Academic literature on the topic 'Laminar geometry constant'
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Journal articles on the topic "Laminar geometry constant"
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Thomas, Scott K., Richard C. Lykins, and Kirk L. Yerkes. "Fully-Developed Laminar Flow in Sinusoidal Grooves." Journal of Fluids Engineering 123, no. 3 (April 16, 2001): 656–61. http://dx.doi.org/10.1115/1.1385832.
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The flow of a constant property fluid through a sinusoidal groove has been analyzed. A numerical solution of the conservation of mass and momentum equations for fully developed flow is presented. The mean velocity, volumetric flow rate, and Poiseuille number are presented as functions of the groove geometry, meniscus contact angle, and shear stress at the liquid-vapor interface. In addition, a semi-analytical solution for the normalized mean velocity in terms of the normalized shear stress at the meniscus is shown to agree with the numerical data quite well.
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Xu, Yang, Jin-Jun Wang, Li-Hao Feng, Guo-Sheng He, and Zhong-Yi Wang. "Laminar vortex rings impinging onto porous walls with a constant porosity." Journal of Fluid Mechanics 837 (January 5, 2018): 729–64. http://dx.doi.org/10.1017/jfm.2017.878.
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For the first time, an experiment has been conducted to investigate synthetic jet laminar vortex rings impinging onto porous walls with different geometries by time-resolved particle image velocimetry. The geometry of the porous wall is changed by varying the hole diameter on the wall (from 1.0 mm to 3.0 mm) when surface porosity is kept constant ($\unicode[STIX]{x1D719}=75\,\%$). The finite-time Lyapunov exponent and phase-averaged vorticity field derived from particle image velocimetry data are presented to reveal the evolution of the vortical structures. A mechanism associated with vorticity cancellation is proposed to explain the formation of downstream transmitted vortex rings; and both the vortex ring trajectory and the time-mean flow feature are compared between different cases. It is found that the hole diameter significantly influences the evolution of the flow structures on both the upstream and downstream sides of the porous wall. In particular, for a porous wall with a small hole diameter ($d_{h}^{\ast }=0.067$, 0.10 and 0.133), the transmitted finger-type jets will reorganize into a well-formed transmitted vortex ring in the downstream flow. However, for the case of a large hole diameter of $d_{h}^{\ast }=0.20$, the transmitted vortex ring is not well formed because of insufficient vorticity cancellation. Additionally, the residual vorticity gradually evolves into discrete jet-like structures downstream, which further weaken the intensity of the transmitted vortex ring. Consequently, the transmitted flow structures for the $d_{h}^{\ast }=0.20$ case would lose coherence more easily (or probably even transition to turbulence), resulting in a faster decay of the axial velocity and stronger entrainment of the transmitted jet. For all porous wall cases, the velocity profile of the transmitted jet exhibits self-similar behaviour in the far field ($z/D_{0}\geqslant 6.03$), which agrees well with the velocity distribution of free synthetic jets. With the help of the control-volume approach, the time-mean drag of the porous wall is evaluated experimentally for the first time. It is shown that the porous wall drag increases with the decrease in the hole diameter. Moreover, for a porous wall with a small hole diameter ($d_{h}^{\ast }=0.067$, 0.10 and 0.133), it appears that the porous wall drag mainly derives from the viscous effect. However, as $d_{h}^{\ast }$ increases to 0.20, the form drag associated with the porous wall geometry becomes significant.
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Lecampion, Brice, and Haseeb Zia. "Slickwater hydraulic fracture propagation: near-tip and radial geometry solutions." Journal of Fluid Mechanics 880 (October 10, 2019): 514–50. http://dx.doi.org/10.1017/jfm.2019.716.
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We quantify the importance of turbulent flow on the propagation of hydraulic fractures (HF) accounting for the addition of friction reducing agents to the fracturing fluid (slickwater fluid). The addition in small quantities of a high molecular weight polymer to water is sufficient to drastically reduce friction of turbulent flow. The maximum drag reduction (MDR) asymptote is always reached during industrial-like injections. The energy required for pumping is thus drastically reduced, allowing for high volume high rate hydraulic fracturing operations at a reasonable cost. We investigate the propagation of a hydraulic fracture propagating in an elastic impermeable homogeneous solid under a constant (and possibly very high) injection rate accounting for laminar and turbulent flow conditions with or without the addition of friction reducers. We solve the near-tip HF problem and estimate the extent of the laminar boundary layer near the fracture tip as a function of a tip Reynolds number for slickwater. We obtain different propagation scalings and transition time scales. This allows us to easily quantify the growth of a radial HF from the early-time turbulent regime(s) to the late-time laminar regimes. Depending on the material and injection parameters, some propagation regimes may actually be bypassed. We derive both accurate and approximate solutions for the growth of radial HF in the different limiting flow regimes (turbulent smooth, rough, MDR) for the zero fracture toughness limit (corresponding to the early stage of propagation of a radial HF). We also investigate numerically the transition(s) between the early-time MDR regime to the late-time laminar regimes (viscosity and toughness) for slickwater fluid. Our results indicate that the effect of turbulent flow on high rate slickwater HF propagation is limited and matters only at early times (at most during the first minutes for industrial hydraulic fracturing operations).
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Littlefield, D., and P. Desai. "Buoyant Laminar Convection in a Vertical Cylindrical Annulus." Journal of Heat Transfer 108, no. 4 (November 1, 1986): 814–21. http://dx.doi.org/10.1115/1.3247017.
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Solution to natural convective motion in a vertical cylindrical annulus of large aspect ratio is examined, with the inner wall subject to a constant heat flux. Similar transformations of the appropriately simplified Navier–Stokes model of the annular flow are sought. The issue of boundary condition limitations for the considered flow is resolved in terms of acceptable error bounds for valid solutions. Results are generated for a variety of outer wall boundary conditions over various ranges of the Rayleigh number, highlighting the effects on the patterns of streamlines and “heatlines.” Correlations presented for the Nusselt number are shown to be dependent on both the boundary conditions and the geometry.
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Kurnia, Jundika, Agus Sasmito, and Arun Mujumdar. "Laminar convective heat transfer for in-plane spiral coils of noncircular cross sections ducts: A computational fluid dynamics study." Thermal Science 16, no. 1 (2012): 109–18. http://dx.doi.org/10.2298/tsci100627014k.
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The objective of this study was to carry out a parametric study of laminar flow and heat transfer characteristics of coils made of tubes of several different cross-sections e.g. square, rectangular, half-circle, rectangular and trapezoidal. For the purpose of ease of comparison, numerical experiments were carried out base on a square-tube Reynolds number of 1000 and a fixed fluid flow rate while length of the tube used to make coils of different diameter and pitch was held constant. A figure of merit was defined to compare the heat transfer performance of different geometry coils; essentially it is defined as total heat transferred from the wall to the surroundings per unit pumping power required. Simulations were carried out for the case of constant wall temperature as well as constant heat flux. In order to allow reasonable comparison between the two different boundary conditions - constant wall temperature and constant wall heat flux - are tested; the uniform heat flux boundary condition was computed by averaging the heat transferred per unit area of the tube for the corresponding constant wall temperature case. Results are presented and discussed in the light of the geometric effects which have a significant effect on heat transfer performance of coils.
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Rastogi, Pallavi, and Shripad P. Mahulikar. "Geometry-Based Entropy Generation Minimization in Laminar Internal Convective Micro-Flow." Journal of Non-Equilibrium Thermodynamics 44, no. 1 (January 28, 2019): 81–90. http://dx.doi.org/10.1515/jnet-2018-0036.
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Abstract In this theoretical study, fully developed forced convective laminar water flow is considered in circular micro-tubes, for the constant wall heat flux boundary condition. The change in entropy generation rate (\Delta {\dot{S}_{\mathrm{gen}}}) for N micro-tubes (each of diameter {D_{\mathrm{N}}}) relative to a reference tube (of 1 mm diameter) was investigated towards the micro-scale, for different tube length (l). A given total heat flow rate is to be removed using a fixed total mass flow rate through N tubes. Hence, the wall heat flux for one of the N tubes decreases towards the micro-scale, which is “thermal under-loading”. For given l, \Delta {\dot{S}_{\mathrm{gen}}} due to fluid conduction decreases and \Delta {\dot{S}_{\mathrm{gen}}} due to fluid friction increases towards the micro-scale. There exists an optimum {D_{\mathrm{N}}} (={D_{\mathrm{N},\mathrm{opt}}}) at which the change in sum-total {\dot{S}_{\mathrm{gen}}} (\Delta {\dot{S}_{\mathrm{gen},\mathrm{tot}}}) is minimum; where {D_{\mathrm{N},\mathrm{opt}}} decreases with decreasing l. For given l, cooling capacity of the heat sink increases towards the micro-scale. A general criterion for minimization of \Delta {\dot{S}_{\mathrm{gen},\mathrm{tot}}} is obtained in terms of Reynolds number, Brinkman number, and dimensionless l.
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Minea, Alina Adriana, Razvan Silviu Luciu, and Oronzio Manca. "Influence of Microtube Heating Geometry on Behavior of an Alumina Nanofluid at Low Reynolds Numbers." Applied Mechanics and Materials 371 (August 2013): 596–600. http://dx.doi.org/10.4028/www.scientific.net/amm.371.596.
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A numerical program is employed to solve two-dimensional continuum-based governing differential equations for liquid flow in axisymmetric circular microchannel geometry. The effects of variable thermal properties in single-phase laminar forced convection with constant wall heat flux boundary conditions are studied. The numerical analysis of fully developed flow behavior investigates the effect of tube length on convection characteristics. The governing equations were discretized using the control volume method and solved numerically via the SIMPLE algorithm. Water - Al2O3nanofluids with different volume fractions ranged from 1% to 3% were used. This investigation covers Reynolds number in the range of 500 to 1500. The results have shown that convective heat transfer coefficient for a nanofluid is enhanced than that of the base liquid. Wall heat transfer flux is increasing with the particle volume concentration and Reynolds number. Moreover, a study on microtube length influence on heat transfer was attempted and few correlations were established. As a conclusion, a 6-11% decrease in heat transfer enhancement was noticed when the tube length is increasing in laminar flow.
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Damian, Iulia Rodica, Nicoleta Octavia Tănase, Ștefan Mugur Simionescu, and Mona Mihăilescu. "Vortex Rings - Experiments and Numerical Simulations." Mathematical Modelling in Civil Engineering 10, no. 4 (December 1, 2014): 1–8. http://dx.doi.org/10.2478/mmce-2014-0017.
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Abstract The present paper was concerned with the experimental study of the time evolution of a single laminar vortex ring generated at the interface between water and isopropyl alcohol. The experiment was performed by the submerged injection of isopropyl alcohol in a water tank of 100×100×150 mm. A constant rate of Q0 = 2 ml/min was maintained using a PHD Ultra 4400 Syringe Pump with a needle having the inner diameter D0 = 0.4 mm. The dynamics of the vortex formation was recorded with a Photron Fastcam SA1 camera at 1000 fps equipped with an Edmund Optics objective VZM1000i. The numerical simulations were performed on a 2D geometry using the ANSYS-FLUENT code with the Volume of Fluid multiphase model and the viscous-laminar solver. The numerical flow patterns were found to be in good agreement with the experimental visualizations
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Jaona Mamy Nindrina, RAMIARAMANANJAFY. "Numerical study of laminar natural convection in a half ellipsoid of revolution subjected to heat flux of constant density." International Journal of Progressive Sciences and Technologies 34, no. 1 (September 4, 2022): 01. http://dx.doi.org/10.52155/ijpsat.v34.1.4528.
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In this article, we numerically study the natural convection in a half-eliipsoid of revolution filled with a Newtonian fluid (air). The ellipsoid wall is isothermal which is maintained at a heat flux of constant density. The equations that govern the flow and heat transfer are described by the so-called Navier-Stokes equation of motion accompanied by the so-called Fourier equation of heat. The finite element method is used to solve the system of equations. We consider the effect of the shape factor of the elliptical wall and the Grashof number on the results obtained in the form of streamlines, and mean Nusselt numbers. The Nusselt numbers for natural convection inside a system formed by a rectangular geometry and for a curved shape are comparer and analyzed each other. We find that this number is quite higher for a curved system than that of a planar shape. It shows the importance of the form factor, particularly, in circular shape which is much more advantageous compared to the straight shape.In terms of inertia, the geometry of rounded shape ensures the best distribution of energy. In fact, the half ellipsoidal greenhouse with a circular base studied during this research offers a better distribution for the flow of the convection currents from the bottom to the top of the system.
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Nayak H. S., Sathvik, Nitesh Kumar, S. M. A. Khader, and Raghuvir Pai. "Effect of dome size on flow dynamics in saccular aneurysms – A numerical study." Journal of Mechanical Engineering and Sciences 14, no. 3 (September 30, 2020): 7181–90. http://dx.doi.org/10.15282/jmes.14.3.2020.19.0564.
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Image-based Computational Fluid Dynamic (CFD) simulations of anatomical models of human arteries are gaining clinical relevance in present days. In this study, CFD is used to study flow behaviour and hemodynamic parameters in aneurysms, with a focus on the effect of geometric variations in the aneurysm models on the flow dynamics. A computational phantom was created using a 3D modelling software to mimic a spherical aneurysm. Hemodynamic parameters were obtained and compared with the available literature to validate. Further, flow dynamics is studied by varying the dome size of the aneurysm from 3.75 mm to 6.25 mm with an increment of 0.625 mm keeping the neck size constant. The aneurysm is assumed to be located at a bend in the arterial system. Computational analysis of the flow field is performed by using Navier – Stokes equation for laminar flow of incompressible, Newtonian fluid. Parameters such as velocity, pressure, wall shear stress (WSS), vortex structure are studied. It was observed that the location of the flow separation and WSS vary significantly with the geometry of the aneurysm. The reduction of WSS inside the aneurysm is higher at the larger dome sizes for constant neck size.
Book chapters on the topic "Laminar geometry constant"
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Magee, Patrick, and Mark Tooley. "Behaviour of Fluids (Liquids and Gases, Flow and Pressure)." In The Physics, Clinical Measurement and Equipment of Anaesthetic Practice for the FRCA. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199595150.003.0011.
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A fluid can be either a liquid or a gas. Fluids exhibit different flow behaviours depending on their physical properties, in particular viscosity and density. Flow characteristics also depend on the geometry of the pipes or channels through which they flow, and on the driving pressure regimes. These principles can be applied to any fluid, and the complexity of the analysis depends on the flow regimes described in this section [Massey 1970]. Fluid flow is generally described as laminar or turbulent. Laminar flow, demonstrated by Osborne Reynolds in 1867, is flow in which laminae or layers of fluid run parallel to each other. In a circular pipe, such as a blood vessel or a bronchus, velocity within the layers nearest the wall of the pipe is least; in the layer immediately adjacent to the wall it is probably actually zero. In fully developed laminar flow, the velocity profile across the pipe is parabolic, as shown in Figure 7.1, and as discussed in Chapter 1. Peak velocity of the fluid occurs in the mid line of the pipe, and is twice the average velocity across the pipe at equilibrium, and layers equidistant from the wall have equal velocity. The importance of laminar flow is that there is minimum energy loss in the flow, i.e. it is an efficient transport mode. This is in contrast to turbulent flow, where eddies and vortices (flow in directions other than the predominant one) mean that energy in fluid transport is wasted in production of heat, additional friction and noise. The result is that the pressure drop required to drive a given flow from one end of the pipe to the other is greater in turbulent than in laminar flow. The shear stress τ, which is the mechanical stress between layers of fluid and between the fluid and the tube wall, is proportional to the velocity gradient across the tube (dv/dr) of the fluid layers. The constant of proportionality between these two variables is the dynamic viscosity, η.
Conference papers on the topic "Laminar geometry constant"
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Lienau, Jeffrey J. "The Recommended Geometry for Laminar Microchannel Heat Sinks." In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-1213.
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Abstract Rectangular laminar microchannel heat sinks have been used for cooling banks of integrated circuits, semiconductor laser diodes, radar components and optical devices all of which may generate high heat flux. The effect of varying the fin width to channel width ratio and the channel aspect ratio was investigated for silicon heat sinks and the design which provided the minimum base temperature for a given heat transfer rate and given pumping power was recommended. The recommended design had fin width to channel width ratios of 1.3 and 2.4 and channel aspect ratios of 21.2 and 32.8 for water and Fluorinert (FC-5312) coolants respectively. The constant properties, fully developed assumptions were evaluated and were shown to be acceptable for the recommended geometry.
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Upadhye, Harshal R., and Satish G. Kandlikar. "Optimization of Microchannel Geometry for Direct Chip Cooling Using Single Phase Heat Transfer." In ASME 2004 2nd International Conference on Microchannels and Minichannels. ASMEDC, 2004. http://dx.doi.org/10.1115/icmm2004-2398.
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Direct cooling of an electronic chip of 25mm × 25mm in size is analyzed as a function of channel geometry for single-phase flow of water through small hydraulic diameters. Fully developed laminar flow is considered with both constant wall temperature and constant channel wall heat flux boundary conditions. The effect of channel dimensions on the pressure drop, the outlet temperature of the cooling fluid and the heat transfer rate are presented. The results indicate that a narrow and deep channel results in improved heat transfer performance for a given pressure drop constraint.
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Karami, Mohammad, Mojtaba Jarrahi, Zahra Habibi, Ebrahim Shirani, and Hassan Peerhossaini. "Chaotic Heat Transfer in a Laminar Pulsating Flow With Constant Wall Temperature." In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-21358.
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The correlation between heat transfer enhancement and secondary flow structures in laminar flows through a chaotic heat exchanger is discussed. The geometry consists of three bends; the angle between curvature planes of successive bends is 90°. Numerical simulations are performed for both steady and pulsating flows when the walls are subjected to a constant temperature. The temperature profiles and secondary flow patterns at the exit of bends are compared in order to characterize the flow. Simulations are carried out for the Reynolds numbers range 300≤Re≤800, velocity amplitude ratios (the ratio of the peak oscillatory velocity component to the mean flow velocity) 1≤β≤2.5, and wall temperatures 310 ≤ Tw(K) ≤ 360. The results show that in the steady flow, heat transfer enhancement occurs with increasing Reynolds number and wall temperature. However, heating homogenization becomes almost independent of Reynolds number when homoclinic connections exist in the flow. Moreover, at high values of wall temperature, heat transfer enhancement is greater than mixing improvement due to the presence of homoclinic connections. In the pulsating flow, Nusselt number improves with β, and β≥2 is a sufficient condition for heat transfer enhancement. The formation and development of homoclinic connections are correlated with the heating homogenization.
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Sciubba, Enrico. "Entropy Generation in Isothermal Laminar Flow Through Bifurcated Tubes With Wall Suction." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-39911.
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The paper presents an analysis of the entropy generation in the bifurcation of a fluid-carrying tube in the presence of wall suction. The objective is to minimize the entropy generation rate due to the viscous flow within the tubes. Several simplifying assumptions are made to reduce the problem to a multi-objective optimization in 3 independent variables: the aspect ratio of the domain served by the flow, the diameter ratio of the primary and secondary branches, and the length of the secondary branch (the location of both the “source” of the fluid and the “sink”, i.e. the place of desired delivery of the fluid, being a datum). The wall suction is assumed to be proportional to the wetted area. For three different initial assumptions (constant Re, constant fluid velocity, constant fluid volume) it is shown that an “optimal shape” exists and is identified by the minimum entropy generation. But, this minimum is always higher than the value pertaining to the unsplit tube with no wall suction. The study demonstrates that, for a given design goal (i.e., for an assigned “function” the configuration is called to perform) Entropy Generation Minimization is a feasible “topological Lagrangian” for the bifurcation geometry.
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Olayiwola, B. O., and P. Walzel. "Convective Heat Transfer Intensification in Laminar Duct Flow." In ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98064.
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An experimental investigation was carried out to study the influence of pulsation and special surface geometry on the convective heat transfer in laminar flow. The experiments were performed using a glycerol-water mixture of 23 wt% glycerol. Ethanol was used as a coolant. The amplitude of pulsation was between 0.37 and 0.91 mm and the frequency range was 26.7 to 42.7 Hz. The mean flow Reynolds number range was between 50 and 1143. All the geometrical parameters of the channel such as the relative fin spacing and relative fin thickness were constant. The enhancement factor E, i.e. the ratio of heat transfer coefficient due to pulsation compared to steady flow diminishes at low Pe. A maximum E was observed in medium ranges of Pe and small Pe. The amount of heat transferred from the working fluid also depends on κ value. So far, a maximum heat transfer enhancement of E = 2.5 at κ = 3 and Pe = 2750 was obtained. The enhancement factor also increases with increasing pulsation amplitude.
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Glasgow, Ian K., and Nadine Aubry. "Mixing Enhancement in Simple Geometry Microchannels." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41586.
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Many microfluidic applications require the mixing of reagents, but efficient mixing in these laminar (i.e., low Reynolds number) systems is typically difficult. Instead of using complex geometries and/or relatively long channels, we demonstrate the merits of flow rate time dependency through periodic forcing. We illustrate the technique by studying mixing in three different simple channel intersection geometries (“⊢”, “Y”, and “T”) by means of computational fluid dynamics (CFD) as well as physically mixing two aqueous reagents. In these geometries, both inlet channel segments (upstream of the confluence) and the outlet channel segment (downstream from the confluence) are 200 μm wide by 120 μm deep, a practical scale for mass-produced disposable devices. The flow rate and average velocity after the confluence of the two reagents are 48 nl s−1 and 2 mm s−1 respectively, which, for aqueous solutions at room temperature, corresponds to a Reynolds number of 0.3. We use a mass diffusion constant of 10−10 m2 s−1, typical of many BioMEMS applications, and vary the flow rates of the reagents such that the inlet time-averaged flow rate remains unchanged but the instantaneous flow rate is sinusoidal (with a DC bias) with respect to time. We analyze the effect of pulsing the flow rate in both inlets at 90 and 180 degrees out of phase in all three geometries. While mixing is good in all six cases, we demonstrate that the best results occur when both inlets are pulsed 90 degrees out of phase in the “T” geometry. In all six cases, the interface is shown to stretch, retain two folds, and sweep through the confluence zone, leading to good mixing within 2 mm downstream of the confluence, i.e. about 1 s of contact. From a practical viewpoint, the case where the inlet pulsing is 180 degrees out of phase is of particular interest as the outflow is constant.
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Clifford, Corey E., and Mark L. Kimber. "Optimization of Confined Laminar Natural Convection for Dry Cask Storage Systems." In 2014 22nd International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icone22-30862.
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Although high-density pool storage provides an acceptable method for housing used fuel elements, a number of concerns have triggered a call for the reduction of current inventories by mandating a maximum permissible time in which assemblies may be placed in wet storage before transfer to passive, dry storage conditions. In anticipation of an accelerated fuel transfer program, the principal goal of this investigation is to develop a fundamental understanding of the physics associated with the buoyancy-induced flow around dry casks in an effort to improve the heat rejection capability of the overall system. The aim of this research initiative is to minimize the amount of active pool cooling necessary by maximizing the thermal capacity of dry storage casks. A simplified geometry of a heated horizontal cylinder confined between two, vertical adiabatic walls is employed to evaluate the coupled heat and mass transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. Each of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the pseudo-unconfined cylinder at the largest confinement ratio, a 54.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 46.6% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions.
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Lietmeyer, Christoph, Karsten Oehlert, and Joerg R. Seume. "Optimal Application of Riblets on Compressor Blades and Their Contamination Behavior." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-46855.
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During the last decades, riblets have shown a potential for viscous drag reduction in turbulent boundary layers. Several investigations and measurements of skin-friction in the boundary layer over flat plates and on turbomachinery type blades with ideal riblet geometry have been reported in the literature. The question where riblets must be applied on the surface of a compressor blade is still not sufficiently answered. In a first step, the profile loss reduction by ideal triangular riblets with a trapezoidal groove and a constant geometry along the surface on the suction and pressure side of a compressor blade is investigated. The results show a higher potential on the profile loss reduction by riblets on the suction side. In a second step, the effect of laser-structured ribs on the laminar separation bubble and the influence of these structures on the laminar boundary layer near the leading edge are investigated. After clarifying the best choices where riblets should be applied on the blade surface, a strategy for locally adapted riblets is presented. The suction side of a compressor blade is laser-structured with a segmented riblet-like structure with a constant geometry in each segment. The measured profile loss reduction shows the increasing effect on the profile loss reduction of this locally adapted structure compared to a constant riblet-geometry along the surface. Furthermore, the particle deposition on a riblet-structured compressor blade is investigated and compared to the particle deposition on a smooth surface. Results show a primary particle deposition on the riblet tips followed by an agglomeration. The particle deposition on the smooth surface is stochastic.
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Alves, Thiago Antonini, and Carlos A. C. Altemani. "Thermal Design of a Protruding Heater in Laminar Channel Flow." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22906.
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The conjugate heat transfer from a single block heater mounted on a conductive wall of a parallel plates channel was investigated under conditions of laminar airflow. The heater cooling was attained by direct forced convection to the airflow and by conduction through its contact with the channel wall. The investigation was performed for a two-dimensional configuration with fixed channel geometry and variable heater height, where the heater upstream edge was centered on the channel wall. At the channel entrance the flow velocity and temperature were uniform. The channel wall thickness was constant and its thermal conductivity was varied in the range from 0 to 80 that of the air, while the heater block thermal conductivity was equal to 500 that of the air. The conservation equations were solved numerically by the control volumes method with the SIMPLE algorithm. The results were expressed in dimensionless form, considering three distinct constraints: fixed flow rate, fixed channel flow pressure drop and fixed pumping power. The last two constraints present an optimum heater height, but care was taken to avoid that the flow recirculation downstream the heater extended beyond the channel length. The heat transfer enhancement promoted by wall conduction was clearly indicated.
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Koronaki, I. P., M. T. Nitsas, and Ch A. Vallianos. "A Numerical Investigation of Nanofluids Thermal Behavior in Microchannels Under Laminar Flow Conditions." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-53442.
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Due to large amounts of heat flux developed in electronic devices, it is essential to propose and investigate effective mechanisms of cooling them. Although microchannels filled with flowing coolant are a geometry often met in such devices, new techniques need to be developed in order to increase their effectiveness. Recent studies on nanofluids, i.e. mixtures of nanometer size particles well-dispersed in a base fluid, have demonstrated their potential for augmenting heat transfer. In the present work the 2D steady state laminar flow of different nanofluids along a microchannel is examined. It is considered that the microchannel walls receive uniform and constant heat flux. The problem’s modelling has as parameters the volume fraction of nanoparticles ranging from 0 to 5% and Reynolds number varying between 50 and 500. The results of the problem’s numerical solution are used to calculate the heat transfer coefficient, the pressure drop along the microchannel and the destroyed exergy. It is found that heat transfer is enhanced due to the presence of nanoparticles. On the contrary, pressure drops faster due to nanofluids increased viscosity leading to more pump power needed. Finally, further exergy destruction is observed when nanoparticles volume fraction increases.