The tube-fin exchanger is used to contain the high-pressure fluid on the tube side if only one fluid is at a high pressure. Fins on the liquid or phase-change side generally have "low" heights. to provide reasonably high fin efficiencies. Turb may be used within tubes for flow mixing. Tube-fin exchangers with or without shells are designed to cover the operating ten perature range from low cryogenic temperatures to about 870 C (1600 F) For ultra high temperature (870 to 2000 C (1600 to 3600 F) and near-atmospheric pressures, as in high-temperature waste heat recovery, either rotary regenerators (870 to l 100 C) or fixed-matrix regenerators (up to 2000 C) are used