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Thermofluidic analysis and design of passive two phase heat transfer devices for electronics cooling applications
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Date
2025-12
Abstract
Fifth generation wireless cells rely on a dense network of high-power integrated circuits (ICs) to deliver high-speed, low-latency data transmission. While essential for performance and power efficiency, high packing densities lead to thermal crosstalk, where heat from one IC adversely affects the performance of others. To mitigate this, passive thermal management strategies have been proposed that enable thermal segregation. In particular, the use of thermally-partitioned heat sinks in conjunction with embedded heat pipes has emerged as a promising solution. However, severe spatial constraints and complex routing requirements pose significant challenges to the effective deployment of heat pipes. In particular, it has been extensively documented that bending-induced deformation degrades performance. This thesis investigates the physical mechanisms and performance impacts of bending-induced deformation in heat pipes, with the objective of enhancing their performance for deployment in 5G wireless cells. In pursuit of this, three aspects were considered:
Firstly, a thermoelectric-based methodology for the performance characterization of heat pipes was developed. High-precision heat flow measurement assemblies, comprising cubic copper interface blocks and thermoelectric modules, were used to directly measure the flow of heat, while precise, well-calibrated (± 0.01 K) thermistors were used to monitor surface temperature uniformity. Compared to existing methodologies, this approach reduced measurement error by up to 20%, reduced measurement uncertainties to less than ± 3.8% (thermal resistance) and ± 3% (heat transfer limit), and increased characterization throughput by up to 400%.
Secondly, an experimental investigation was carried out, and a thermo-fluidic model was developed to analyze the performance of deformed, multiple heat source heat pipes. The model, incorporating a semi-empirical methodology to account for bending-induced deformation, was validated against new and existing data, indicating agreement within ± 8% (thermal resistance) and ± 7.5% (heat transfer limit). The results revealed that heat source distribution significantly influences performance. The addition of a single source closer to the condenser increased the heat transfer limit by over 7.75 W (75%) but reduced the limit of the most distant heat source by 1.25 W (10%). Bending reduced the heat transfer limit by up to 5 W (26.7%) per bend, with minimal effect on thermal resistance, indicating wick deformation is the primary degradation mechanism. Furthermore, bending-induced performance losses were found to be cumulative and, for multiple heat source heat pipes, dependent on bend location.
Lastly, a screen mesh heat pipe featuring enhanced resilience to the degenerative effects of bending-induced deformation was designed and fabricated. A novel manufacturing method was employed, wherein the cross-members of the screen mesh wick were oriented on a bias relative to the longitudinal axis of the heat pipe. This approach enhanced the flexibility and pliability of the wick. The results revealed that the biased wick heat pipe exhibited minimal degradation, with the heat transfer limit decreasing by no more than 2.5 W (6%) after bending. In contrast, the conventional orthogonal wick heat pipe exhibited significant degradation of up to 15 W (27.3%) due to severe wick deformation, as confirmed through Micro-CT (MCT) imaging. Additionally, deformation was postulated to extend beyond the bend region, highlighting the importance of minimizing bend proximity to evaporator and condenser regions to avoid increased thermal resistance.
Cumulatively, the findings of this thesis advance the field of passive thermal management by delivering novel characterization methodologies, modelling tools, and manufacturing approaches tailored to enhancing the performance of deformed, multiple source heat pipes for deployment in 5G and future wireless cells.
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University of Limerick
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Sustainable Development Goals
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Attribution-NonCommercial-ShareAlike 4.0 International