Two-phase liquid immersion cooling has not yet reached its full potential because of two technological issues. The first issue is the boiling crisis and the second is the reliability risk caused by ...the immersed components, which are designed to work in air cooling applications. Experimental and numerical studies were performed to find the heat transfer limits of immersion cooling of microprocessor and new heat transfer design parameters are proposed. Pool boiling experiments were performed on bare copper surfaces for two dielectric fluids, Novec 649 and Novec 7100, and the critical heat fluxes were found to be 19.5 W/cm 2 and 23.8 W/cm 2 , respectively. Three-dimensional conduction models of a microprocessor were built to predict the junction temperature and junction-to-ambient thermal resistance. Effect of the integrated heatsink (IHS) thickness at different heat transfer coefficients have been investigated and the optimal thickness for the IHS is predicted to be around 4 mm while the heat transfer coefficient is less than 20 000 W/m 2 K on the IHS. Boiling directly on the silicon die has been studied, in order to examine the effect of a decreased thermal resistance by removing the thermal interface material and IHS. In this case, the heat transfer coefficient is predicted to be more than 20 000 W/m 2 K and to have better heat dissipation.
•SiNW, SiMP, and SiNW/MP two-tier structure were employed to enhance immersion cooling of Novec 649.•Novec 649 possesses low global warming potential and therefore it is environmentally ...benign.•Compared to a plain SiO2 surface, the CHF and HTC could be enhanced by 30% and 455%, respectively, on the SiNW/MP surface.•This result suggests the efficacy of the SiNW/MP two-tier structure for enhancing immersion cooling.
Continual increases in the functionality and miniaturization of electronic devices have resulted in a rapid increase in the power density of such devices. Thus, an efficient cooling technology is required to maximize heat dissipation and prevent electronic failure. Immersion cooling is a promising technique for the thermal management of high-power-density electronics. However, common working fluids in immersion cooling have high global warming potential, and the heat transfer performance of immersion cooling requires improvement to achieve efficient cooling of state-of-the-art high-power-density electronics. In this study, Novec 649, which has low global warming potential and a low boiling point, was applied as a working fluid for immersion cooling. A Si nanowire (SiNW) array, Si micropillar (SiMP) array, and Si nanowires on a Si micropillar (SiNW/MP) two-tier structure were employed to enhance boiling performance. The SiMP surface exhibited the highest critical heat flux (CHF) of 23.5 ± 1.3 W/cm2, whereas the SiNW surface exhibited the lowest CHF but a relatively high heat transfer coefficient (HTC). The SiNW/MP surface exhibited the highest HTC of 23611.7 ± 1586.2 W/m2 K and a relatively large CHF of 17.4 ± 1.2 W/cm2. Compared with a plain SiO2 surface, the CHF and HTC of the SiNW/MP two-tier structure could be enhanced by 30% and 455%, respectively. These results suggest that the SiNW/MP surface is effective for enhancing immersion cooling.
A thermosyphon loop, designed for the thermal management of a large Medium voltage power converter 5 MW overall, corresponding to a 2.4 kW thermal load per cooling unit) is presented. The device is ...mainly made of an evaporator, a condenser and a reservoir connected with plastic liquid and vapor lines. Novec 649 (3M) has been chosen as the working fluid due to environmental and electrical concerns. A model of the loop is described, and its predictions are compared with experiments. A first comparison yields a maximum mean deviation of 20 % between experimental results and numerical simulation at the maximum coolant temperature. The main sources of errors are identified, and improvements are proposed for better model accuracy.
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•Selection of an environment-friendly fluid (Novec 649).•Entire model of the loop thermo-syphon is presented.•Experimental validation on a full-scale protype (up to 2400 W thermal load) shows <20% deviation.
Increasing heat dissipation requirements of small and miniature devices demands advanced cooling methods, such as application of immersion cooling via boiling heat transfer. In this study, ...functionalized copper surfaces for enhanced heat transfer are developed and evaluated. Samples are functionalized using a chemical oxidation treatment with subsequent hydrophobization of selected surfaces with a fluorinated silane. Pool boiling tests with water, water/1-butanol mixture with self-rewetting properties and a novel dielectric fluid with low GWP (Novec™ 649) are conducted to evaluate the boiling performance of individual surfaces. The results show that hydrophobized functionalized surfaces covered by microcavities with diameters between 40 nm and 2 µm exhibit increased heat transfer coefficient (HTC; enhancements up to 120%) and critical heat flux (CHF; enhancements up to 64%) values in comparison with the untreated reference surface, complemented by favorable fabrication repeatability. Positive surface stability is observed in contact with water, while both the self-rewetting fluids and Novec™ 649 gradually degrade the boiling performance and in some cases also the surface itself. The use of water/1-butanol mixtures in particular results in surface chemistry and morphology changes, as observed using SEM imaging and Raman spectroscopy. This seems to be neglected in the available literature and should be focused on in further studies.
Characterisation results of the complex permittivity of select dielectric cooling fluids at room temperature and over a broad frequency range found using a low-loss printed circuit board microstrip ...ring resonator technique are presented. ANSYS HFSS, a finite-element full-wave electromagnetic simulation environment, was used to fit the simulated insertion loss to the calibrated measurements of the microstrip ring resonator in air and submerged in different dielectric fluids. The resulting frequency-dependent relative permittivity and loss tangent are provided up to 50 GHz for three dielectric cooling fluids: 3M™ Novec™ 649, 3M™ Novec™ HFE-7100 and 3M™ Fluorinert™ FC-72.
This study compares three different liquid cooling technologies to determine which of the three methods is able to cool the highest power density processor chips. The first method consists of pumping ...a liquid coolant through a cold plate mounted over a 25.4 mm square heat source. The second method is two-phase immersion cooling of the 25.4 mm square heat source in a bath of 3M Novec® 649 liquid with a boiling point of 49°C. The third method of cooling consists of single-phase immersion cooling of the 25.4 mm square heat source using mineral oil as the coolant. This method was tested under both natural convection and forced convection conditions. An experimental setup, consisting of a heater module with attachment to the cooling solution was designed and built. The apparatus was used to determine the maximum power dissipation that can be supported in a 25.4 mm x 25.4 mm area for each of the three cooling solutions. Note that uniform power dissipation is assumed over the die surface. The measured temperature is assumed to be equivalent to the temperature of a die with the same surface area. The maximum die temperature was set to 100 °C and the power required to reach that temperature was recorded for each of the cooling methods.
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