scholarly journals Design of a Novel μ-Mixer

2017 ◽  
Author(s):  
Athanasios G. Kanaris ◽  
Aikaterini A. Mouza
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Swirling Flow ◽  
Numerical Data ◽  
Secondary Flows ◽  
Design Parameters ◽  
Mixing Efficiency ◽  
Geometrical Parameters ◽  
Straight Tube ◽  
Propeller Blades

In this work the efficiency of a new μ-mixer design is investigated. As in this type of devices the Reynolds number is low, mixing is diffusion dominated and it can be enhanced by creating secondary flows. In this study we propose the introduction of helical inserts into a straight tube to create swirling flow. The influence of the insert’s geometrical parameters (pitch and length of the propeller blades) and of the Reynolds number on the mixing efficiency and on the pressure drop are numerically investigated. The mixing efficiency of the device is assessed by calculating a number, i.e. the Index of Mixing Efficiency that quantifies the uniformity of concentration at the outlet of the device. The influence of the design parameters on the mixing efficiency is assessed by performing a series of “computational” experiments, in which the values of the parameter are selected using DOE methodology. Finally using the numerical data, appropriate design equations are formulated, which, for given values ​​of the design parameters, can estimate with reasonable accuracy both the mixing efficiency and the pressure drop of the proposed mixing device.

Numerical and Experimental Investigation of the Effect of Geometrical Parameters on the Performance of a Contraction-Expansion Helical Mixer

2014 ◽  
Vol 12 (1) ◽  
pp. 465-475 ◽  
Author(s):  
Liang Dong ◽  
Zhang Shufen
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Coupling Reaction ◽  
Secondary Flows ◽  
Sudden Expansion ◽  
Mixing Efficiency ◽  
Radius Of Curvature ◽  
Geometrical Parameters ◽  
Diazo Coupling ◽  
Diazo Coupling Reaction

Abstract In this study, the mixing efficiency of a passive contraction-expansion helical mixer, which combines several features, such as helical pipes for induction of secondary flows and sudden expansion and contraction array for expansion vortices, was numerically and experimentally studied. We employed the method of Box–Behnken to select the appropriate design points. Then, various configurations were investigated via computational fluid dynamics (CFD) simulations. The extent of mixing was evaluated by monitoring the residence time distribution (RTD) and observing the shape of the RTD curves. A fast competitive-consecutive diazo coupling reaction is carried out to validate the RTD results. The influences of radius of curvature of the helical mixer, ratio of the length of the contraction part to expansion part, pitch of helical mixer, and the Reynolds number (Re) on mixing efficiency, and pressure drop were also investigated. As expected, the radius of curvature of the helical mixer, ratio of the length of the contraction part to expansion part, and the Reynolds number affected significantly the mixing efficiency, while the pitch of helical mixer had little influence on mixing efficiency. Quadratic models for mixing efficiency and pressure drop were then proposed and could be used for designing the optimal contraction-expansion helical mixer for the required pumping power.

Parametric Study of Obstacle Geometry Effect on Mixing Performance in a Convergent-Divergent Micromixer with Sinusoidal Walls

2017 ◽  
Vol 12 (1) ◽  
Author(s):  
Fazlollah Heshmatnezhad ◽  
Halimeh Aghaei ◽  
Ali Reza Solaimany Nazar
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Molecular Diffusion ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Mixing Efficiency ◽  
Main Concept ◽  
Mixing Index ◽  
Operational Parameter

Abstract This study presents a numerical simulation through computational fluid dynamics on mixing and flow structures in convergent-divergent micromixer with a triangular obstacle. The main concept in this design is to enhance the interfacial area between the two fluids by creating a transverse flow and split, and recombination of fluids flow due to the presence of obstacles. The effect of triangular obstacle size, the number of units, changing the position of an obstacle in the mixing channel and operational parameter like the Reynolds number on the mixing efficiency and pressure drop are assessed. The results indicate that at inlet Reynolds numbers below 5, the molecular diffusion is the most important mechanism of mixing, and the mixing index is almost the same for all cases. By increasing the inlet Reynolds number above 5, mixing index increases dramatically, due to the secondary flows. Based on the simulation results, due to increasing the effect of dean and separation vortices as well as more recirculation of flow in the side branches and behind the triangular obstacle, the highest mixing index is obtained at the aspect ratio of 2 for the triangular obstacle and its position at the front of the mixing unit. Also the highest value of mixing index is obtained by six unit of mixing chamber. The effect of changing the position of the obstacle in the channel and changing the aspect ratio of the obstacle is evident in high Reynolds numbers. An increase in the Reynolds number in both cases (changing the aspect ratio and position of the obstacle) leads to pressure drop increases.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Analysis and Optimization of a Passive Micromixer With Curved-Shaped Baffles for Efficient Mixing With Low Pressure Loss in Continuous Flow

2010 ◽  
Author(s):  
Cesar A. Cortes-Quiroz ◽  
Alireza Azarbadegan ◽  
Emadaldin Moeendarbary ◽  
Mehrdad Zangeneh
Keyword(s):  
Pressure Loss ◽  
Cost Effective ◽  
Optimization Method ◽  
Secondary Flows ◽  
Design Parameters ◽  
Mixing Efficiency ◽  
Outlet Section ◽  
Optimization Strategy ◽  
Mixing Index ◽  
Trade Offs

Numerical simulations and an optimization method are used to study the design of a planar T-micromixer with curved-shaped baffles in the mixing channel. The mixing efficiency and the pressure loss in the mixing channel have been evaluated for Reynolds number (Re) in the mixing channel in the range 1 to 250. A Mixing index (Mi) has been defined to quantify the mixing efficiency. Three geometric dimensions: radius of baffle, baffles pitch and height of the channel, are taken as design parameters, whereas the mixing index at the outlet section and the pressure loss in the mixing channel are the performance parameters used to optimize the micromixer geometry. To investigate the effect of design and operation parameters on the device performance, a systematic design and optimization methodology is applied, which combines Computational Fluid Dynamics (CFD) with an optimization strategy that integrates Design of Experiments (DOE), Surrogate modeling (SM) and Multi-Objective Genetic Algorithm (MOGA) techniques. The Pareto front of designs with the optimum trade-offs of mixing index and pressure loss is obtained for different values of Re. The micromixer can enhance mixing using the mechanisms of diffusion (lower Re) and convection (higher Re) to achieve values over 90%, in particular for Re in the order of 100 that has been found the cost-effective level for volume flow. This study applies a systematic procedure for evaluation and optimization of a planar T-mixer with baffles in the channel that promote transversal 3-D flow as well as recirculation secondary flows that enhance mixing.

A study of non-redirection louvre fin-and-tube heat exchangers

1998 ◽  
Vol 212 (1) ◽  
pp. 1-14 ◽  
Author(s):  
C-C Wang ◽  
Y-P Chang ◽  
K-Y Chi ◽  
Y-J Chang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Wind Tunnel ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Geometrical Parameters ◽  
Tube Size ◽  
Collar Diameter ◽  
Fanning Friction Factor

Extensive experiments on the heat transfer and pressure drop characteristics of louvre finand-tube heat exchangers were carried out. In the present study, 14 samples of non-redirection louvre fin-and-tube heat exchangers with different geometrical parameters, including the number of tube row, fin pitch and tube size, were tested in a wind tunnel. Results are presented as plots of the Fanning friction factor f and the Colburn j factor against Reynolds number based on the tube collar diameter in the range of 300–8000.

Hydrodynamic and Thermal Performance of Microchannels With Different Staggered Arrangements of Cylindrical Micro Pin Fins

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Ali Mohammadi ◽  
Ali Koşar
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Design Parameters ◽  
Interaction Patterns ◽  
Wake Region ◽  
Pin Fins ◽  
Micro Pin Fins

This study focuses on microheat sinks with different staggered arrangements of micro pin fins (MPFs). A rectangular microchannel with the dimensions of 5000 × 1500 × 100 μm3 (l′ × w′ × h′) was considered for all the configurations while different MPF diameters, height over diameter ratio (H/D), and longitudinal and transversal pitch ratios (SL/D and ST/D) were considered in different arrangements. Using the ansys fluent 14.5 commercial software, the simulations were done for different Reynolds numbers between 20 and 160. A constant heat flux of 30 W/cm2 was applied through the bottom heating section. The performances of the microheat sinks were evaluated using design parameters, namely pressure drop, friction factor, Nusselt number, and thermal-hydraulic performance index (TPI). The effect of each geometrical parameter as well as wake-pin fin interaction patterns were carefully studied using the streamline patterns and temperature profiles of each configuration. The results reveal a great dependency of trends in pressure drops and Nusselt numbers on the wake region lengths as well as the local velocity and pressure gradients. Moreover, the wake region lengths mostly contribute to the increase in obtained pressure drop and Nusselt number with Reynolds number. Although an increase in the H/D and SL/D ratios results in an increase and a decrease in pressure drop, respectively, the effect on the Nusselt number depends on other geometrical parameters and Reynolds number. A larger ST/D ratio generally results in a decrease in the pressure drop and Nusselt number. Finally, while the friction factor decreases with Reynolds number, two different trends are seen for the TPI values of configurations with the H/D ratio of 1 and 2 (D = 100 and 50 μm). While the trend in the TPIs is increasing for Reynolds numbers between 20 and 40, it reverses for higher Reynolds numbers with a steeper slope in the configurations with the ST/D ratio of 1.5.

Multi-Objective Optimization of Double-Tube Once-Through Steam Generator

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Xinyu Wei ◽  
Chunhui Dai ◽  
Yun Tai ◽  
Fuyu Zhao
Keyword(s):  
Optimal Design ◽  
Pressure Drop ◽  
Steam Generator ◽  
Flow Distribution ◽  
Tube Length ◽  
Design Parameters ◽  
Straight Tube ◽  
Nsga Ii ◽  
Primary Fluid ◽  
Helical Tube

This paper presents a double-tube once-through steam generator (DOTSG) consisting of the outer straight tube and the inner helical tube. The tube length and pressure drop of are important parameters in optimal design of DOTSG. For optimal design of such a system, it was modeled to estimate its tube length and pressure drop. Pitch of inner helical tube, flow distribution ratio of the primary fluid, and tube assemblage are considered as design parameters. Then fast and elitist nondominated sorting genetic algorithm-II (NSGA-II) method was applied to find the optimum values of design parameters. In the presented optimal design approach, the tube length and the total pressure drop are two objective functions. The results of optimal designs were a set of multiple optimum solutions, called “Pareto optimal solutions.” The sensitivity analysis of change in optimum tube length and pressure drop with change in design parameters of the DOTSG is also performed and the results are reported.

Numerical simulation of pressure drop for three-dimensional rectangular microchannels

2018 ◽  
Vol 35 (6) ◽  
pp. 2234-2254 ◽  
Author(s):  
Zhipeng Duan ◽  
Peng Liang ◽  
Hao Ma ◽  
Niya Ma ◽  
Boshu He
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Friction Factor ◽  
Three Dimensional ◽  
Numerical Data ◽  
Rectangular Microchannels ◽  
Content Type ◽  
Aspect Ratios ◽  
Rectangular Channels

Purpose The purpose of this paper is to numerically investigate the flow characteristics and extend the data of friction factor and Reynolds number product of hydrodynamically developing laminar flow in three-dimensional rectangular microchannels with different aspect ratios. Design/methodology/approach Using a finite-volume approach, the friction factor characteristics of Newtonian fluid in three-dimensional rectangular ducts with aspect ratios from 0.1 to 1 are conducted numerically under no-slip boundary conditions. A simple model that approximately predicts the apparent friction factor and Reynolds number product fappRe is referenced as a semi-theoretical fundamental analysis for numerical simulations. Findings The accurate and reliable results of fappRe are obtained, which are compared with classic numerical data and experimental data, and the simple semi-theoretical model used and all comparisons show good agreement. Among them, the maximum relative error with the classic numerical data is less than 3.9 per cent. The data of fappRe are significantly extended to other different aspect ratios and the novel values of fappRe are presented in the tables. The characteristics of fappRe are analyzed as a function of a non-dimensional axial distance and the aspect ratios. A more effective and accurate fourth-order fitting equation for the Hagenbach's factor of rectangular channels is proposed. Originality/value From the reliable data, it is shown that the values of fappRe and the model can be references of pressure drop and friction factor for developing laminar flow in rectangular channels for researchers and engineering applications.

Comparison of Staggered and In-Line V-Shaped Dimple Arrays Using S-PIV

2015 ◽  
Author(s):  
Charles P. Brown ◽  
Lesley M. Wright ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Spanwise Direction ◽  
Reduced Pressure ◽  
Line Array

As a result of the reduced pressure loss relative to ribs, recessed dimples have the potential to increase the thermal performance of internal cooling passages. In this experimental investigation, a Stereo-Particle Image Velocimetry (S-PIV) technique is used to characterize the three-dimensional, internal flow field over V-shaped dimple arrays. These flowfield measurements are combined with surface heat transfer measurements to fully characterize the performance of the proposed V-shaped dimples. This study compares the performance of two arrays. Both a staggered array and an in-line array of V-shaped dimples are considered. The layout of these V-shaped dimples is derived from a traditional, staggered hemispherical dimple array. The individual V-shaped dimples follow the same geometry, with depths of δ / D = 0.30. In the case of the in-line pattern, the spacing between the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. For the staggered pattern, a spacing of 3.2D in the spanwise direction and 1.6D in the streamwise direction is examined. Each of these patterns was tested on one wide wall of a 3:1 rectangular channel. The Reynolds numbers examined range from 10000 to 37000. S-PIV results show that as the Reynolds numbers increase, the strength of the secondary flows induced by the in-line array increases, enhancing the heat transfer from the surface, without dramatically increasing the measured pressure drop. As a result of a minimal increase in pressure drop, the overall thermal performance of the channel increases as the Reynolds number increases (up to the maximum Reynolds number of 37000).

Analysis of mixing performances in microchannel with obstacles of different aspect ratios

2019 ◽  
Vol 233 (5) ◽  
pp. 1045-1051 ◽  
Author(s):  
Bappa Mondal ◽  
Sukumar Pati ◽  
PK Patowari
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Flow Condition ◽  
Schmidt Number ◽  
Mixing Efficiency ◽  
Rectangular Microchannel ◽  
Mixing Performance ◽  
Aspect Ratios ◽  
Flow Through

In this study, the mixing performance and pressure drop characteristics have been numerically analyzed for flow through rectangular microchannel with obstacles in the walls arranged in a staggered manner. Three different aspect ratios (AR) of the obstacles are considered, namely 4:1, 1:1, and 1:4. The effects of aspect ratio of the obstacles on the mixing efficiency and the pressure drop are analyzed and compared with that of the channel without obstacle. The results are presented in terms of Reynolds number (Re) and Schmidt number (Sc) in the following range: 0.2 ≤ Re ≤ 1 and 500 ≤ Sc ≤ 1500. Enhanced mixing efficiency is achieved for the case of microchannel with obstacles and the corresponding pressure drop is also found to be higher. The mixing efficiency as well as the pressure drop is maximum for AR = 1:4 among all the geometries considered in the analysis in same flow condition. Furthermore, for a given configuration of the microchannel the mixing efficiency is governed by the mass Peclet number and, accordingly, the mixing efficiency increases with the decrease in Schmidt number for a given Reynolds number.

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