function [dp] = friction(u)
w=u;
d=20*0.0254;
A=pi*(d/2)^2
v=w/rho/(A) %velocity
mu=0.00011; % viscosity for propane
Re=rho*v*d/mu;
Rugh=0.001;
fric_fac=(1/(-1.8*log10(6.9/Re+(Rugh/d/3.7)^1.11)))^2;% Darcy friction factor
L=200;
dp=4*fric_fac*L/d*rho*v^2/2 %head loss
end