% Fully developed Nusselt number for isosceles triangular ducts. 
function [Nu, fReD, Dh, Ph] = IsoTriNuFD(Wall,H,W)
  theta=atan(W/2./H);
  Dh=2*H.*sin(theta)./(1+sin(theta));                      
  Ph=W.*(1+1./sin(theta));
  fReD=48.0+25.47*theta-43.08*theta.^2+...
       35.33*theta.^3-19.32*theta.^4+4.912*theta.^5;       
  switch Wall
  case 'T'
    i=find(theta <= pi/40);
    Nu(i)=0.943+9.0145*theta(i);
    i=find(pi/40 < theta < 4*pi/9);
    Nu(i)=1.18+7.02*theta(i)-14.09*theta(i).^2+...
      14.14*theta(i).^3-8.02*theta(i).^4+1.87*theta(i).^5; 
    i=find(theta >= 4*pi/9);
    Nu(i)=5.461-2.876*theta(i);
  case 'H1'
    Nu=2.059+5.122*theta-8.729*theta.^2+...
       6.802*theta.^3-3.201*theta.^4+0.692*theta.^5;       
  otherwise
    error('Wall= ''T'' or ''H1''');
  end
end
