Experimental Investigation of the Effect of Heat Spreading on Boiling of a Dielectric Liquid for Immersion Cooling of Electronics

This paper investigated the effect of heat spreading on the boiling of the Novec 649TM for two-phase immersion cooling of electronics. Reference pool boiling tests were performed by attaching a 25.4 by 25.4 mm square plate square copper plate to a same-sized heater, thus minimizing lateral heat spreading. Experimental measurements showed that the critical heat flux (CHF) happened at a heat flux of 17.4 ±0.8 W/cm2. Then, lateral heat spreading through the heat spreader was studied by attaching larger (47 mm by 47mm) spreaders with four different thicknesses to the copper plate. With an increase in the integrated heat spreader (IHS) thickness from 1 mm to 6 mm, the CHF increased by more than 60% at the saturation condition. One plate was a 1 mm-thick IHS removed from a commercial microprocessor. In this case, the CHF happens at 8.6 W/cm2 (50% lower compared to the reference case) in the saturation condition. At CHF, the boiling can be observed on the whole surface, with columns and slugs regime at the center and the fully developed nucleate boiling regime at the edges. This non-uniform boiling was more pronounced in sub-cooled conditions, in which the CHF occurred at the center while there were regions at the edges that had no boiling. Finally, the performance of a micro porous-coated IHS (with 3.15 mm thickness) was compared to the 6mm thick IHS. The thermal resistance was almost equal for powers above 200 W. This indicates that lateral heat spreading is a critical parameter for the thermal design of immersion cooling along with micro-porous coating.

Determining the Thermal Effects of Channels on Porous Heat Sinks Under Forced Convection Conditions with Nanofluid: An Experimental and Numerical Study

The present study determines the effects which foam metals and Nanofluid have on the performance of a simulated CPU. The present study employs yAl2O3-water Nanofluid and 6061- T6 Aluminum foam metal with a porosity of 0.91 and permeability of 40 pores per linear inch formed in bulk media and porously filled channels. The concentrations evaluated are 0.1%, 0.3%, and 0.6% by volume. The study shall consider both original empirical results and numerical results obtained from COMSOL Multiphysics, showing good agreement with a maximum error of 4.3%. The present study. When considering the average Nusselt number as the representation of the strength of the heat transfer mechanism, and as such ignoring pumping requirements, it is shown that the use of porously filled channels interacting with 0.6% Nanofluid produces the most effective combination. However, when pumping power is relevant, a combination of bulk porous media interacting with 0.3% Nanofluid is observed. The results obtained herein can be applied to the cooling of electronics, or any other system wherein a general inward heat flux is applied.

Determining the Thermal Effects of Channels on Porous Heat Sinks Under Forced Convection Conditions with Nanofluid: An Experimental and Numerical Study

The present study determines the effects which foam metals and Nanofluid have on the performance of a simulated CPU. The present study employs yAl2O3-water Nanofluid and 6061- T6 Aluminum foam metal with a porosity of 0.91 and permeability of 40 pores per linear inch formed in bulk media and porously filled channels. The concentrations evaluated are 0.1%, 0.3%, and 0.6% by volume. The study shall consider both original empirical results and numerical results obtained from COMSOL Multiphysics, showing good agreement with a maximum error of 4.3%. The present study. When considering the average Nusselt number as the representation of the strength of the heat transfer mechanism, and as such ignoring pumping requirements, it is shown that the use of porously filled channels interacting with 0.6% Nanofluid produces the most effective combination. However, when pumping power is relevant, a combination of bulk porous media interacting with 0.3% Nanofluid is observed. The results obtained herein can be applied to the cooling of electronics, or any other system wherein a general inward heat flux is applied.

Numerical survey on performance of hybrid NePCM for cooling of electronics: Effect of heat source position and heat sink inclination

This paper reports on numerical simulations of passive cooling of an electronic component. The strategy is based on the fusion of a nano-enhanced phase change material (NePCM) by insertion of hybrid Cu-Al2O3 nanoparticles. This study analyses the combined effects of the position of the electronic component and the inclination of the heat sink for rectangular and square geometries on the heat transfer and flow structure of liquid NePCM. The heat sink is heated by a protuberant heat source simulating the role of an electronic component generating a volumetric power. The electronic component is mounted on a substrate modelling the role of a motherboard. All the walls of the heat sink are adiabatic. The development of a 2D mathematical model is based on the equations of conservation of mass, momentum and energy. This system of equations is solved using the finite volume method and the SIMPLE algorithm for velocity-pressure coupling. The enthalpy-porosity approach is adopted to model the phase change. The results obtained show that the position of the electronic component and the inclination of the enclosure have important effects on the efficiency of the cooling strategy. The inclination of 900 and the position of d=0.5 represent the case where the cooling of the electronic component is guaranteed and operates safely with a minimum temperature difference recorded along it. The electronic component is well cooled in a rectangular heat sink than in a square one.

Experimental Investigation of a PCM-Based Topology Optimized Heat Sink for Passive Cooling of Electronics

A thermal energy storage unit filled with phase change material (PCM) can serve as a heat sink for the cooling of electronics with intermittent or periodic heat dissipation rates. The use of thermal conductive structures (TCS) is an effective method of improving the thermal performance of a PCM-based heat sink. In this paper, topology optimization is explored to develop a new class of TCS with a tree-like structure to enhance the thermal performance of a trapezoidal heat sink. The topology-optimized heat sink was then fabricated by Selective Laser Melting (SLM) using an aluminum alloy, AlSi10Mg, as the base powder. Experiments were performed to evaluate the thermal performance of the topology-optimized heat sink with the tree-like structure. In addition, a conventional longitudinal-fin heat sink of the same solid volume fraction (φ = 16.2%) and a heat sink without enhanced structure were also fabricated and experimentally investigated for comparison. Rubitherm RT-35HC paraffin wax was used as the PCM. Three different heat fluxes of 4.00 kW/m2, 5.08 kW/m2 and 7.24 kW/m2 were applied at the base of each specimen by a silicone rubber heater. The structure wall and the PCM temperatures were measured over time. Our results show that, for all heat rates tested, the topology-optimized heat sink was able to maintain a lower base temperature as compared to the fin-structure and the plain heat sinks. A thermal enhancement ratio (ε) is defined to evaluate the performance of the heat sinks with and without the use of PCM. From the experimental results, the highest ε value of 8.6 was achieved by the topology-optimized heat sink. These results indicate the better performance of the topology-optimized heat sink in dissipating heat as compared to the other specimens.

Temperature Effect on Capillary Flow Dynamics in 1D Array of Open Nanotextured Microchannels Produced by Femtosecond Laser on Silicon

Capillary flow of water in an array of open nanotextured microgrooves fabricated by femtosecond laser processing of silicon is studied as a function of temperature using high-speed video recording. In a temperature range of 23–80 °C, the produced wicking material provides extremely fast liquid flow with a maximum velocity of 37 cm/s in the initial spreading stage prior to visco-inertial regime. The capillary performance of the material enhances with increasing temperature in the inertial, visco-inertial, and partially in Washburn flow regimes. The classic universal Washburn’s regime is observed at all studied temperatures, giving the evidence of its universality at high temperatures as well. The obtained results are of great significance for creating capillary materials for applications in cooling of electronics, energy harvesting, enhancing the critical heat flux of industrial boilers, and Maisotsenko cycle technologies.