Process of using a submerged combustion melter to produce hollow glass fiber or solid glass fiber having entrained bubbles, and burners and systems to make such fibers

A process comprising:

• a) feeding at least one partially or wholly vitrifiable feed material into a feed inlet of a melting zone of a melter vessel comprising a floor, a ceiling, and a wall connecting the floor and ceiling at a perimeter of the floor and ceiling, the meter vessel comprising a feed opening in the wall or ceiling and an exit end comprising a melter exit structure for discharging molten material formed in the melting zone;
• b) heating the at least one partially or wholly vitrifiable material with at least one burner directing combustion products of an oxidant and a first fuel into the melting zone under a level of the molten material in the zone, one or more of the burners configured to impart heat and turbulence to at least some of the molten material in the melting zone, producing a turbulent molten material comprising a plurality of bubbles suspended in the molten material, the bubbles comprising at least some of the combustion products;
• c) discharging the molten material comprising bubbles from the melter vessel through the inciter exit structure into a forehearth having a plurality of bushings connected to the forehearth producing fibers of the same outside diameter, the process comprising controlling flow of the molten material comprising bubbles through the forehearth and bushings so that fibers produced through the bushings are substantially consistent in volume of regions devoid of glass, the controlling comprising inclining the forehearth at an angle to horizontal of no more than about 30 degrees to horizontal, the angle causing a distal end of the forehearth furthest from the melter exit structure to be raised above a horizontal plane, while a proximal end of the forehearth remains at a level equal to that of the melter exit;
• and
• d) drawing the molten material comprising bubbles through the bushings to produce glass fibers comprising a plurality of interior regions substantially devoid of glass.