Abstract

Numerical simulations were performed using Fluent 14.5 to investigate single phase flow and conjugate heat transfer in copper rectangular microchannels. Two different configurations were simulated: (1) single channel with hydraulic diameter of 0.561 mm and (2) multichannel configuration consisting of inlet and outlet manifolds and 25 channels with hydraulic diameter of 0.409 mm. In the single channel configuration, four numerical models were investigated namely, 2D thin-wall, 3D thin-wall (heated from the bottom), 3D thin-wall (three side heated) and 3D full conjugate models. In the multichannel configuration, only 3D full conjugate model was used. The simulation results of the single channel configuration were validated using experimental data of water as a test fluid while the results of the multichannel configuration were validated using experimental data of R134a refrigerant. In the multichannel configuration, flow distribution among the channels was also investigated. The 3D thin-wall model simulation was conducted at thermal boundary conditions similar to those assumed in the experimental data reduction (uniform heat flux) and showed excellent agreement with the experimental data. However, the results of the 3D full conjugate model demonstrated that there is a significant conjugate effect and the heat flux is not uniformly distributed along the channel resulting in significant deviation compared to the experimental data (more than 50%). Also, the results demonstrated that there is a significant difference between the 3D thin-wall and full conjugate models. The simulation of the multichannel configuration with an inlet manifold having gradual decrease in cross sectional area achieved very reasonable uniform flow distribution among the channels which will provide uniform heat transfer rates across the base of the microchannels.

Highlights

  • Microchannel heat exchangers have several advantages over macro scale ones due to their high surface-to-volume ratio and their small overall volume

  • Investigate flow phenomena in microchannels. These researchers focused on understanding the characteristics of heat transfer and fluid flow at the micro scale level in order to improve the design and optimize the performance of microchannel heat exchangers

  • 2D, 3D thin-wall, 3D thin-wall and 3D fully conjugated heat transfer model in a single channel system to consider the conjugate effect on heat transfer

Read more

Summary

Introduction

Microchannel heat exchangers have several advantages over macro scale ones due to their high surface-to-volume ratio and their small overall volume. The growing interest in micro heat exchangers and their applications especially in cooling high-heat-flux devices such as electronic systems motivated many researchers to investigate flow phenomena in microchannels. The discrepancies reported in the literature can be due to measurement uncertainties and scaling effects as reported by Rosa et al [9] They concluded that macro scale theory and correlations are valid at micro scale if measurement uncertainty and scaling effects were carefully considered. These scaling effects include: entrance effects, viscous heating, conjugate heat transfer, electric double layer effects, surface roughness, and properties dependent on temperature, compressibility and rarefactions (for gas flow only)

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call