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The gas side pressure drop may be calculated by any number of methods available today, but the following procedures should give sufficient results for heater design.
Bare Tube Pressure Loss | ||
Fin Tube Pressure Loss | ||
Stud Tube Pressure Loss |
Dp = Pressure drop, inH2O |
Pv = Velocity head of gas, inH2O |
Nr = Number of tube rows |
Gn = Mass velocity of gas, lb/hr-ft2 |
rg = Density of gas, lb/ft3 |
Wg = Mas gas flow, lb/hr |
An = Net free area, ft2 |
Ad = Convection box area, ft2 |
do = Outside tube diameter, in |
Le = Tube length, ft |
Pt = Transverse pitch of tubes, in |
Nt = Number of tubes per row |
Dp = Pressure drop, inH2O |
rb = Density of bulk gas, lb/ft3 |
rout = Density of outlet gas, lb/ft3 |
rin = Density of inlet gas, lb/ft3 |
Gn = Mass gas flow, lb/hr-ft2 |
Nr = Number of tube rows |
do = Outside tube diameter, in |
df = Outside fin diameter, in |
Ad = Cross sectional area of box, ft2 |
Ac = Fin tube cross sectional area/ft, ft2/ft |
Le = Effective tube length, ft |
Nt = Number tubes wide |
And, |
Ac = (do + 2 * lf * tf * nf) / 12 |
tf = fin thickness, in |
nf = number of fins, fins/in |
mb = Gas dynamic viscosity, lb/ft-hr |
lf = Fin height, in |
sf = Fin spacing, in |
Nr = Number of tube rows |
Pl = Longitudinal tube pitch, in |
Pt = Transverse tube pitch, in |
Dp = Pressure drop across tubes, inH2O |
Nr = Number of tube rows |
Cmin = Min. tube space, diagonal or transverse, in |
do = Outside tube diameter, in |
ls = Length of stud, in |
G = Mass gass velocity, lb/sec-ft2 |
Tg = Average gas Temperature, °F |
Wg = Mass flow of gas, lb/hr |
An = Net free area of tubes, ft2 |
Le = Length of tubes, ft |
Nt = Number of tubes wide |
Pt = Transverse tube pitch, in |
ls = Length of stud, in |
ts = Diameter of stud, in |
rs = Rows of studs per foot |