Nanofluid-cooled Microchannel Heat Sink Research Articles

Optimization of a boron nitride nanotubes nanofluid-cooled microchannel heat sink at different concentrations

The microchannel heat sink (MCHS) has become the most relevant micro-heat exchanger for a small area in need of an effective high heat removal system. However, heat dissipation from the microchips where the MCHS is utilized—the microprocessor and microcontroller—is getting higher with the sizes getting smaller. A more effective coolant is needed to address the increasing heat load from the microchip and nanofluid, nanosized particles dispersed in a base fluid, is among those explored. This paper reports a new potential use of non-metallic nanofluid, boron nitride nanotube (BNN), that is capable of improving the overall performance of a rectangular MCHS. A heuristic method, multi-objective genetic algorithm (MOGA), is employed to simultaneously minimize the thermal resistance and pressured drop of a boron nitride nanotubes (BNN) nanofluid-cooled MCHS to obtain optimized dimensions at various mass concentrations. The method is capable in achieving conflicting objectives, minimization of the thermal resistance and the pressure drop; an increase in the former decreases the latter and vice versa. In addition, experimental thermophysical properties of the BNN nanofluid are used to provide reliability to the optimization outcomes in identifying the best BNN concentration for cooling of a MCHS at 50 °C. The optimization results showed that as the thermal resistance decreases, the pressure drop decreases. For mass concentrations of 0.001, 0.003, 0.005, 0.01 and 0.03% the thermal resistance is the lowest, 0.0711 K/W at 0.01 mass.%. at 0.0115 W. The thermal resistance is lowered by 5.34% compared to water for the same operating conditions. These results indicate the great potential of BNN nanofluid as a coolant in the electronics cooling system. Optimization with the MOGA provides a fast analysis into the potentials of any coolants for MCHS applications as shown here, reliability being provided by experimentally obtained thermophysical properties.

Nanofluid-Cooled Microchannel Heat Sink with Carbon Nanotube

Nanofluid-Cooled Microchannel Heat Sink with Carbon Nanotube

Topology optimization design of nanofluid-cooled microchannel heat sink with temperature-dependent fluid properties

The geometric structure of a two-dimensional (2-D) nanofluid-cooled microchannel heat sink (NMHS) is optimized using a topology optimization method. We describe the flow and heat transfer in the NMHS as a single-phase nanofluid-based convective heat transfer model. Since the thermophysical properties of the nanofluid strongly depend on temperature, the temperature-dependent fluid properties are considered in the model. A heat transfer maximization problem is studied under a constant pressure difference using a density based topology optimization method to optimize configurations of NMHS. In the optimization, the material density is adopted as the design variable to control the variation of the fluid domain. An adjoint-based sensitivity analysis method is applied to obtain the gradient information used for updating the design variable. In numerical examples, the effects of temperature-dependent fluid properties on the optimal configurations of the NMHS are first investigated. Additionally, the effects of the characteristics of the nanofluid, such as the base fluid, nanoparticle volume fraction and diameter, on optimized designs are assessed. The numerical results reveal that the temperature-dependent fluid properties can significantly affect the optimal results; more branched flow channels are produced in the optimal configurations as the pressure difference or heat generation coefficient increases; and more complex optimal configuration can be obtained by reducing the nanoparticle volume fraction. From an engineering standpoint, this study provides an applicable optimization method for the design of a well-performing NMHS.

Thermal management of high-power LED based on thermoelectric cooler and nanofluid-cooled microchannel heat sink

Effective thermal management for light-emitting diodes (LEDs) is critical, as temperature significantly affects their lifetime and performance. In this study, a system combining a thermoelectric cooler (TEC) and a microchannel heat sink (MHS) is investigated experimentally for thermal management of high-power LEDs. Nanofluids and water are used as coolant. The LED substrate temperature (Ts) is measured at various TEC powers, nanofluid concentrations, ambient temperatures of LED (Ta), and ambient temperatures of the fluid radiator (Ta,f). The effective thermal resistance (Rs-fa) of the LED substrate to the ambient of the fluid radiator is analyzed. Correlations of Ts and Rs-fa are obtained. Results show that the Ts is lowest when the TEC works at its rated power, and Ts is lower than Ta at Ta ≥ 55 °C. Using nanofluids instead of water as coolant reduces the Ts by up to 18.5 °C and decreases the thermal resistance by as much as 42.4%. The MHS heat transfer capacity is increased by 38.6%. The Ta,f exhibites greater influence on Ts compared to Ta. Results show that favorable performance of the thermal management of the high-power LED is obtained by the proposed nanofluid-cooled TEC-MHS system, particularly at high ambient temperature of LED.

Heat Transfer Enhancement of Nanofluid Cooled Microchannel Heat Sink

Heat Transfer Enhancement of Nanofluid Cooled Microchannel Heat Sink

On the effectiveness of a nanofluid cooled microchannel heat sink under non-uniform heating condition

This present experimental study investigates the combined effect of nanofluid and non-uniform heating on the cooling performance of a microchannel heat sink. The microchannel heat sink considered in this study has evenly spaced 30 rectangular channels with a hydraulic diameter of 0.727mm. Three separate heaters of identical dimensions are used in the experimental study. Non-uniform heating condition is provided by switching on any two of the three heaters at a time. Al2O3/water nanofluid of volume concentration 0.1% and 0.25% and deionized water are used as working fluid. Results show that Al2O3/water nanofluid of 0.25% volume concentration exhibit lower maximum surface temperature and average surface temperature than with Al2O3/water nanofluid of 0.1% volume concentration and water in uniform and non-uniform heating condition. For a given heat transfer fluid and a given heat input, the position of heater (heat source) has a significant effect on the maximum temperature (hotspot) of the heat sink. The maximum surface temperature of the microchannel heat sink is the lowest when the heaters are placed at the upstream of the flow. The values of thermal effectiveness obtained for nanofluids encourage the use of nanofluids in microchannel heat sinks for thermal management of temperature sensitive cooling applications.

Optimization of nanofluid-cooled microchannel heat sink

The optimization of a nanofluid-cooled rectangular microchannel heat sink is reported. Two nanofluids with volume fraction of 1 %, 3 %, 5 %, 7 % and 9 % are employed to enhance the overall performance of the system. An optimization scheme is applied consisting of a systematic thermal resistance model as an analysis method and the elitist non-dominated sorting genetic algorithm (NSGA-II). The optimized results showed that the increase in the particles volume fraction results in a decrease in the total thermal resistance and an increase in the pumping power. For volume fractions of 1 %, 3 %, 5 %, 7 % and 9 %, the thermal resistances were 0.072, 0.07151, 0.07075, 0.07024 and 0.070 [oK W-1] for the SiC-H2O while, they were 0.0705, 0.0697, 0.0694, 0.0692 and 0.069 [oK W-1] for the TiO2-H2O. The associated pumping power were 0.633, 0.638, 0.704, 0.757 and 0.807 [W] for the SiC-H2O while they were 0.645, 0.675, 0.724, 0.755 and 0.798 [W] for the TiO2-H2O. In addition, for the same operating conditions, the nanofluid-cooled system outperformed the water-cooled system in terms of the total thermal resistance (0.069 and 0.11 for nanofluid-cooled and water-cooled systems, respectively). Based on the results observed in this study, nanofluids should be considered as the future coolant for electronic devices cooling systems.

Optimization of a Refrigerant Base Nanofluid-Cooled Microchannel Heat Sink with Pumping Power Consideration

In this paper, the optimization of a nanofluid-cooled microchannel heat sink was reported. Al2O3-NH3 with three different volume fractions (1 %, 3 % and 5 %) was examined. An optimization scheme which is comprised of two objective functions (thermal resistance and pumping power) and the elitist non-dominated sorting genetic algorithm (NSGA-II) was employed to optimize the overall performance of the considered system. Under the same operating conditions, the ammonia-base nanofluid (Al2O3-NH3) exceeded other coolants (Al2O3-H2O and H2O) in terms of the required pumping power (0.144, 1.015 and 0.94 W for Al2O3-NH3, Al2O3-H2O and H2O, respectively). When the refrigerant base nanofluid is used as a cooling fluid, a lighter heat sink was produced. Finally, more studies should be dedicated to explore this nanofluid and the possibility of considering it for electronic systems cooling.

Inverse geometric optimization for geometry of nanofluid-cooled microchannel heat sink

An inverse geometric optimization for nanofluid-cooled microchannel heat sink (MCHS) considering effects of temperature-dependent thermophyiscal properties for the water-based Al2O3 nanofluid with 1% particle volume fraction was performed under a constant pumping power constraint. A three-dimensional fluid-solid conjugated MCHS model combining the simplified-conjugate-gradient-method was used as the optimization tool. The channel number, N, the channel aspect ratio, α, and the width ratio of channel to pitch, β, affect the cooling performance of MCHS, and were all incorporated in the present, three-parameter optimization study. Increase in viscosity of the nanofluid did not always lead to enhanced MCHS performance under fixed pumping power constraint, contradicting to the results for pure water. The optimal MCHS design is closely related to the assigned pumping power: increase in the pumping power enhances cooling performance; however, in high pumping power regime the performance enhancement is not as effective as in low pumping power regime. At pumping power of 0.05 W and a uniform heat flux of qw = 100 W cm−2, the optimal design for the nanofluid-cooled MCHS presented N = 51, α = 5.69 and β = 0.62, yielding the optimal thermal resistance of RT = 0.1059 K W−1.

Optimal geometric structure for nanofluid-cooled microchannel heat sink under various constraint conditions

A numerical model is developed to analyze the flow and heat transfer in nanofluid-cooled microchannel heat sink (MCHS). In the MCHS model, temperature-dependent thermophysical properties are taken into account due to large temperature differences in the MCHS and strong temperature-dependent characteristics of nanofluids, the model is validated by experimental data with good agreement. The simplified conjugate-gradient method is coupled with MCHS model as optimization tool. Three geometric parameters, including channel number, channel aspect ratio, and width ratio of channel to pitch, are simultaneously optimized at fixed inlet volume flow rate, fixed pumping power, and fixed pressure drop as constraint condition, respectively. The optimal designs of MCHS are obtained for various constraint conditions and the effects of inlet volume flow rate, pumping power, and pressure drop on the optimal geometric parameters are discussed.

Study on the thermal behavior and cooling performance of a nanofluid-cooled microchannel heat sink

This paper presents an analysis of the heat transfer characteristics and cooling performance of a microchannel heat sink with water– γAl 2O 3 nanofluids having different nanoparticle volume fraction. In view of the small dimensions of the microstructures, the microchannel heat sink is modeled as a fluid-saturated porous medium for problem solving. The Forchheimer–Brinkman–extended Darcy equation is used to describe the fluid flow and the two-equation model with thermal dispersion is utilized for heat transfer. Typical results for the temperature distributions of the fluid phase and the channel wall are presented for various values of nanoparticle volume fraction and the inertial force parameter. It is found that the temperature distribution of the channel wall is practically not sensitive to the inertial effect, while the fluid temperature distribution and the total thermal resistance change significantly due to the inertial force effect. In general, the effect of fluid inertia is to reduce the total thermal resistance and the temperature difference between the channel wall and the fluid phase. The total thermal resistances obtained from the present model with inertial effect match well with the existing experimental results, whereas the thermal resistance is overestimated as the inertial effect is neglected.

An experimental investigation of forced convective cooling performance of a microchannel heat sink with Al 2O 3/water nanofluid

Experiments were conducted to investigate forced convective cooling performance of a copper microchannel heat sink with Al 2O 3/water nanofluid as the coolant. The microchannel heat sink fabricated consists of 25 parallel rectangular microchannels of length 50 mm with a cross-sectional area of 283 μm in width by 800 μm in height for each microchannel. Hydraulic and thermal performances of the nanofluid-cooled microchannel heat sink have been assessed from the results obtained for the friction factor, the pumping power, the averaged heat transfer coefficient, the thermal resistance, and the maximum wall temperature, with the Reynolds number ranging from 226 to 1676. Results show that the nanofluid-cooled heat sink outperforms the water-cooled one, having significantly higher average heat transfer coefficient and thereby markedly lower thermal resistance and wall temperature at high pumping power, in particular. Despite the marked increase in dynamic viscosity due to dispersing the alumina nanoparticles in water, the friction factor for the nanofluid-cooled heat sink was found slightly increased only.

Investigation of a nanofluid-cooled microchannel heat sink using Fin and porous media approaches

The present paper focuses on analytical and numerical study on using nanofluids as coolant of a microchannel heat sink. The nanofluid studied in this paper is made from copper oxide (CuO) and water. Two common analytical approaches are used: the Fin model and the porous media approach. The Fin model is based on the assumption of uniform fluid temperature in the direction normal to the fluid flow which causes inaccuracy in the predictions of this approach. On the other hand, modified Darcy equation for the fluid and two-equation model for heat transfer between fluid and solid sections are employed in porous media approach. In addition, to deal with nanofluid heat transfer, a model based on Brownian-motion of nanoparticles is used. The model evaluates the thermal conductivity of nanofluid considering the thermal boundary resistance, nanoparticle diameter, volume fraction and the fluid temperature. This model is included in heat transfer equations of the two approaches, and the velocity profile is obtained analytically considering the transport properties of nanofluids. Firstly, the effects of particle volume fraction and Brownian–Reynolds number on temperature distribution and overall heat transfer coefficient are investigated. After that, the influence of different channel aspect ratios and porosities are studied. Both approaches are considered and compared in details. Furthermore, an optimum aspect ratio is found to minimize the friction factor in different Reynolds numbers.

Evaluation of Heat Transfer Augmentation in a Nanofluid-Cooled Microchannel Heat Sink

Present investigation deals with appraising heat transfer enhancement of single phase microchannel heat sink (MCHS) by ultra fine Cu particle incorporation in base coolant fluid. The particle diameter is of nanometer size and base fluid in combination of nanoparticles is called nanofluid. Governing equations for fluid flow and heat transfer are based on well established “porous medium model” and accordingly, modified Darcy equation and two-equation model are employed. Appropriate equations for both fluid flow and heat transfer are derived and cast into dimensionless form. Velocity profile is obtained analytically and in order to solve conjugate heat transfer problem a combined analytical–numerical approach is employed. For heat transfer analysis, thermal dispersion model is adopted and latest proposed model for effective thermal conductivity – which considers the salient effect of interfacial shells between particles and base fluid – is integrated into model. The effects of dispersed particles concentration, thermal dispersion coefficient and Reynolds number are investigated on thermal fields and on thermal performance of MCHS. Additionally, the impact of turbulent heat transfer on heat transfer enhancement is considered.

Experimental microchannel heat sink performance studies using nanofluids

In this study, microchannel heat sink (MCHS) performance using nanofluids as coolants is addressed. We first carried out a simple theoretical analysis that indicated more energy and lower MCHS wall temperature could be obtained under the assumption that heat transfer could be enhanced by the presence of nanoparticles. Experiments were then performed to verify the theoretical predictions. A silicon MCHS was made and CuO–H 2O mixtures without a dispersion agent were used as the coolants. The CuO particle volume fraction was in the range of 0.2 to 0.4%. It was found that nanofluid-cooled MCHS could absorb more energy than water-cooled MCHS when the flow rate was low. For high flow rates, the heat transfer was dominated by the volume flow rate and nanoparticles did not contribute to the extra heat absorption. The measured MCHS wall temperature variations agreed with the theoretical prediction for low flow rate. For high flow rate, the measured MCHS wall temperatures did not completely agree with the theoretical prediction due to the particle agglomeration and deposition. It was also found that raising the nanofluid bulk temperature could prevent the particles from being agglomerated into larger scale particle clusters. The experimental result also indicated that only slightly increase in pressure drop due to the presence of nanoparticles in MCHS operation.