Reducing pressure drop in microscale channel using constructal theory

• Main Author: Cheng, Kai Xian
• Other Authors: Ooi Kim Tiow
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/63970
• Institution: Nanyang Technological University

The augmented heat transfer in the semiconductor industry proves the effectiveness of microchannels in enhancing heat transfer. In order to tap the microscale heat transfer into macro geometries, overcoming the cost and technological constraints, microchannels are created in macro geometries using conventional methods to achieve a heat transfer coefficient exceeding 10 kW/m2•K [1]. Surface profiles were created on the heating region of the insert to enhance steady-state single-phase liquid heat transfer. However, the heat transfer enhancement was accompanied by undesirable pressure drop increment. This project aims to address the high pressure drop issue using the Constructal theory, a universal design law for both animate and inanimate systems. Two designs based on Constructal theory were used to study the effectiveness of constructal features in reducing the pressure drop increment as compared to parallel channels which are ubiquitous in microchannel fabrication. The hydrodynamic and heat transfer performance for Tree insert and Cfin insert were studied using experimental methods, and the underlying mechanism was substantiated by numerical results. In technical terms, the objective is to achieve at least comparable increment in both heat transfer coefficient and pressure drop, if not higher increment in the former parameter Results show that the Tree insert improved the heat transfer of the microchannel by more than 16 percent at low flow rates, as compared to the Tree-parallel insert. However, the heat transfer enhancement reduced to less than 5 percent beyond the laminar region. On the other hand, the pressure drop increment stayed almost constant at 20 percent. This suggests that the Tree insert has desirable heat transfer and hydrodynamic effects, particularly in the laminar region. More importantly, results show that, the Cfin insert improved both the heat transfer and hydrodynamic performance, as compared to Cfin-parallel insert, at all flow rates in this study. The enhancement of heat transfer was more than 30 percent at 2 L/min at only 20 percent pressure drop increment as compared to Cfin-parallel insert. Furthermore, comparable increment in both heat transfer coefficient and pressure drop was observed at 8 L/min. This phenomenon is rarely seen in conventional microchannels. This suggests that the Cfin insert successfully achieved the objective of this project. Analysis of the results suggests that bifurcation of flows is effective in reducing the increment in pressure drop relative to heat transfer enhancement. Optimizing the geometries of the constructal fins is therefore the potential future study in achieving bigger stride in energy efficiency at much lower costs.