# Resistance Coefficient

on . Posted in Dimensionless Numbers

Resistance coefficient, abbreviated as K, a dimensionless number, is how much resistance to the flow an obstacle has.  This is the opposite of flow coefficient which is how much flow capacity an obstacle allows.  It describe the resistance of a fluid object (such as a sphere, cylinder, or airfoil) to flow through a fluid.  The resistance coefficient formula depends on the shape of the object and the Reynolds number of the flow.

The coefficient is proportional to the drag force acting on the object and inversely proportional to the density, velocity squared, and reference area of the object.  The value of the resistance coefficient depends on the shape and size of the object and the flow conditions, such as the Reynolds number.  The resistance coefficient is commonly used in the design and analysis of fluid systems, such as aerodynamics, hydrodynamics, and fluid flow in pipes and channels.

## Resistance Coefficient formula

$$\large{ K = f_d \; \frac {l} {d} }$$
Symbol English Metric
$$\large{ K }$$ = resistance coefficient $$\large{dimensionless}$$
$$\large{ f_d }$$ = Darcy friction factor $$\large{dimensionless}$$
$$\large{ l }$$ = lenght of the pipe $$\large{ft}$$ $$\large{m}$$
$$\large{ d }$$ = inside diameter of the pipe $$\large{in}$$ $$\large{mm}$$
$$\large{ i }$$ = $$\large{ \frac{l}{d} }$$ = equivalent length of the obstruction $$\large{dimensionless}$$ 