Neutron Imaging of an Unbalanced Flat-Plate Oscillating Heat Pipe

Monroe, J. G., Thompson, S.M., Aspin, Z. S., Jacobson, D. L., & Hussey, D. S. (2013). Neutron Imaging of an Unbalanced Flat-Plate Oscillating Heat Pipe. AIAA 52nd Aerospace Sciences Meeting 2014 at the AIAA SciTech Forum. National Harbor, MD: AIAA. 10, 8047. DOI:10.2514/6.2014-0859.

Abstract

The flat-plate oscillating heat pipe is a two-phase heat transfer device that consists of a hermetically-sealed, flat substrate with milled mini/micro channels along its surface that form a closed-loop. The start-up and heat transfer performance of a FP-OHP is dependent upon many parameters including: channel geometry, working fluid, filling ratio, orientation and heat input. The current experimental investigation focuses on the thermal performance and start-up behavior of a copper FP-OHP with non-equal channel lengths, i.e. ‘unbalanced’ design, and a copper FP-OHP with equal channel lengths, i.e. ‘balanced’ design, at different heat inputs. Using neutron radiography to see the working fluid directly inside each FP-OHP, statistical assessments of the internal fluid dynamics were made. Both FP-OHPs were charged with water at a filling ratio of approximately 80 % and each had bulk dimensions of 127 mm x 76.2 mm x 3.2 mm consisting of 20 channel sections each having a square, 1.5 mm x 1.5 mm cross-section. The FP-OHPs were experimented in the vertical, bottom-heating orientation at cooling temperature of either 20ºC or 60ºC. Results indicate that the unbalanced design provides for a higher effective thermal conductivity and enhanced fluid circulation in the evaporator for both cooling temperatures investigated. The balanced design, however, began circulation at a lower heat input and provided for a higher maximum heat input than the unbalanced design.