Performance Of Microchannel Heat Exchanger Research Articles

Study of impact of nano fluids on performance of microchannel heat exchangers using CFD

Addressing the critical issue of heat generation in electronic devices due to miniaturization and higher power density is essential. As electronic components become more compact, they generate more heat flux, necessitating efficient thermal management solutions. Traditional methods and fluids, such as water, struggle to meet the demand for efficient heat dissipation. To address this challenge, the utilization of nanofluids presents a promising solution. The objective of this study is to use CFD methods to examine how a nanofluid can improve heat transmission and lower the maximum temperature in a microchannel heatsink. This article presents the study of microchannel heatsinks with two distinct channel counts (five and eight). A constant flow, incompressible, laminar model was used to verify the findings. The working fluids used in the study were water in various concentrations, water-based nanofluids of Fe3O4-water and MWCNTs. CFD simulations revealed that a MWCNT-water nanofluid at 0.2 % concentration significantly improved cooling performance compared to water, demonstrating the potential of nanofluids for efficient thermal management in electronic devices.

Study on the Flow and Heat Transfer Performance of Microchannel Heat Exchangers With Different Elliptical Concave Cavities

AbstractEllipticity has a significant impact on the flow and heat transfer performance of microchannel heat exchangers (MHEs) with elliptical concave cavities. In this study, five types of MHEs with different elliptical concave cavities (ellipticities of 0.4, 0.6, 0.8, 1.0, and 1.2) were designed. The influence of ellipticity on the flow and heat transfer performance of MHEs was numerically investigated using ANSYS Fluent 21.0 R1. Moreover, MHEs with corresponding elliptical concave cavities structures were processed and manufactured, and then an experimental platform was designed and built for experimental verification. The results showed that the fluid velocity distribution in MHEs with elliptical concave cavities was symmetrical, and the formation of secondary flow in the elliptical concave cavities led to the continuous destruction and reconstruction of the flow and thermal boundary layer in the microchannel, which is conducive to mass and heat transfer in the MHEs with elliptical concave cavities. The inlet and outlet pressure drop of MHEs with elliptical concave cavities increased as the inlet flow rate increased. At the same inlet flow rate, the inlet and outlet pressure drop of the MHE with elliptical concave cavities first increased and then decreased with increasing ellipticity. At an ellipticity of 1.0, the inlet and outlet of MHE exhibited the lowest pressure drop indicating that the MHE with an ellipticity of 1.0 featured the highest pressure drop performance. The cold‐water outlet temperature of the MHEs with elliptical concave cavities first decreased and then increased as the inlet flow rate increased. At the same inlet flow rate, the cold‐water outlet temperature of the MHEs with elliptical concave cavities first increased and then decreased with increasing ellipticity, while the hot‐water outlet temperature of the MHEs first decreased and then increased with increasing flow rate. This indicated that the MHE with an ellipticity of 1.0 exhibited excellent heat transfer performance.

Comparative study of the parameters affecting the performance of microchannels' heat exchangers: Latest advances review

AbstractMicrochannel heat exchangers are heat exchangers with a tube diameter of less than 1 mm. Conventional cooling approaches such as the forced‐air cooling technique fail in high technological compact systems because of the small‐sized surfaces of chips and circuits. In comparison, microchannel heat exchangers are being extensively utilized in compact‐sized devices where a high heat‐transfer medium is required. Moreover, consumers' continued desire for compact products has prompted researchers to study microchannel heat exchangers for their ability to boost the rate of heat transfer that ensures the safety of compact designs. This study presents the evaluation of performance parameters and the manufacturing aspects of microchannel heat exchangers. This study also examines how microchannel heat exchangers are affected by several parameters, including the type of working fluid used, Brownian motion, geometry of the channel, Reynolds number, Nusselt number, Knudsen number, wall resistance of the channel, the effect of gravity, and inlet and outlet arrangement for fluid. Investigating the various geometries for the microchannel indicates that the least pressure drop occurs in square shape cross‐section channels while the highest pressure drop occurs in channels with triangular cross‐sections. Moreover, it has been observed that, with the addition of nanoparticles to the working fluid, the thermal properties of the exchangers as well as the pressure drop increases while at the same time it reduces the boundary layer thickness. In addition, the Reynolds number affects the performance irrespective of the channel geometry. When the fluid is added with nanoparticles, like, Al2O3 and copper oxide (CuO) with different volumetric fractions (φ) of 0%, 0.5%, 1%, 1.5%, and 2%, the performance of the microchannel rises with rising the Reynolds number but conversely when the fluid is used in pure form the performance decreases with the rising value of Reynolds number. In addition, it has been observed that the overall improvement is obtained at φ = 2% and Re = 100 for CuO–water nanofluid. Apart from this, the least heat transfer is recorded at φ = 0.5% and Re = 1.00 for both nanofluids. Moreover, this study concludes that the Nusselt number is independent of the Reynolds number in the regime of laminar flow. It is further evident that as the nanoparticle size reduces, the Nusselt number rises when all the remaining conditions are the same. Apart from this, investigating the inlet/outlet arrangement through finite volume method for D‐, I‐, N‐, S‐, U‐, and V‐type arrangements, it is evident that the V‐type sink has overall greater performance. In terms of gravity, it is observed that it has no effect on the performance of microchannel heat exchangers. This study further illustrates the effects of the fabrication method on the performance of the microchannel heat exchangers.

Pressure drop and heat transfer performance of microchannel heat exchangers with elliptical concave cavities

For a microchannel heat exchangers (MHE) with an elliptical concave cavity, the ellipticity of the cavity has a significant effect on the pressure drop and heat transfer performance of the MHE. In this study, five types of MHEs with elliptical concave cavities were designed—with ellipticities of 0.4, 0.6, 0.8, 1.0, and 1.2—and the effects of ellipticity on pressure drop and heat transfer performance were investigated numerically and also measured experimentally, using a self-designed experimental platform. The results show that at the same inlet flow rate the pressure drop of an MHE with elliptical concave cavity becomes smaller and then larger as the ellipticity increases, and that the pressure drop at the inlet and outlet of the MHE with ellipticity 1.0 is the smallest, providing the best pressure-drop performance. When the inlet flow rate increased from 10 ml/min to 60 ml/min, the inlet-to-outlet pressure drop of the MHE with ellipticity 1.0 increased from 20.6 to 152.9 Pa, an increase of 132.3 Pa. As the inlet flow rate increases, the hot-water outlet temperature of the MHE with elliptical concave cavity first decreases and then increases, while the cold water outlet temperature behaves oppositely. When the inlet flow rate is 30 ml/min, the hot water outlet temperatures of all the MHEs with elliptical concave cavities reach their lowest values. These minimum outlet temperatures are 316.2 K for ellipticity 1.0, 317.9 K for ellipticity 0.8, 318.9 K for ellipticity 0.6, 320.4 K for ellipticity 0.4, and 319.9 K for ellipticity 1.2. Results indicate that among the configurations tested the MHE with ellipticity 1.0 exhibits the best heat transfer performance.

Multiobjective geometry optimization of microchannel heat exchanger using real-coded genetic algorithm

• A weight-based, real-coded genetic algorithm optimization was performed. • Air-side Nusselt number, friction factor, and fin efficiency were modeled. • The fin pitch imposed the most significant effect on the volume and the fan power. • The microchannel heat exchanger became more compact at higher target heat duties. • The optimization approach provides optimal solutions at given design dimensions. In this paper, a multiobjective optimization of the structure of a flat-tubed microchannel heat exchanger is performed to reduce its volume and fan power at a specified capacity. Design variables include tube height, tube width, tube length, fin height, and fin pitch. A weight-based, real-coded genetic algorithm is implemented to optimize the design variables within their specified range of dimensions. To further improve the numerical simulations of the microchannel heat exchanger performance, correlations for the air-side Nusselt number, friction factor, and fin efficiency are developed and validated. In the optimization, the Pareto optimal fronts are obtained by varying weights of the two conflicting objectives. A reference microchannel heat exchanger operating at different capacities is optimized. Results show that the volume and fan power of the reference microchannel heat exchanger can be reduced by up to 45% and 51% respectively, depending on the weighting factor selected. The optimization approach of this study provides the optimal solutions at the given domain of geometric parameter dimensions.

Research on Pressure Drop and Heat Transfer Performance of Microchannel Heat Exchangers with Elliptical Concave Cavities

Research on Pressure Drop and Heat Transfer Performance of Microchannel Heat Exchangers with Elliptical Concave Cavities

Void fraction in vertical intermediate and inlet headers of microchannel heat exchangers: Experiments and models

The void fraction in headers of microchannel heat exchangers (MCHEs) affects the refrigerant charge, distribution, pressure drop, and heat transfer coefficient of MCHEs. However, due to the complex geometries of headers, experimental measurements of void fraction in headers with refrigerant are still missing in the open literature. A model that predicts local void fraction between microchannel tubes in headers is also widely needed when predicting the refrigerant charge and the performance of MCHEs. This paper first presents experimentally measured void fraction between microchannel tubes in a intermediate (five inlets and five outlets) and inlet headers (ten or five outlets) with R134a by calibrated capacitive sensors. For the intermediate header, the ranges of inlet mass flow rate and quality are 3.2 g s−1 to 5.2 g s−1 and 0.2 to 0.8, respectively. The inlet mass flow rates vary from 3.2 g s−1 to 7.2 g s−1 and qualities range from 0.1 to 0.82 for the inlet headers. As the inlet quality increases, the average void fraction in headers becomes larger. Other local parameters in the headers, such as mass flux, quality, superficial velocity together with the visualization results are also obtained. Void fraction shows a strong relation to the local quality in headers and the refrigerant distribution in microchannel tubes. A drift-flux void fraction model based on the local variables is proposed in this paper. The local void fraction predicted by the model agrees well with the experimentally measured values, with most of the predictions falling into ± 15% deviations. The proposed model has better accuracy when predicting void fraction in headers comparing to some widely used correlations.

Smart microchannel heat exchanger based on the adaptive deformation effect of shape memory alloys

Microchannel heat exchangers that are compact and have high efficiency have significant application value in the cooling of high-power electronic components. In this study, a smart microchannel heat exchanger with a shape memory alloy vortex generator (SMA-VG) was proposed to address the challenges associated with complex working conditions and random hotspots of electronic components. Owing to the shape memory effect, the structure of the SMA-VG can automatically adjust to change the flow characteristics of the microchannel, such that the cooling capacity and heat dissipation demand can be matched intelligently without external control. Herein, the principle underlying smart microchannel heat exchangers is analyzed, and a relationship between coil deformation and the Nusselt number (Nu) is proposed. Subsequently, the responses of the SMA-VG to different heat fluxes and Reynolds numbers are revealed, and a SMA-VG of three unequal lengths is proposed. The performance of microchannel heat exchangers with SMA-VG was investigated by combining experimental and numerical methods. The results showed that the SMA-VG adaptively adjusted its pitch configuration with changes in heat flux, improving the overall heat transfer performance of the channel in comparison to the non-deformed vortex generator (NDF-VG). The channel with the SMA-VG exhibited a stronger localized disturbance performance. When the heat flow density was 100 000 W/m2, Nu increased by 112% relative to that of the channel without a vortex generator, which was 9% higher than that of the channel with NDF-VG. Therefore, this novel heat exchanger resolves the challenges of poor automatability that are associated with traditional microchannel heat exchangers, in addition to removing random hotspots. Moreover, it facilitates the achievement of different levels of heat dissipation demands without external control, and it has potential for application in fields involving the usage of high-heat-flux chips.

OPTIMIZATION OF THE MICROELECTROMECHANICAL PROPERTIES OF HEAT EXCHANGE SYSTEMS THROUGH MICROCHANNEL TECHNOLOGY

Abstract: Performance of microchannel heat exchangers is highly dependent on their geometry and shape. Hence, the structural design is as equally important as the material components. This paper expounds the development and applications of microchannel technology thereby proposing an optimal applicability on the microelectromechanical properties of heat exchange systems.

Numerical investigation of the electric double-layer effect on the performance of microchannel heat exchanger at combined electroosmotic and pressure-driven flow


 
 
 Numerically investigated the electric double layer (EDL) Effects on the performance of the square microchannel heat exchanger (MCHE) at combined electro-osmotic and pressure-driven flow with compared pure pressure-driven with a hydraulic diameter (10 – 50) μm. We defined at any size (Dh) of microchannel heat exchanger become the impact of EDL very slight with the studied effect of electric double layer thickness λ. The diluted water 1:1 potassium chloride (KCl) solution is used as a working fluid at an ionic concentration , , silicon microchannel at zeta potential of surface -0.2 volt.
 A three-dimensional (3D) Poisson-Boltzmann equations and Naiver-stoke equations with applied electric field solved by using the finite volume scheme in this work. The results show an increase in pressure drop of the microchannel heat exchanger at combined flow electroosmotic and pressure-driven flow with a percentage of 31.09 % at an ionic concentration and 42.71 % at increase in pumping power, especially at low ionic concentration. Slight enhancement in average heat transfer rate and effectiveness due to an increase in average temperature difference. Decrease in overall performance at combined electroosmotic and pressure-driven flow compared with pure pressure driven.
 
 

Efficacy of a novel graphene quantum dots nanofluid in a microchannel heat exchanger

Utilizing nanofluids is a suitable method to improve the performance of microchannel heat exchangers. Moreover, graphene quantum dots nanofluid, as a novel nanofluid with its unique features, can be a proper choice for employment in heat exchangers. In this article, for the first time, a graphene quantum dots nanofluid is employed as the working fluid of a microchannel heat exchanger. For this purpose, the graphene quantum dots nanofluid at concentrations of 0–0.5% and Reynolds numbers ranging from 50 to 200 is utilized as the hot fluid, while pure water with a Reynolds number of 100 is considered as the cold fluid. The problem-solving approach is the 3D numerical method based on the finite-volume technique. Moreover, temperature-dependent thermophysical properties are assumed for the hot and cold fluids. The results reveal that at Reynolds numbers of 50 and 100, utilizing the nanofluid greatly improves the heat transfer rate for a slight increase in the pressure drop, so that in the case of using the 0.5% nanofluid at Reynolds number of 50, the heat transfer rate improves 14% for only an 8% increase in the pressure drop. However, at Reynolds numbers of 150 and 200, the use of the nanofluid imposes a large pressure drop on the system. Based on the obtained results, utilizing the graphene quantum dots nanofluid at Reynolds numbers of 50 and 100 is suggested since the heat exchanger performance enhances, while at Reynolds numbers of 150 and 200, using the nanofluid is not recommended due to the high pressure drop penalty.

Experimental study and performance analysis of high-performance micro-channel heat exchanger for hypersonic precooled aero-engine

The microchannel heat exchanger is a critical component of hypersonic precooled aero-engines, facing huge challenges from design and manufacture due to the demanding requirements of higher power-weight ratio and lower pressure loss. In this paper, a segmental method (SEG) taking the influence of fin efficiency into consideration is proposed to analyze and evaluate the performance of microchannel heat exchanger for precooled engines. In order to validate the method and investigate the flow and heat transfer characteristic, a microchannel heat exchanger with the hydraulic diameter of 263.6 μm was fabricated and measured on a 3 kW open loop experimental platform. The experimental results indicate that the maximum deviation between the heat transfer rate predicted by the SEG method and the experimental data does not exceed 5% on the condition of balanced flow and unbalanced flow. Furthermore, a new correlation for pressure drops based on experimental results without heat transfer is developed to correct the results predicted by the SEG method and the maximum deviation does not exceed 3%. At last, the influence of the geometric parameter of the basic heat transfer unit was thoroughly discussed for further understand the performance of microchannel heat exchanger under typical working conditions. It is indicated that potential channel width should not be more than 0.5 mm (dh=0.305 mm) in the case of integrating various factors.

Study the hydro and thermal performance of microchannel heat exchanger with hybrid suspension of nanoparticles and MEPCM particles

This paper aims to study the flow and heat transfer of hybrid suspension in counter flow micro channel heat exchanger (CFMCHE). In order to enhance the thermal properties of micro encapsulated phase change material (MEPCM) suspension. The hybrid suspension studied in this paper consists of nanoparticles and MEPCM particles, these particles are suspended in water as abase fluid, two types of hybrid suspension are used (Cu + MEPCM suspension) and (Al2O3+ MEPCM suspension) by n-octadecane as a PCM for both of them. The hydrodynamic and thermal characteristics of thes suspensions flow in micro channels of CFMCHE is numerically investigated. From obtained results, using of hybrid suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increase its effectiveness but it also lead to high increasing in pressure drop. The results showed considerable enhancement in cooling effectiveness of (Al2O3 + MEPCM suspension) above of the pure PCM suspension, Nanofluids, and water. While (Cu + MEPCM suspension) showed enhancement above of the pure PCM suspension and water, but was not best effectiveness than Nanofluids. Extra increase in pressure drop in both types of hybrid suspension above are leads to reduce the overall performance compared with pure PCM suspension. Therefore its use depends on the application at which this heat exchanger is employed

Pressure drop and heat transfer performance of microchannel heat exchanger with different reentrant cavities

The shape of the reentrant cavities has a great effect on the pressure drop and heat transfer performance of microchannel heat exchanger (MHE). In present study, MHEs with three reentrant cavity, i.e. circular, trapezoidal, and rectangular, were designed and manufactured. The influence of the cavity shape on the pressure drop performance, heat transfer performance and comprehensive performance of the MHEs were investigated. The pressure drop and Darcy friction coefficients were largest for the rectangular reentrant cavities, indicating that it exhibited the best pressure drop performance. At the same flow rate, the MHE with circular reentrant cavities had the lowest hot water outlet temperature and the MHE with rectangular reentrant cavities had the highest temperature, whereas the results were the opposite for the cold water outlet temperature. The Nusselt number was largest for the circular reentrant cavities. This indicates that the MHE with circular reentrant cavities had the best heat performance. Finally, the comprehensive performance index η was put forward. And the result found that the MHE with circular reentrant cavities had the highest comprehensive performance.

Experimental and numerical studies on heat transfer enhancement of microchannel heat exchanger embedded with different shape micropillars

The experimental and numerical investigations on heat transfer enhancement by different shapes of micropillars embedded in microchannel heat exchanger were performed. The temperature, velocity and vorticity contour distribution were obtained through numerical simulation. A series of experiments were conducted to validate the simulation model. The simulation results agreed well with the experimental results. Later, Nusselt number (Nu), pressure loss, and the overall thermal performance parameter (TP) at a range of Reynolds numbers (Re) were presented and compared. The experimental results showed that the Nu/Nu0 ratios for the tested microchannels fell in the ranges of 1.65–1.9 for micropillars of square (type A), circle (type B), fan-shaped (type C), and 1.6–1.7 for micropillars of drop-shaped (type D) and irregular drop-shaped (type E). However, the microchannels with micropillars of type D and E show an increase of about 20–40% in the pressure loss, while the microchannels with micropillars of type A, B and C showed an increase of above 60%. Furthermore, much higher TP values were observed for type D and E micropillars, indicating better heat transfer performance of microchannel heat exchanger in the tested range of Reynolds number.

Pressure Drop and Heat Transfer Performance of Microchannel Heat Exchanger With Circular Reentrant Cavities and Ribs

Abstract The rib arrangement has an important influence on the pressure drop and heat transfer performance of a microchannel heat exchanger (MHE) with circular reentrant cavities and ribs. In this study, four kinds of MHEs with circular reentrant cavity and ribs were designed, namely, circular reentrant cavities (circular), circular reentrant cavities and single-sided ribs (circular—single), circular reentrant cavities and odd-symmetric ribs (circular—odd), and circular reentrant cavities and double symmetric ribs (circular—double). The effect of the rib arrangement on the pressure drop and heat transfer performance of MHEs was numerically investigated by ansysfluent 15.0. The experimental platform was then designed and built for the subsequent experimental verification. The results showed that the pressure drop between the inlet and outlet of the MHE with circular reentrant cavities and ribs increased as the inlet flow increased. At the same inlet flowrate, the pressure drop between the inlet and outlet of the MHEs was largest for the circular reentrant cavities and double symmetric ribs, followed by the circular reentrant cavities and odd-symmetric ribs, circular reentrant cavities and single-sided ribs, and the circular reentrant cavities. The presence of the rib structure increased the inlet and outlet pressure drop of the MHE. The MHE with circular reentrant cavities and double symmetric ribs had the largest inlet and outlet pressure drop, followed by that with circular reentrant cavities and odd-symmetric ribs, that with circular reentrant cavities and single-sided ribs, and that with circular reentrant cavities, indicating that the latter exhibited the best pressure drop performance. At the same inlet flowrate, the MHE with circular reentrant cavities had the highest hot water outlet temperature and the MHE with circular reentrant cavities and double symmetric ribs had the lowest temperature, whereas the results were the opposite for the cold-water outlet temperature. This indicates that the heat transfer performance was best for the MHE with circular reentrant cavities and double symmetric ribs, followed by that with circular reentrant cavities and odd-symmetric ribs and that with circular reentrant cavities and single-sided ribs.

Evaluation of a counter-flow microchannel heat exchanger performance with air-water vapor mixture to liquid water

Given its configuration and operation conditions, the performance of a counter-flow microchannel heat exchanger (MCHX) is evaluated through detailed calculations. The fluids, both liquid water and air, are considered as continuum flow flowing in microchannels. The MCHX has 59 sheets, and each sheet has 48 microchannels. The microchannels for both fluids have the same cross section of 0.8mm×1mm and same length of 200mm. Log mean temperature difference method is adopted for this evaluation. Using appropriate equations, the properties of air-water vapor mixture are calculated based on that of the two components. Given the inlet temperature for liquid water(35℃) and air (170℃),the calculated outlet temperature for both fluids are 55.5℃ and 43.3℃, respectively. The results also show that the air at the outlet is saturated. The overall heat transfer coefficient reaches 100W/m2ꞏK, which is much higher than that of conventional heat exchanger with similar fluid combinations.

Experimental investigation of the heat transfer performance of microchannel heat exchangers with fan-shaped cavities

The microchannel heat exchanger has been applied in many field because of its advantages, such as miniaturization, large specific surface area, and high heat and mass transfer rate. In this work, a microchannel heat exchanger with fan-shaped cavities (FSCs) was developed, and used to conduct comparative experimental studies with the conventional rectangular straight microchannel heat exchanger. The effects of structural parameters, such as the deviation degree, coincidence degree and distribution of FSCs, on the heat transfer performance of the microchannel heat exchanger were investigated. The results indicate that the performance of the microchannel heat exchanger with FSCs is better than that without FSCs and the pressure drop is smaller. It is also revealed that the deviation degree, coincidence degree and distribution of the FSCs have important effects on the heat transfer performance.

Multi-blade milling process of Cu-based microchannel for laminated heat exchanger

A combined tool with stacked blades was developed to efficiently fabricate microchannel plates by using the multi-blade milling process. The microchannel plates with 0.632 mm in hydraulic diameter and 40 mm in length were then used to assemble the microchannel heat exchanger. The thermal performance of microchannel heat exchanger was experimentally investigated with different flow rates. After the forming mechanism of multi-blade milling process was analyzed, the influence of processing parameters on microchannel geometry was investigated. The results showed that the cutting depth and feed rate exhibited great influence on the top width and the spacing of microchannel. On the other hand, the microchannel geometry had been less affected by the cutting speed. Compared with a heat exchanger without microchannels, the heat transfer coefficient per unit volume of the microchannel heat exchanger was significantly increased. When the flow rate was 900 ml min−1, the heat transfer coefficient per unit volume of the microchannel heat exchanger could reach to 735 kW m−3 K−1 with a corresponding pressure drop of 18.2 kPa. In a word, the developed heat exchanger with microchannel plates exhibits an enhanced thermal performance and good pressure drop characteristics.

Air-side thermal hydraulic performance of microchannel heat exchangers with different fin configurations

This paper presents three-dimensional steady state analysis of compact multi-louvered fin and flat tube heat exchangers applicable in domestic and mobile air conditioning systems. Conjugate heat transfer analysis has been conducted for five geometric configurations of the heat exchanger based on the louver pitch values (0.8, 1.0, 1.4, 1.7 and 2.0mm) in the laminar range of Reynolds number 50–450. For all geometric configurations, local air-side heat transfer coefficient and pressure drop are presented in terms of Colburn j factor and Fanning friction f factor, respectively. In addition, the effect of fin height on thermal hydraulic performance has also been addressed based on local Nusselt number distribution along the fin height. The results reveal that geometric configuration with the louver pitch of l.0mm showed the highest average Nusselt number of 123% at the penalty of 116% pressure drop compared to louver pitch of 2.0mm at the Reynolds number of 50.