% Fully developed Nusselt number for rhombic ducts. 
function [Nu, fReD, Dh, Ph] = RhombNuInf(Wall,H,W)
  r=H./W;
  r(r>1)=1./r(r>1);
  phi=atan(r);
  Dh=H.*cos(phi);                                                        
  Ph=2*W./cos(phi);
  fReD=48-4.676*phi+120.8*phi.^2-279.5*phi.^3+282.9*phi.^4-114.4*phi.^5; 
  switch Wall
  case 'T'
    Nu=0.943+6.658*phi-16.94*phi.^2+41.94*phi.^3+...
                                             -53.61*phi.^4+24.55*phi.^5; 
  case 'H1'
    Nu=2.059+1.388*phi+7.232*phi.^2-12.65*phi.^3+5.598*phi.^4;           
  otherwise
    error('Wall= ''T'' or ''H1''');
  end
end
