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MAPPING OF PRESSURE LOSSES THROUGH MICROCHANNELS WITH SWEEPING-BENDS OF VARIOUS ANGLE AND RADII
Title
MAPPING OF PRESSURE LOSSES THROUGH MICROCHANNELS WITH SWEEPING-BENDS OF VARIOUS ANGLE AND RADII.
Creator
hansel, chase, Chew, Larry, University of Central Florida
Abstract / Description
MEMS (Micro Electro Mechanical Systems) have received a great deal of attention in both the research and industrial sectors in recent decades. The broad MEMS category, microfluidics, the study of fluid flow through channels measured on the micrometer scale, plays an important role in devices such as compact heat exchangers, chemical and biological sensors, and lab-on-a-chip devices. Most of the research has been focused on how entire systems operate, both experimentally and through simulation...
Show moreMEMS (Micro Electro Mechanical Systems) have received a great deal of attention in both the research and industrial sectors in recent decades. The broad MEMS category, microfluidics, the study of fluid flow through channels measured on the micrometer scale, plays an important role in devices such as compact heat exchangers, chemical and biological sensors, and lab-on-a-chip devices. Most of the research has been focused on how entire systems operate, both experimentally and through simulation. This paper strives, systematically, to map them through experimentation of the previous to untested realm of pressure loss through laminar square-profile sweeping-bend microchannels. Channels were fabricated in silicone and designed so a transducer could detect static pressure across a very specific length of channel with a desired bend. A wide variety of Reynolds numbers, bend radii, and bend angles were repeatedly tested over long periods in order to acquire a complete picture of pressure loss with in the domain of experimentation. Nearly all situations tested were adequately captured with the exception of some very low loss points that were too small to detect accurately. The bends were found to match laminar straight-duct theory at Reynolds numbers below 30. As Reynolds numbers increased, however, minor losses began to build and the total pressure loss across the bend rose above straight-duct predictions. A new loss coefficient equation was produced that properly predicted pressure losses for sweeping-bends at higher Reynolds numbers; while lower flow ranges are left to laminar flow loss for prediction.
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Date Issued
2008
Identifier
CFE0002091, ucf:47537
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002091
LOW REYNOLDS NUMBER WATER FLOW CHARACTERISTICS THROUGH RECTANGULAR MICRO DIFFUSERS/NOZZLES WITH A PRIMARY FOCUS ON MAJOR/MINOR PRESSURE LOSS, STATIC PRESSURE RECOVERY, AND FLOW SEPARATION
Title
LOW REYNOLDS NUMBER WATER FLOW CHARACTERISTICS THROUGH RECTANGULAR MICRO DIFFUSERS/NOZZLES WITH A PRIMARY FOCUS ON MAJOR/MINOR PRESSURE LOSS, STATIC PRESSURE RECOVERY, AND FLOW SEPARATION.
Creator
Hallenbeck, Kyle, Chew, Larry, University of Central Florida
Abstract / Description
The field of microfluidics has recently been gathering a lot of attention due to the enormous demand for devices that work in the micro scale. The problem facing many researchers and designers is the uncertainty in using macro scaled theory, as it seems in some situations they are incorrect. The general idea of this work was to decide whether or not the flow through micro diffusers and nozzles follow the same trends seen in macro scale theory. Four testing wafers were fabricated using PDMS...
Show moreThe field of microfluidics has recently been gathering a lot of attention due to the enormous demand for devices that work in the micro scale. The problem facing many researchers and designers is the uncertainty in using macro scaled theory, as it seems in some situations they are incorrect. The general idea of this work was to decide whether or not the flow through micro diffusers and nozzles follow the same trends seen in macro scale theory. Four testing wafers were fabricated using PDMS soft lithography including 38 diffuser/nozzle channels a piece. Each nozzle and diffuser consisted of a throat dimension of 100μm x 50μm, leg lengths of 142μm, and half angles varying from 0o – 90o in increments of 5o. The flow speeds tested included throat Reynolds numbers of 8.9 – 89 in increments of 8.9 using distilled water as the fluid. The static pressure difference was measured from the entrance to the exit of both the diffusers and the nozzles and the collected data was plotted against a fully attached macro theory as well as Idelchik's approximations. Data for diffusers and nozzles up to HA = 50o hints at the idea that the flow is neither separating nor creating a vena contracta. In this region, static pressure recovery within diffuser flow is observed as less than macro theory would predict and the losses that occur within a nozzle are also less than macro theory would predict. Approaching a 50o HA and beyond shows evidence of unstable separation and vena contracta formation. In general, it appears that there is a micro scaled phenomenon happening in which flow gains available energy when the flow area is increased and looses available energy when the flow area decreases. These new micro scaled phenomenon observations seem to lead to a larger and smaller magnitude of pressure loss respectively.
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Date Issued
2008
Identifier
CFE0002391, ucf:47772
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002391
PRESSURE LOSSES EXPERIENCED BY LIQUID FLOW THROUGH PDMS MICROCHANNELS WITH ABRUPT AREA CHANGES
Title
PRESSURE LOSSES EXPERIENCED BY LIQUID FLOW THROUGH PDMS MICROCHANNELS WITH ABRUPT AREA CHANGES.
Creator
Wehking, Jonathan, Chew, Larry, University of Central Florida
Abstract / Description
Given the surmounting disagreement amongst researchers in the area of liquid flow behavior at the microscale for the past thirty years, this work presents a fundamental approach to analyzing the pressure losses experienced by the laminar flow of water (Re = 7 to Re = 130) through both rectangular straight duct microchannels (of widths ranging from 50 to 130 micrometers), and microchannels with sudden expansions and contractions (with area ratios ranging from 0.4 to 1.0) all with a constant...
Show moreGiven the surmounting disagreement amongst researchers in the area of liquid flow behavior at the microscale for the past thirty years, this work presents a fundamental approach to analyzing the pressure losses experienced by the laminar flow of water (Re = 7 to Re = 130) through both rectangular straight duct microchannels (of widths ranging from 50 to 130 micrometers), and microchannels with sudden expansions and contractions (with area ratios ranging from 0.4 to 1.0) all with a constant depth of 104 micrometers. The simplified Bernoulli equations for uniform, steady, incompressible, internal duct flow were used to compare flow through these microchannels to macroscale theory predictions for pressure drop. One major advantage of the channel design (and subsequent experimental set-up) was that pressure measurements could be taken locally, directly before and after the test section of interest, instead of globally which requires extensive corrections to the pressure measurements before an accurate result can be obtained. Bernoulli's equation adjusted for major head loses (using Darcy friction factors) and minor head losses (using appropriate K values) was found to predict the flow behavior within the calculated theoretical uncertainty (~12%) for all 150+ microchannels tested, except for sizes that pushed the aspect ratio limits of the manufacturing process capabilities (microchannels fabricated via soft lithography using PDMS). The analysis produced conclusive evidence that liquid flow through microchannels at these relative channel sizes and Reynolds numbers follow macroscale predictions without experiencing any of the reported anomalies expressed in other microfluidics research. This work also perfected the delicate technique required to pierce through the PDMS material and into the microchannel inlets, exit and pressure ports without damaging the microchannel. Finally, two verified explanations for why prior researchers have obtained poor agreement between macroscale theory predictions and tests at the microscale were due to the presence of bubbles in the microchannel test section (producing higher than expected pressure drops), and the occurrence of localized separation between the PDMS slabs and thus, the microchannel itself (producing lower than expected pressure drops).
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Date Issued
2008
Identifier
CFE0002289, ucf:47865
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002289
INTERACTION BETWEEN SECONDARY FLOW AND FILM COOLING JETS OF A REALISTIC ANNULAR AIRFOIL CASCADE (HIGH MACH NUMBER)
Title
INTERACTION BETWEEN SECONDARY FLOW AND FILM COOLING JETS OF A REALISTIC ANNULAR AIRFOIL CASCADE (HIGH MACH NUMBER).
Creator
Nguyen, Cuong, Kapat, Jayanta, University of Central Florida
Abstract / Description
Film cooling is investigated on a flat plate both numerically and experimentally. Conical shaped film hole are investigated extensively and contribute to the current literature data, which is extremely rare in the open public domain. Both configuration of the cylindrical film holes, with and without a trench, are investigated in detail. Design of experiment technique was performed to find an optimum combination of both geometrical and fluid parameters to achieve the best film cooling...
Show moreFilm cooling is investigated on a flat plate both numerically and experimentally. Conical shaped film hole are investigated extensively and contribute to the current literature data, which is extremely rare in the open public domain. Both configuration of the cylindrical film holes, with and without a trench, are investigated in detail. Design of experiment technique was performed to find an optimum combination of both geometrical and fluid parameters to achieve the best film cooling performance. From this part of the study, it shows that film cooling performance can be enhanced up to 250% with the trenched film cooling versus non-trenched case provided the same amount of coolant. Since most of the relevant open literature is about film cooling on flat plate endwall cascade with linear extrusion airfoil, the purpose of the second part of this study is to examine the interaction of the secondary flow inside a 3D cascade and the injected film cooling jets. This is employed on the first stage of the aircraft gas turbine engine to protect the curvilinear (annular) endwall platform. The current study investigates the interaction between injected film jets and the secondary flow both experimentally and numerically at high Mach number (M=0.7). Validation shows good agreement between obtained data with the open literature. In general, it can be concluded that with an appropriate film coolant to mainstream blowing ratio, one can not only achieve the best film cooling effectiveness (FCE or η) on the downstream endwall but also maintain almost the same aerodynamic loss as in the un-cooled baseline case. Film performance acts nonlinearly with respect to blowing ratios as with film cooling on flat plate, in the other hand, with a right blowing ratio, film cooling performance is not affect much by secondary flow. In turn, film cooling jets do not increase pressure loss at the downstream wake area of the blades.
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Date Issued
2010
Identifier
CFE0003546, ucf:48944
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003546