Liquid-cooled Heat Sink Research Articles

A new design of liquid-cooled heat sink by altering the heat sink heat pipe application: Experimental approach and prediction via artificial neural network

The main contribution of the current study is to improve the heat transfer performance of available cooling modules in the electronics market. To this end, by altering the conventional heat sink heat pipe configuration, a new design of a liquid-based heat sink for the thermal management is presented. In this design, pure water with various flow rates ranged from 50 ml/min to 200 ml/min passes through a heat sink connected to a printed circuit board where heat fluxes of 4000 W/m2–12,000 W/m2 are applied. To further increase the performance of the liquid-based heat sink, pure water is replaced with two mass fractions of MWCNT/water nanofluid (0.15% and 0.3%). To compare the performance of the new design with that of the conventional heat sink, several important parameters are investigated. These parameters include the printed circuit board transient/steady temperature, the time required to reach steady-state condition, the average thermal resistance of the cooling module, the system cooling under intermittent loads, and the energy efficiency. At a heat flux of 4000 W/m2, the printed circuit board steady-state temperature is reduced by 5.3 °C for the water-based heat sink compared to that of the conventional cooling module. When the heat flux is increased, the effect of the new cooling design in reducing the temperature of the printed circuit board is further pronounced. For example at a heat flux of 12,000 W/m2, the printed circuit board steady-state temperature is reduced by 14.9 °C. The average thermal resistance of the water-based and nanofluid-based heat sinks at a flow rate of 100 ml/min compared with that of the air-based heat sink is decreased by approximately 0.28 °C/W and 0.34 °C/W, respectively. At the highest applied heat flux, when the MWCNT/water nanofluid with a mass fraction of 0.3% is used, the maximum energy efficiency is calculated to be about 59.2%. Finally, to predict the steady-state temperature of the printed circuit board using the introduced cooling module for other operating conditions, two artificial neural network methods (radial-basis function and multi-layer perceptron) are utilized.

Effect of branching level on the performance of constructal theory based Y-shaped liquid cooling heat sink

Most of heat in data centers is released from electronic chips in servers. Thus, it is more effective to mitigate the heat from electronic chips directly. Furthermore, the cooling load as well as the energy consumption of air conditionings will also be significantly decreased account for the rapid heat removal from electronic chips. The Y-shaped liquid cooling heat sink (YLCHS) has been demonstrated as an effective way to mitigate the heat from electronic chips with specified flow channels. To further optimize the structure of YLCHS, the effect of branching level on the cooling performance of YLCHS based on constructal theory is studied in this paper. By comparing the cooling performances for YLCHSs with 1 to 4 branching level, the relationship between peak temperature and branching level is modelled. The results show that the peak temperature and average temperature of YLCHS are reduced by 28.8% and 13.5% while the number of branching level is increased from 1 to 4, however, the increases of pressure loss for these YLCHSs are lower than 0.04 kPa. Furthermore, the optimal branching level for the proposed YLCHS is determined at 4 by considering the improvement on the cooling performance and the limited size of heat sink.

Optimal design and thermal modelling for liquid-cooled heat sink based on multi-objective topology optimization: An experimental and numerical study

This work suggests a design method of liquid-cooled heat sink based on topology optimization. First, a multi-objective optimization problem is developed in order to manage the tradeoff between the minimization of fluid power dissipation and the maximization of heat exchange. The novel cooling channels with clear topology information are generated under both single-uniform and the multiple-non uniform heat source conditions. The effects of initial guess, weighting factor, and Reynolds number on the Pareto optimal solutions are discussed. Next, a full scale 3D conjugate heat transfer numerical model is built to test the flow and thermal performances of the heat sinks. The results show that the optimized cooling channel can achieve a lower thermal resistance and a higher Nusselts number in comparison to the conventional parallel channel, which means the optimal channel can remove more heat energy while the pumping power supply is minimum. Finally, both traditional parallel and topology optimized channel are manufactured by CNC machine and the high performance of the optimally designed heat sink is validated by conducting experimental tests.

The Effectiveness of the Unit Cell Method in Numerically Modeling and Designing Liquid Cooled Heatsinks

This study compares two numerical strategies for modeling flow and heat transfer through mini- and microchannel heatsinks, the unit cell approximation, and the full 3D model, with the objective of validating the former approach. Conjugate heat transfer and laminar flow through a 2 × 2 cm2 copper–water heatsink are modeled using the finite element package COMSOL Multiphysics 5.0. Parametric studies showed that as the heatsink channels’ widths were reduced, and the total number of channels increased, temperature and pressure predictions from both models converged to similar values. Relative differences as low as 5.4% and 1.6% were attained at a channel width of 0.25 mm for maximum wall temperature and channel pressure drop, respectively. Due to its computational efficiency and tendency to conservatively overpredict temperatures relative to the full 3D method, the unit cell approximation is recommended for parametric design of heatsinks with channels’ widths smaller than 0.5 mm, although this condition only holds for the given heatsink design. The unit cell method is then used to design an optimal heatsink for server liquid cooling applications. The heatsink has been fabricated and tested experimentally, and its thermal performance is compared with numerical predictions. The unit cell method underestimated the maximum wall temperature relative to experimental results by 3.0–14.5% as the flowrate rose from 0.3 to 1.5 gal/min (1.1–5.7 l/min).

Thermal Optimization and Characterization of SiC-Based High Power Electronics Packages With Advanced Thermal Design

A single-phase high power electronics package is designed and developed in this paper. The developed power package achieves a significant thermal performance improvement compared with the conventional wire-bonded power package. The improvement is attributed to two features of the package design. First, the SiC chips are embedded into the active metal brazed (AMB) substrates with specially designed cavities, as such the heat transfer path from the embedded SiC chips to the liquid-cooled heat sink attached to the bottom side of the AMB substrate is shortened. Hence, the thermal performance of the package is improved. Moreover, customized copper clips are introduced as the electrical interconnections between the SiC chips and the top metal layer of the substrate at the same level, and the top surface of the power package remain flat. As such another heat sink can be added to the top side of the package to further improve the thermal performance of the power package through the double-side cooling (DSC) scheme. The simulation results show that the junction-to-case thermal resistance (Theta JC) of the optimized power package is about 50% less than the Theta JC of the conventional wire-bonded power package with the same package size and the same power rate. Further applying the DSC scheme to the proposed power package, which is not suitable to the conventional wire-bonded power package, the Theta JC of the proposed power package reduces another 20%. In addition, the effects of the core layer (i.e., material and thickness) and the metal layer (i.e., materials and thicknesses) of the AMB substrate, as well as the die attach (i.e., material and thickness) on the Theta JC of the proposed power package are investigated systematically. As such the thermal performance of the power inverter package is further elaborated. Finally, the thermally enhanced power package is fabricated and assembled. Thermal characterization has been conducted, and the thermal performance of the developed power package has been evaluated. The simulation results and characterization results match well with each other.

Fractal channel manifolds for microjet liquid-cooled heat sinks

A parametric optimization of a novel hybrid configuration of liquid-cooled heat sinks is presented herein. Such a hybrid design encompasses a combination of channels and microjets for optimal performance of chip scale high-power density electronic packages. Fractal flow channel geometries were used to create variants consisting of 16, 32, and 64 channels and a corresponding number of microjets in the impingement cavity. In addition to the conventional coplanar setup, where channels and area enhancing features align with the main flow direction, an out-of-plane network of channels was created to allow for removal of the cooling fluid in the opposite direction of the impinging jets. The parametric analysis was performed via 3-D CFD simulations to investigate the tradeoff between hydraulic and thermal resistances in jet cooling systems. The thermal resistance of the heat sinks was estimated and the pressure losses were calculated for every design. Observations of the flow patterns were used to inform on the optimization process of the architecture of the flow channels. A metric able to merge thermal and hydraulic performance was defined, such that the thermo-fluid characteristics of a liquid cooled heat sink are represented using one parameter. The utilization of this parameter led to a unique performance assessment of the proposed hybrid liquid-cooled heat sinks and allowed to identify an optimum design, which yields the lowest thermal resistance with minimum pumping power input.

Optimization of 3D printed liquid cooled heat sink designs using a micro-genetic algorithm with bit array representation

The advancement of additive manufacturing enables significantly greater freedom of design compared to conventional techniques. Of significant interest is the potential improvements in the design of cold plates and heat sinks for electronics cooling. Greater design freedom could enable new designs that reduce thermal resistance and hydraulic resistance, enabling the usage of higher power systems while maintaining an equivalent heat sink volume. Parts made by using additive manufacturing are built layer by layer, and can be conceptualized as a bit array in a 2D plane. Therefore, this work explores the feasibility of combining computational fluid dynamics and micro-genetic algorithms to produce optimum shapes for liquid cooled heat sinks represented as bit arrays.A 50 mm × 10 mm area is discretized into a grid space. An initial bit array geometry is developed using a heat flux dependent probability function based on two representative chip power distribution profiles. One distribution is a symmetric flux map, and the other uses a non-symmetric map, more representative of a real processor. The performance of generated designs is determined using a commercial computational fluid dynamics code, after which an optimization algorithm is applied. Solution ranking in each generation is based on the system entropy generation rate, which is dependent on the fluid pressure drop and overall heat sink thermal resistance. Crossover, mutation and elitism operations are used to create new generations of designs. Results after one hundred generations are compared with a baseline straight finned cold plate to determine the advantages of designing for an unrestricted manufacturing process. Results indicate that the optimization methods reduced entropy generation rate by 26.4% and 21.7% for the symmetric and non-symmetric power maps, respectively.

The heat transfer characteristics of liquid cooling heat sink with micro pin fins

This paper numerically and experimentally investigated the liquid cooling efficiency of heat sinks containing micro pin fins. Aluminum prototypes of heat sink with micro pin fin were fabricated to explore the flow and thermal performance. The main geometry parameters included the diameter of micro pin fin and porosity of fin array. The effects of the geometrical parameters and pressure drop on the heat transfer performance of the heat sink were studied. In the experiments, the heat flux from base of heat sink was set as 300kW/m2. The pressure drop between the inlet and the outlet of heat sink was set <3000Pa. Numerical simulations with similar flow and thermal conditions were conducted to estimate the flow patterns, the effective thermal resistance. It was found that the effective thermal resistance would reach an optimum value for various pressure drops. It was also noted that the effective thermal resistance was not sensitive to porosity for sparsely packed pin fins.

Liquid cooling of non-uniform heat flux of a chip circuit by subchannels

Experimental and numerical analyses have been carried out to study the effect of using subchannels in a liquid cooled heat sink for minimising the effect of hotspots generated on a chip or circuit. Two heat sinks – with and without subchannels – were fabricated in order to investigate this effect. The first device was manufactured with normal parallel channels while the second was designed to extract more heat by dividing the main channels above the hotspot into two subchannels. The inlet and outlet manifolds were designed with two inlet ports to minimise any potential mal-distribution of mass flow rate through the channels. Three thermocouples were attached to the bottom surface of the inlet manifold and another three attached to the outlet manifold to record surface temperature. Five different mass flow rates were generated under gravity by changing water container height. The results show that adding subchannels improves the uniformity of temperature distribution and reduces the maximum temperature. Moreover, at the same pressure head 79cm the thermal resistance is reduced 20% whereas the pumping power is increased by 11%.

Performance improvement of high power liquid-cooled heat sink via non-uniform metal foam arrangement

The present study proposes a novel concept by employing non-uniform arrangements of metal foams alongside the heat sink applicable for liquid cooling. A total of 7 arrangements by varying PPI (pores per inch) of metal foam are made and additional 4 multiple channel designs are fabricated for comparison. Test results indicate that non-linearity term in Forchheimer equation rises significantly with increase of PPI (or with the decrease of permeability). The results suggest that the transition from the linear Darcy regime to the quadratic Forchheimer regime depends on the metal foam structure. It is also found that metal foam appreciably outperforms conventional multiple channel heat sink. The thermal resistance can be reduced by more than 62% as compared to that of empty plate design. For a given pumping power, the non-uniform arrangement of metal foam shows the best performance by employing a larger PPI metal foam at the inlet, followed by a smaller PPI metal foam, and the least PPI metal foam should be placed at the rear part of the heat sink.

Study of Thermally Enhanced 2.5D Packages with Multi-chips Molded on Silicon Interposer

The 2.5D package with distributed vias on silicon interposer has received great attention due to its potential for heterogeneous integration. The overmolded 2.5D package protects the silicon die and interposer from environmental damage, which, on the other hand, induces undesirable thermal resistance due to low thermal conductivity of the molding compound. In this paper, a thermally enhanced 2.5D package with exposed die is proposed, fabricated and examined from the thermal enhancement viewpoint. The high power thermal test die was first assembled on a silicon interposer with through silicon vias and connected to the substrate, which was followed by the overmolding and back-grinding processes to form the partially molded (PM) package with exposed die for direct heat sink attachments. Experiments were conducted to examine the thermal performance under different thermal conditions. Under natural convection without thermal enhancement, there was no performance difference between the PM package and the overmolded package. However, when the package top was mounted with a thermally enhanced structure such as a pin fin heat sink, the thermal resistance of PM package was significantly reduced. The advantage was more prominent with the attachment of a high performance liquid cooling heat sink. Thermal simulation models were also constructed to examine the thermal performances under different test conditions, and the realistic thermal interface resistance of 0.5 Kcm2/W was estimated based on the package warpage. The computed thermal resistances agreed with measurement results.

Study on Losses Calculation and Design of DC Boost Chopper

In view of the cooling of Insulated-gate bipolar transistors (IGBTs) in the parallel DC boost chopper, this paper presents a method to calculate the power loss of IGBTs. It involves functions of equivalent heat circuit of liquid cooling system based on the similarity theory, and the design of the parameters in the cooling system for DC boost chopper. It solves the problems of parameters designing of liquid-cooled heat sink. Taking the cooling system of IGBTs as an example, the experiment shows that the cooling system based on this method has excellent performances in the worksite, and the method is practical and effective.

A topology optimization method for a coupled thermal–fluid problem using level set boundary expressions

This paper presents a topology optimization method for a coupled thermal–fluid problem based on the two- and three-dimensional steady-state Navier–Stokes and energy equations. In this research, the optimization problem is formulated as a heat exchange maximization problem to obtain structures that function as high-performance cooling devices. Such devices, for example, liquid-cooled heat sinks, have recently attracted considerable attention as an engineering application for thermal cooling devices. The proposed optimization method employs level set boundary expressions and a Tikhonov-based regularization scheme enables qualitative control of the geometric complexity of the optimal configurations. Using the developed methodology, we provide two- and three-dimensional numerical examples that confirm the applicability, from an engineering standpoint, of the optimization method for the design of cooling devices.

Solving Thermal Issues in a Three-Dimensional-Stacked-Quad-Core Processor by Microprocessor Floor Planning, Microchannel Cooling, and Insertion of Through-Silicon-Vias

The electronics industry is heading toward the three-dimensional (3D) microprocessor to cope with higher computing workloads. The 3D stacking of the processor and the memory components reduces the communication delay in multicore system-on-a-chip (SoCs), owing to reduced system size and shorter interconnects. The shorter interconnects in a multicore system lowers the memory access latencies and contributes to improvements in memory access bandwidth. The shorter interconnects in stacked architectures also enables small drivers for interconnections which further reduce interconnection-level-energy dissipations. On the down side, the 3D-stacked architectures have high thermal resistance, which in conjunction with poor thermal management techniques, poses a thermal threat to the reliability of the device. This paper establishes the significance of the microprocessor floor planning and single-phase microchannel cooling for solving the thermal issues arising in the 3D-stacked-quad-core processor. The 3D-stacked-quad-core processor considered in this study comprises of symmetric nonuniformly powered quad-core processor, liquid-cooled microchannel heat sink, dynamic random access memory (DRAM), thermal interface material (TIM), and heat spreader. The electrical through-silicon-vias (TSVs) between the processor and DRAM serve as interconnects, while the thermal TSVs reduce the internal thermal resistance. The effective cooling of the 3D-stacked-quad-core processor depends on the TSVs, quad-core layout and the optimized design of the microchannel heat sink for the desired coolant. The microchannel cooling of the 3D-stacked processor is done both by planar flow and impingement flow. The thermal efficiency of the cooling techniques is evaluated on the basis of hot spot temperature, hot spot spread, and number of hot spots.

Numerical Analysis on the Heat Transfer of Heatsink with Micro-Pin-Fins

This paper numerically studies the heat transfer in heat sinks with micro-pin-fins. Commercial software, ICEPAK, was used to explore the effect of micro-pin-fin array design on the flow rate and heat transfer characteristics of liquid cooling heat sink. The parameters include the diameter of pin fin, the gap between the pin fins, and the relative position between the pin fins. The diameters of the pin fin are 0.5mm, 0.6mm, and 0.7mm, respectively. The gap between the pin fins are 0.2mm, 0.25mm, 0.3mm, 0.4mm, and 0.5mm, respectively. Three types of fin array arrangements are set with different longitudinal spacing and transverse spacing. The driving force of the working fluid is the pressure head with 500, 1500, and 3000 Pa, respectively. Results show that the effective thermal resistance ranges from 0.27 to 0.55 with the power density of 300kW/m2.

Optimization of convective heat transfer in micro-scale electronics cooling applications

Selected state of the art micro scale convective heat transfer techniques are presented for use in heat sinks and heat exchangers. Hereby focus is put on optimal design aspects for micro channel components and their effect on the over-all system performance in micro-electronics cooling applications. For direct liquid cooled heat sink applications, steady and unsteady single-phase flow operation are discussed and compared with possible operating conditions for two-phase flow. Regarding compact heat exchanger applications, the effects of downscaling are discussed in terms of the penalties on hydraulic and thermal performance. Comparing the optimal design of heat sinks (minimal thermal resistance and thermal gradients as well as maximal energy recovery) and heat exchangers (maximal power density), different criteria for flow conditions and material properties emerge.

Analysis of Liquid-Cooled Heat Sink Used for Power Electronics Cooling

Liquid-cooled heat sink (cold plate) used for power electronics cooling is numerically studied. Thermal performance and hydraulic resistance are analyzed, with emphasis on geometric construction of cooling channels. Two heat transfer enhancing channel shapes are investigated, such as alternating elliptical channel and alternating rectangular channel (AR-C). Their performances are compared with that of three traditional straight channel shapes, as straight circular channel, straight elliptical channel, and straight rectangular channel. A heat sink with uniform and discrete heat sources is studied. Thermal and hydraulic characteristics in the heat sink are simulated using computational fluid dynamics approach, with water as coolant. The results show that the AR-C has the highest thermal performance with a little penalty on pressure drop, considering fixed channel hydraulic diameter and coolant volumetric flow rate. Geometry optimization is investigated for the AR-C, as well as the effect of channel density. It is found that higher channel density can improve both thermal performance and hydraulic resistance. It is concluded that alternating channel can improve cold plate performance and should be taken into application to power electronics cooling.

A Study of Liquid Cooling Heat Sink Fabrication and Development in Notebook

Liquid cooling heat sink has excellent heat dissipation ability at the personal computer. It can also produce the similar effect at the notebook when the same heat sink is used. However, under the installing space is limited in notebook, the size and weight of heat sink must be limited too. Therefore a novel liquid cooling heat sink was fabricated herein to understand the heat dissipation efficiency in the notebook. Wire electrical discharge machining (WEDM) uses heat erosion effect to remove material and only produces little cutting force on the working surface. Therefore, WEDM has excellent ability to fabricate the straight micro fins (high 1000 μm, width 250 μm, fin gap 400 μm). The WEDM parameters were used to find the precision micro fins in this experiment. The precision micro fins were made when the cutting path offset was 185 μm in WEDM. WEDM would produce over cutting during long pulse duration and it caused oblique micro fins. The appropriate off time in cutting process would promote the WEDM efficiency. However, a liquid cooling heat sink with uniform micro fins and slits was obtained using WEDM.

An integrated methodology for multiobjective optimal component placement and heat sink sizing

The advances in power electronics packaging resulting from the integration of various high power devices into single programmable blocks are projected to significantly increase heat dissipation rates up to 2-3 W/mm/sup 2/ within the next decade. Conventional thermal management schemes such as air-cooled heat sinks are inadequate at these high power levels, requiring the use of forced liquid cooled heat sinks, or cold plates. A primary issue concerning the thermal-packaging designers today is the selection of a suitable cold plate and the optimum placement of components on it. This paper focuses on a methodology for selection of cold plates and the optimal placement of power modules on them. The basis of the methodology is the integration of computationally efficient reduced or "compact" thermal models within a genetic algorithm based multiobjective optimization framework. This methodology is used to optimize the placement of multiple power modules on a cold plate. It is also extended to perform a tradeoff analysis between multiple competing objectives for cold plate selection. Compact thermal models for power electronics and heat sinks are developed, validated, and integrated within the optimization framework. The effectiveness of the methodology as a rapid scouting tool to arrive at an optimum tradeoff solution set for further analysis by detailed numerical simulation is discussed. The methodology is general in the sense that it allows for incorporation of changes in optimization criteria or improvements in the heat transfer solver.