A thermal-management system, for use in controlling temperature of a first workpiece of workpieces being joined by welding. The system includes a micro heat exchanger including a heat-transfer fluid tube extending between an inlet and an outlet. The system in some implementations has a body and the inlet and outlet are connected to the body. The heat-transfer fluid tube is configured to channel heat-transfer fluid, such as a nanofluid, to heat or cool the workpiece(s). The heat-transfer fluid is configured to cool or heat at least the first workpiece when the heat-transfer fluid is channeled through the heat-transfer fluid-tube section in operation of the thermal-management system. The technology further includes methods and hardware-based controlling apparatus for using the micro heat exchanger to cool or heat the workpieces.