K_bend_rect

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K_bend_rect

The K_Bend_rect(rtoW, btoW, alpha, Re) function returns the resistance coefficient for a rectangular duct bend given its vane radius to height ratio, width to height ratio, the turning angle, and the Reynolds number. Note that the function DuctBend_Rect_CL in the component library implements the dimensional version of this function.

Inputs:
rtoW = ratio of vane radius (R) to duct height (W) - note, set this to a negative number if there are no turning vanes present
btoW = ratio of duct width (b) to duct height (W)
alpha = bend turning angle (Degree or Radian)
Re = Reynolds number based on hydraulic diameter of the duct (set to <0 if you do not want to implement a Reynolds number correction to the K value)

Example:
$UnitSystem SI Mass J C kPa Degree
rtoW = 1.2
btoW = 1.5
alpha = 90 [degree]
Re = 1e5
K = k_bend_rect(rtoW, btoW,alpha, Re)
vel = 15 [m/s]
P = Po#
T = 20 [C]
F$ = 'Air'
rho=density(F$,P=P,T=T)
DELTAP = rho*vel^2/2*K

{Solution
DELTAP=12.53 [Pa]
K=0.09247
}

Reference:
Legg, R., 2017, "Chapter 14: Ducted Air Systems" in Air Conditioning System Design, Butterworth-Heinemann,

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