scholarly journals Pressure Losses in a Network of Triangular Microchannels

2003 ◽  
Author(s):  
Mariusz Niklas ◽  
M. Favre-Marinet
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Flow Characteristics ◽  
Fully Developed Flow ◽  
Pressure Losses ◽  
Head Losses ◽  
Large Pressure ◽  
Micro Channels ◽  
Parallel Microchannels ◽  
Micro Heat Pipes

The flow characteristics of a network of parallel microchannels (hydraulic diameter: 110 μm) were investigated both experimentally and numerically in the present work. The cross-section of the micro-channels was triangular for further application to micro heat pipes. Measurements of the pressure drop across the microchannels network showed a dramatic increase of the pressure losses and a departure from the law of fully developed flow as soon as the Reynolds number of the flow exceeded about 10. Numerical computations of the flow were performed by using the classical laws of hydrodynamics in order to explain this surprizing result. They showed a good agreement with the experimental results, which suggests that there are no size effects at the length scale used in the experiments. Moreover, the mechanisms responsible of the large pressure drop in the high-range of Reynolds number are identified by the numerical analysis. They correspond to extra head losses due to separation in several parts of the test cell.

scholarly journals Measurement and Modeling of the Flow Characteristics of Micro Disc Valves

2000 ◽  
Author(s):  
J. A. Carretero ◽  
K. S. Breuer
Keyword(s):  
Reynolds Number ◽  
Flow Characteristics ◽  
Microfluidic Systems ◽  
Pressure Losses ◽  
Head Losses ◽  
Flow Losses ◽  
Discharge Coefficients ◽  
Low Reynolds

Abstract The head losses in microfluidic systems such as micropumps are dominated by losses in microvalves, where microfabrication constraints limit significantly possible microvalve designs. This makes them quite different from conventional valves. In particular, flow characteristics in the laminar and low-Reynolds turbulent regimes are not understood clearly, and detailed information about the flow losses is lacking. This paper addresses this issue by using a scaled-up (10:1) valve experiment to measure pressure losses in typical microfabricated valve geometries. The macroscale model is fully instrumented and discharge coefficients and sensitivities to stroke, seat width and Reynolds number are presented.

Experimental Investigation of Effect of Tip Coolant Ejection on Internal Flow Characteristics Within a Realistic Blade Coolant Channel

2013 ◽  
Author(s):  
Jian Pu ◽  
Zhaoqing Ke ◽  
Jianhua Wang ◽  
Lei Wang ◽  
Hongde You
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Turbine Blade ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Flow Ratio ◽  
Lp Turbine ◽  
Mass Flow Ratio

This paper presents an experimental investigation on the characteristics of the fluid flow within an entire coolant channel of a low pressure (LP) turbine blade. The serpentine channel, which keeps realistic blade geometry, consists of three passes connected by a 180° sharp bend and a semi-round bend, 2 tip exits and 25 trailing edge exits. The mean velocity fields within several typical cross sections were captured using a particle image velocimetry (PIV) system. Pressure and flow rate at each exit were determined through the measurements of local static pressure and volume flow rate. To optimize the design of LP turbine blade coolant channels, the effect of tip ejection ratio (ER) from 180° sharp bend on the flow characteristics in the coolant channel were experimentally investigated at a series of inlet Reynolds numbers from 25,000 to 50,000. A complex flow pattern, which is different from the previous investigations conducted by a simplified square or rectangular two-pass U-channel, is exhibited from the PIV results. This experimental investigation indicated that: a) in the main flow direction, the regions of separation bubble and flow impingement increase in size with a decrease of the ER; b) the shape, intensity and position of the secondary vortices are changed by the ER; c) the mass flow ratio of each exit to inlet is not sensitive to the inlet Reynolds number; d) the increase of the ER reduces the mass flow ratio through each trailing edge exit to the extent of about 23–28% of the ER = 0 reference under the condition that the tip exit located at 180° bend is full open; e) the pressure drop through the entire coolant channel decreases with an increase in the ER and inlet Reynolds number, and a reduction about 35–40% of the non-dimensional pressure drop is observed at different inlet Reynolds numbers, under the condition that the tip exit located at 180° bend is full open.

A New Tailpipe Design for GE Frame-Type Gas Turbines to Substantially Lower Pressure Losses

2003 ◽  
Vol 125 (1) ◽  
pp. 128-132
Author(s):  
Richard Golomb ◽  
Vivek Sahai ◽  
Dah Yu Cheng
Keyword(s):  
Power Systems ◽  
Gas Turbines ◽  
Large Angle ◽  
Flow Characteristics ◽  
Exhaust System ◽  
Sudden Expansion ◽  
Pressure Losses ◽  
Turbine Efficiency ◽  
Fluid Systems ◽  
Large Pressure

Many GE frame gas turbines have a unique 90-deg tailpipe exhaust system that contains struts, diffusers, and turning vanes. As confirmed in a recent report by GE and other authors, it is known in the industry that this tailpipe design has large pressure losses. In this recent report a pressure loss as high as 60 in. of water (0.15 kgs/sqcm) was cited. Due to the flow separations they create, the report indicates that the struts can cause very high-pressure losses in the turbine. The report also states that these pressure losses can vary with different turbine load conditions. Cheng Fluid Systems and Cheng Power Systems have conducted a study aimed at substantially reducing these pressure losses. Flow control technology introduced to the refinery industry, i.e., the Cheng Rotation Vane (CRV) and the Large Angle Diffuser (LAD) can be used to mitigate the flow separation and turbulence that occurs in turns, bends, and large sudden expansions. Specifically the CRV addresses the flow separations in pipe turns, and the LAD addresses the flow problems that occur with large sudden expansion areas. The paper will introduce the past experience of the CRV and LAD, and will then use computer simulations to show the flow characteristics around a new design. First, the study meticulously goes through the entire GE exhaust system, starting with the redesign of the airfoil shape surrounding the struts. This new design has a larger angle of attack and minimizes the flow separations over a much wider operating range. Second, the pros and cons of the concentric turning vanes are studied and it is shown that they are more flow restrictive, rather than flow enhancing. Third, it is shown that the highly turbulent rectangular box-type exhaust ducting design, substantially contributes to high noise levels and pressure losses. In this paper a completed design will be shown that incorporates a new airfoil shape for the struts, and by using CRV flow technology in combination with the LAD flow technology, the pressure recovery can be enhanced. If the pressure losses could be reduced by 40 inches of water (0.10 kgs/sqcm), the turbine efficiency could be increased by 5%, and the power output could be increased by 6%.

Comparative Study of Effective Cooling in Microchannel Heat Sinks (MCHS) With Nanofluid and Hydrophobic Nanostructures Using Computational Fluid Dynamics

2020 ◽  
Author(s):  
Darryl Jennings ◽  
Sonya Smith
Keyword(s):  
Pressure Drop ◽  
Analytical Model ◽  
Convection Heat Transfer ◽  
Flow Characteristics ◽  
Heat Sinks ◽  
Cross Sectional ◽  
Ansys Fluent ◽  
Cooling Flow ◽  
Micro Channels ◽  
The Impact

Abstract The goal of this research is to present an analytical model of nanostructures and study the effects of their geometry on the performance of micro channels. The pressure drop experienced by micro channels is of interest as it presents a limit on forced convection heat transfer. This work will demonstrate how the presence of nanostructures primarily affects pressure drop as well as other cooling flow characteristics. Additional work in the impact of microchannel cross-sectional geometry and friction factor formulation is provided as well. Multiple transient analyses were performed in ANSYS FLUENT to ascertain performance characteristics of microchannels without the presence of hydrophobic nanostructures. The results were compared to the analytical model developed in this study.

NUMERICAL STUDY OF THE EFFECT OF AREA OF MANIFOLD AND INLET/OUTLET FLOW ARRANGEMENT 0N FLOW DISTRIBUTION IN PARALLEL RECTANGULAR MICROCHANNEL COOLING SYSTEM

2017 ◽  
Vol 79 (7-3) ◽  
Author(s):  
Amirah M. Sahar ◽  
A. I. M. Shaiful
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Cooling System ◽  
Numerical Study ◽  
Flow Distribution ◽  
Fluid Temperature ◽  
Rectangular Microchannel ◽  
Temperature Distributions ◽  
Micro Channels ◽  
Parallel Microchannels

Parallel microchannels have been widely used in cooling of compact electronic equipment due to large contact area with liquid and availability of large mass of fluid to carry away heat. However, understanding of flow distribution for microchannel parallel system is still unclear and there still lack of studies give a clear pictures to understand the complex flow features which cause the flow maldistribution. Generally, the geometrical structure of the manifold and micro channels play an important role in flow distribution between micro channels, which might affects the heat and mass transfer efficiency, even the performance of micro exchangers. A practical design of exchanger basically involves the selection of an optimized solution, keeping an optimal balance between gain in heat transfer and pressure drop penalty. A parallel microchannels configurations consisting inlet and outlet rectangular manifold were simulated to study flow distribution among the channels were investigated numerically by using Ansys Fluent 14.5. The numerical results was validated using existing experimental data and showed a similar trend with values 1% higher than experimental data. The influence of inlet/outlet manifold area and inlet/outlet arrangement on flow distribution in channels were carried out in this study. Based on the predicted flow non-uniformity value, 𝜙, Z- type flow arrangement exhibits higher value of 𝜙, which is 8%, followed by U-type, 2.6% and the I-type, 2.49%. Thus, a better uniformity of velocity and temperature distributions can be achieved in I-shape flow arrangement. The behavior of the flow distributions inside channels is due to the vortices that occurred at manifold. Besides comparing the pressure drop for case 1(D1) and case 2(D2), it is worth to mention that, as the area of inlet and outlet manifold decrease by 50%, the pressure drop is increasing about 5%. However, the inlet/outlet area of manifold on velocity and fluid temperature distributions was insignificant.

Reduction of Drag Force on a Circular Cylinder and Pressure Drop Using a Square Cylinder as Disturbance Body in a Narrow Channel

2014 ◽  
Vol 493 ◽  
pp. 192-197 ◽  
Author(s):  
Wawan Aries Widodo ◽  
Randi Purnama Putra
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Wind Tunnel ◽  
Circular Cylinder ◽  
Drag Force ◽  
Bluff Body ◽  
Flow Characteristics ◽  
Narrow Channel ◽  
Square Cylinder ◽  
Cross Sectional

Many studies related with characteristics of fluid flow acrossing in a bluff body have been conducted. The aim of this research paper was to reduce pressure drop occuring in narrow channels, in which there was a circular cylindrical configuration with square cylinder as disturbance body. Another goal of this research was to reduce the drag force occuring in circular cylinder. Experimentally research of flow characteristics of the wind tunnel had a narrow channel a square cross-section, with implemenred of Reynolds number based on the hydraulic diameter from 5.21x104 to 1.56x105. Wind tunnel that was used had a 125x125mm cross-sectional area and the blockage ratio 26.4% and 36.4%. Specimen was in the form of circular cylinder and square cylinder as disturbance body. Variation of angle position was the inlet disturbance body with α = 200, 300, 400, 500 and 600, respectively. The results was obtained from this study was Reynolds Number value was directly linear with pressure drop there, it was marked by increasing of Reynolds number, the value was also increasing pressure drop. Additional information was obtained by adding inlet disturbance body shaped of square cylinder on the upstream side of the circular cylinder that could reduce pressure drop in the duct and reduce drag happening on a circular cylinder. The position of the optimum angle to reduce pressure drop and drag force was found on the inlet disturbance body with angle α = 300.

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.

Compressibility and Rarefaction Effects on Pressure Drop in Rough Microchannels

2006 ◽  
Author(s):  
Giulio Croce ◽  
Paola D’Agaro ◽  
Alessandro Filippo
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Pressure Drop ◽  
Slip Flow ◽  
Major Effect ◽  
Flow Conditions ◽  
Fully Developed Flow ◽  
Compressibility Effect ◽  
Wide Range ◽  
Poiseuille Number

A numerical analysis of the flow field in rough microchannel is carried out with a finite volume compressible solver, including generalized Maxwell slip flow boundary conditions suitable for arbitrary geometries. Roughness geometry is modeled as a series of triangular shaped obstructions. Relative roughness from 0% to 2.65% were considered. Since for truly compressible flow we have no fully developed flow condition, the simulation is performed over the whole length of the channel. A wide range of Mach number is considered, from nearly incompressible to chocked flow conditions. Flow conditions with Reynolds number up to around 200 were computed. The outlet Knudsen number corresponding to the chosen range of Mach and Reynolds number ranges from very low value to 0.0249. Performance charts are presented in terms of both average and local Poiseuille number as a function of local Kn, Ma and Re. In particular, it appears that roughness strongly decreases the reduction in pressure loss due to rarefaction. Thus, roughness effect is stronger at high Kn. Furthermore, compressibility effect has a major effect on pressure drop, as soon as local Mach number exceed 0.3.

A New Tailpipe Design for GE Frame Type Gas Turbines to Substantially Lower Pressure Losses

2002 ◽  
Author(s):  
Richard Golomb ◽  
Vivek Sahai ◽  
Dah Yu Cheng
Keyword(s):  
Power Systems ◽  
Gas Turbines ◽  
Large Angle ◽  
Flow Characteristics ◽  
Exhaust System ◽  
Sudden Expansion ◽  
Pressure Losses ◽  
Turbine Efficiency ◽  
Fluid Systems ◽  
Large Pressure

Many GE frame gas turbines have a unique 90-degree tailpipe exhaust system that contains struts, diffusers, and turning vanes. As confirmed in a recent report by GE and other authors [1], it is known in the industry that this tailpipe design has large pressure losses. In this recent report a pressure loss as high as 60 inches of water (0.15 kgs/sqcm) was cited. Due to the flow separations they create, the report indicates that the struts can cause very high-pressure losses in the turbine. The report also states that these pressure losses can vary with different turbine load conditions. Cheng Fluid Systems and Cheng Power Systems have conducted a study aimed at substantially reducing these pressure losses. Flow control technology introduced to the refinery industry, i.e., the Cheng Rotation Vane (CRV) and the Large Angle Diffuser (LAD) can be used to mitigate the flow separation and turbulence that occurs in turns, bends, and large sudden expansions. Specifically the CRV addresses the flow separations in pipe turns, and the LAD addresses the flow problems that occur with large sudden expansion areas. The paper will introduce the past experience of the CRV and LAD, and will then use computer simulations to show the flow characteristics around a new design. First, the study meticulously goes through the entire GE exhaust system, starting with the redesign of the airfoil shape surrounding the struts. This new design has a larger angle of attack and minimizes the flow separations over a much wider operating range. Second, the pros and cons of the concentric turning vanes are studied and it is shown that they are more flow restrictive, rather than flow enhancing. Third, it is shown that the highly turbulent rectangular box type exhaust ducting design, substantially contributes to high noise levels and pressure losses. In this paper a completed design will be shown that incorporates a new airfoil shape for the struts, and by using CRV flow technology in combination with the LAD flow technology, the pressure recovery can be enhanced. If the pressure losses could be reduced by 40 inches of water (0.10 kgs/sqcm), the turbine efficiency could be increased by 5%, and the power output could be increased by 6%.

Effect of Header Design on Pressure Drop in Microchannel Heat Sink for MEMS Applications

2014 ◽  
Vol 984-985 ◽  
pp. 1184-1189
Author(s):  
Chelliah Anbumeenakshi ◽  
M.R. Thansekhar ◽  
M. Radhakrishnan
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Heat Sink ◽  
Deionized Water ◽  
Microchannel Heat Sink ◽  
Micro Channel ◽  
Cross Sectional ◽  
Parallel Microchannels ◽  
Sectional Shape ◽  
Header Design

Experiments have been performed to investigate the pressure drop in the microchannel heat sink by varying the cross sectional shape of the header at the inlet and at the outlet for two types of arrangement U type and Z type. The experiments are performed by using deionized water as a coolant for a mass flow rate of 50 – 120 kg/hr and Reynolds number of range 100 - 600 in an Al microchannel rectangular heat sink with 25 numbers of parallel microchannels. Experiment was carried out to find the suitable inlet and outlet header combination for both U type heat sink and Z type heat sink. The various cross sectional shapes used in this micro channel are triangular, trapezoidal and rectangular.

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