Abstract: An icemaking apparatus includes an evaporator tube, a driving vessel charged with liquid ammonia and a driving gas, a heat source, a return system, and a target material reservoir adapted to be placed in an operating position over the evaporator tube. The evaporator tube has a heat transfer feature formed on and extending from a generally cylindrical outer evaporator tube surface. The heat source applies heat to the driving vessel to force liquid ammonia through an evaporator supply line to an expansion chamber inlet associated with the evaporator tube. The liquid ammonia goes to a gas as it enters the expansion chamber portion of the evaporator tube resulting in a transfer of heat from water or other target material contained in the target material reservoir secured over the evaporator tube in the operating position. The return system returns ammonia and hydrogen gas from the evaporator to the driving vessel.