Effects Of Channel Dimensions Research Articles

Effect of channel dimensions and Reynolds numbers on the turbulence modulation for particle-laden turbulent channel flows

The addition of particles to turbulent flows changes the underlying mechanism of turbulence and leads to turbulence modulation. The important parameters are particle Stokes number, mass loading, particle Reynolds number, fluid bulk Reynolds number, etc., that act together and affect the fluid phase turbulence intensities. In the present study, simulations are carried out for different system sizes (2δ/dp=54,81, and 117) and fluid bulk Reynolds numbers (Reb = 5600 and 13 750) to quantify the extent of turbulence attenuation. Here, δ is the half-channel width, dp is the particle diameter, and Reb is the fluid Reynolds number based on the fluid bulk velocity and channel width. Our study shows that system size and fluid bulk Reynolds number are the two crucial parameters that affect the particle feedback force and turbulence modulation more significantly than the other. The extent of turbulence attenuation increases with an increase in system size for the same volume fraction while keeping the Reynolds number fixed. However, for the same volume fraction and fixed channel dimension, the extent of attenuation is low at a higher Reynolds number. The streamwise turbulent structures are observed to become lengthier and fewer with an increase in system size for the same volume fraction and fixed bulk Reynolds number. However, the streamwise high-speed streaks are smaller, thinner, and closely spaced for higher Reynolds numbers than the lower ones for the same volume fraction. Particle phase velocity statistics for different cases have also been reported.

Star-shaped polymer translocation into a nanochannel: Langevin dynamics simulations

The dynamics of a star-shaped polymer translocation pulled by a single arm through a nanochannel is investigated using three-dimensional Langevin dynamics simulations. The pulling force is applied on the terminal monomer of the leading arm in order to mimic the motion of chains subject to a combination of magnetic and optical tweezers in real experimental setups. The effect of channel dimensions and magnitude of the pulling force as well as the chain size and functionality on the chain’s translocation dynamics is extensively examined. The variation of the mean translocation time 〈τ〉 with respect to channel length and diameter exhibits a non-trivial behavior characterized by an abrupt change in the translocation dynamics for chains with higher functionalities f. The dependence of 〈τ〉 upon channel aspect ratio yields also a regime change for the transport dynamics for chains with larger functionalities. Moreover, the average exit time with respect to chains total mass N and to the magnitude of the pulling force F are found to follow scaling laws in agreement with theoretical predictions.

The effect of channel dimensions and configuration of thermoelectric elements on the performance of thermoelectric generator module for waste heat recovery

The use of thermoelectric modules can be effective in recovering waste heat in combustion gasses due to their special properties. In this study, due to the low efficiency of thermoelectric generators, the effects of channel dimensions and configuration of thermoelectric element pairs on heat transfer between a working fluid and a pair of PN elements were studied horizontally and vertically. To develop the simulation of the present model, temperature dependence of generator properties, variations in the convective heat transfer coefficient, temperature gradient, and pressure drop in both hot and cold working fluids along the channel were considered simultaneously. Additionally, it was found that geometric dimensions of rectangular channels affected the four main factors of temperature difference between the two sides of generators, pumped power, number of generators, and type of flow regime. Besides, the findings revealed that the increase in each dimension of the channel reduced the temperature difference between the two sides of elements. This factor was found to play a major role in the efficiency of the thermoelectric generator device, production of power peak, optimal module, channel area, and optimal channel height. In addition, the flow regime changed from turbulent to laminar at cold channel widths greater than 0.11 m. As a result, the total power dropped. Furthermore, the configuration model of PN elements affected the dimensions of the channel. At the length of 1.275 m of the channel, the power generation capacity of the vertical model was by 2.138 times greater than that of the horizontal model per 100 thermoelectric generators.

Low cost and miniaturized NDIR system for CO2 detection applications

Purpose The importance of Carbon dioxide (CO2) gas detection as a greenhouse and exhale breathe gas is an undeniable issue. This study aims to propose a new miniaturized, low cost and portable no dispersive infrared (NDIR) system for detecting CO2 gas. Design/methodology/approach Poly(methyl methacrylate) (PMMA)-based channels with Au coating because of its high reflection properties in IR region were used in this work. The optical windows were fabricated using PDMS polymer which is cost effective and novel in comparison to other conventional methods. The effects of channel dimensions, lengths and entrance angle of light on optical path length and losses were analyzed with four types of channel using both simulation and experimental tests. Findings The simulation results indicate that the 0 degree light entrance angle is the most efficient angle among different investigated conditions. The experimental data are in agreement with the simulation results regarding the loss and optical path length in different types of channel. The experimental tests were performed for the 0.5% up to 20% of CO2 concentration under constant temperature and humidity condition. The results show that the device with 5 and 2 cm channels length were saturated in 4% and 8% concentration of CO2 gas, respectively. Response and recovery times were depending on gas concentration and channels specifications that in average found to be 10 S and 14 S, respectively, for the largest size channel. Moreover, the environment humidity effect on detection system performance was investigated which had no considerable influence. Also, the saturation fraction absorbance value for devices with various dimensions were 0.62 and 0.8, respectively. Practical implications According to the performed curve fitting for practical situation and selected CO2 concentration range for experimental tests, the device is useful for medical and environmental applications. Originality/value PMMA with Au deposition layer was used as a basic material for this NDIR system. Besides, a novel PDMS optical window helps to have a low cost device. The effects of channel dimensions, lengths and entrance angle of light on optical path length and losses were analyzed using both simulation and experimental tests. Using narrowband optical filter (100 nm bandwidth) helps to have a system with good CO2 selectivity. In addition, experimental tests with different channel dimensions and lengths covered a considerable range of CO2 concentration useful for medical and environmental applications. Finally, curve fitting was adopted for a modified Beer–Lambert law as a practical situation.

Effect of channel dimension on biodiesel yield in millireactors produced by stereolithography

ABSTRACT Industrial research departments and chemical engineering institutes have begun to adopt additive manufacturing technologies, such as stereolithography for producing special types of reactors for continuous production. Microreactors have been widely used to improve the mass and heat transfer processes between immiscible liquid-liquid phases, but with the disadvantage of requiring sophisticated technology for their manufacture. In this paper, an approach for producing millireactors by stereolithography and rapid optimization of millireactor design with circular cross-section is presented. Transesterification of vegetable oils with alcohols is widely used method for biodiesel synthesis, generally taking place in a batch reactor. Microreactors due to their short residence times and high biodiesel yields are currently being explored for continuous production, but have disadvantages in low production volumes and high pressure drops. To overcome above-mentioned problems, millireactors with channel diameters from 1.5 mm to 3.5 mm were produced in order to investigate the impact of channel dimensions on conversion of sunflower oil to fatty acid methyl esters (FAME). Transesterification reaction of sunflower oil using methanol with addition of KOH base catalyst to FAME was monitored by Fourier-transform infrared spectroscopy, gas chromatography, and nuclear magnetic resonance. Results show that millireactors with smaller channel dimensions and processes with higher temperatures at certain residence times can be used to achieve better biodiesel yield in much shorter time than batch reactors. In addition, continuous way of FAME production in millireactors is presented. Production in millireactors provided an improvement when compared to microreactors because they have low pressure drops and higher production volumes.

Design Issues of Thermally Integrated Methanol Reforming Systems for the Production of Hydrogen: Effects of Channel Dimensions and Catalyst Properties

In spite of the increasing importance of methanol as a source of hydrogen for fuel cell applications, there does not exist a unified understanding of what factors are important in the design of the...

Acoustic cavitation and ultrasound-assisted nitration process in ultrasonic microreactors: The effects of channel dimension, solvent properties and temperature

Experimental studies on acoustic cavitation and ultrasound-assisted nitration reaction were systematically investigated in two laboratory-built ultrasonic microreactors by tuning the microchannel dimension, solvent properties and temperature. Under ultrasound irradiation, acoustic cavitation microbubbles were generated and underwent violent oscillation in microchannel. With the decrease of channel size, acoustic cavitation was largely confined, and channel size 1 × 1 mm2 was recognized as the critical size to eliminate the confinement effect. Acoustic cavitation was also highly dependent on the properties of sonicated liquids. The onset of surface wave oscillation on gas bubble was obviously promoted with decreasing solvent viscosity and surface tension. Additionally, ultrasound-assisted nitration process of toluene was studied in a temperature-controlled ultrasonic microreactor. The effects of channel size as well as liquid properties on ultrasound intensification agreed well with the finding in cavitation research. Under ultrasound power 50 W, toluene conversion was enhanced by 9.9%–36.3% utilizing 50 vol.% ethylene glycol aqueous solution as ultrasound propagation medium, exhibiting ultrasound applicability on intensifying fast reaction processes in microreactors.

Effect of flow-field dimensions on the formability of Fe–Ni–Cr alloy as bipolar plate for PEM (proton exchange membrane) fuel cell

The Fe–Ni–Cr alloy is a potential material as bipolar plate for PEMFC (proton exchange membrane fuel cell), and the stamped metallic bipolar plate is a promising candidate instead of traditional graphite due to the advantages of mass production, low cost and excellent performance. The flow-field geometrical dimensions and the operating conditions of the stamp forming have vital influences on the formability of the alloy plate during the stamping process. Therefore, the aim of this study is to investigate the performance of the Fe–Ni–Cr alloy during the stamping process so as to optimize the flow channel dimensions. Effects of channel dimensions and operating conditions on the formability of Fe–Ni–Cr alloy performance are analyzed by numerical simulation method. Furthermore, experiments are conducted to validate the dimension accuracy of numerical methods. The results demonstrate excellent agreement between the experimental and numerical method.

Osteocyte culture in microfluidic devices.

This paper presents a microfluidic device (poly-dimethylsiloxane micro channels bonded with glass slides) enabling culture of MLO-Y4 osteocyte like cells. In this study, on-chip collagen coating, cell seeding and culture, as well as staining were demonstrated in a tubing-free manner where gravity was used as the driving force for liquid transportation. MLO-Y4 cells were cultured in microfluidic channels with and without collagen coating where cellular images in a time sequence were taken and analyzed, confirming the positive effect of collagen coating on phenotype maintaining of MLO-Y4 cells. The proliferating cell nuclear antigen based proliferation assay was used to study cellular proliferation, revealing a higher proliferation rate of MLO-Y4 cells seeded in microfluidic channels without collagen coating compared to the substrates coated with collagen. Furthermore, the effects of channel dimensions (variations in width and height) on the viability of MLO-Y4 cells were explored based on the Calcein-AM and propidium iodide based live/dead assay and the Hoechst 33258 based apoptosis assay, locating the correlation between the decrease in channel width or height and the decrease in cell viability. As a platform technology, this microfluidic device may function as a new cell culture model enabling studies of osteocytes.

Effect of Channel Dimensions on Micro PEM Fuel Cell Performance Using 3D Modeling

Proton exchange membrane fuel cells are electrochemical devices which are emerging as promising power sources for portable electronic applications. One of the key component of the fuel cell is the flow channel. The flow channel ensures uniform distribution of the fuel and oxygen to the reaction sites. If the distribution is non uniform , it will affect the performance of the fuel cell.The width of the channel and the rib plays a significant role in uniform fuel distribution . Here we build a three dimensional model for a fuel cell using COMSOL Multiphysics. The performance of the cell is studied under varying channel widths and rib widths

Evaluation of Correlations of Flow Boiling Heat Transfer of R22 in Horizontal Channels

The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels.

Premix microchannel emulsification using uniform droplets: Effects of channel dimension and operating condition

Premix microchannel emulsification using uniform droplets: Effects of channel dimension and operating condition

Effects of channel dimension, heat flux, and mass flux on flow boiling regimes in microchannels

Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to investigate the effects of channel size and mass flux (225–1420 kg/m 2s) on microchannel flow boiling regimes by means of high-speed photography. Seven different silicon test pieces with parallel microchannels of widths ranging from 100 to 5850 μm, all with a depth of 400 μm, are considered. Flow visualizations are performed with a high-speed digital video camera while local measurements of the heat transfer coefficient are simultaneously obtained. The visualizations and the heat transfer data show that flow regimes in the microchannels of width 400 μm and larger are similar, with nucleate boiling being dominant in these channels over a wide range of heat flux. In contrast, flow regimes in the smaller microchannels are different and bubble nucleation at the walls is suppressed at a relatively low heat flux for these sizes. Two types of flow regime maps are developed and the effects of channel width on the flow regime transitions are discussed.

Numerical study of laminar heat transfer and pressure drop characteristics in a water-cooled minichannel heat sink

With the rapid development of the information technology (IT) industry, the heat flux in integrated circuit (IC) chips cooled by air has almost reached its limit about 100 W/cm 2. Some applications in high technologies require heat fluxes well beyond such a limitation. Therefore the search of a more efficient cooling technology becomes one of the bottleneck problems of the further development of IT industry. The microchannel flow geometry offers large surface area of heat transfer and a high convective heat transfer coefficient. However, it has been hard to implement because of its very high pressure head required to pump the coolant fluid though the channels. A normal channel could not give high heat flux although the pressure drop is very small. A minichannel can be used in heat sink with a quite high heat flux and a mild pressure loss. A minichannel heat sink with bottom size of 20 mm × 20 mm is analyzed numerically for the single-phase laminar flow of water as coolant through small hydraulic diameters and a constant heat flux boundary condition is assumed. The effects of channel dimensions, channel wall thickness, bottom thickness and inlet velocity on the pressure drop, thermal resistance and the maximum allowable heat flux are presented. The results indicate that a narrow and deep channel with thin bottom thickness and relatively thin channel wall thickness results in improved heat transfer performance with a relatively high but acceptable pressure drop. A nearly-optimized configuration of heat sink is found which can cool a chip with heat flux of 256 W/cm 2 at the pumping power of 0.205 W. The nearly-optimized configuration is verified by an orthogonal design. The simulated thermal resistance agrees quite well with the result of conventional correlations method with the maximum difference of 12%.

Numerical Study of Turbulent Heat Transfer and Pressure Drop Characteristics in a Water-Cooled Minichannel Heat Sink

With the rapid development of the Information Technology (IT) industry, the heat flux in integrated circuit (IC) chips cooled by air has almost reached its limit at about 100W∕cm2. Some applications in high technology industries require heat fluxes well beyond such a limitation. Therefore, the search for a more efficient cooling technology becomes one of the bottleneck problems of the further development of the IT industry. The microchannel flow geometry offers a large surface area of heat transfer and a high convective heat transfer coefficient. However, it has been hard to implement because of its very high pressure head required to pump the coolant fluid through the channels. A normal channel size could not give high heat flux, although the pressure drop is very small. A minichannel can be used in a heat sink with quite a high heat flux and a mild pressure loss. A minichannel heat sink with bottom size of 20mm×20mm is analyzed numerically for the single-phase turbulent flow of water as a coolant through small hydraulic diameters. A constant heat flux boundary condition is assumed. The effect of channel dimensions, channel wall thickness, bottom thickness, and inlet velocity on the pressure drop, temperature difference, and maximum allowable heat flux are presented. The results indicate that a narrow and deep channel with thin bottom thickness and relatively thin channel wall thickness results in improved heat transfer performance with a relatively high but acceptable pressure drop. A nearly optimized structure of heat sink is found that can cool a chip with heat flux of 350W∕cm2 at a pumping power of 0.314W.

Application of an intensified narrow channel reactor to the aqueous phase precipitation of barium sulphate

A homogeneous liquid phase reaction between barium chloride (BaCl 2) and sodium sulphate (Na 2SO 4) was conducted in a narrow channel reactor to produce barium sulphate (BaSO 4) precipitate. The effects of channel dimensions and channel residence times on crystal size, crystal size distribution, nucleation rates, crystal morphology and conversion of reactants were investigated at different levels of reactant supersaturation ratio. Our results indicate that the smallest particle sizes are favoured when supersaturation ratios and channel velocities are high. The minimum average particle diameter observed was approximately 0.2 μm in a channel of hydraulic diameter 0.5 mm and length 20 cm at an initial supersaturation ratio of 4483 (0.1 M), which correspond to conditions giving rise to the highest nucleation rates. It has also been observed that particle size depends on the conversion to product, the smallest particles being formed when conversion lies within the range of 30 to 40%. Conversions in excess of 60% have been reached but there is a detectable limiting effect with increased supersaturation and reduced residence times. Experiments conducted at similar levels of supersaturation under stirred tank conditions showed that particle size was consistently larger and particle size distribution was much broader than that achieved in the narrow channel reactor. Scanning electron microscopy (SEM) images of the crystals formed in the narrow channels show that spherical particles dominate in the smallest channels at high velocities whilst coarse, tabular crystals are obtained in the larger channels. Greater tendency to agglomerate is also observed at high supersaturation ratios, after one minute of reaction.

Intensification of Precipitation Using Narrow Channel Reactors: Magnesium Hydroxide Precipitation

Precipitation of magnesium hydroxide using narrow channel reactors has been studied. Effects of channel dimensions (two square cross-sectional area channels with areas 1 and 2 mm2), type of mixer (Y and cross mixer), flow rate of the reaction mixture, and reaction parameters on the particle size and particle size distribution of magnesium hydroxide have been studied. Reaction parameters studied were the effect of the concentration of magnesium chloride, temperature, pH, and addition of the cation Al3+. Some tests were carried out in a stirred batch reactor for comparison with the narrow channel reactors. Comparison of mean particle size of the two reactors on a power consumption basis clearly indicates the superiority of the narrow channel reactor. The results clearly show that the narrow channel reactor is a much more compact process equipment having significantly lower capital and operating costs as compared to a conventional stirred reactor yielding simultaneously a better product. All these advantages lead to an intensified process.

Modeling multilayered MEMS-based micro-fluidic systems

This article describes the design, fabrication, and simulation of two micro-electromechanical systems-based micro-fluidic systems. The first system, a lab-on-a-chip, enables electrochemical immunoassay-based chemical/biological detection. The second is a micro-fluidic bio-impedance sensor. The relevance of fluidic dynamics in micro-fluidic channels is discussed in context of fluid paths and misalignments in the channels that appear during multi-level structure integration. Also discussed is the effect of channel dimensions on the flow profile and on performance within the micro-systems.

Electroosmotic flow in channels with step changes in zeta potential and cross section

We consider the effects that step changes in zeta potential and cross section have on electroosmosis in long-and-narrow channels with arbitrary cross-sectional shapes. The Stokes equation of flow is solved analytically utilizing the thin Debye layer approximation to provide effective slip velocities on the channel walls. The effects of channel dimensions, surface potentials, applied pressure drop, and applied voltage are discussed. One anecdotal case, a two-region rectangular channel, is presented to illustrate the solution. The flow in each region is a combination of a uniform electroosmotic flow and a nonuniform pressure-driven flow. The electroosmotic pumping causes the pressure gradient in each region to adjust so that the flow rate is the same in each region and the overall applied pressure drop is met, resulting in convex velocity profiles in some regions and concave velocity profiles in other regions. By appropriate choice of the applied pressure drop, flat velocity profiles may be achieved in one or more regions.