   SPHERE_RANZ_MARSHALL = uint8(1);
        SPHERE_WHITAKER      = uint8(2);
    end
    
    %% Public properties
    properties (SetAccess = public, GetAccess = public)
        % Identification
        type uint8 = uint8.empty;   % flag for type of model
    end
    
    %% Constructor method
    methods
        function this = Nusselt(type)
            if (nargin > 0)
                this.type = type;
            end
        end
    end
    
    %% Abstract methods: implemented in derived sub-classes
   