Rapid and Tunable Cooling Technology for Vacuum Furnaces

In response to DOE’s SBIR topic 18-a, “Instrumentation and Tools for Materials Research Using Neutron Scattering: a. Advanced Sample Environments”, Advanced Cooling Technologies, Inc. ACT) proposes a novel thermal management system for improving the cooling rate of the high temperature vacuum furnaces. The proposed method is able to achieve up to 18X cooling rate comparing to the current-state- of-art cooling methods. The increased cooling rate significantly reduces the down time for several types of high-throughput experiments. 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. While back filling with nitrogen has been explored to increase the cooling rate, the low thermal conductivity of nitrogen limits heat transport improvement. In addition, the limited nitrogen flow rate due to thin wall thickness of the radiation shield) and small channel width result in laminar flow that has fixed heat transfer coefficients. Moreover, nitrogen has relatively higher neutron absorption and scattering coefficients, which prevent it from in-situ cooling. To tackle this challenge, ACT proposes to circulate high thermal conductivity helium into the furnace with self-induced vortexes between the radiation shields to provide a fast and controllable convective heat transfer path between the heat sources and the cooling water sink. The helium stream is designed to tangentially flow inside the circular channels of radiation shields. The centrifugal instability will create Dean vortices even at low Reynolds numbers Re). Special designed vortex generators VG) that match the dominant vortices frequency mode is applied to further amplify the vortices intensity and therefore the convective heat transfer. Since the vortices intensity can be tuned at slow flow rates, the cooling rate is controllable. The proposed method will not consume helium. After the furnace is cooled down to room temperature, the helium will be evacuated out and stored in a reservoir for repeated use. The main benefits for this solution are: Reduce in the cooling time from > 5 hours to about 20 minutes, Enable in-situ cooling with controllable cooling rate, Can easily be applied to retrofit the existing furnace, No consumables such as venting inert gases). The Phase I work will focus on demonstrating the cooling rate improvement of the proposed vortex generator design. The relation between helium flow rate and the overall thermal resistance will be determined to establish the controllability of the cooling rate. In Phase II, ACT will incorporate the Phase I design into the state-of-the-art MICAS furnace to evaluate the cooling rate improvement. Integration issues, such as leak check via using non-helium detector e.g. forming gas detector) will be addressed. The signal-to-noise ratio during the operation of helium cooling loop will also be measured to determine the feasibility of in-situ cooling. In addition, other applications such as using the proposed concept for improving cryostat heating rate will be explored.