A humid air turbine cycle (HAT Cycle) has been proposed and studied for use in power generation. Its proponents claim a number of techno-economic advantages over other power cycles, but it has yet to become widely used in practice. Nonetheless, THERMOFLEX is a perfect tool to analyze potential cycle performance and behaviour. This model (sample file named (S5-04)HAT_Cycle.tfx on the Thermoflow CD) illustrates a HAT Cycle with 52% nominal efficiency that uses 48:1 compressor pressure ratio and a combustor exit temperature of 1400 °C. Red lines carry air or combustion products, blue lines carry water or steam. Four separate compressor sections, and three expander groups comprise the turbomachinery shown in the yellow region. This cycle incorporates the practical reality of expander cooling by extracting air from the compressor. The compressor uses both inter- and after-cooling. Compressed air is humidified in a saturator prior to combustion. Exhaust heat is recovered in a recuperator that preheats humid air. Further heat recovery from exhaust gas stream preheats water for admission to the saturator.