Thermal management systems

A thermal management system comprising:

• a refrigerant receiver configured to store a refrigerant fluid;
• at least one evaporator that removes heat from a heat load converting a portion of the refrigerant fluid to refrigerant vapor;
• a liquid separator having an inlet, a liquid side outlet, and a vapor side outlet;
• a pump that pumps the refrigerant fluid, the pump having a pump inlet coupled to the liquid side outlet of the liquid separator;
• a closed-circuit refrigeration system having a closed-circuit fluid path that includes the refrigerant receiver, the liquid separator, the pump, and the at least one evaporator, the closed-circuit refrigeration system further comprising:
• a compressor coupled to the vapor side outlet of the liquid separator;
• and
• a condenser coupled to an outlet of the compressor, with refrigerant liquid from the condenser returning to the refrigerant receiver;
• an open-circuit refrigeration system having an open-circuit fluid path that includes the refrigerant receiver, the liquid separator, the pump, and the at least one evaporator, the open-circuit refrigeration system further comprising:
• a controllable back-pressure regulator having a back-pressure regulator signal input configured to receive a set point pressure signal from a controller and controllably open and close to govern a rate of exhaust of refrigerant vapor based on the set point pressure signal, a back-pressure regulator inlet, and a back-pressure regulator outlet, with the controllable back-pressure regulator configured to receive refrigerant vapor at the back-pressure regulator inlet from the vapor side outlet of the liquid separator;
• and
• an exhaust line coupled to the back-pressure regulator outlet of the controllable back-pressure regulator, with refrigerant vapor from the exhaust line not returning to the refrigerant receiver, wherein the controllable back-pressure regulator is configured to govern the rate of exhaust of refrigerant vapor through the exhaust line by controllably opening and closing based on the set point pressure signal received at the back-pressure regulator signal input, wherein the at least one evaporator is configured to provide a first cooling capacity based at least in part on the controller controlling the controllable back-pressure regulator to a closed configuration, and provide a second cooling capacity that is greater than the first cooling capacity based at least in part on the controller controlling the controllable back-pressure regulator to an open configuration;
• and
• a junction comprising an inlet fluidly connected to an outlet of the at least one evaporator, a first outlet fluidly coupled to the exhaust line, and a second outlet fluidly coupled to a suction of the compressor.