C ⋅︒()
冷侧:()()
1
1c
20.6338c
c c 0.6338
f 33
f
f
3.27510h 0.137Re
Pr 0.13788840.687d 0.032
λ-⨯=⋅
⋅=⨯⨯⨯
= 32.53 2
W /(m C)⋅︒
⑤、求翅片效率f η
94.116
15
160=+=r r f ,故取20=r r f
热侧:=⋅⋅
f
w h f
h
f h l δλ2245.67
0.0150.55480.0014⨯⨯
=⨯
冷侧:=⋅⋅
f
w c f
c f
h l δλ2239.3
0.0150.50500.0014
⨯⨯
=⨯
由图3—71 查得,h
f η = 083,c
f η = 0.84
⑥、求每米长热管管外总表面积h A
每米长热管的翅片表面积f A 为:
(
)
22
024f f f f f A d d d n π
πδ⎡
⎤
=⨯⋅-+⋅⋅⨯⎢⎥⎣⎦
22
2
2(0.0620.032)0.0620.00121850.8695m 4π
π⎡
⎤
=⨯⨯-+⨯⨯⨯=⎢⎥⎣⎦ ; 每米长翅片间管表面积r A 为: (
)01r f f
A d n πδ
=⋅⋅-⋅=3.140.032(11850.0⨯
⨯-⨯2
0.0745
m =; 每米热管管外总表面积h A 为:
h r f A A A =+2
0.86950.0745
0.944m
=+
= 单根热管两侧总面积
热侧:h
h h
h A A l =⋅20.944 1.8 1.699m =⨯= 冷侧:c
c h
h A A l =⋅20.944 1.33 1.255m =⨯= 中径传热面积
热侧:h
h w
w A d l π=⋅⋅23.140.0285 1.80.161m =⨯⨯= 冷侧:c
c w
w A d l π=⋅⋅23.140.0285 1.330.119m =⨯⨯= 内径传热面积
热侧:h h i i A d l π=⋅⋅23.140.025 1.80.141m =⨯⨯=
冷侧:c c i i A d l π=⋅⋅23.140.025 1.330.104m =⨯⨯=
⑦、求管外有效换热系数fe h
=
⋅+=
h
h
h
f h f h r h f h fe
A A A h h )
(η热侧:()
45.670.07450.830.869538.50.944⨯+⨯=2W /(m C)⋅︒; c
h
c
f c f c r c f c fe
A A A h h )
(⋅+=
η冷侧:()
39.30.07450.840.869533.50.944
⨯+⨯=
=2W /(m C)⋅︒
⑧、求污垢热阻r y 及管壁热阻r w
查《换热器原理与设计》附录
D ,取值
0.00017h
y r =热侧:2
m C /W ⋅︒ 0.000086c
y r =冷侧:2
m C /W ⋅︒
金属管壁热阻:
==
h w w h
w r λδ 0.00350.000087548=2m C /W ⋅︒ ==
c w w c
w r λδ 0.00350.0000750
=2
m C /W ⋅︒ ⑨、求总传热系数h H U
5810h c HP HP h h ==()
2
W /m C ,
⋅︒
11h h h
h h h h
h w y h h h h h h H fe w y HP i
A A A r r U h A A h A =+⋅+⋅+
1 1.699 1.699
0.00008750.0001738.50.16158100.141
=
+⨯++⨯
11c c c
c c h h
h w y c c c c c c H fe w y HP i
A A A r r U h A A h A =+⋅+⋅+
1 1.416 1.416
0.000070.00008633.50.13458100.118
=
+⨯++⨯
可得
h H U =
()
234.34W /m C ,⋅︒
c
H
U =()230.59W /m C ,⋅︒
11
11
11
34.3430.59
H h c H H
U U U =
=
=++
216.18m C /W
⋅︒
(5)求放热侧总传热面积A H
h
1210.491000
16.18103c c H
H m Q A U t ⨯===⋅∆⨯2
726.7m
(6)求所需热管数n 、
726.75791.255c H c h A n A ===根
(7)求换热器纵深排数m
57930.4m 3219n m B =
===排,取排
排列方式:1918191819181918191819181918191819181918191819181918191819181918
19161816592
n =⨯+⨯=管子总数根
(8)求通过热管换热管的压力降 ①NFV
求换热器的净自由容积
()
f
f f T L n d d d S S NFV ⋅⋅---⋅⋅=δ2
022044866.0ππ ()2222330.8660.0810.0320.0620.0320.0014185 4.310m /m
44ππ
-=⨯-⨯-⨯-⨯⨯=⨯
②ev D 求当量直径
344 4.310^(3)
20.05100.944h
ev h NFV D A -⨯⨯-=
==⨯热侧:m
0.0182c c
ev ev D D ==冷侧:m
③'Re f 求
m a x
6
0.018222267.44R e '4502.925.057103600h h h ev f
h f D G μ-⋅⨯===⨯⨯热侧:
m a x
6
0.018222338.4R e '5064.320.35103600c c c
ev f
c f D G μ-⋅⨯===⨯⨯冷侧:
④f 求摩擦系数
()
0.145
h f 1.92R e '0.567
h
f -==热侧:
()
0.145
c f 1.92R e '0.557
c f -==冷侧:
⑤ 求平均管壁温度w t
3
124810215182.838.5 1.699592h h h
w f h h fe h Q t t h A n ⨯=-=-=⋅⋅⨯⨯热侧:C
︒
31210.4910
110158.533.5 1.255592c c
c
w
f c c fe h Q t t h A n ⨯=-=+=⋅⋅⨯⨯冷侧:C
︒
⑥w
μ 求壁温下的流体黏度
6
23.4810h w μ-=⨯热侧:()k g /m
s ⋅
624.6310c w μ-=⨯冷侧:()k g /m
s ⋅
⑦P
∆ 求通过换热器的压降
()20.14
0.40.6
m a x
2h
h h h
f h ev L h h h c ev f w T T G
L D S f P g D S S μρμ-⋅⎛⎫⎛⎫⎛⎫∆=⋅⋅ ⎪ ⎪ ⎪ ⎪⋅⋅⎝⎭⎝⎭⎝⎭热侧:
0.14
0.4
270.55625384.90.0810.8663225.05650.0182997Pa
2 1.3100.01820.728422.450.081-⨯⨯⨯⎛⎫
⎛⎫
=⨯⨯⨯= ⎪
⎪⨯⨯⨯⎝⎭
⎝⎭
()20.14
0.4
0.6
c
c c c
m a x
c
ev f L c
c c c ev f w T T G L D S f P 2g D S S μρμ-⋅⎛⎫⎛⎫⎛⎫∆=⋅
⋅ ⎪ ⎪ ⎪⋅⋅⎝⎭⎝⎭⎝⎭
冷侧:
0.14
0.4
270.57118816.40.0810.8663220.350.0182797Pa
2 1.3100.01820.92224.10.081-⨯⨯⨯⎛⎫⎛⎫
=⨯⨯⨯= ⎪
⎪⨯⨯⨯⎝⎭⎝⎭
(9)求热管的第一排的管内流体温度t v
第一排烟气温度1h
t =280℃
密度 1h f ρ =0.6432 kg/m 3;
导热系数 1h f λ=4.674210-⨯ W/(m C ⋅︒);
黏度
1
h f μ=27.468610-⨯ kg/(m ⋅s); 普朗特数 Pr h1
= 0.654
第一排空气温度c
2t =160℃
密度 2c f ρ=0.815 kg/m 3;
导热系数 2c f λ=3.642
10-⨯ W/(m C ⋅︒)
; 黏度
2c f μ=24.56
10-⨯ kg/(m ⋅s);
普朗特数 Pr c2
= 0.682
①f Re 求
max 0
1
-6
1
22267.440.032
Re 720627.468103600h h
f h f G d μ⋅⨯=
=
=⨯⨯热侧: max 0
2
-62
22338.40.032
Re
810424.5103600
c c
f c f G d μ⋅⨯=
=
=⨯⨯冷侧:
②f h 求
()()
1
120.63381
10.6338
33
1
10
4.674100.137Re
Pr
0.13772060.6540.032
h f h
h h f f h d λ-⨯=⋅
⋅⋅=⨯⨯⨯热侧:
2
50.2W /m C =⋅︒() ()()
1
120.63382
20.6338
33
2
20
3.64100.137Re
Pr
0.13781040.6820.032
c f c
c
c f f h
d λ-⨯=⋅
⋅⋅=⨯⨯⨯冷侧:
2
42.7W /m C =⋅︒()
③f η 求
12
0.820.84
h f c
f ηη
==热侧:冷侧:
④fe
h 求
()111
()
50.20.07450.820.869541.870.944h h
f r f f h fe h
h A A h
A η+⋅⨯+⨯=
=
=热侧:2
W /m C ⋅︒(
)
()222
()
42.70.07450.840.86936.40.944c c
f r f f c
fe h
h A A h
A η+⋅⨯+⨯=
==冷侧:2
W /m C ⋅︒(
)
⑤H U 求
11110.03037h h h
h c h h
h w y h h h h h h
H fe w y HP i
A A A r r U h A A h A =+⋅+⋅+=⋅热侧:
36.97h
H U =2W /m C ⋅︒()
22110.03037c
c c
c c h h
h w y c c c c c c
H fe w
y HP i
A A A r r U h A A h A =+⋅+⋅+⋅=⋅冷侧:
32.9c H U =2W /(m C )
⋅︒
⑥求热导S
1136.97 1.69962.81h h h
H h S U A =⋅=⨯=热侧:W /C ︒
2232.9 1.25541.29c c c
H h S U A =⋅=⨯=冷侧:W /C
︒
⑦求t v
x =()()
h h c c v v Q S t t S t t -=-
由上式可以得
1122
1228062.8116041.29
232.462.8141.29
h h
c c v h c
t S t S t S S ⋅+⋅⨯+⨯=
=
=++C
︒
(11)、求蒸发段热管的最后一排管壁温度t w h
最后一排烟气温度2h
t =150℃
密度 2h f ρ =0.849 kg/m
3 导热系数 2h f λ=3.57210-⨯ W/(m C ⋅︒)
黏度
2
h f μ=2.2456
10-⨯ kg/m ⋅s 普朗特数 Pr h2
= 0.68; 最后一排空气温度c
1t =20℃
密度 1
c f ρ=1.205 kg/m 3
导热系数
1c f λ=2.592
10-⨯ W/(m C ⋅︒)
黏度 1
c
f μ=1.81610-⨯ kg/m ⋅s 普朗特数 Pr c1
= 0.703;
①f
Re 求
max 02-6222267.440.032Re 8816.622.45103600h h f h f G d μ⋅⨯===⨯⨯热侧: max 01-6122338.40.032Re 10970.418.1103600c c
f c
f G d μ⋅⨯==
=⨯⨯冷侧: ②f h 求
()()110.6338220.6338332200.03570.137Re
Pr 0.1378816.60.680.032h f h
h h f f h d λ=⋅⋅⋅=⨯⨯⨯热侧: 242.6W /m C =⋅︒()
()()110.6338110.6338331100.02590.137Re
Pr 0.13710970.40.7030.032c f c
c c f f h
d λ=⋅⋅⋅=⨯⨯⨯冷侧: 235.9W /m C =⋅︒()
③f η 求
120.84
0.85h f c
f ηη==热侧:冷侧:
④fe
h 求
()222()42.60.07450.840.869535.90.944h h f r f f h
fe h h A A h A η+⋅⨯+⨯=
==热侧:2W /m C ⋅︒()
()111()
35.90.07450.850.86930.90.944c
c f r f f c
fe h h A A h A η+⋅⨯+⨯===冷侧:2W /m C ⋅︒()
⑤H
U 求
22110.0307h h h h c h h h w y h h h h h h H fe w y HP i A A A r r U h A A h A =+⋅+⋅+=⋅热侧:
32.56h H U =2W /m C
⋅︒
11110.03518c c c c c h h h w y c c c c c c
H fe w y HP i A A A r r U h A A h A =+⋅+⋅+⋅=⋅冷侧:
28.4c H U =2W /m C ⋅︒()
⑥求热导S
2232.56 1.69955.32h h h H h S U A =⋅=⨯=热侧:W /C ︒
1128.4 1.25535.6c c c H h S U A =⋅=⨯=冷侧:W /C
︒
⑦求t w
2211w 2115055.322035.69955.3235.6h h c c h c t S t S t S S ⋅+⋅⨯+⨯===++C ︒。