Numerical Study of the Temperature Effects on Heat Transfer Coefficient in Mini-Channel Pin-Fin Heat Sink
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-02-28 |
| Journal | International Journal of Heat and Technology |
| Authors | Nabil Bessanane, Mohamed SiâAmeur, Mourad Rebay |
| Institutions | Université de Reims Champagne-Ardenne, University of Batna 1 |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis numerical study investigates flow and heat transfer characteristics in mini-channel heat sinks, focusing on developing a robust method for calculating the Heat Transfer Coefficient (HTC) in complex geometries used for high-flux cooling.
- Core Innovation: A Variable Reference Temperature (VRT) approach was developed and validated to accurately estimate the wall-fluid temperature difference (ÎTm), which is critical for calculating the local and averaged HTC in mini-channels where fluid temperature varies significantly.
- Performance Comparison: Diamond-shaped Pin-Fin Heat Sinks (PFHS) arranged in a staggered configuration demonstrated superior thermal performance compared to simple Rectangular Mini-Channels (RMC), even at lower mass flow rates.
- Validation Success: The numerical procedure, utilizing the Realizable k-Δ turbulence model, was successfully validated against experimental pressure drop and averaged HTC data from literature and Synchrotron SOLEIL prototypes.
- HTC Profile Accuracy: The VRT approach yielded a physically consistent HTC profile that maintained a constant value in the thermally established region, unlike traditional methods (using Tin, Tbulk, or Tout-in average) which produced non-physical discontinuities (ÎT = 0) or exaggerated entrance effects.
- Geometric Effects: The local HTC profile in PFHS exhibits a characteristic zigzag curvature due to the periodic alternation of high heat flux on the pin front faces and low heat flux in the recirculation zones behind the pin back faces.
- Application Context: The research directly supports the optimization of cooling systems for high heat flux components, such as absorbers and mirrors in Synchrotron facilities (tested flux: 100 kW/m2).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Heat Sink Length (L) | 100 | mm | Overall geometry |
| Heat Sink Width (W) | 16 | mm | Overall geometry |
| Heat Sink Height (H) | 1.6 | mm | Overall geometry |
| Pin-Fin Shape | Diamond | N/A | Square section (1.7 x 1.7 mm2) oriented at 45° |
| Base Thickness | 3 | mm | Top and bottom planes of the domain |
| Applied Heat Flux (q) | 100 | kW/m2 | Constant flux imposed on the solid bottom |
| Fluid Passage Spacing (e) | 0.35 to 1.6 | mm | Varied geometric parameter |
| Coolant Fluid | Water (implied, based on Tin and application) | N/A | Thermo-physical properties vary polynomially |
| Inlet Temperature (Tin) | 303 | K | Fixed fluid inlet condition |
| Outlet Pressure | 3 | bars | Fixed outlet condition (based on experimental data) |
| Mass Flow Rate (m) | 0.05 to 3 | kg/mn | Range tested, corresponding to varying Reynolds numbers |
| Maximum Re Tested (PFHS) | ~6000 | N/A | Used for comparison with experimental data |
Key Methodologies
Section titled âKey Methodologiesâ- Numerical Solver: Computational Fluid Dynamics (CFD) simulations were performed using the ANSYS FLUENT code, employing the Finite Volume Method approach.
- Turbulence Model: The Realizable k-Δ turbulence model was selected as optimal, coupled with âEnhanced-Wall-Treatmentâ to ensure accurate resolution of velocity and temperature gradients near the walls, crucial for mini-channel analysis.
- Conjugate Heat Transfer: Conjugate conduction-convection heat transfer was modeled at the fluid-solid interfaces (pin walls and channel base). Radiation effects were neglected.
- Grid Independence: An unstructured mesh (1 to 2 million nodes) was adapted to the complex geometry. Grid independence was confirmed when deviations in averaged HTC and fluid temperature were less than 2% between successive refinements.
- Variable Reference Temperature (VRT) Approach:
- The reference fluid temperature (Tf) used for calculating HTC was defined as the local average fluid temperature (Tave(x)) measured along the channel axis (the middle face), opposite the pin face.
- This VRT method ensures that the temperature difference (ÎTm = Tw - Tf) remains positive and physically meaningful throughout the channel length, especially in the thermally developing region.
- HTC Calculation: Local face-average HTC (have(i)) was computed for each pin face (front and back) using the local average heat flux (qw,ave(i)) and the VRT approach for the temperature difference. The global average HTC (h) was then calculated as the arithmetic mean of all N pin face averages.
- Correlation Development: Simplified fit functions (power laws) were developed to correlate the averaged HTC (have) as a function of the Reynolds number (Re) for both RMC and PFHS configurations, useful for engineering design.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings regarding optimized heat transfer coefficient calculation and the superior performance of PFHS are highly relevant for industries requiring compact, high-efficiency thermal management solutions:
- High-Performance Computing (HPC): Cooling high-density microprocessors and GPUs where heat fluxes routinely exceed 100 W/cm2.
- Hydrogen Fuel Cells: Enhancing heat dissipation within fuel cell stacks to maintain optimal operating temperatures and improve efficiency.
- Aerospace and Defense: Thermal management in compact electronic warfare systems, avionics, and power electronics where size and weight constraints are critical.
- Scientific Instrumentation: Direct application in cooling high-power optical components (mirrors, monochromators, absorbers) used in Synchrotron facilities (like SOLEIL) and high-energy laser systems.
- Power Electronics: Cooling IGBT modules and inverters in electric vehicles and renewable energy systems where reliable heat extraction is essential.
View Original Abstract
Pin-fins are frequently used to increase the heat transfer surface and promote turbulent motion, which improves the devices cooling process by enhancing heat dissipation, as in hydrogen fuel cells applications. The application has burst out this last decade and became vital in several industrial devices. The present study is a numerical investigation of flow and heat transfer in rectangular mini-channels (RMC) and pin-fin heatsinks (PFHS). The pin-fins have a diamond shape arranged in segregated disposition (corrugated channel). In order to adequately calculate the heat transfer coefficient within this complex thermal system; several parameters, such as mass flow rate, geometry dimensions, heat flux and reference temperature are extensively examined. The importance in way the reference temperature was calculated was highlighted. A correct estimation of the heat transfer coefficient led to a better optimisation of the cooling process performances. The aim of this study was to elaborate a technique to correctly estimate the temperature difference between the cooler fluid and the heat sink wall, leading to a better approach for heat transfer coefficient estimation. For this purpose, an approach with variable reference temperature (VRT) has been adopted in the calculation of the wall-fluid temperature difference. Flow field and heat transfer are analysed qualitatively (visualisations of sensible zones) and quantitatively (profiles of heat transfer coefficient, heat flux, wall and fluid temperaturesâŠ). The numerical procedure has been validated by experimental measurements. The results showed that the proposed approach to calculate the reference temperature leads to a better presentation of the heat transfer coefficient. In addition, new fit function was involved, in particular the variation of the averaged heat transfer coefficient against Reynolds number.