Fan-shaped Cavities Research Articles

Optimal Design of Microchannel Heat Sink with Staggered Fan-Shaped Cavities and Ribs

In the present study, a three-dimensional numerical simulation is conducted to study the characteristics of fluid flow and heat transfer in a newly designed microchannel heat sink with fan-shaped cavities and ribs (MC-FCFR). The Reynolds number ranges from 147 to 736. A straight rectangular microchannel (MC-RC) is used as the baseline. The geometric parameters include the relative spacing θ, relative width α, and relative height β of the fan-shaped cavities and ribs. The overall performance index (OPI) of the MC-FCFR is evaluated in terms of the friction factor and Nusselt number. The OPI for the MC-FCFR with θ=3.56, α=1.63, and β=0.5 reaches 1.70.

Investigation on thermal performance of nanofluids in a microchannel with fan-shaped cavities and oval pin fins

In this paper, a combined structure of fan-shaped cavities and oval pin fins is designed for the rectangular microchannel heat sink with an aspect ratio of 2. Four structural parameters are investigated, including cavity height (hr), chord length (Ir), rib offset distance (S0) and rib height (Hf). Overall performance factor and total thermal resistance are used to reflect the microchannel performance. In the Reynolds number range of 132–531, the microchannel shows the best hydrothermal performance under hr of 0.05 mm, Ir of 0.2 mm, S0 of 0, and Hf of 0.1 mm. When the Reynolds number is 398, the overall performance factor of the microchannel with optimal parameter combination is 33% higher than that of a rectangular microchannel. Field synergy angle in the microchannel is calculated based on the field synergy principle. According to the KKL (Koo-Kleinstreuer-Li) model, the local thermal conductivity distribution of Al2O3 nanofluids is studied at different nanoparticle diameters. Moreover, the overall performance factors of the heat sink are investigated at several volume fractions of Al2O3 nanofluids. Under the Reynolds number of 132, the Nusselt number of 0.04 vol% nanofluid is 9.5% higher than the deionised water. Based on optimal structural parameters, compared with deionised water, Al2O3 nanofluid with a diameter of 10 nm and volume fraction of 0.04 further improve the overall performance factor of micro-channels by 5.8% and reduce the total thermal resistance by 2.9%.

Computational study of rib shape and configuration for heat transfer and fluid flow characteristics of microchannel heat sinks with fan-shaped cavities

Cavities and ribs are usually utilized in the design of microchannel heat sink systems, and their combination may lead to the optimum overall performance. However, it remains unclear how different combination methods contribute to the performance and efficiency of the systems. Computational fluid dynamics simulations were conducted to identify the optimum rib shape and configuration for the systems with fan-shaped cavities. The ribs are rectangular, diamond, hexagonal, or elliptic in cross-section. The effects of rib shape, dimensions, and configuration are investigated, and the optimum comprehensive performance was determined. The results indicated that the shape, dimensions, and configuration of ribs are important factors that affect performance and heat transfer efficiency. The shape and position of ribs must be optimized to minimize pressure drop while maximizing heat removal efficiency. The shape of ribs can be an important factor in obtaining high efficiency of heat removal while limiting the pressure drop across the channels. When the ribs are rectangular in shape, the maximum pressure drop occurs but the maximum relative Nusselt number is achieved. The maximum comprehensive performance factor is achieved when the ribs are elliptic in shape and the Reynolds number is highest. Further improvement in performance can be achieved by choosing particular rib dimensions and configuration. In order to provide appropriate benefit to such a microchannel heat sink system without inducing additional pressure drop that reduces the performance of the system, it is desirable to properly shape and position the ribs relative to the cooling flow and the cavities in a way that takes best advantage of the benefits provided by the combination of cavities and ribs. The effect of trailing edge vortexes on heat transfer performance is significant. A maximum comprehensive performance factor of 1.96 is achieved when the Reynolds number of the laminar flow is 460.

Numerical investigation on fluid flow and convective heat transfer in a microchannel heat sink with fan-shaped cavities and ribs

In the present study, a detailed numerical simulations of liquid flow in microchannel heat sink with four different geometry of ribs: rectangular (RR), backward triangular (BTR), forward triangular (FTR) and diamond (DR) arranged symmetrically inside reentrant fan shaped cavities (FC) on side walls has been conducted and compared with smooth channel (SC) to acquire fluid flow and heat transfer characteristics between Reynolds numbers of 136−588. The local pressure, temperature and heat transfer coefficients were determined to understand the convective heat transfer regimes and to analyze local flow behavior. The three-dimensional conjugate heat transfer model, investigation is done extensively to identify the influence of geometrical parameters towards augmenting thermal performance with parametric optimization. Evolved governing equations are solved by using SIMPLEC algorithm. Attempt has been made to improve heat extraction ability with reasonable pressure drop by replacing the existing simple design of microsink. It is observed that Nusselt number and friction factor are in good agreement with previous experimental data. Based on detailed parametric study, it was found that FC-RR is good in achieving maximum Nusselt number, but due to higher pressure drop penalty giving lower performance. Out of four proposed, FC-DR is conferring upstanding balance between heat transfer, pressure drop and giving the best thermal performance of 1.97 at Re = 391.47.

Numerical simulation of the fluid flow and heat transfer characteristics of microchannel heat exchangers with different reentrant cavities

PurposeWith the increasing heat dissipation of electronic devices, the cooling demand of electronic products is increasing gradually. A water-cooled microchannel heat exchanger is an effective cooling technology for electronic equipment. The structure of a microchannel has great impact on the heat transfer performance of a microchannel heat exchanger. The purpose of this paper is to analyze and compare the fluid flow and heat transfer characteristic of a microchannel heat exchanger with different reentrant cavities.Design/methodology/approachThe three-dimensional steady, laminar developing flow and conjugate heat transfer governing equations of a plate microchannel heat exchanger are solved using the finite volume method.FindingsAt the flow rate range studied in this paper, the microchannel heat exchangers with reentrant cavities present better heat transfer performance and smaller pressure drop. A microchannel heat exchanger with trapezoidal-shaped cavities has best heat transfer performance, and a microchannel heat exchanger with fan-shaped cavities has the smallest pressure drop.Research limitations/implicationsThe fluid is incompressible and the inlet temperature is constant.Practical implicationsIt is an effective way to enhance heat transfer and reduce pressure drop by adding cavities in microchannels and the data will be helpful as guidelines in the selection of reentrant cavities.Originality/valueThis paper provides the pressure drop and heat transfer performance analysis of microchannel heat exchangers with various reentrant cavities, which can provide reference for heat transfer augmentation of an existing microchannel heat exchanger in a thermal design.

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.

Effects of structural parameters on fluid flow and heat transfer in a serpentine microchannel with fan-shaped reentrant cavities

A three-dimensional numerical model has been conducted to study the laminar flow and heat transfer characteristics in serpentine microchannel with different geometric fan-shaped reentrant cavities for Reynolds number ranging from 150 to 980. The microchannel has the width of 0.1 mm and depth of 0.2 mm in the rectangular cross-section. The geometric parameters of fan-shaped reentrant cavities examined in this paper are 0.04058 mm for the width (Wc), 0.0084–0.02029 mm for the height (Hc) and 0.04058–0.12174 mm for the spacing (Sc).This study firstly presents the comparison of the thermal and hydraulic characteristics of serpentine microchannel with fan-shaped reentrant cavities with the conventional microchannels heat sink. Then the effects of fan-shaped cavities on velocity contour, temperature distribution and secondary flow features in such microchannel heat sinks are given. It is apparent that the fan-shaped cavities can effectively reduce the flow resistance and improve the temperature distribution uniformity. The effects of developed non-dimensional variables on the frictional pressure drop, average Nusselt number and the relationship between thermal resistance and pumping power in the novel channel are investigated. Compared with rectangular serpentine channel, heat transfer is enhanced for all cases and flow resistance is decreased besides Re = 980 and Hc/Wc = 0.2887. The best performance of serpentine microchannel with fan-shaped reentrant cavities is found at Sc/Wc = 3 and Hc/Wc = 0.2887.

Molecular Barrel by a Hooping Strategy: Synthesis, Structure, and Selective CO2 Adsorption Facilitated by Lone Pair−π Interactions

A sophisticated molecular barrel 5 was efficiently constructed by hooping a 63-membered loop around a D3h-symmetric, shape-persistent bis(tetraoxacalix[2]arene[2]triazine) core. The hooping strategy involved 3-fold ring-closing metathesis (RCM) reactions of six branched olefin arms which were preanchored on the inner core. Through hooping, the loop tightens the cage structure and significantly enhances its stability toward nucleophilic decomposition. The X-ray crystal structure showed the molecular barrel bears three enclosed fan-shaped cavities as divided by the triazine rings and each of the cavities can hold a solvent CHCl3 or CH2Cl2 molecule. With the intrinsic porosity, the amorphous solids of 5 exhibit considerable CO2 uptake with an exceptionally large isosteric enthalpy. Lone pair (lp)-π interactions between the electron-deficient triazine rings and CO2 could contribute to the strong adsorption as supported by IR studies and DFT modeling.

Analysis of Flow and Mixing Characteristics of Planar Asymmetric Split-and-Recombine (P-SAR) Micromixers with Fan-Shaped Cavities

A modified micromixer design based on the concept of multidirectional vortices and unbalanced splitting and recombining of fluid streams is described in this work. The purpose of this study was to demonstrate that the combination of unbalanced inertial collisions, multidirectional vortices, and converging/diverging flow caused by the fan-shaped cavities contributes to the improvement of the mixing effectiveness. By using computational fluid dynamics (CFD), numerous studies of the mixing performance and flow features were completed at moderately low Reynolds numbers ranging from 1 to 80. Experimental analysis of the mass transfer and mixing quality along this modified micromixer was performed to validate the numerical results. The computational and experimental results for the concentration distributions and flow patterns reveal the following trends: (i) The combination of transverse Dean vortices effect (vertical plane) and expansion vortices (horizontal plane) effectively contribute to the considerable i...

Flow direction when fan shaped geometry is applied in gas-assisted injection molding: 2. Development of flow model and its predictions

In part 2 of the paper simplified unsteady-mass (and momentum-) balance equations of melt polymer resin in the cavities of GAIM were proposed, as a time-dependent rule of thumb, to constitute a novel flow model in GAIM under the configuration of two fan-shaped geometries connected with a gas nozzle. Upon performing a simulation on them with commercial software (MOLDFLOW), we compared the time evolution of simulated gas penetration lengths with the those of unsteady trajectory on the gas flow in GAIM by the suggested novel flow model in the fan-shaped cavities in order to check the precision of model-predicted gas penetration lengths as well as the consistency of its predicted direction. The results by the suggested novel flow model were satisfactory to fit the trajectory simulated with commercial software (MOLDFLOW).

Flow direction when fan shaped geometry is applied in gas-assisted injection molding: 1. Flow model theory and its criteria for predicting flow directions

In part 1 of this paper a qualitative analytical method to predict the preferred gas flow direction in gasassisted injection molding (GAIM), which involves flow through panel-areas of various fan-shaped geometries, and the criteria to apply the method were presented with appropriate assumptions. Then the definition of a resistance to initial velocity was proposed as a rule of thumb, by which the gas directions of GAIM were predicted under various fan-shaped geometries. Upon performing the simulation on them with commercial software (MOLDFLOW), we compared the ratio of simulated gas penetration lengths to both directions with the predicted ratio of resistances as well as the predicted direction of the gas flow in GAIM using the suggested rule of thumb herein presented. The predictions with the suggested rule of thumb were generally quite consistent with the results of simulation (MOLDFLOW). However the discrepancy between the ratio of gas penetration lengths and the ratio of resistances was observed to increase as the ratio $$\left( {\frac{{more(H/R_0 )(one - side)}}{{less(H/R_0 )(the other - side)}}} \right)$$ of the values of H/R0 on both sides of fan-shaped cavities became bigger even though the suggested rule of thumb was assumed adequate to use until the case met the condition of (H/R0)2 $$1/\hat \theta ^2 \ll 1$$ and (H/R0)2≪1. Nevertheless, the suggested rule of thumb was still effective as far as the direction of gas flow was concerned.