blob: f06516247ef8bb7ebbf51ca18e569cfeccdcc5c1 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
|
//Variable declaration:
h1 = 13.0 //Air-side heat transfer coefficient (W/m^2.K)
A = 1.0 //Base wall area (m^2)
L = 2.5/100 //Length of steel fins (m)
L2 = 1.5/10**3 //Length of steel wall (m)
k = 13.0 //Thermal conductivity of fin (W/m.K)
k1 = 38.0 //Thermal conductivity of steel wall (W/m.K)
h2 = 260.0 //Water side heat transfer coefficient (W/m^2.K)
T4 = 19.0 //Air temperature ( C)
T1 = 83.0 //Water temperature ( C)
t = 1.3/10**3 //Thickness of steel fins (m)
w = 1.0 //Width of wall (m)
S = 1.3/100 //Fin pitch(m)
//Calculation:
R1 = 1/(h1*A) //Air resistance ( C/W) (part 1)
R2 = L2/(k1*A) //Conduction resistance ( C/W)
R3 = 1/(h2*A) //Water resistance ( C/W)
Rt = (R1+R3) //Total resistance ( C/W) (part 2)
Q = (T1-T4)/Rt //Total heat transfer (W)
Nf = 1/S //Number of fins (part 3)
Lbe = w - Nf*t //Unfinned exposed base surface
Abe = w*Lbe //Exposed base surface area (m^2)
Lc = L+t/2 //Corrected length (m)
Ap = Lc*t //Profile area (m^2)
Af = 2*w*Lc //Fin surface area (m^2)
Bi = h1*(t/2)/k1 //Biot number
a = sqrt(Lc**3*h1/(k*Ap)) //Abscissa of the fin efficiency
//From figure 17.3:
nf = 0.88 //Fin efficiency
Rb = 1/(h1*Abe) //Air thermal resistance of base wall ( C/W)
Rf = 1/(h1*Nf*Af*nf) //Air thermal resistance of fins ( C/W)
RT1 = 1/(1/Rb+1/Rf) //Total outside resistance of the fin array ( C/W)
Rt3 = RT1+R3 //Total resistance on air side fins ( C/W)
Qt = (T1-T4)/Rt3 //Heat transfer rate on air side fins (W)
I = (Qt/Q - 1)*100 //Percent increase in heat transfer rate to air side fins (W)
A = sqrt(Lc**3*h2/(k1*Ap)) //Abscissa of the new fin efficiency (part 4)
//From figure 17.3:
nf2 = 38.0 //New fin efficiency
Rb2 = 1/(h2*Abe) //Thermal resistance of base wall ( C/W)
Rf2 = 1/(h2*Nf*Af*nf2) //Thermal resistance of fins ( C/W)
Rt4 = 1/(1/Rb2+1/Rf2) //Total resistance of the finned surface ( C/W)
Rt5 = R1+Rt4 //Total resistance on water side fins ( C/W)
QT1 = (T1-T4)/Rt5 //Heat transfer rate on water side fins (W)
I2 = (QT1/Q - 1)*100 //Percent increase in heat transfer rate to water side fins (W)
//Result:
if (R2<R1 | R2<R3) then
printf("1. The conduction resistance may be neglected.")
else
printf("1. The conduction resistance can not be neglected.")
end
printf("2. The rate of heat transfer from water to air is : %.1f W .",Q)
printf("3. The percent increase in steady-state heat transfer rate by adding fins to the air side of the plane wall is : %.1f %%",I)
printf("4. The percent increase in steady-state heat transfer rate by adding fins to the water side of the plane wall is : %.1f %%",I2)
printf("____There is a calculation mistake in book in calculating Qt(83-19/0.0214 = 2999), hence slight differences in answer______")
|
