Rapid and Tunable Cooling Technology for Vacuum Furnaces

The need for high temperature furnaces for neutron scattering experiments has been increasing considerably. One of the major limiting factors of these furnaces is the cooling rate. Currently, the vacuum furnace relies on the radiation to dissipate heat, takes at least 5 hours to cool the furnace to room temperature resulting in significant limitation of using expensive neutron beam time. To tackle this challenge, ACT proposes an innovative active cooling system to significantly reduce the down time for neutron scattering furnaces. The system includes a closed helium (He) circulation loop, a flow distributor nozzle, an external heat exchanger, and a chiller to achieve fast and controllable cooling. Due to the much higher thermal conductivity of the He gas compared to other inert gases (e.g. nitrogen, argon), heat can be removed from the system more effectively. By introducing the He flow inside the radiation shields via a flow distributor nozzle, the cooling rate can also be controlled by adjusting the flow rate. The proposed active cooling system has no consumables (full recycling of the helium) and requires minimal human operation. In Phase I, a prototype neutron scattering vacuum furnace was fabricated with the support from Oak Ridge National Laboratory (ORNL). The furnace served as a platform to test the proposed He circulation cooling system. Under vacuum conditions, the system required 6.6 hours for the heating element to be cooled from 400oC to 100oC. By using a flow distributor nozzle to introduce the He flow into the radiation shield and heating element, the cooling rate can be further reduced to 11 minutes. With the capability of controlling the cooling rate, the team has demonstrated the feasibility of achieving a linear temperature drop (constant cooling rate). The controllability together with low neutron scattering and adsorption coefficients of helium provide the potential of in-situ cooling for advanced material experiments. This will allow experimenters to perform controlled transient thermal tests that could not have been done before. In Phase II, ACT will continue working with ORNL to optimize the system performance. A control method will be developed to achieve precise controlled cooling rate. The cooling system will be integrated into one neutron furnace at ORNL to demonstrate the cooling performance under actual neutron experiment. In addition to the neutron furnace, the proposed cooling technology is able to be applied to most heat treatment furnaces that can be benefited from fast and controlled cooling.