A cooling system includes a device to be cooled and a cooling device integrated with the device to be cooled. A cooling volume has cavities and active coolant flow controls configured to adjust coolant flow through the cavities. A reservoir is in fluid communication with the cavities and has a liquid outlet and an inlet for a gas or gas-liquid mixture. A two-phase coolant is in the reservoir and cavities. The two-phase coolant has a phase transition temperature between an ambient temperature and an expected device temperature. A capacitance sensor is configured to determine a coolant capacitance in the cavities. A control module is configured to determine a vapor quality and void fraction of the coolant based on the measured capacitance and to increase coolant flow if the determined vapor quality and void fraction indicate a dry-out condition. A secondary cooling line removes heat from the cooling device.