[Heat Exchanger Calculation] Heat Exchanger Calculation Formula Heat Exchanger Heat and Surface Calculation Method
I. Heat Calculation
1, General
Q=Wh(Hh, 1-Hh, 2)=Wc(Hc, 2-Hc, 1)
where:
Q is the heat load of the heat exchanger, kj/h or kw;
W is the mass flow of the fluid, kg/ h;
H is the enthalpy of fluid per unit mass, kj/kg;
Subscripts c and h represent cold fluid and hot fluid, respectively, and subscripts 1 and 2 represent heat transfer, respectively import and export of appliances.
2, no phase change
Q=Whcp, h(T1-T2)=Wccp, c(t2- t1)
where:
cp is the average constant pressure specific heat capacity of the fluid, kj/(kg.℃);
T is the temperature of the hot fluid, ℃ ;
T is the temperature of the cold fluid, °C.
Second, area calculation
1, total heat transfer coefficientK
The K value in the shell and tube heat exchanger is as follows:
Note:
1w=1J/ s=3.6kj/h=0.86kcal/h
1kcal=4.18kj
2, temperature difference
(1) Counterflow
Hot fluid temperature T: T1→T2
Cold fluid temperature t: t2←t1
Temperature difference △t: △t1 →△t2
△tm=(△t2-△t1)/㏑(△t2/△t1)
(2) Parallel flow
Thermal fluid Temperature T: T1→T2
Cold fluid temperature t: t1→t2
Temperature difference △t: △t2→△t1
△tm=(△t2 -△t1)/㏑(△t2/△t1)
3, area calculation
S=Q/( K.△tm)
III. Calculation of the area of shell and tube heat exchanger
S=3.14ndL
Among them, S is the heat transfer area m2, n is the number of tubes in the tube bundle, d is the diameter of the tube, m; L is the length of the tube, m.
Four. Precautions
Condensing section: latent heat (calculated according to the heat of vaporization)
Cooling section: sensible heat (based on specific heat capacity calculation)
