Total Pressure or Head Loss in Pipe or Duct Systems

Major and minor loss in pipe, tubes and duct systems

The head loss of a pipe, tube or duct system, is the same as that produced in a straight pipe or duct whose length is equal to the pipes of the original systems plus the sum of the equivalent lengths of all the components in the system. This can be expressed as:

h_loss = Σ h_{major_losses} + Σ h_{minor_losses} (1)

where

h_loss = total head loss in the pipe or duct system

h_{major_losses} = major loss due to friction in the pipe or duct system

h_{minor_losses} = minor loss due to the components in the system

• Major Head Loss - head loss or pressure loss - due to friction in pipes and ducts.
• Minor Head Loss - head loss or pressure loss - due to components as valves, bends, tees and the like in the pipe or duct system.

Summarized Major Losses

The major head loss for a single pipe or duct can be expressed as:

h_{major_loss} =λ (l / d_h) (v² / 2 g) (2)

where

h_loss = head loss (m, ft)

λ = friction coefficient

l = length of duct or pipe (m)

d_h = hydraulic diameter (m)

v = flow velocity (m/s, ft/s)

g = acceleration of gravity (m/s², ft/s²)

Summarized Minor Losses

Minor head loss can be expressed as:

h_{minor_loss} = ξ v²/ 2 g (3)

where

ξ = minor loss coefficient

Since the velocity - v - in equation (2) in general is related to the pipe or duct where the component is located, the sum of the minor losses in a pipe or duct can be expressed as:

Σ h_{minor_losses} = Σ ξ (v²/ 2 g) (3)

The minor loss can be calculated by summarizing the minor loss coefficients - and multiplying the sum with the dynamic pressure head.

Total Head Loss in a Single Pipe or Duct

The total head loss for a single pipe can be calculated by using equation (1) and (3):

h_{loss_single} =λ (l / d_h) (v² / 2 g) + Σ ξ v²/ 2 g (4)

or

h_{loss_single} = (λ (l / d_h) + Σ ξ ) (v²/ 2 g) (5)

Total Head Loss in Serial Connected Pipes

The total head loss in several serial connected pipes can be calculated by adding the total head loss in each pipe or duct. The total head loss can be expressed as:

h_{loss_serial} = Σ [(λ₁ (l₁ / d_h1) + Σ ξ₁) (v₁²/ 2 g) + .. + λ_n (l_n / d_hn) + Σ ξ_n) (v_n²/ 2 g)] (6)

for 1 to n serial connected pipes

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