Effectiveness Analysis of Non-Mechanical Micro-Valvular Conduit in Single Phase Flow

2012 ◽  
Author(s):  
Bong Joo Lee ◽  
J. R. Culham
Keyword(s):  
Single Phase ◽  
Complex Geometry ◽  
Flow Direction ◽  
Thermal Dissipation ◽  
Computational Simulations ◽  
Steady State Condition ◽  
Diaphragm Pump ◽  
Effectiveness Analysis ◽  
Mechanical Valves ◽  
Macro Scale

The non-mechanical valvular conduit, which uses no moving parts but instead relies on a complex geometry to regulate flow, is studied through a combination of numerical, computational and experimental methods. This study is based on using water as the fluid at standard state properties. A numerical model is developed to evaluate the effectiveness of the non-mechanical valve’s intricate geometry. Then computational simulations of the oscillating/pumping sequence of the valvular conduit are conducted to examine the effectiveness of the valve when placed in use for a diaphragm pump. Results demonstrate that the non-mechanical valvular conduit can be an effective application for a diaphragm pump at the micro or macro-scale without requiring valvular mechanics. In computational simulations, when non-mechanical valves are positioned at both the inlet and exit of a diaphragm, the positive circulation of fluid is enhanced by 38% which is sufficient to meet the thermal dissipation requirements of an Intel Pentium D processor (i.e. 130 W). In addition, the experimental results in steady state condition demonstrated that the valvular design regulates the flow direction by producing diodicity (a measure of favorable flow direction) of 2.44.

Single-Phase Heat Transfer in Micro-Tubes: A Critical Review

2007 ◽  
Author(s):  
Chandramoulee Krishnamoorthy ◽  
Rahul P. Rao ◽  
Afshin J. Ghajar
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Single Phase ◽  
Review Paper ◽  
Measurement Techniques ◽  
Data Bank ◽  
Macro Scale ◽  
Small Scales ◽  
Gaseous Flows ◽  
Effect Of Surface

This review paper specifically concentrates on heat transfer in micro-tubes and eleven experiments (on liquid flow) and two experiments (on gaseous flow) from 1991 to 2007 are reviewed critically with respect to measurement techniques, instrumentation; and factors like surface roughness and diameter that may play an important role at these small scales. Moreover, a comprehensive list of numerical and analytical results (for both liquid and gaseous flows) is presented in this paper. Interestingly, the effect of surface roughness on heat transfer does not seem to have been investigated thoroughly, as it has been observed to play a key role in influencing heat transfer at small diameters. The state-of-art review thus provides the contemporary experimenters in the field of mini-micro channel heat transfer, this tabulated data that can be used to understand how the different parameters affect the heat transfer in these small scales and a data-bank to validate future numerical and experimental work. The present study identifies the various factors that have contributed in the disparity of results found in the literature and finds that there is a need to investigate certain issues like the effects of roughness, diameter, and secondary flow due to buoyancy on heat transfer and transition. Moreover, it was observed that the start and end of the transition region at these small diameters are not validated by the any of the existing macro-scale correlations.

Computational Study of Grooved Microchannel Enhancements

2008 ◽  
Author(s):  
Stephen A. Solovitz
Keyword(s):  
Thermal Management ◽  
Computational Study ◽  
Internal Flow ◽  
Reynolds Numbers ◽  
Thermal Dissipation ◽  
Two Dimensional ◽  
Macro Scale ◽  
Flow Heat ◽  
Alternate Solution ◽  
Selection Of

As electronics devices continue to increase in thermal dissipation, novel methods will be necessary for effective thermal management. Many macro-scale enhancement techniques have been developed to improve internal flow heat transfer, with a dimple feature being particularly promising due to its enhanced mixing with potentially little pressure penalty. However, because dimples may be difficult to fashion in microchannels, two-dimensional grooves are considered here as a similar alternate solution. Computational fluid dynamics methods are used to analyze the flow and thermal performance for a groove-enhanced microchannel, and the effectiveness is determined for a range of feature depths, diameters, and flow Reynolds numbers. By producing local impingement and flow redevelopment downstream of the groove, thermal enhancements on the order of 70% were achieved with pressure increases of only 30%. Further optimization of this concept should allow the selection of an appropriate application geometry, which can be studied experimentally to validate the concept.

An Experimental Investigation of Gas-Liquid Heat Transfer in Rectangular Micro-Channels

2013 ◽  
Author(s):  
Sira Saisorn ◽  
Somchai Wongwises ◽  
Piyawat Kuaseng ◽  
Chompunut Nuibutr ◽  
Wattana Chanphan
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Camera System ◽  
Micro Channels ◽  
Flow Mechanisms

The investigations of heat transfer and fluid flow characteristics of non-boiling air-water flow in micro-channels are experimentally studied. The gas-liquid mixture from y-shape mixer is forced to flow in the 21 parallel rectangular microchannels with 40 mm long in the flow direction. Each channel has a width and a depth of 0.45 and 0.41 mm, respectively. Flow visualization is feasible by incorporating the stereozoom microscope into the camera system and different flow patterns are recorded. The experiments are performed under low superficial velocities. Two-phase heat transfer gives better results when compared with the single-phase flow. It is found from the experiment that heat transfer enhancement up to 53% is obtained over the single-phase flow. Also, the change in the configuration of the inlet plenum can result in the different two-phase flow mechanisms.

The Grounding Zone of Thwaites Glacier Explored by Icefin

2020 ◽  
Author(s):  
Britney Schmidt ◽  
Keith Nicholls ◽  
Peter Davis ◽  
James Smith ◽  
Kiya Riverman ◽  
...  
Keyword(s):  
Data Collection ◽  
Complex Geometry ◽  
Flow Direction ◽  
Rapid Change ◽  
Hot Water ◽  
Sea Floor ◽  
Fine Grained ◽  
In Situ Data ◽  
Ice Conditions ◽  
Basal Melting

<p>Icefin performed the first long range robotic exploration of the grounding zone of Thwaites Glacier from January 9-12 2020. Icefin was part of the MELT project of the International Thwaites Glacier Collaboration deployed to the grounding zone of Thwaites Glacier, West Antarctica over the period December 2019-February 2020.<span>  </span>MELT is an interdisciplinary project to explore rapid change across the grounding zone, and in particular basal melting.<span>  </span>The subglacial cavity ~2km north of the grounding zone was accessed via hot water drilling on January 7-8, 2020.<span>  </span>Icefin, a hybrid autonomous and remotely operated underwater vehicle designed for sub-ice and borehole operations, conducted over 15km of round-trip data collection under the ice along a section of the glacier from the grounding zone extending to a point 4 km oceanward. <span>  </span>The vehicle collected data with ten different science sensors including cameras, sonars, conductivity/temperature and dissolved oxygen.<span>  </span>Overall, the water column ranged from ~100m downstream that narrowed quickly to an average of 50m that spanned over 2km, to a long segment of ~30m thickness before quickly narrowing over 500m towards the grounding zone. The seafloor structures run roughly parallel to ice flow direction, consisting of furrows, ridges, and grooves in some cases mirrored by the ice structure. The Icefin dives revealed a diverse set of basal ice conditions, with complex geometry, including a range of terraced features, smooth ablated surfaces, crevassing, sediment rich layers of varying kinds, as well as interspersed clear, potentially accreted freshwater ice.<span>  </span>The ocean directly beneath the ice varies spatially, from moderately well-mixed near the grounding zone to highly stratified within and below concavities in the ice downstream.<span>  </span>Sediments along the sea floor range from fine grained downstream to course angular gravel near the grounding zone distributed between larger boulders.<span>  </span>We observed rocky material in the ice that ranged from fine grained layers compressed within the ice to small angular particles volumetrically distributed within ice, to gravel and cobbles, as well as trapped boulders up to meter scale. In addition to the oceanographic, glaciological and sea floor conditions, we also catalogued communities of organisms along the seafloor and ice-ocean interface. We will report the highlights and initial conclusions from Icefin’s in situ data collection, and offer perspectives on change at the grounding zone.</p>

Stability of Single-Phase Natural Circulation With Inverted U-Tube Steam Generators

1988 ◽  
Vol 110 (3) ◽  
pp. 735-742 ◽  
Author(s):  
J. Sanders
Keyword(s):  
Mathematical Model ◽  
Single Phase ◽  
Flow Direction ◽  
Natural Circulation ◽  
Boussinesq Equations ◽  
Test Facility ◽  
Normal Flow ◽  
Steam Generators ◽  
One Dimensional ◽  
Water Flows

For natural circulation it is shown that parallel flow in the tubes of an inverted U-tube steam generator can be, at certain power levels, unstable. A mathematical model, based on one-dimensional Oberbeck-Boussinesq equations, shows that stability can be attained if in some tubes the water flows backward, opposite to the normal flow direction. The results are compared to measurements obtained from the natural circulation test A2-77A in the LOBI-MOD2 integral system test facility.

Cryogenic Single-Phase Heat Transfer in a Microscale Pin Fin Heat Sink

2013 ◽  
Author(s):  
Eric D. Truong ◽  
Erfan Rasouli ◽  
Vinod Narayanan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
Single Phase ◽  
Flow Direction ◽  
Heat Sinks ◽  
Variable Cross ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients

A combined experimental and computational fluid dynamics study of single-phase liquid nitrogen flow through a microscale pin-fin heat sink is presented. Such cryogenic heat sinks find use in applications such as high performance computing and spacecraft thermal management. A circular pin fin heat sink in diameter 5 cm and 250 micrometers in depth was studied herein. Unique features of the heat sink included its variable cross sectional area in the flow direction, variable pin diameters, as well as a circumferential distribution of fluid into the pin fin region. The stainless steel heat sink was fabricated using chemical etching and diffusion bonding. Experimental results indicate that the heat transfer coefficients were relatively unchanged around 2600 W/m2-K for flow rates ranging from 2–4 g/s while the pressure drop increased monotonically with the flow rate. None of the existing correlations in literature on cross flow over a tube bank or micro pin fin heat sinks were able to predict the experimental pressure drop and heat transfer characteristics. However, three dimensional simulations performed using ANSYS Fluent showed reasonable (∼7 percent difference) agreement in the average heat transfer coefficients between experiments and CFD simulations.

On the definition of the secondary flow in three-dimensional cascades

2009 ◽  
Vol 223 (6) ◽  
pp. 667-676 ◽  
Author(s):  
G Persico ◽  
P Gaetani ◽  
V Dossena ◽  
G D'Ippolito ◽  
C Osnaghi
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Secondary Flow ◽  
Boundary Layers ◽  
Complex Geometry ◽  
Flow Direction ◽  
Flow Analysis ◽  
Secondary Flows ◽  
Streamwise Vorticity ◽  
Reference Flow

The present article proposes a novel methodology to evaluate secondary flows generated by the annulus boundary layers in complex cascades. Unlike two-dimensional (2D) linear cascades, where the reference flow is commonly defined as that measured at midspan, the problem of the reference flow definition for annular or complex 3D linear cascades does not have a general solution up to the present time. The proposed approach supports secondary flow analysis whenever exit streamwise vorticity produced by inlet endwall boundary layers is of interest. The idea is to compute the reference flow by applying slip boundary conditions at the endwalls in a viscous 3D numerical simulation, in which uniform total pressure is prescribed at the inlet. Thus the reference flow keeps the 3D nature of the actual flow except for the contribution of the endwall boundary layer vorticity. The resulting secondary field is then derived by projecting the 3D flow field (obtained from both an experiment and a fully viscous simulation) along the local reference flow direction; this approach can be proficiently applied to any complex geometry. This method allows the representation of secondary velocity vectors with a better estimation of the vortex extension, since it offers the opportunity to visualize also the region of the vortices, which can be approximated as a potential type. Furthermore, a proficient evaluation of the secondary vorticity and deviation angle effectively induced by the annulus boundary layer is possible. The approach was preliminarily verified against experimental data in linear cascades characterized by cylindrical blades, not reported for the sake of brevity, showing a very good agreement with the standard methodology based only on the experimental midspan flow field. This article presents secondary flows obtained by the application of the proposed methodology on two annular cascades with cylindrical and 3D-designed blades, stressing the differences with other definitions. Both numerical and experimental results are considered.

Heat Transfer Enhancement in Microchannels Incorporating Slanted Grooves

2008 ◽  
Author(s):  
Poh-Seng Lee ◽  
Chiang-Juay Teo
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Fluid Temperature ◽  
Additional Energy ◽  
Pressure Drops ◽  
Microchannel Heat Sinks ◽  
Significant Temperature

The ever-increasing density, speed, and power consumption of microelectronics has led to a rapid increase in the heat fluxes which need to be dissipated in order to ensure their stable and reliable operation. The shrinking dimensions of electronics devices, in parallel, have imposed severe space constraints on the volume available for the cooling solution, defining the need for innovative and highly effective compact cooling techniques. Microchannel heat sinks have the potential to satisfy these requirements. However, significant temperature variations across the chip persist for conventional single-pass parallel flow microchannel heat sinks since the heat transfer performance deteriorates in the flow direction in microchannels as the boundary layers thicken and the coolant heats up. To accommodate higher heat fluxes, enhanced microchannel designs are needed. The present work presents an idea to enhance the single-phase convective heat transfer in microchannels. The proposed technique is passive, and does not require additional energy to be expended to enhance the heat transfer. The idea incorporates the generation of a spanwise or secondary flow to enhance mixing and hence decrease fluid temperature gradients across the microchannel. Slanted grooves can be created on the microchannel wall to induce the flow to twist and rotate thus introducing an additional component to the otherwise laminar flow in the microchannel. Numerical results are presented to demonstrate the effectiveness of such an enhanced microchannel heat sink. The heat transfer was found to increase by up to 12% without incurring substantial additional pressure drops.

Microscopic Observation of Energy Propagation in Polymeric Fluids Crossing a Barrier

2008 ◽  
Author(s):  
Rashad Aouf ◽  
Vojislav Ilic
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Large Scale ◽  
Complex Geometry ◽  
Molecular Model ◽  
Heat Transfer Process ◽  
Transfer Model ◽  
Energy Propagation ◽  
Lennard Jones ◽  
Macro Scale

A major challenge facing tumour treatment procedures, including hyperthermia, is the inadequate modelling of the bio-heat transfer process. Therefore, an accurate mathematical bio-heat transfer model has to precisely quantify the temperature distribution within a complex geometry of a tumour tissue, in order to help optimize unwanted side effects for patients and minimize (avoid) collateral tissue damage. This study examines the three-dimensional molecular dynamics (MDs) simulation of a Lennard-Jones fluid in the hope of contributing to the understanding of the propagation of a thermal wave in fluids causing phase change i.e. irreversible gelation. It is intended to establish, from such information, a useful benchmark for application to large scale phenomena involving macro scale heat transfer. Specifically, this study examines assemblies of N particles (N = 500 atoms) and analyses the microscopic simulation of double well interaction with permanent molecular bond formation at various temperatures within the range 1–2.5Kb/εT. The dynamics of the fluid is also being studied under the influence of a temperature gradient, dt/dx, where neighbouring particles (i.e. atoms/molecules) are randomly linked by permanent bonds to form clusters of different sizes. The atomic/molecular model consist of an isothermal source and sink whose particles are linked by springs to lattice sites to avoid melting, and a bulk of 500 atoms/molecules in the middle representing the Lennard-Jones fluid. Then, this study simulates the energy propagation following the temperature gradient between the heat source and heat sink at T1 = 2.5 and T2 = 1.5 respectively. The potential equation involved in this study is given by the Finitely Extensible Non Elastic (FENE) and Lennard-Jones (LJ) interaction potential. It is observed that the atoms of the bulk start to form a large cluster (∼ 300 atoms) with long time of simulation estimated by 106 time steps where τ = SQRT(ε/mσ2) and Δt = 10−3. It is also obtained that the potential energy of 13.65KbT across a barrier to establish permanent bonds giving rise to irreversible gel formation. All the parameters used in this study are expressed in Lennard-Jones units.

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