= + Pfriction Pp Pf Similarly, the total friction loss, as fluid flows through pipes is the sum of the hfriction, head loss from friction with the pipes, and the head loss from friction through the hp, fittings, hf. = + hfriction hp hf The next two sections describe how to calculate pressure loss due to friction through and fittings. Pressure Loss Due to Friction through Pipes and Ducts Friction Factor Method The pressure loss from friction with the pipes and ducts, can be calculated Pp, from = (f L V2) / (2 D) Pp where f is the friction factor, L is the pipe/duct length, the fluid density and D is the is pipe/duct diameter. An explicit algebraic expression for friction factor, f, was developed by Churchill. This relationship is valid for all ranges of Reynolds numbers. Source: ASHRAE, 2005, pg 2.7. The Reynolds number is: Re = V D / V D / = fluid  where is the kinematic viscosity (air at 60 F = 0.572 ft2/h and at 60 F = 0.044  water ft2/h), and is the dynamic viscosity (air at 60 F = 0.043 lbm/h-ft andwater at 60 F =  2.71 lbm/h-ft). The equivalent diameter, De, for a rectangular duct with dimensions L and W is: De = 1.3 (L W)5/8 / (L + W)1/4 Typical values for pipe roughness factors, e, are shown in the figure below.
Pfriction = Pp + Pf Similarly, the total friction loss, hfriction, as fluid flows through pipes is the sum of the head loss from friction with the pipes, hp, and the head loss from friction through the fittings, hf. hfriction = hp + hf The next two sections describe how to calculate pressure loss due to friction through and fittings. Pressure Loss Due to Friction through Pipes and Ducts Friction Factor Method The pressure loss from friction with the pipes and ducts, Pp, can be calculated from Pp = (f L V2) / (2 D) where f is the friction factor, L is the pipe/duct length, is the fluid density and D is the pipe/duct diameter. An explicit algebraic expression for friction factor, f, was developed by Churchill. This relationship is valid for all ranges of Reynolds numbers. Source: ASHRAE, 2005, pg 2.7. The Reynolds number is: Re = V D / = fluid V D /  where  is the kinematic viscosity (air at 60 F = 0.572 ft2/h and water at 60 F = 0.044 ft2/h), and  is the dynamic viscosity (air at 60 F = 0.043 lbm/h-ft andwater at 60 F = 2.71 lbm/h-ft). The equivalent diameter, De, for a rectangular duct with dimensions L and W is: De = 1.3 (L W)5/8 / (L + W)1/4 Typical values for pipe roughness factors, e, are shown in the figure below.
EnergyEfficientFluidFlow.docx