Multi-channel Heat Sink Research Articles

Performance evaluation and experimental verification of optimizing fin angles in adjustable- configuration heat sinks

Current heat sink designs typically assume uniform heat flux densities. However, applications such as integrated circuit chips and aircraft power modules often face nonuniform or even time-varying heat fluxes. Under these conditions, conventional fixed-configuration heat sinks are inadequate, and corresponding research is insufficient. This paper presents an adjustable-configuration heat sink with a rotatable fin and explores its flow and heat transfer characteristics under water cooling via simulations and experiments. Genetic algorithms optimize the fin angles for various heat flux densities to reduce the substrate temperatures, and compute numerical control (CNC) technology is used to fabricate and adjust the experimental components for optimal performance under different conditions. The proposed adjustable-configuration heat sink exhibited superior temperature uniformity and cooling performance under various heat flux density conditions. Under uniform heating, peak substrate temperatures are reduced by 15.68 and 14.01 K for the I-type and Z-type adjustable configuration heat sinks, respectively, compared to conventional multi-channel heat sink. For non-uniform heating, the optimized configurations lowered the temperatures in the high-heat regions by 2.8 to 5.1 K. This design, which incorporates an adjustable heat sink configuration, effectively adapts to varying heat flux density scenarios, making it a strong candidate for advanced thermal management applications.

Multiple hot spot cooling with flow boiling of HFE-7000 in a multichannel pin fin heat sink

Electronics cooling applications require a high cooling performance due to increasing power consumption. Phase change heat transfer is a popular approach for offering high heat flux cooling. Controlling temperature distribution and mitigating boiling instabilities under high heat flux conditions present a significant challenge. While numerous studies investigated the effect of pin fins in a minichannel with single hotspots on boiling enhancement, few research studies are available for minichannels with multiple segmented hotspots. This study's primary objective is to dissipate high heat (1.4 kW) using flow boiling of a dielectric fluid, namely HFE-7000, which has lower thermophysical properties than water, to achieve a uniform temperature distribution, and to suppress boiling instabilities. The boiling performance of a pin fin multichannel heat sink with dimensions of 3 × 14 × 300 mm (H × W × L) subjected to 8 hotspots with uniform heating was investigated in this regard. Flow boiling experiments were performed over a wide range of input heat power from ∼0.1 to ∼1.4 kW with a coolant mass flux of 500 kg/m2 s in the three parallel minichannels having staggered elliptical pin fins with no tip clearance on each hotspot and distribution pins at the inlet. High-speed visualization was used to relate the heat transfer coefficient variations along the channel to flow patterns. The heat transfer performance and flow regimes at different locations were obtained and discussed. Thanks to the mixing effect of elliptical micro pin fins with optimum geometrical parameters along the heat sink, the presence of distribution pin fins at the inlet for suppressing boiling instabilities and early transition to stable annular flow, the temperature uniformity (∼2.3 °C, temperature difference between the inlet and outlet hotspots) could be achieved at the highest heat input. Heat transfer coefficient reduction upto 27 % was reported along the channel when comparing inlet (1st) and outlet (8th) hotspots.

An LBM study of multichannel flow boiling for electronic thermal management coupling flow instability mitigation

The rising heat dissipation requirement on electronic devices urges a more efficient and energy-saving cooling strategy to keep the equipment operating within a safe temperature range. Multichannel flow boiling provides a straightforward solution to this challenge due to enormous latent energy of vapor preventing heat accumulation. However, pressure drop minimization and flow instability mitigation should also be considered for optimizing multichannel design. Hence, a Lattice Boltzmann Method (LBM) study on multichannel flow boiling process is conducted to provide design-based suggestions. The effects of surface wettability, channel number, input heat flux, and inlet velocity on the two-phase flow characteristics, heat transfer coefficient enhancement, dimensionless pressure drop, and flow instability are compared to examine the overall performance. Non-dimensional pressure drop is proposed for comparison through dividing the pressure drop under two-phase flow stage by the pressure drop under single-phase flow stage. Results show that hydrophilic coating prevents the film boiling transition at high input heat flux and reduces the maximum temperature for safer electronic operation. Designing a dense channel array can enhance the overall HTC but also significantly increase flow instability on the inlet, leading to shorter pumping operation life. A hybrid design of multichannel with downstream microgap region is proposed, and results indicate great mitigation ability with the increase of gap length and inlet velocity. These findings offer an invaluable blueprint for multichannel heat sink design and reveal the mechanisms of flow boiling enhancement.

Numerical and experimental investigation of a multi-channel heat sink distribution header designed by topology optimization

The fluid distribution had a significant effect on the performance of the I-shaped multichannel heat sink. Previous researchers have improved fluid distribution by arranging baffles; however, this resulted in an increased pressure drop. In this study, a multichannel radiator distribution header was designed using a topological optimization method, and experimental and numerical studies were conducted. Both a numerical model and physical prototype were created and subsequently evaluated to assess the performance of the resultant distribution header. The effects of the distribution and conventional headers on the performance of a multichannel heat sink were compared. The results demonstrated that the distribution header designed using the topology optimization method can significantly improve multichannel performance. The optimized header design exhibited improved flow distribution rationality, enhanced heat dissipation, and reduced pressure drop compared to the two conventional designs. The volume flow rate was reduced by 58.66% and 59.29%, the heat transfer coefficient was increased by 29.39% and 21.42%, and the pressure drop was reduced by 9.38% and 16.98%. A peach-shaped baffle plays an important role in fluid distribution. These findings highlight the effectiveness and potential of topology optimization in the design of complex fluid distribution systems for heat exchanger.

Two-phase flow oscillation and distribution in parallel channels during R1233zd(E) subcooled flow boiling: A numerical study

The uniformity of two-phase flow distribution in a multi-channel heat sink is important for heat transfer performance. During flow boiling, flow oscillations such as transient reverse flow could cause severe flow mal-distribution, thus degrading heat transfer performance and thermal uniformity. Due to the shortcomings of experimental instruments, a 3D numerical simulation was conducted on a heat sink with 21 parallel micro-channels to study the transient flow oscillations and distributions during the subcooled flow boiling of R1233zd(E). The numerical model was validated by the flow pattern visualization experiments. The flow instability was studied on its cause and phenomenon like reversed flow and asymmetric flow. The two-phase flow pattern, heat transfer performance and pressure drop oscillation was also researched and a relationship between them was built. Based on the results, an optimized structure is conducted. The comparison between the optimized and original structure showed that the optimized structure could mitigate the reversed flow, meanwhile the uniformity of mass and temperature distribution were improved by 11.2 % and 8.89 %, respectively. The heat transfer performance of side channels was also enhanced, which in turn improved the overall heat transfer performance.

Experimental study on single-phase convective heat transfer of interlocking double-layer counterflow mini-channel heat sink

This study proposes an interlocking double-layer mini-channel heat sink that can realize counterflow in which the flow direction is opposite in the adjacent channel. The heat sink consists of two-channel layers and a header/plenum structure serving as a pre-flow path for counterflow into the channels. The novelty and significance of the current study are that the counterflow multi-channel heat sink was first experimentally implemented through the design of a new internal flow distribution structure. The test data are obtained from the experimental evaluation of the single-phase flow cooling performance of the heat sink. The heat transfer characteristics of the heat sink are analyzed by separating the change in the single channel heat transfer coefficient increased by the counterflow channel effect. The thermal resistance representing the overall cooling performance of the proposed heat sink shows a significantly small value of 10-4 K-m2/W order, which indicates the heat transfer performance advantage of the new heat sink. The beneficial effect of counterflow is verified by comparing the heat transfer coefficient obtained from the proposed heat sink and the prediction using the previous correlation for unidirectional single-phase flow heat transfer coefficient. The measured heat transfer coefficients are much larger than the predicted values by all kinds of past correlations. The difference between the measured value and the predicted value is much greater at low flow conditions where the temperature gradient increases more significantly with the flow direction. It can be concluded that this indirectly implies the fact that temperature gradient mitigation by counterflow results in an additional heat transfer improvement that is unpredictable in the previous unidirectional flow correlations. A new correlation is proposed to predict the heat transfer coefficient affected by the counterflow. This study is the first to experimentally implement a counterflow heat sink, confirming the distinct advantage of improved cooling performance over conventional heatsinks. In addition, this study is meaningful in that it presents a performance prediction model that can be used in design for the practical application of counterflow heat sinks.

A tapered inlet/outlet flow manifold for planar, air-cooled oblique-finned heat sink

Flow maldistribution compromises thermal and hydraulic performances of heat sinks. The oblique-finned heat sink is a multichannel heat sink comprising parallel (primary) and collinear oblique (secondary) channels and it was reported to suffer from a self-induced flow migration in liquid and air cooling. In this study, a novel tapered inlet/outlet flow manifold was proposed for the planar oblique-finned heat sink. Two heat sink configurations (oblique angles of 30° and 45°) and three flow manifold configurations (of 5%, 10%, and 20% wider flow domains) were investigated. Flow migration characteristics were studied via numerical simulations. Wind tunnel measurements, supported by infrared thermography, were performed to characterize thermal and hydraulic performances on a wide range of air flow rates. The flow manifold was observed to provide a favorable distribution of secondary flows in the spanwise direction of the heat sink. Up to 50% increase in Nusselt number with a negligible increase in pressure drop was observed with the 45° oblique-finned heat sink once the flow manifold was incorporated. 30° oblique angle −10% flow manifold combination provided the lowest heat sink temperature and the most uniform wall temperature. The novel tapered inlet/outlet flow manifold is the first effort reported in the literature to reduce the adverse effects of flow migration through the planar oblique-finned heat sinks.

Cooling Performance of a Novel Circulatory Flow Concentric Multi-Channel Heat Sink with Nanofluids.

Heat rejection from electronic devices such as processors necessitates a high heat removal rate. The present study focuses on liquid-cooled novel heat sink geometry made from four channels (width 4 mm and depth 3.5 mm) configured in a concentric shape with alternate flow passages (slot of 3 mm gap). In this study, the cooling performance of the heat sink was tested under simulated controlled conditions.The lower bottom surface of the heat sink was heated at a constant heat flux condition based on dissipated power of 50 W and 70 W. The computations were carried out for different volume fractions of nanoparticles, namely 0.5% to 5%, and water as base fluid at a flow rate of 30 to 180 mL/min. The results showed a higher rate of heat rejection from the nanofluid cooled heat sink compared with water. The enhancement in performance was analyzed with the help of a temperature difference of nanofluid outlet temperature and water outlet temperature under similar operating conditions. The enhancement was ~2% for 0.5% volume fraction nanofluids and ~17% for a 5% volume fraction.

Thermal management of high concentrator solar cell using new designs of stepwise varying width microchannel cooling scheme

High concentrator photovoltaic (HCPV) system are generally exposed to high solar concentration ratios and reach high temperatures. An advanced cooling technique is compulsory to attain the highest net output power along with the safe operation of the system components. Different designs of stepwise varying width microchannel heat sink are investigated in this study. The main purpose of this study is to investigate the influence of the channel geometry of longitudinal rectangular internal fins and different water inlet mass flow rates on the performance of an HCPV system. A three-dimensional thermal model is developed and used to compare the performance of four different designs of stepwise varying width microchannel heat sinks. These designs are compared with the conventional multichannel heat sink design. The results show that the heat sink design and the coolant mass flow rate have a significant impact on the cell temperature, electrical cell efficiency, system thermal efficiency, electrical exergy efficiency, thermal exergy efficiency, total exergy efficiency and thermal resistance of the heat sinks. For instance, using one of the proposed stepwise varying width microchannel heat sink at solar concentration ratio of 1000 suns and increasing the coolant flowrate from 25 to 1000 g/min decreased the solar cell temperature from around 71.7° C to 40° C with solar cell temperature non-uniformity decreased from 15.5 °C to 9 °C respectively.

Heat transfer enhancement of air-cooled heat sink channel using a piezoelectric synthetic jet array

In the last decade, active devices, such as synthetic jets have been intensively studied for electronics cooling. The present study experimentally and computationally investigates heat transfer performance of synthetic jet arrays used in heat sink channels. The heat sink of the present study consists of multiple flow channels that are parallel to one another. The channel walls behave like fins in that their tops are exposed to the flow. The jets are designed to impinge on the tops and sides of those fins to augment heat transfer. The current study employs a single channel of the heat sink to investigate heat transfer augmentation performance by the jets. The oscillating diaphragms that create the jets are driven by a piezo-bow operating at its second resonant vibrational mode to generate a large oscillatory displacement at a high working frequency. The frequency for this study is 1240 Hz and the measured displacement of the jet-driving diaphragm is 0.5 mm. The corresponding peak velocity of each jet is around 45 m/s and the total power consumption is 1.6 W when operating with 20 jets. Heat transfer experiments using jet arrays of different jet orifice configurations are conducted in a single narrow channel that represents one of the channels of a multi-channel heat sink. With a through-flow velocity of 14.7 m/s driven by a centrifugal fan, the synthetic jet arrays with square orifices achieve 9.3% enhancement on heat transfer coefficient averaged over the entire fin (channel wall) surface, compared to the value for a case with through-flow only. When the channel through-flow velocity decreases to 8 m/s spatially-averaged heat transfer enhancement by the jets is 21.7%; again, averaged over the entire fin (channel wall) surface. In a computational study, the jet diaphragm movement is realized with a dynamic mesh available within the commercial software package ANSYS Fluent. Computed surface-average Nusselt numbers show good agreement with the experimental data, differing by no more than 10%. The numerical study was performed to quantify the effects of system parameters, such as the jet and channel flow rates and orifice-to-fin-surface distance, on heat transfer performance over different sections of the channel (fin) wall. According to the results of the numerical study, the synthetic jets have a strong cooling effect on the channel wall tip region, the nearest surface to the jet orifice, and a weaker effect on the channel side surfaces. It is found that the synthetic jet can enhance locally-averaged heat transfer coefficients at the fin tip by up to 413%, compared to a case with cooling by channel through-flow only.

Time-resolved PIV measurement and thermal-hydraulic performance evaluation of thin film self-agitators in a rectangular channel flow

This study experimentally investigates the vortex dynamics induced by thin film self-agitators in a rectangular channel and the resultant thermal-hydraulic performance due to the disruption of the thermal boundary layer. Four channel flow features are compared: a clean channel without any agitators, a channel with double rectangular-shaped self-agitators in thicknesses of 25 µm and 125 µm, and a channel with double fishtail-shaped self-agitators in thickness of 25 µm. The effect of the self-agitator motion on the dynamic vortex shedding is characterized by employing time-resolved particle image velocimetry (TR-PIV) at the midspan of the agitator within a Reynolds number range of about 1300–6800 in a customized single channel. The instantaneous and time-averaged flow field are quantified in terms of velocity magnitude, vorticity contour, and turbulence intensity distribution. Results show that the added self-agitator designs all have positive effects on the flow mixing, especially during the flapping mode region. Near wall flow dynamics measurements quantitatively confirm the enhancement of flow boundary layer disturbance. In addition, an off-the-shelf multi-channel heatsink with an identical cross-section profile is tested under the same flow conditions to quantify the heat transfer enhancement as well as the pressure loss penalty for the four channel design features. A dimensionless synthetic thermal-hydraulic performance factor η is used to evaluate the overall benefits of the three self-agitator designs compared to the clean channel. A maximum enhancement factor of approximately 1.42 can be achieved while keeping above 1 for most of the test conditions. Therefore, there is great potential for integrating this external-energy-free vibration motion into plate fin heat exchanger applications.

Optimization of the Micro Channel Heat Sink by Combing Genetic Algorithm with the Finite Element Method

The design of a micro multi-channel heat sink to achieve the minimum thermal resistance is the purpose of this study. The numerical package is employed by using the genetic algorithm to process the heat dissipation optimization of the micro multi-channel heat sink (the genetic algorithm employs the numerical package). The variables of this optimal design include channel number, channel aspect ratio and the ratio of channel width to pitch, as well as considering the weight of this micro channel heat sink in the optimal design process. Therefore, this optimization is a multi-objective function design. The results show that the thermal resistance is decreased as 0.144 W/K, and the weight of this micro channel heat sink can be decreased, individually or simultaneously.

A multi-channel cooling system for multiple heat source

High-power electronic devices with multiple heating elements often require temperature uniformity and operating within their functional temperature range for optimal performance. A multi-channel cooling experiment apparatus is developed for studying heat removal inside an electronic device with multiple heat sources. It mainly consists of a computer-controlled pump, a multi-channel heat sink for multi-zone cooling and the apparatus for measuring the temperature and pressure drop. The experimental results show the system and the designed multi-channel heat sink structure can control temperature distribution of electronic device with multiple heat sources by altering coolant flow rate.

Enhancing heat transfer in air-cooled heat sinks using piezoelectrically-driven agitators and synthetic jets

Air-cooled heat sinks are widely used for microelectronics cooling. Piezoelectrically-driven agitators and synthetic jets (syn-jets) have been reported as good options in enhancing heat transfer on nearby surfaces. This study proposes that agitators and syn-jets be integrated within air-cooled heat sinks to significantly augment heat transfer performance. The proposed integration is investigated experimentally and computationally in a single-channel heat sink with one agitator and two syn-jet arrays. The study of a single channel between two fins is a precursor to the design of a full scale, multi-channel heat sink. The agitator and syn-jet arrays are separately driven by three piezoelectric stacks operating at their individual resonant frequencies to actively disrupt and mix the bulk air flow within the channel. The experiments show that the combination of the agitator and syn-jets raises the heat transfer coefficient of the channel by 82.4%, compared with a same channel having channel flow only. The computations show similar rises that agree well with the experiments. The numerical simulations attribute the active heat transfer enhancement to the turbulence introduced in the channel flow near the tips of the fins which constitute the channel walls by the syn-jets and the vortices introduced in the channel flow near the side and base of the channel walls by the agitator plate. Heat transfer enhancement by the agitator and syn-jets increases as their amplitude or frequency increases, but the increase percentage by these active components decreases as the channel flow velocity increases. A correlation between the average Nusselt number for the channel walls and the Reynolds numbers for the channel flow, agitator, and syn-jet is established.