Thermal management system

A gas turbine engine comprising:

• a turbomachine;
• and
• a thermal management system comprising
• a first heat exchanger configured to collect heat from the turbomachine during certain operations;
• a second heat exchanger;
• and
• a thermal transport bus configured to have a heat exchange fluid flow therethrough at a pressure within an operational pressure range, the first heat exchanger and second heat exchanger each fluidly coupled to the thermal transport bus such that the first heat exchanger is operable to transfer heat to the heat exchange fluid during at least the certain operations and the second heat exchanger is operable to transfer heat from the heat exchange fluid during at least the certain operations, the thermal management system defining an operational temperature range for the heat exchange fluid, the operational temperature range having a lower temperature limit less than about zero degrees Fahrenheit at a pressure within the operational pressure range and an upper temperature limit of at least about 1000 degrees Fahrenheit at a pressure within the operational pressure range.