Which device is used to protect a heat exchanger from overpressure?

The correct choice is the thermal expansion safety relief valve, which is crucial for protecting a heat exchanger from overpressure. This device is designed to automatically release excess pressure that may build up inside the heat exchanger due to thermal expansion of the fluid when it is heated. If the temperature and, consequently, the pressure within the heat exchanger exceed safe levels, the thermal expansion safety relief valve opens, allowing the excess pressure to escape and preventing potential damage or catastrophic failure of the system.

This is critical in systems where fluids can expand significantly when heated, as the pressure increase can lead to structural failure of the heat exchanger or other components, creating safety hazards. By allowing steam or other gases to vent, the safety relief valve maintains a secure operating environment within the system.

Thermostats, flow meters, and pressure gauges serve different functions: thermostats regulate temperature, flow meters measure the rate of fluid flow, and pressure gauges provide information about the pressure within a system. While relevant to system operation, they do not directly protect the heat exchanger from overpressure in the way that a thermal expansion safety relief valve does.