Effect of Cross Aspect Ratio on Flow in Diverging and Converging Microchannels

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
V. S. Duryodhan ◽  
Shiv Govind Singh ◽  
Amit Agrawal
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Hydraulic Diameter ◽  
Working Fluid ◽  
Cross Sectional ◽  
Flow Acceleration ◽  
Three Dimensional Models

Aspect ratio is an important parameter in the study of flow through noncircular microchannel. In this work, three-dimensional numerical study is carried out to understand the effect of cross aspect ratio (height to width) on flow in diverging and converging microchannels. Three-dimensional models of the diverging and converging microchannels with angle: 2–14 deg, aspect ratio: 0.05–0.58, and Reynolds number: 130–280 are employed in the simulations with water as the working fluid. The effects of aspect ratio on pressure drop in equivalent diverging and converging microchannels are studied in detail and correlated to the underlying flow regime. It is observed that for a given Reynolds number and angle, the pressure drop decreases asymptotically with aspect ratio for both the diverging and converging microchannels. At small aspect ratio and small Reynolds number, the pressure drop remains invariant of angle in both the diverging and converging microchannels; the concept of equivalent hydraulic diameter can be applied to these situations. Onset of flow separation in diverging passage and flow acceleration in converging passage is found to be a strong function of aspect ratio, which has not been shown earlier. The existence of a critical angle with relevance to the concept of equivalent hydraulic diameter is identified and its variation with Reynolds number is discussed. Finally, the effect of aspect ratio on fluidic diodicity is discussed which will be helpful in the design of valveless micropump. These results help in extending the conventional formulae made for uniform cross-sectional channel to that for the diverging and converging microchannels.

Performance Simulations of Tesla Microfluidic Valves

2007 ◽  
Author(s):  
S. Zhang ◽  
S. H. Winoto ◽  
H. T. Low
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Rate ◽  
Three Dimensional ◽  
Model Performance ◽  
Hydraulic Diameter ◽  
Cross Sectional ◽  
Pressure Flow ◽  
Aspect Ratios ◽  
Tesla Valve

A three-dimensional (3-D) parametric model of Tesla-type valves is proposed. A geometrical relationship is derived for optimization study, and based on the model, performance investigations in terms of diodicity and pressure-flow rate characteristics of the valve are numerically carried out with same hydraulic diameter and different aspect ratios (of the model cross-sectional dimensions) ranging from 0.5 to 4. The 3-D computational simulations show that, for the same hydraulic diameter, the unity aspect ratio gives higher diodicity at Reynolds number less than 500 and higher will be achieved with bigger aspect ratio when the Reynolds number is above 500. Investigations of pressure-flow rate characteristics of the Tesla valve show that Tesla valve with high aspect ratio gives more flow control ability.

Experiment Study and Numerical Analysis of Flow and Heat Transfer in (110) Silicon Base Microchannel

2008 ◽  
Vol 594 ◽  
pp. 351-356
Author(s):  
Sheng Hong Tsai ◽  
Yu Tang Chen
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Hydraulic Diameter ◽  
Working Fluid ◽  
Surface Geometry ◽  
Micro Scale ◽  
Conductive Surface ◽  
Flow Phenomena

Microchannel heat sink is fabricated on silicon wafer by anisotropic etching, and used Pyrex #7740 as a transparent cover that integrated by anodic bonding. Rectangular microchannel presents the flow phenomena of fluid in micro scale, and this study focus on the boundary conditions which hydraulic diameter (Dh) is from 80m to 350m and Aspect ratio is from 0.24~7.8 of working fluid (DI water). While the size of microchannel is decreasing, laminar flow occurs on the low Reynolds number, which caused by the interaction of viscosity and friction on boundary layer. Sequentially, the influence of dimension decreasing on microchannel that induced transition and turbulent flow in early stage as Reynolds number is still in the range of 600~800. Pressure drop is high (2 bar) when fluid flows through the micro channel, and flux is constrained by the flow resistance during experiment operating. In this study, it takes effect by increasing aspect ratio to reduce pressure drop and enlarge the conductive surface. Geometry of microchannel, hydraulic diameter, and aspect ratio are the key factors in flow phenomena investigation. This research presents the difference between micro scale flow and traditional pipe flow by consideration of Reynolds number. By using computer aided engineering to optimize the aspect ratio of microchannel, which can find the maximum conductive surface under the limitation of pressure drop. The best value of aspect ratio is 0.88~1.22. The simulation result makes good sequence with experiment data. Based on this methodology, numerical analysis can be used to design the optimal microchannel on wafer for cooling hot spot.

Numerical Investigation on Turbulence Statistics and Heat Transfer of a Circular Jet Impinging on a Roughened Flat Plate

2021 ◽  
Vol 13 (4) ◽  
Author(s):  
Abdulrahman Alenezi ◽  
Abdulrahman Almutairi ◽  
Hamad Alhajeri ◽  
Abdulaziz Gamil ◽  
Faisal Alshammari
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Roughness Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Target Plate ◽  
Cross Sectional ◽  
Flow Physics ◽  
Baseline Case

Abstract A detailed heat transfer numerical study of a three-dimensional impinging jet on a roughened isothermal surface is presented and is investigated from flow physics vantage point under the influence of different parameters. The effects of the Reynolds number, roughness location, and roughness dimension on the flow physics and heat transfer parameters are studied. Additionally, the relations between average heat transfer coefficient (AHTC) and flow physics including pressure, wall shear and flow vortices with thermodynamic nonequilibrium are offered. This paper studies the effect of varying both location and dimension of the roughness element which took the shape of square cross-sectional continuous ribs to deliver a favorable trade-off between total pressure loss and heat transfer rate. The roughness element was tested for three different radial locations (R/D) = 1, 1.5, and 2 and at each location its height (i.e., width) (e) was changed from 0.25 to 1 mm in incremental steps of 0.25. The study used a jet angle (α) of 90 deg, jet-to-target distance (H/D = 6), and Re ranges from 10,000 to 50,000, where H is the vertical distance between the target plate and jet exit. The results show that the AHTC can be significantly affected by changing the geometry and dimensions of the roughness element. This variation can be either an augmentation of, or decrease in, the (HTC) when compared with the baseline case. An enhancement of 12.9% in the AHTC was achieved by using optimal location and dimensions of the roughness element at specific Reynolds number. However, a diminution between 10% and 30% in (AHTC) was attained by the use of rib height e = 1 mm at Re = 50k. The variation of both rib location and height showed better contribution in increasing heat transfer for low-range Reynolds numbers.

scholarly journals STUDI NUMERIK PRESSURE DROP PADA SILINDER TANDEM DENGAN PENAMBAHAN SPLITTER PLATE DAN VORTEX GENERATOR DI PENAMPANG SEMPIT

Otopro ◽  
2021 ◽  
pp. 15-20
Author(s):  
Diastian Vinaya Wijanarko
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Circular Cylinder ◽  
Numerical Study ◽  
Vortex Generator ◽  
Splitter Plate ◽  
Blockage Ratio ◽  
Cross Sectional ◽  
The Cross

The numerical study of pressure drop on a tandem cylinder with the addition of a splitter plate and a vortex generator with the effect of a blockage ratio has been completed. The cross-sectional height and diameter of the cylinder in this study used H= 125 mm and D= 37.5 mm, respectively. The blockage ratio is 30%. The Reynolds number (Re) is 52100 ≤ Re ≤ 156000. The distance between cylinders is 5 to 8, where “s” is the distance from cylinder one to cylinder two. The dimensions of the splitter plate are L=D, L=1,5D, and L=2D where "L" is the length of the splitter plate, while the thickness in this study is 1, 75mm. The dimensions of the vortex generator in this study are used those of Hu, et al. [6]. The angle of the vortex generator is = 350 while the length of the vortex generator is H = 3 mm. All variations of this numerical study were carried out using the URANS (Unsteady Reynold Average Navier Stoke) method with a Reynolds number (Re) 52,100 Re 156,000. The smallest pressure drop value is obtained at the Reynolds number 52.100 for all variations, while the highest Reynolds number is obtained at Re 156.000. the addition of a splitter plate and a vortex generator, gives a higher pressure drop when compared to a circular cylinder.

Effect of Inlet Plenum on Pressure Drop and Velocity in Fractal Micro Channels

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Gurjit Singh ◽  
S.S. Sehagal
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Constant Velocity ◽  
Computational Analysis ◽  
Three Dimensional ◽  
Micro Channel ◽  
Ratio Model ◽  
Micro Channels ◽  
Inner Channel

The computational analysis for micro channel flow in a branched network was investigated by three dimensional CFD approach. The effect of the change of Inlet Plenum (IP) size at a constant Aspect Ratio (AR) of the outermost channel on pressure drop in a fractal branched micro channel was performed. The properties are compared along a particular path and it was observed that the pressure drop along a bifurcated path has considerably less effect when compared to that of the outer most straight branched channel for a constant aspect ratio model. Pressure does not change significantly if we change the IP radius even when all other parameters are constant. Velocity in the inner channel after a straight run has reduced significantly even for same AR and Reynolds Number (Re). This leads to the conclusion that the IP size affects the velocity after the bifurcation.

Effect of Cylinder Aspect Ratio and Channel Dimensions on the Fluid Flow and Heat Transfer in Parallel-Plate Channel Heat Exchangers

2002 ◽  
Author(s):  
A. K. Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Heat Exchangers ◽  
Parallel Plate ◽  
Numerical Study ◽  
Three Dimensional ◽  
Channel Height ◽  
Flow And Heat Transfer ◽  
Plate Channel

A comparative numerical study has been carried out to analyze the unsteady three-dimensional flow and heat transfer in a parallel-plate channel heat exchangers with in-line arrays of periodically mounted square cylinders (pins) at various Reynolds number and geometrical configurations. The geometry considered represents the narrow trailing edge region of the blade where pin fins are used to serve both a structural and a heat transfer role. The three-dimensional unsteady Navier-Stokes and energy equations are solved using higher order temporal and spatial discretizations. The simulations have been carried out for a range of Reynolds number based on cylinder width (180–600) and a Prandtl number of 6.99 (corresponding to water). Conjugate heat transfer calculations have been employed to account for the conduction in the solid cylinder and convection in the fluid. The thermal performance factor (TPF) increases significantly when the flow becomes unsteady. The choice of aspect ratio of the cylinders is judged by their relative increase in friction factor and heat transfer at transitional Reynolds number. The TPF is found to increase with the increase in pitch of the cylinders. The increase in channel height enhances the TPF though the heat transfer decreases at higher channel height.

Parametric and Numerical Study of Fully-Developed Flow and Heat Transfer in Rotating Rectangular Ducts

1990 ◽  
Author(s):  
H. Iacovides ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Initial Conditions ◽  
Numerical Study ◽  
Suction Side ◽  
Rossby Number ◽  
Constant Density ◽  
Pressure Side ◽  
Cross Sectional

This work is concerned with fully-developed constant-density turbulent flow through rectangular straight ducts rotating in an orthogonal mode. Ducts of both square and 2:1 aspect ratio cross-sections have been examined. For the square duct, predictions have been performed for Reynolds numbers of 33,500 and 97,000 and for the 2:1 aspect ratio duct the computations were carried out for a Reynolds number of 33,500. Values of the inverse Rossby number (Ro = ΩD/Wb) ranged from 0.005 to 0.2. Except in the immediate vicinity of the wall, the standard high-Reynolds-number version of the k-ε model is used to account for the effects of turbulence. Across the near-wall sublayer the damping of turbulence is modelled through a low-Reynolds-number one-equation model. Low rotational speeds cause the formation of a pair of symmetric streamwise vortices. At higher rotational speeds, flow instabilities on the pressure side lead to transition to a more complex four-vortex structure. The transition point depends on both the cross-sectional geometry and the flow Reynolds number. Moreover, over a range of Rossby number, either two- or four-vortex solutions are possible depending upon initial conditions. The rotation leads to significant differences between the values of friction factor and Nusselt number on the suction and pressure surfaces of the duct. The degree of heat transfer augmentation on the pressure side is found to depend on the Reynolds number as well as on Rossby number. In contrast, heat-transfer attenuation on the suction side is only Rossby-number dependent.

Effect of Aspect Ratio on the Buoyancy Driven Reverse Flow Near the Leading Wall of Rotating Cooling Passages

1996 ◽  
Author(s):  
Prabhat Tekriwal
Keyword(s):  
Aspect Ratio ◽  
Rotation Number ◽  
Numerical Study ◽  
Reverse Flow ◽  
Fluid Velocity ◽  
Three Dimensional ◽  
Hydraulic Diameter ◽  
Flow Reversal ◽  
Aspect Ratios ◽  
Reversal Phenomenon

The present work is concerned with the flow reversal phenomenon that is caused by the centrifugal buoyancy forces in the case of three-dimensional radially outward flow through rectangular ducts rotating in orthogonal mode. Due to the flow reversal, regions of zero to low fluid velocity (stagnation) are created near the leading wall and the heat transfer, consequently, is impaired causing concerns for the design engineers. Three duct cross-sections of the same hydraulic diameter but different aspect ratios (1:1, 2:1 and 3.33:1) have been examined in this numerical study for flows at different rotation numbers and different temperature ratios. The rotation number examined ranged from 0.08 to 0.35. For each rotation number the temperature ratio is increased until the flow reversal phenomenon is observed in the CFD predictions. For all the three ducts, computations have been carried out for Reynolds number equal to 80,000. The onset of the flow reversal near the leading wall and at the exit of the single-pass flow passage is studied with the buoyancy number variation. As the aspect ratio is increased while keeping the duct hydraulic diameter fixed, the buoyancy number required to cause the onset of flow reversal decreases. Also, for each of the three ducts examined it has been found that the buoyancy number required for the predicted reverse flow to occur increases as the rotation number is increased.

Parametric and Numerical Study of Fully Developed Flow and Heat Transfer in Rotating Rectangular Ducts

1991 ◽  
Vol 113 (3) ◽  
pp. 331-338 ◽  
Author(s):  
H. Iacovides ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Initial Conditions ◽  
Numerical Study ◽  
Suction Side ◽  
Rossby Number ◽  
Constant Density ◽  
Pressure Side ◽  
Cross Sectional

This work is concerned with fully developed constant-density turbulent flow through rectangular straight ducts rotating in an orthogonal mode. Ducts of both square and 2:1 aspect ratio cross sections have been examined. For the square duct, predictions have been performed for Reynolds numbers of 33,500 and 97,000 and for the 2:1 aspect ratio duct the computations were carried out for a Reynolds number of 33,500. Values of the inverse Rossby number (Ro = ΩD/Wb) ranged from 0.005 to 0.2. Except in the immediate vicinity of the wall, the standard high-Reynolds-number version of the k–ε model is used to account for the effect of turbulence. Across the near-wall sublayer the damping of turbulence is modeled through a low-Reynolds-number one-equation model. Low rotational speeds cause the formation of a pair of symmetric streamwise vortices. At higher rotational speeds, flow instabilities on the pressure side lead to transition to a more complex four-vortex structure. The transition point depends on both the cross-sectional geometry and the flow Reynolds number. Moreover, over a range of Rossby number, either two– or four–vortex solutions are possible depending upon initial conditions. The rotation leads to significant differences between the values of friction factor and Nusselt number on the suction and pressure surfaces of the duct. The degree of heat transfer augmentation on the pressure side is found to depend on the Reynolds number as well as on Rossby number. In contrast, heat transfer attenuation on the suction side is only Rossby-number dependent.

Heat Transfer and Pressure Loss in a Two-Pass, Rectangular Channel Featuring a Reduced Cross-Sectional Area After the 180-Degree Tip Turn With Different Turning Vane Configurations

2020 ◽  
Author(s):  
Sulaiman M. Alsaleem ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Cross Section ◽  
Pressure Loss ◽  
Circular Cross Section ◽  
Sectional Area ◽  
Cross Sectional ◽  
Number Range

Abstract Serpentine, varying aspect ratio cooling passages, are typically used in cooling advanced gas turbine blades. These passages are usually connected by sharp, 180-deg bends. In the open literature, most of the internal cooling studies use a fixed cross-sectional area for multi-pass channels. Studies that use varying aspect ratio channels, along with a guide (turn) vane to direct the flow with turning, are scarce. In general, studies show that the incorporation of turning vanes in the bend region of a multi-pass channel keeps the heat transfer rate high while reducing pressure loss. Therefore, the current study investigates the effect of using different guide (turn) vane designs on both the detailed heat transfer distribution and pressure loss in a multi-pass channel with an aspect ratio of (4:1) in the entry passage and (2:1) in the second passage downstream of the vane (s). The first vane configuration is one solid-vane with a semi-circular cross-section connecting the two flow passages. The second configuration has three broken-vanes with a quarter-circular cross-section; two broken vanes are located downstream in the first passage (entering the turn), and one broken vane is upstream in the second passage (exiting the turn). For a Reynolds number range 15,000 to 45,000, detailed heat transfer distributions were obtained on all surfaces within the flow passages by using a transient liquid crystal method. The results show that the turning vane configurations have large effects on the heat transfer, in the turning bend and second passage, and the overall pressure drop. Results show that including the semi-circular vane in the turning region of a multi-pass channel enhanced the overall heat transfer by around 29% with a reduction in pressure loss by around 20%. Moreover, results show that the quarter-circular vane design provides higher overall averaged heat transfer enhancement than the semi-circular vane design by around 9% with penalty of higher pressure drop by 6%, which yields higher thermal performance by 7%, over the Reynolds number range.

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