CPU Surface Research Articles

A novel concept for performance enhancement of immersion-cooled data center servers

Efficient thermal management of highly densified data centers is important for carbon-neutral strategies. To this end, this work experimentally explored the most promising single-phase immersion cooling (SPIC) systems. Moreover, it proposed an active performance enhancement technology for SPIC systems. The results indicate that increasing the coolant immersion height helps to improve the SPIC performance, and the resulting increase in flow resistance is negligible. Increasing the volume flow rate improves heat transfer performance while also increasing flow resistance. Moreover, there exists a critical volume flow rate (i.e., 8 L/min) beyond which fails to significantly enhance the SPIC performance. The cooling water temperature is positively correlated with the device temperature but negatively correlated with flow resistance. The micropump-based flow turbulence enhancement and the fan-based flow redistribution techniques reduce the maximum CPU surface temperature by 6.1 % and 5.0 %, respectively. Compared to the micropump method, the fan-based technique degrades the thermal uniformity of coolants but does not significantly increase flow resistance. The economic benefit of the micropump-based strategy is greater for upstream CPUs than downstream CPUs, while the fan-based method is more economically advantageous for downstream CPUs. Moreover, the micropump-based strategy outperforms the fan-based method and demonstrates a 21.39 % increase in energy-economic performance.

Analysis of Nanofluid Heat Transfer and Entropy Generation in a Novel Metal Foam Heat Sink

This study investigated the impact of key parameters, including Re (300 ≤ Re ≤ 1800), Φ (0% ≤ Φ ≤ 2.5%), ɛ (0.2 ≤ ɛ ≤ 0.9), and Da (10−4 ≤ Da ≤ 10−1), on heat transfer and entropy generation in a novel metal foam heat sink. Results show that increasing the Darcy number to 10−1 can enhance the average Nusselt number by approximately 18.05% while placing Al.Cu foam in the middle of the heat sink can significantly reduce the CPU surface temperature by up to 15 .C. Additionally, increasing the Reynolds number from 300 to 1800 can lower the thermal entropy generation by up to 51.55%. The metal foam’s effectiveness was evaluated using performance evaluation criteria (PEC).

Improvement of cooling of a high heat flux CPU by employing a cooper foam and NEPCM/water suspension

In the current simulation, a copper porous media was inserted on a hot surface of a CPU releasing high heat flux and then embedded within a mini-channel. The working fluid was a mixture of water and Nano-encapsulated phase change material (NEPCM) with fusion temperature of 303.47 K. The proposed model was simulated by computational fluid dynamic (CFD) based on finite volume method (FVM) to evaluate the impacts of Reynolds number (Re = 80, 90, 100, 110, and 120), porous medium with different porosity number (ε = 0.9, 0.925, 0.95, 0.975, and 1). The important parameters in CPU cooling was selected including pressure drop and maximum temperature of CPU's surface. The evidence said that inserting a copper foam with 0.95 porosity can reduce the maximum temperature of CPU's surface and increase the pressure drop by 40 K and 100 times compared to without porous media, respectively. Also, rising Reynolds number from 80 to 120 enhanced the pressure drop by 57 % and decreased the maximum temperature of CPU's surface by only 5.4 K.

Multi-objective optimization of microchannel heatsink with wavy microtube by combining response surface method and genetic algorithm

This paper utilizes a combination of response surface method and genetic algorithm to provide an optimized model for microchannel heatsink with wavy microtube. The effect of flow rate in microchannel and microtube, location and diameter of microtube on the desired response surfaces, including hydrodynamic, thermal, and entropy parameters is examined. Then, the correlation between the variables is determined using a non-parametric regression model. The optimal design points are identified by multi-objective optimization and the Pareto diagram. The greatest effect is related to the nominal Reynolds number, with is directly related to the pumping power and entropy generation. The next effective parameter is the diameter of the microtube, which is inversely related to the pumping power, average surface temperature, and entropy generation. It is found that the maximum temperature difference on the hot surface is 3.1 K for optimal design HS3. For the geometry HS1, this value is less than 0.9 K by examining the optimal geometries of the micro heatsink based on the simultaneous study of the uniformity of CPU surface temperature and average CPU temperature. In addition, the flow velocity in the microtube of the design HS1 is much higher than that of the design HS3.

Cooling a central processing unit by installing a mini channel and flowing nanofluid, and investigating economic efficiency

CPUs are widely used in many industries. These components require electrical energy for processing and generating heat due to their electrical resistance. On the other hand, they have a very high heat flux due to their small size and high energy consumption. Therefore, their cooling with new methods helps their performance a lot. In this study, water flow with Nano-encapsulated phase change material (NPCM) was simulated to cool an embedded CPU inside a mini channel. These NPCMs have a significant effect on heat transfer parameters due to their ability to phase change in their core. On the other hand, examining the exert economy broadens our horizons to choose an appropriate system in practical problem engineering. Numerical simulation by the FVM method was utilized to study the effects of Reynolds numbers, heat flux of CPU's surface, and volume fraction on the temperature distribution, the maximum temperature of CPU's surface, and economic efficiency. Evidence showed that increasing Reynolds number from 50 to 100 at zero volume fraction reduces the maximum temperature of the CPU's surface from 98.4to82.5°C. Also, mixing a 3% volume fraction of NPCM with pure water can decrease the maximum temperature of the CPU's surface by 2.27°C relative to pure water. Moreover, rising Reynolds number from 50 to 100 enhanced the net profit per unit transferred heat load (ηp) by 100 times.

Thermo-hydraulic performance of nanofluids in a bionic heat sink

A bionic surface based on the wing structure of the dragon louse is developed and applied in the thermal management system of electronic components. Fe3O4-water nanofluids are introduced and their thermal-hydrodynamic behaviors under magnetic field are studied. The influence of nanofluids concentration (ξ = 0.1–0.5%), Reynolds numbers (Re = 712–1400), tilt angles of magnetic field (θ = 0°, 30°, 60°) and intensity of magnetic field (β = 0.0 T, 0.005 T, 0.010 T, 0.015 T) on the heat transfer are considered in the system. Exergy efficiency and entropy production of CPU cooling system are analyzed. Results presented that the bionic surface based on the wing structure of the dragon louse shows an excellent drag reduction effect compared with the smooth surface, which can reach 35.4%. The maximal reduced ratio of CPU surface temperature under magnetic field is 34.42% in comparison with that under no magnetic field, and the maximal reduced ratio of CPU surface temperature with θ = 60° is 14.96% in comparison with θ = 0°. It shows an augmentation of heat transfer for most cases with the identical rate of flow from the point of exergy efficiency. When nanofluids concentration is ξ = 0.3%, Reynolds number is Re = 1402, tilt angle is θ = 60°, and magnetic field strength is β = 0.015 T, the minimum entropy production is obtained.

Comparative thermal performance evaluation of a heat sink based on geometrical and material amendments: A numerical study

The study focuses on the design and materialistic amendments for thermal performance evaluation of a heat sink which is a just modified version of the conventional heat sink used for processor Ryzen 5 3600, introduced by a company named Advanced Micro Devices (AMD) for cooling applications in High-Performance Gaming PCs. The enhancement of the cooling strategy is achieved within dimensional and cost constraints by modifying the parametric dimensions, increasing the surface area, and introducing metal to the air-fluid boundary layer aspects into it. In this study, the heat sink is designed with a core of cylindrical shape, keeping a height of 20 mm and a diameter of 90 mm. Also, the universal dimensional compatibility of this heat sink is considered for the performance evaluation, followed by design and angle of air-fin interaction, swapped center rectangle shape with a frustum to decrease the thermal hindrance and to increase the surface area without any increment in overall volume. Moreover, the fin density in the module of the heat sink has also been increased to enhance the convective heat transfer strategy from the surface. Both designing & simulation have been carried out on the FEM tool Autodesk Fusion 360 and based on the numerical investigation on the modified design as per the conventional design, although our design is much more complex to manufacture in the first place. It has been observed that the new design is capable of providing 64.23% convective heat dissipation from the surface as well as able to reduce 50.9% of CPU surface temperature in comparison to the existing design of heat sink.

Application of an ecofriendly nanofluid containing graphene nanoplatelets inside a novel spiral liquid block for cooling of electronic processors

The present research is carried out to examine the efficiency of a novel spiral liquid block for the cooling of electronic processors. To enhance the cooling efficiency, a biologically produced nanofluid having graphene nanoplatelets is considered. The numerical analyses are performed at different concentrations ranging from 0 to 0.1% for different Reynolds numbers (Re) and pumping powers. Furthermore, the performance of the spiral liquid block is compared with serpentine and base-plate liquid blocks. In the case of the spiral liquid block made from nickel, the mean temperature of the CPU surface reduces around 7 K when the concentration increases from 0 to 0.1% at Re = 500. Moreover, the thermal resistance declines up to 11.7% with increasing the concentration by 0.1%. In the case of constant pumping power, the spiral liquid block demonstrates the best cooling efficiency compared to the other types. The maximum value of the Figure of Merit (FoM) for the spiral liquid block is 4 times greater than that for the serpentine liquid block. Indeed, the unique structure of the spiral liquid block allows superior heat transfer with moderate pumping power, and this liquid block is recommended from the energy efficiency viewpoint.

Hydrothermal and entropy generation specifications of a hybrid ferronanofluid in microchannel heat sink embedded in CPUs

The objective of this numerical work is to evaluate the first law and second law performances of a hybrid nanofluid flowing through a liquid-cooled microchannel heatsink. The water-based hybrid nanofluid includes the Fe3O4 and carbon nanotubes (CNTs) nanoparticles. The heatsink includes a microchannel configuration for the flow field to gain heat from a processor placed on the bottom of the heatsink. The effects of Fe3O4 concentration (φFe3O4), CNT concentration (φCNT) and Reynolds number (Re) on the convective heat transfer coefficient, CPU surface temperature, thermal resistance, pumping power, as well as the rate of entropy generation due to the heat transfer and fluid friction is examined. The results indicated higher values of convective heat transfer coefficient, pumping power, and frictional entropy generation rate for higher values of Re, φFe3O4 and φCNT. By increasing Re, φFe3O4and φCNT, the CPU surface temperature and the thermal resistance decrease, and the temperature distribution at the CPU surface became more uniform. To achieve the maximum performance of the studied heatsink, applying the hybrid nanofluid with low φFe3O4and φCNT was suggested, while the minimum entropy generation was achieved with the application of nanofluid with high φFe3O4and φCNT.

Taguchi–based sensitivity analysis of hydrodynamics and heat transfer of nanofluids in a microchannel heat sink (MCHS) having porous substrates

In this work, hydrodynamics and heat transfer of alumina–water nanofluid in a microchannel heat sink (MCHS) are simulated and discussed. Attention in focused to analyze how the use of nanofluids as well as vertical/horizontal porous substrates on the channel walls may alter performance of the system, compared to other design variables. To this aim, a three–dimensional solid–fluid conjugate model in conjunction with the two–phase mixture model for the nanofluid and the Dacry–Brinkman–Forchheimer model for the porous medium is utilized. Sensitivity analysis of design variables is performed using the Taguchi method and analysis of variance (ANOVA). The mean temperature of the CPU surface, the overall thermal resistance, the required pumping power, and the figure of merit are considered as the performance parameters. An L27 orthogonal array is utilized as the experimental plan for the current design variables including thickness of the vertical/horizontal porous substrates, material of the MCHS and the porous substrates, the inlet velocity, and the nanoparticles fraction. It is found that the highest contribution on the mean temperature of the CPU surface, the overall thermal resistance, and the figure of merit belongs to the material of the MCHS and the porous substrates.

Design of a single-phase immersion cooling system through experimental and numerical analysis

Cooling electronics systems more effectively could enable computer systems to utilize power more efficiently. Immersion cooling is a potential method to cool computers and other electronics by submerging them into a thermal conductive dielectric liquid or coolant. In this study, an innovative cooling structure and procedure of a single-phase immersion cooling system using heat sink and forced circulation is presented. The straight finned heat sink is attached on the CPU surface, and the entire mainboard is submerged in an engineered fluid, 3 M Novec 7100, which is able to dissipate heat and is used in immersion cooling applications. An experimental test is utilized to verify a simulation model built using the computer simulation software. Three circulating speeds of the liquid coolant along with the use of two different materials for the heat sink are chosen to explore the cooling effects of a single-phase immersion cooling system. The heat distribution of the designed model at various flow rates of liquid coolant and materials was observed through the cross-sectional viewpoint and 3D isothermal surface model. The results of the simulations show that the faster flowing speed of liquid coolant would remove more heat, and cause lower temperature of CPU. However, the flow of coolant was encumbered due to slower circulating speed. It also caused the higher temperature values and unbalanced heat distribution. The highest temperatures were measured, and the unbalanced heat distribution of the model was observed. It is noted that the material of the heat sink do not significantly affect the results. These outcomes are able to provide the system designer with useful information to increase power densification and guarantee the safe operation of the related computer, server and communication systems.

Two-phase mixture simulation of the effect of fin arrangement on first and second law performance of a bifurcation microchannels heatsink operated with biologically prepared water-Ag nanofluid

Abstract The goal of this numerical investigation is to evaluate the impact of fin arrangement on the hydrothermal and irreversibility analysis of a biologically ecofriendly prepared water-Ag nanofluid flowing inside a microchannel heatsink. Three bifurcation microchannels heatsinks with straight channels, inline fins, and staggered fins are considered. Two-phase mixture method is used to model the nanofluid behaviour precisely. The influences of nanoparticle volume fraction (φ) and Reynolds number (Re) on the parameters of convective coefficient, CPU surface temperature, pumping power, heat transfer and fluid friction irreversibilities are examined. It was found that the hydrothermal characteristics and irreversibility behaviour of the heatsinks equipped with fins are better than those of the heatsink with straight channels. The results showed that the best overall first-law and second law performances respectively belong to the heatsink equipped with staggered (except for the φ = 0.1%, φ = 0.5% and Re = 500) and inline fins. Moreover, the application of water-Ag nanofluid in the studied heatsinks was more justifiable for high Re and φ. Finally, it was revealed that boosting both the Re and φ results in an augmentation in the second law performance of nanofluid in the studied heatsinks.

MHD enhanced nanofluid mediated heat transfer in porous metal for CPU cooling

In this study, impingement cooling of a porous metal CPU cooler saturated with nanofluid under the effects of magnetic field was modeled analytically. Darcy-Brinkman-Forchheimer model and viscous dissipation effect were considered to simulate fluid flow of nanofluid through the porous media under magnetic field. Proper similarity variables were proposed and the original partial differential governing equations were converted to nonlinear ordinary differential equations (ODEs), and the resulted ODEs were solved numerically. A system of water-alumina nanofluid flowing through a rectangular porous metal foam with top impinging jet (fan) and hot bottom wall (CPU surface) was modeled. The analytical solver was first validated against CFD and experimental data. Next, effects of different critical parameters including Darcy number (5×10-4≤DaL≤5×10-2), Reynolds number (50≤ReL≤500), aspect ratio (0.25≤H/L≤1.0), Eckert number (0≤EcL≤5×10-2), Hartmann number (0≤HaL≤200), porosity (0.85≤ε≤0.95), and dimensionless distance from the axis of symmetry plane (0≤XL≤1.0), on fluid flow and heat transfer behaviors were investigated. Results indicate that the increase of DaL can enhance heat transfer performance, while opposite trends are found for aspect ratio and Eckert number. However, the behavior of HaL is more complex. At a low porosity, Nusselt number slightly decreases as HaL increases, while an opposite behavior is observed at a high porosity. Overall, the use of a stronger magnetic field is beneficial to enhance the impingement cooling heat transfer with highly porous metal foam.

Numerical investigation of forced convection heat transfer and flow irreversibility in a novel heatsink with helical microchannels working with biologically synthesized water-silver nano-fluid

This paper aims to evaluate the hydrothermal and irreversibility behaviour of a biological water-Ag nano-fluid in a new heatsink with helical microchannels. Two-phase mixture model is applied to precisely simulate the behavior of nanofluid in the nanoadditive concentration (φ) range of 0–1% and Reynolds number (Re) range of 500–1500. The influences of φ and Re on the convective heat transfer coefficient, CPU surface temperature, pumping power, as well as the irreversibilities due to heat transfer and fluid friction are examined. The findings depict that boosting the Re and φ augments the performance of heatsink by intensifying the convective heat transfer coefficient of the working fluid which favourably declines the CPU surface temperature and the heat transfer irreversibility and importantly results in the temperature uniformity of the CPU surface. However, intensification in Re adversely affects the pumping power, the fluid friction and total irreversibilities in the system. Furthermore, it is revealed that the nano-fluid always has a superior cooling performance as compared with the pure water. Finally, it is found that the best hydrothermal performance of the nano-fluid in the proposed heatsink occurs at Re = 1500 and φ = 1%, while the minimum total irreversibility occurs at Re = 500 and φ = 1%.

Numerical investigation of non-Newtonian water-CMC/CuO nanofluid flow in an offset strip-fin microchannel heat sink: Thermal performance and thermodynamic considerations

This paper aims to investigate the hydrothermal and entropy generation characteristics of a non-Newtonian nanofluid containing CuO nanoparticles in an offset strip-fin microchannel heat sink (MCHS). The base fluid is solution of 0.5 wt% Carboxymethyl Cellulose (CMC) in water. This study investigates the effects of nanoparticles concentration, Reynolds number and geometric size of strip-fin on the performance of MCHS from the viewpoint of both the first and the second thermodynamic law. The results reveal that enhancing the Reynolds number improves the performance of MCHS by boosting the convective heat transfer coefficient of the working fluid which favourably reduces the CPU surface temperature and thermal entropy generation rate and importantly leads to the temperature uniformity of the CPU surface. However, increase in Reynolds number adversely affects both the pumping power and the frictional entropy generation in the system. Therefore, the optimal strip-fin size is investigated to find the optimum performance of the offset strip-fins MCHS from the viewpoint of both the first and the second thermodynamic law. The optimal results show that the highest ratio of heat transfer enhancement to pressure drop increment, using the nanofluid instead of base fluid, is 2.29. In addition in the optimal case, the minimum total entropy generation rate of the nanofluid is 2.7% less than the base fluid.

Numerical assessment into the hydrothermal and entropy generation characteristics of biological water-silver nano-fluid in a wavy walled microchannel heat sink

The objective of this numerical assessment is to examine the hydrothermal and irreversibility behaviour of a biologically synthesized water-silver nano-fluid in a wavy microchannel heat sink (MCHS). The green tea leaf extract is utilized to prepare silver nanoadditives. The impacts of nanoadditives volume fraction, Reynolds number, amplitude and wavelength of the channel on the convective heat transfer coefficient, CPU surface temperature, pumping power, as well as the thermal, frictional, and total irreversibilities are investigated. The results show that enhancing the Reynolds number and nanoadditives fraction intensifies the performance of heat sink by boosting the convective heat transfer coefficient of the working fluid which favorably reduces the CPU surface temperature and the rate of thermal and total irreversibilities and importantly leads to the temperature uniformity of the CPU surface. However, increase in Reynolds number adversely affects both the pumping power and the frictional irreversibility in the system. In addition, it is found that the nano-fluid always has a better cooling performance in comparison with the pure water. Moreover, it is reported that augmenting the wavelength results in an increase in the hydrothermal performance of nano-fluid and decrease in the global total entropy generation rate.

Efficacy of a novel liquid block working with a nanofluid containing graphene nanoplatelets decorated with silver nanoparticles compared with conventional CPU coolers

This research attempts to investigate the efficacy and entropy generation of a hybrid nanofluid containing graphene nanoplatelets decorated with silver nanoparticles in three different liquid blocks for CPU cooling. A novel distributor liquid block is evaluated compared with two conventional liquid blocks including serpentine and parallel geometries. Comparisons of the flow distribution uniformity, maximum CPU temperature, average CPU temperature, temperature uniformity on CPU surface, and pumping power consumption of liquid blocks with novel and conventional configurations are made. The results show that the novel distributor liquid block has a superior efficacy based on both thermal performance and irreversibility rates. In addition, the merit of using the nanofluid in the liquid blocks is greater than pure water, and this hybrid nanofluid shows a promising view for cooling improvement in electronics.

Development of a Miniature Vapor-Compression Refrigeration System for Computer CPU Cooling

A miniature vapor-compression refrigeration system for cooling high power CPUs has been developed and tested. The refrigeration system is so small that it can be embedded into the computer case. The refrigerant used in the system is R-134a. The system consists of a miniature rotary DC compressor, a micro-channel condenser, a specially designed cold plate, a short tube restrictor, and related controlling electronics. The compressor is powered directly by the 12V DC power supply of the computer. The cold plate contacts the CPU surface directly and carries away the heat dissipation by conductivity. In a series of tests to cool an Intel Core i7-990X CPU that has 12 cores inside with the refrigeration system, the CPU core temperature can be kept at 23°C in default frequency 3.5GHz and 100% of workload. When the CPU is overclocked to 4.8GHz, the core temperature can be maintained at 59°C. Even when overclocked to 5.0GHz, the core temperature does not exceed 78°C. The test results validate the ability and potential of using vapor-compression refrigeration technology in high heat flux CPU cooling.

Active CPU Cooling System with Piezoelectric Actuated Droplet Generator

ABSTRACTInk jet technology is applied to the industry application of CPU cooling in this study. The PZT actuated micro-cooling device which generating the micro-scale liquid droplet is used in the CPU cooling of desktop and laptop PCs. It consists the advantages of long lifetime of operation, simple and easily manufactured of the structure with PZT actuator. Since the high latent heat transfer rate, 2260 J/g, of water droplet for the liquid-vapor phase change cooling system, it removes heat from the CPU surface effectively for over 100 W. In order to design an efficient cooling device, it is important to study the PZT material property varies after the laser cutting process and the dimensional effects of PZT actuator on the nozzle plate vibration mode. The frequency and amplitude of the voltage used to energize the PZT transducer are also important parameters that should be properly controlled in order to achieve the optimal liquid breakup conditions. It also reveals the low noise and power consumption in the CPU cooling system with some appropriate operational conditions.

Bioengineering of a novel small diameter polyurethane vascular graft with covalently bound recombinant hirudin.

Development of a small diameter prosthetic vascular graft with surface based antithrombin properties should aid in maintaining early graft patency in small vessel reconstruction. The purpose of this study was to bind covalently a basecoat protein (canine serum albumin [CSAJ) and a potent antithrombin agent (recombinant hirudin [rHir]) to 4 mm inner diameter poly(carbonate urea) urethane grafts with reactive carboxylic acid groups (cPU). 125I-CSA was covalently bound to 1 cm length segments of cPU grafts using the carbodimide cross-linker, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). To bind 125I-rHir covalently, CSA was modified with the heterobifunctional cross-linker sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) before linkage to the cPU surface with EDC (cPU-CSA-SMCC). 125I-rHir was modified with Traut's reagent and reacted with the cPU-CSA-SMCC surface, covalently linking 125I-rHir to surface bound CSA. 125I-CSA binding to the cPU graft surface (34,235 ng/segment) was ninefold, sevenfold, and 10-fold greater than controls with nonspecifically bound 125I-CSA. Covalent linkage of 125I-rHir to the cPU-CSA-SMCC surface (9,974 ng/segment) was 172, 192, and 142-fold greater than controls with nonspecifically bound 125I-rHir. Surface antithrombin properties were characterized using a chromogenic assay to measure residual thrombin activity. Evaluation of surface antithrombin activity showed significantly greater 131I-thrombin inhibition and binding by the cPU surface with covalently bound 125I-rHir, as compared with controls. Release of 125I-rHir from the cPU surface was minimal as compared with controls. Therefore, rHir can be covalently linked to a novel small diameter polyurethane vascular graft surface while maintaining its potent antithrombin properties.