% Natural convection from a sphere
function [h, NuD, RaD] = SphereNatNuT(Ts,Tinf,D,mat)
  [RaD,Pr,kf] = Ra(Ts,Tinf,D,mat);                          
  % published limit of Pr>=0.71 has been changed to 0.6 below
  if min(Pr) < 0.6   warning = 'SphereNatNuT: Pr < 0.6'   
  end
  if max(RaD) > 1e11 warning = 'SphereNatNuT: RaD > 1e11' 
  end
  NuD = 2+0.589*RaD.^(1/4)./(1+(0.469./Pr).^(9/16)).^(4/9); 
  h   = NuD.*kf./D;                                         
end
