Rapid and Tunable Cooling Technology for Vacuum Furnaces

C49-18a-271181The 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 radiation to dissipate heat and takes at least 2 hours to cool the furnace low enough to safely open for a sample change. This results in significant limitations of using expensive neutron beam time. To tackle this challenge, ACT proposes an innovative active cooling system to significantly reduce neutron scattering furnaces’ downtime. The system includes a closed helium (He) circulation loop, industrial-grade process control, furnace flow distribution nozzles, and a built-in refrigeration unit 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 and overall system pressure. The thermal characteristics and low neutron scattering and adsorption coefficients of He provide the potential for in- situ cooling for advanced material experiments. This will allow experimenters to perform controlled transient thermal tests that could not have been done before. The proposed active cooling system has very low He usage (closed-loop circulation) and requires a minimal human operation. During Phases I and II, a fully operational and mobile prototype cooling system was constructed and tested in the field with an operational HOT-006 neutron furnace at Oak Ridge National Laboratory (ORNL). The He cooling system managed to cool the heating element from 500°C to 100°C in just 8 minutes, a 17 times improvement compared to 2.24 hours for the original radiation-only cooling approach. The thermal stresses on the coil were evaluated, and a proof-of-concept constant cooling rate approach was demonstrated. The successful test at ORNL brings the technology to TRL (Technology Readiness Level) to 7. In Phase IIA, ACT will continue working with ORNL to refine the cooling system, extend its capabilities, and further push for the commercialization of the technology. It will be achieved by extended long-term usage tests at ORNL during mock and live neutron scattering experiments. Furthermore, the capabilities of the cooling system will be extended to include rapid sample quenching and a closed-loop controlled cooling rate. The cooling system will also be validated for operation with a cheaper, lower-performance circulation gas medium (nitrogen, argon) with our special nozzle design. ACT will also explore new industrial applications, such as specialized metal manufacturing (via high-pressure gas quench) and high-quality brazing (via controlled cooling rate inside the process furnace) that can be benefited from the proposed inert gas circulation cooling technology. In addition to the high-temperature neutron furnace cooling efforts, ACT will also investigate a novel cryogenic cooling method to aid ORNL with the long cooldown time of dry He cryostats. ACT aims to reduce a 2-hour cooldown time (300K to 80K) to less than 10 minutes with the innovative sample holder with embedded two-phase nitrogen flow. A range of unique solutions will be utilized to improve the heat exchange limited by the Leidenfrost effect. The impact of reduced cooldown time on cryogenic experiments turnaround should be similar to the effect of a cooling system on neutron furnaces.