This device uses a thermal sensing bulb at the outlet of the evaporator to sense temperature and control superheat.

The thermostatic expansion valve (TXV) is designed to control the flow of refrigerant in an HVAC system based on the temperature of the vapor returning from the evaporator. It utilizes a thermal sensing bulb placed at the outlet of the evaporator to monitor the temperature of the refrigerant. This sensor is crucial because it allows the TXV to adjust the amount of refrigerant flowing into the evaporator, thus controlling the superheat.

Superheat is the difference between the actual temperature of the refrigerant vapor and its saturation temperature at the corresponding pressure. Controlling superheat is essential for an efficient and safe HVAC operation; too little superheat can result in liquid refrigerant entering the compressor, while too much can indicate insufficient refrigerant flow and result in reduced cooling capacity.

By sensing the temperature at the outlet and controlling the refrigerant flow accordingly, the thermostatic expansion valve ensures optimal performance of the cooling system, enhancing efficiency and preventing potential damage.

The other devices mentioned do not utilize a thermal sensing bulb to control superheat in the same manner, making the TXV the correct choice.