传热
1K o =
=1dA o
αi dA i
+
+
δdA o λdA m +1
+
1
αo
=
1πd 2L
α1πd 1L
+
δπd 2L λπd m L
+
1
α2
1d 2
δd 2λd m
α1d 1α2
⎧⎧无相变Q =q m 1C p 1(T 1-T 2)=q m 2C P 2(t 2-t 1)⎪⎪⎪
⎧⎪热量衡算⎨⎪Q =q m 1γ=q m 2C P 2(t 2-t 1)
⎪⎪有相变⎨
Q =q m 1γ+q m 1C p 1(T s -T 2)=q m 2C P 2(t 2-t 1)⎪⎪⎪⎩⎩
⎪
⎧⎧⎪
⎪⎪⎪1⎪⎪无垢层:K 2=⎪
d d 21⎪⎪2⎪++⎪⎪⎪α1d 1λd m α2
⎪⎪⎪
1⎪⎪⎪总传热系数K ⎨或K 1=⎪⎪δd d 111⎪⎪⎪++
⎨⎪αλd αd 2⎪1m 2⎪⎪⎪
1⎪⎪⎪有垢层K =
2⎪传热基本方程式:Q =K ⋅S ⋅∆t m ⎨d 2d 2δd 21⎪
⎪+R 1++R 2+⎪⎪
α1d 1d 1λd m α2⎪⎪⎩
⎪⎪
⎧恒温下传热:∆t m =(T -t )⎪⎪
⎪⎪⎪⎪∆t 2-∆t 1∆t 2∆t 2+∆t 1
平均温差∆t ⎨变温下传热:∆t m =⎪m , 当0. 5 2时,∆t m =⎪
∆t ∆t 2⎪⎪21⎪ln
⎪∆t 1⎪⎩⎪
⎪⎪
⎪⎪
⎪⎪⎩传热面积S :对于列管式换热器S =n πdL (注意S 与d 的对应关系)⎩
吸收常用于分离低浓度的气体混合物,此时液相的浓度通常也很低(稀溶液范围内),稀溶液的溶解度曲线通常为一直线,服从亨利定律。 pe= Ex pe= Hc= HCMx
c = CMx
CM (混合液总摩尔浓度, kmol/m3) ye=mx m —相平衡常数 故有: m=E/P E=CMH
c EcM s ρ p e =H =p e =
H EM s ρ
传质方向的判定
y>ye 或 xxe 解吸
H =
G K Y a
⎰
y 1y 2
∆y 1-∆y 2
G L ∆y y y 1-y 2G y -y 2∆L y 1x d ∆1dy dx G ==⨯⨯ln =H OG N OG H =N OL H =H =⎰y x =∆H K Y a ∆y 1OL -∆y K Y OG a 1a , ∆y 2OL 2y -y e K x -x K K x 2a x e Y G y -y 2∆y 1-∆y 2=⨯1∆y m =
∆y 1K Y a ∆y m
ln
G ⋅y +L ⋅x 2=G ⋅y 2+L ⋅x ∆y 2
y 2
y 2
1
122
H =
G K Y
⎰a
y 1
dy y -y e
=
G K Y a
⨯⎰
y 1
1y -y e
⨯
y 1-y 2
d (∆y )
y =
L G
(x -x 2)+
y 2
x 1=x 2+
G L
(y 1-y 2)
y -y 2⎛L ⎫
=1, ∆y 1=0, H →∞。 ⎪
G x -x ⎝⎭min 1e 2
ϕ=
p p s
k H
(2). H s =0. 622
p s P -p s
r W 1. 09
t W =t -
t as =t -
αr as
C p
r W (H W -H )
t W =t -(H W -H )
(H as -H ) I =(1. 01+1. 88H ) t +2500H
H
-3
N A =k H (H w -H )
+4. 56⨯10
-3
v H =(2. 83⨯10
H )(t +273)
v H
降速 N A =Kx ⨯X
=(
y 2-y 1x 2-x 1
) ⨯X =
N A 恒X c
⨯X
例1:在一连续干燥器中,处理湿物料量为800kg/h,要求物料干燥后含水量由30%减至4%(均为湿基)。干燥介质为空气,初温为15℃,相对湿度为50%。经预热气加热至120℃进入干燥器,出干燥器时45℃,相对湿度为80%,试求: (1)水分蒸发量W; (2)干燥产品量G2;
(3)空气消耗量L;
(4)如鼓风机装在进口处,求风机之风量V 。
t 0+27327315+273273
v H =(0. 722+1. 244H o ) ⨯
=(0. 722+1. 244⨯0. 005) ⨯ =0. 822m /kg
3
L =Vv H =4610⨯0. 822=3790m /h
3
传热
1K o =
=1dA o
αi dA i
+
+
δdA o λdA m +1
+
1
αo
=
1πd 2L
α1πd 1L
+
δπd 2L λπd m L
+
1
α2
1d 2
δd 2λd m
α1d 1α2
⎧⎧无相变Q =q m 1C p 1(T 1-T 2)=q m 2C P 2(t 2-t 1)⎪⎪⎪
⎧⎪热量衡算⎨⎪Q =q m 1γ=q m 2C P 2(t 2-t 1)
⎪⎪有相变⎨
Q =q m 1γ+q m 1C p 1(T s -T 2)=q m 2C P 2(t 2-t 1)⎪⎪⎪⎩⎩
⎪
⎧⎧⎪
⎪⎪⎪1⎪⎪无垢层:K 2=⎪
d d 21⎪⎪2⎪++⎪⎪⎪α1d 1λd m α2
⎪⎪⎪
1⎪⎪⎪总传热系数K ⎨或K 1=⎪⎪δd d 111⎪⎪⎪++
⎨⎪αλd αd 2⎪1m 2⎪⎪⎪
1⎪⎪⎪有垢层K =
2⎪传热基本方程式:Q =K ⋅S ⋅∆t m ⎨d 2d 2δd 21⎪
⎪+R 1++R 2+⎪⎪
α1d 1d 1λd m α2⎪⎪⎩
⎪⎪
⎧恒温下传热:∆t m =(T -t )⎪⎪
⎪⎪⎪⎪∆t 2-∆t 1∆t 2∆t 2+∆t 1
平均温差∆t ⎨变温下传热:∆t m =⎪m , 当0. 5 2时,∆t m =⎪
∆t ∆t 2⎪⎪21⎪ln
⎪∆t 1⎪⎩⎪
⎪⎪
⎪⎪
⎪⎪⎩传热面积S :对于列管式换热器S =n πdL (注意S 与d 的对应关系)⎩
吸收常用于分离低浓度的气体混合物,此时液相的浓度通常也很低(稀溶液范围内),稀溶液的溶解度曲线通常为一直线,服从亨利定律。 pe= Ex pe= Hc= HCMx
c = CMx
CM (混合液总摩尔浓度, kmol/m3) ye=mx m —相平衡常数 故有: m=E/P E=CMH
c EcM s ρ p e =H =p e =
H EM s ρ
传质方向的判定
y>ye 或 xxe 解吸
H =
G K Y a
⎰
y 1y 2
∆y 1-∆y 2
G L ∆y y y 1-y 2G y -y 2∆L y 1x d ∆1dy dx G ==⨯⨯ln =H OG N OG H =N OL H =H =⎰y x =∆H K Y a ∆y 1OL -∆y K Y OG a 1a , ∆y 2OL 2y -y e K x -x K K x 2a x e Y G y -y 2∆y 1-∆y 2=⨯1∆y m =
∆y 1K Y a ∆y m
ln
G ⋅y +L ⋅x 2=G ⋅y 2+L ⋅x ∆y 2
y 2
y 2
1
122
H =
G K Y
⎰a
y 1
dy y -y e
=
G K Y a
⨯⎰
y 1
1y -y e
⨯
y 1-y 2
d (∆y )
y =
L G
(x -x 2)+
y 2
x 1=x 2+
G L
(y 1-y 2)
y -y 2⎛L ⎫
=1, ∆y 1=0, H →∞。 ⎪
G x -x ⎝⎭min 1e 2
ϕ=
p p s
k H
(2). H s =0. 622
p s P -p s
r W 1. 09
t W =t -
t as =t -
αr as
C p
r W (H W -H )
t W =t -(H W -H )
(H as -H ) I =(1. 01+1. 88H ) t +2500H
H
-3
N A =k H (H w -H )
+4. 56⨯10
-3
v H =(2. 83⨯10
H )(t +273)
v H
降速 N A =Kx ⨯X
=(
y 2-y 1x 2-x 1
) ⨯X =
N A 恒X c
⨯X
例1:在一连续干燥器中,处理湿物料量为800kg/h,要求物料干燥后含水量由30%减至4%(均为湿基)。干燥介质为空气,初温为15℃,相对湿度为50%。经预热气加热至120℃进入干燥器,出干燥器时45℃,相对湿度为80%,试求: (1)水分蒸发量W; (2)干燥产品量G2;
(3)空气消耗量L;
(4)如鼓风机装在进口处,求风机之风量V 。
t 0+27327315+273273
v H =(0. 722+1. 244H o ) ⨯
=(0. 722+1. 244⨯0. 005) ⨯ =0. 822m /kg
3
L =Vv H =4610⨯0. 822=3790m /h
3