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 |

For bare tubes we can use the method presented by Winpress(Hydrocarbon Processing, 1963),

D_{p} = Pressure drop, inH_{2}O |

P_{v} = Velocity head of gas, inH_{2}O |

N_{r} = Number of tube rows |

G_{n} = Mass velocity of gas, lb/hr-ft^{2} |

r_{g} = Density of gas, lb/ft^{3} |

W_{g} = Mas gas flow, lb/hr |

A_{n} = Net free area, ft^{2} |

A_{d} = Convection box area, ft^{2} |

d_{o} = Outside tube diameter, in |

L_{e} = Tube length, ft |

P_{t} = Transverse pitch of tubes, in |

N_{t} = Number of tubes per row |

For the fin tube pressure drop, we will use the Escoa method.

For staggered layouts,

D_{p} = Pressure drop, inH_{2}O |

r_{b} = Density of bulk gas, lb/ft^{3} |

r_{out} = Density of outlet gas, lb/ft^{3} |

r_{in} = Density of inlet gas, lb/ft^{3} |

G_{n} = Mass gas flow, lb/hr-ft^{2} |

N_{r} = Number of tube rows |

d_{o} = Outside tube diameter, in |

d_{f} = Outside fin diameter, in |

A_{d} = Cross sectional area of box, ft^{2} |

A_{c} = Fin tube cross sectional area/ft, ft^{2}/ft |

L_{e} = Effective tube length, ft |

N_{t} = Number tubes wide |

And, |

A_{c} = (d_{o} + 2 * l_{f} * t_{f} * n_{f}) / 12 |

t_{f} = fin thickness, in |

n_{f} = number of fins, fins/in |

m_{b} = Gas dynamic viscosity, lb/ft-hr |

For segmented fin tubes arranged in,

C

C

For solid fin tubes arranged in,

C

C

l_{f} = Fin height, in |

s_{f} = Fin spacing, in |

For fin tubes arranged in,

C

C

N_{r} = Number of tube rows |

P_{l} = Longitudinal tube pitch, in |

P_{t} = Transverse tube pitch, in |

We can now use the following script to try some calculations,

For the stud tube pressure loss we will use the Muhlenforth method,

The general equation for staggered or inline tubes,

D_{p} = Pressure drop across tubes, inH_{2}O |

N_{r} = Number of tube rows |

C_{min} = Min. tube space, diagonal or transverse, in |

d_{o} = Outside tube diameter, in |

l_{s} = Length of stud, in |

G = Mass gass velocity, lb/sec-ft^{2} |

T_{g} = Average gas Temperature, °F |

Correction for inline tubes,

W_{g} = Mass flow of gas, lb/hr |

A_{n} = Net free area of tubes, ft^{2} |

L_{e} = Length of tubes, ft |

N_{t} = Number of tubes wide |

P_{t} = Transverse tube pitch, in |

l_{s} = Length of stud, in |

t_{s} = Diameter of stud, in |

r_{s} = Rows of studs per foot |

We can now use the following script to try some calculations,