Influence of Counter-Ion Concentration on the Impinging Jet of Surfactant Solutions

2011 ◽  
Author(s):  
Nguyen Anh Tuan ◽  
Hiroshi Mizunuma
Keyword(s):  
Heat Transfer ◽  
Surfactant Solution ◽  
Impinging Jet ◽  
High Heat ◽  
Ion Concentration ◽  
Past Study ◽  
Surfactant Solutions ◽  
Counter Ion ◽  
High Heat Transfer ◽  
Wall Flow

An impinging jet is characterized by high heat transfer and thus is widely used in cooling and heating process in industry. On the other hand, surfactant solutions reduce pipe friction in turbulent flow and at the same time reduce heat transfer. In our past study, it was found that the surfactant solution with higher counter-ion concentration did not reduce the heat transfer in the impinging jet. This phenomenon suggested that the high heat transfer was characterized by high shear rate in impinging jet and not by turbulence. However, it has not yet been determined satisfactorily how the heat transfer is influenced by surfactant solutions in the impinging jet. Especially, the influence of the counter-ion concentration is important, because the counter-ion changes not only the heat transfer but also the rheology of the surfactant solutions. In this study, we visualized the impinging jet of the surfactant solutions, and the influence of the counter-ion was investigated. The results indicated that the wall flow was remarkably influenced by the counter-ion concentration in the impinging jet. In the case of the surfactant solution with equi-molar counter-ion, the induced wall flow was continued only near the stagnation point. By contrast, the solution with higher molar counter-ion induced the radial boundary layer flow on the wall similar to the water flow. This difference in flow would cause the different heat transfer, and the solution with higher molar counter-ion produces normal heat transfer. When comparing the visualized results of the impinging jet with the numerically simulated results, the qualitative agreement was not satisfactory for the surfactant solution with counter-ion of equi-molar concentration. The simulation used a Bingham model as the rheological equation, the constants of which were obtained from a cone and a plate rheometer. It was suggested that the surfactant solution indicated different rheological behavior in these viscometric flow and impinging jet.

Influence of the Impact Angle and the Gravity Direction on Heat Transfer during the Cooling of a Cylinder by a Free Planar Subcooled Impinging Jet

2013 ◽  
Vol 554-557 ◽  
pp. 1530-1538 ◽  
Author(s):  
Sylvain Devynck ◽  
Sabine Denis ◽  
Jean Pierre Bellot ◽  
Guillaume Maigrat ◽  
Michel Varlez ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Temperature Drop ◽  
Impinging Jet ◽  
High Heat ◽  
Water Jet ◽  
Subcooled Water ◽  
High Heat Transfer ◽  
The Impact ◽  
Transfer Mechanisms

Cooling from impinging jet is nearly compulsory in steel industry processing especially in Run Out Table processing and steel tubes production because of the high heat transfer rates provided by the boiling of the subcooled water jet. As far as metallurgical phase transformations, residual stresses and deformations in the workpiece are concerned, the temperature drop during cooling must be perfectly controlled thanks to a fully understanding of the heat transfer mechanisms. In a previous study [1] the effect of surface to jet velocity ratio on heat transfer has been characterized and it has been shown that this parameter has a significant influence on shoulder of flux collapse. In order to understand the effect of more industrial quench process parameters, an innovative experimental quenching device has been designed and built. It allowed us to make heat transfer measurements at the surface of a hot nickel cylinder impinged by a subcooled water jet, according to several angles of impact and three jet directions against gravity. The results clearly highlight an effect of these two parameters on the heat transfer mechanisms at the surface of the tube. These results allow a better understanding of the origins of temperature heterogeneities inside the tube during the quench.

Flow and Heat Transfer Characteristics of Multi-Armed Impinging Jet Using DNS

2019 ◽  
Author(s):  
Kentaro Echigo ◽  
Koichi Tsujimoto ◽  
Toshihiko Shakouchi ◽  
Toshitake Ando
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Flow Characteristics ◽  
Impinging Jet ◽  
High Heat ◽  
Impinging Jets ◽  
Transfer Performance ◽  
Velocity Magnitude ◽  
High Heat Transfer ◽  
Flow Phenomena

Abstract A single impinging jet (SIJ) produces a high heat transfer rate around an impinging position on an impinging wall, while the heat transfer performance (HTP) decays increasing the distance from the impinging position. Thus in order to overcome the shortcoming of SIJ: the occurrence of both inhomogeneous heat distribution on the wall and the narrow heating area, multiple impinging jets (MIJ) are generally introduced, however, nonuniformity of heat transfer still occurs. Therefore, the viewpoint of new jet control is required in order to further improvement of the uniformity of heat transfer. On the other hand, blooming jets occur with superimposition of axial and helical excitations on the inlet velocity profile. Blooming jets are characterized by vortex rings moving along branches of separate streams. In previous studies, it is observed that blooming jets change its flow pattern with different frequency ratio of axial to helical, and its mixing and diffusion characteristics. However, there are no studies that observe heat transfer performance of the blooming jet. In this study, we conduct a direct numerical simulation of blooming jet that impinges upon the wall, and investigate its flow characteristics and heat transfer performance. As a control parameter, the distance from the wall is varied. From the view of vortex structures and velocity magnitude, it reveals how the generation of flow phenomena are modulated through the blooming control. Further in order to quantify the heat transfer of the blooming, distributions of mean local Nusselt Number are examined. Compared to the uncontrolled jet, it is confirmed that the uniformity of heat transfer is improved, suggesting that the blooming jets can be expected to be useful for the improvement of uniform heat transfer performance of impinging jets.

Influence of tip clearance and cavity depth on heat transfer in a cutback squealer tip

2020 ◽  
pp. 095441002096469
Author(s):  
Weijie Wang ◽  
Shaopeng Lu ◽  
Hongmei Jiang ◽  
Qiusheng Deng ◽  
Jinfang Teng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
High Heat ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Cavity Depth ◽  
High Heat Transfer ◽  
Blade Tip ◽  
High Heat Transfer Coefficient

Numerical simulations are conducted to present the aerothermal performance of a turbine blade tip with cutback squealer rim. Two different tip clearance heights (0.5%, 1.0% of the blade span) and three different cavity depths (2.0%, 3.0%, and 6.0% of the blade span) are investigated. The results show that a high heat transfer coefficient (HTC) strip on the cavity floor appears near the suction side. It extends with the increase of tip clearance height and moves towards the suction side with the increase of cavity depth. The cutback region near the trailing edge has a high HTC value due to the flush of over-tip leakage flow. High HTC region shrinks to the trailing edge with the increase of cavity depth since there is more accumulated flow in the cavity for larger cavity depth. For small tip clearance cases, high HTC distribution appears on the pressure side rim. However, high HTC distribution is observed on suction side rim for large tip clearance height. This is mainly caused by the flow separation and reattachment on the squealer rims.

Possible Mechanisms for Thermal Conductivity Enhancement in Nanofluids

2006 ◽  
Author(s):  
Amit Gupta ◽  
Xuan Wu ◽  
Ranganathan Kumar
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Brownian Dynamics ◽  
Lattice Vibration ◽  
Experimental Studies ◽  
High Heat ◽  
Conductivity Enhancement ◽  
High Heat Transfer ◽  
Dynamics Simulations

This study discusses the merits of various physical mechanisms that are responsible for enhancing the heat transfer in nanofluids. Experimental studies have cemented the claim that ‘seeding’ liquids with nanoparticles can increase the thermal conductivity of the nanofluid by up to 40% for metallic and oxide nanoparticles dispersed in a base liquid. Experiments have also shown that the rise in conductivity of the nanofluid is highly dependent on the size and concentration of the nanoparticles. On the theoretical side, traditional models like Maxwell or Hamilton-Crosser models cannot explain this unusually high heat transfer. Several mechanisms have been postulated in the literature such as Brownian motion, thermal diffusion in nanoparticles and thermal interaction of nanoparticles with the surrounding fluid, the formation of an ordered liquid layer on the surface of the nanoparticle and microconvection. This study concentrates on 3 possible mechanisms: Brownian dynamics, microconvection and lattice vibration of nanoparticles in the fluid. By considering two nanofluids, copper particles dispersed in ethylene glycol, and silica in water, it is determined that translational Brownian motion of the nanoparticles, presence of an interparticle potential and the microconvection heat transfer are mechanisms that play only a smaller role in the enhancement of thermal conductivity. On the other hand, the lattice vibrations, determined by molecular dynamics simulations show a great deal of promise in increasing the thermal conductivity by as much as 23%. In a simplistic sense, the lattice vibration can be regarded as a means to simulate the phononic transport from solid to liquid at the interface.

A Photographic Study of Flow Boiling Stability on a Plain Surface With Tapered Manifold

2015 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Speed ◽  
Flow Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
High Heat Transfer ◽  
Plain Surface ◽  
High Heat Transfer Coefficient

Flow boiling in microchannels offers many advantages such as high heat transfer coefficient, higher surface area to volume ratio, low coolant inventory, uniform temperature control and compact design. The application of these flow boiling systems has been severely limited due to early critical heat flux (CHF) and flow instability. Recently, a number of studies have focused on variable flow cross-sectional area to augment the thermal performance of microchannels. In a previous work, the open microchannel with manifold (OMM) configuration was experimentally investigated to provide high heat transfer coefficient coupled with high CHF and low pressure drop. In the current work, high speed images of plain surface using tapered manifold are obtained to gain an insight into the nucleating bubble behavior. The mechanism of bubble nucleation, growth and departure are described through high speed images. Formation of dry spots for both tapered and uniform manifold geometry is also discussed.

Impact of Stefan blowing and magnetic dipole on bio-convective flow of Maxwell nanofluid over a stretching sheet

2021 ◽  
pp. 095440892110581
Author(s):  
A. Alhadhrami ◽  
Hassan A. H. Alzahrani ◽  
B. M. Prasanna ◽  
N. Madhukeshwara ◽  
K. C. Rajendraprasad ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Brownian Motion ◽  
Magnetic Dipole ◽  
Stretching Sheet ◽  
High Heat ◽  
Hard Drives ◽  
Linear System Of Equations ◽  
High Heat Transfer ◽  
Non Linear System ◽  
The Impact

The features of ferromagnetic fluids make it supportive for an extensive usage in loudspeakers, magnetic resonance imaging, computer hard drives, directing of magnetic drug and magnetic hyperthermia. Owing to all such potential applications, the current investigation is to understand the relationship between the thermal distribution, magnetic field and resulting fluid flow of Maxwell liquid over a stretching sheet. Investigation of thermal energy and concentration is carried out in the presence of thermal radiation, non-uniform heat sink/source, chemical reaction, Stefan blowing, magnetic dipole, thermophoresis and Brownian motion. Also, microorganisms are considered just to stabilize the suspended nanoparticles. Boundary layer approximation is employed during mathematical derivation. Based on a new constitutive relation, the governing equations are formulated and are reduced into a coupled non-linear system of equations using appropriate transformations. Further, these equations are solved numerically using fourth-order Runge–Kutta method with shooting technique. The impact of involved parameters is discussed and analysed graphically. Outcomes disclose that Newtonian liquid shows high heat transfer when compared to non-Newtonian (Maxwell) liquid for increased values of Brownian motion and thermophoresis parameters. Increased values of Peclet number declines the rate of gyrotactic microorganisms. Finally, an increase in Brownian and thermophoresis motion parameters declines the rate of heat transfer.

Heat Transfer Characteristics of a Flow Passage With Long Pin Fins and Improving Heat Transfer Coefficient by Adding Turbulence Promoters on a Endwall

2001 ◽  
Author(s):  
K. Takeishi ◽  
T. Nakae ◽  
K. Watanabe ◽  
M. Hirayama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
High Heat ◽  
Atmospheric Conditions ◽  
Pin Fin ◽  
High Heat Transfer ◽  
Turbine Vanes ◽  
Pin Fins

Pin fins are normally used for cooling the trailing edge region of a turbine, where their aspect ratio (height H/diameter D) is characteristically low. In small turbine vanes and blades, however, pin fins may also be located in the middle region of the airfoil. In this case, the aspect ratio can be quite large, usually obtaining values greater than 4. Heat transfer tests, which are conducted under atmospheric conditions for the cooling design of turbine vanes and blades, may overestimate the heat transfer coefficient of the pin-finned flow channel for such long pin fins. The fin efficiency of a long pin fin is almost unity in a low heat transfer situation as it would be encountered under atmospheric conditions, but can be considerably lower under high heat transfer conditions and for pin fins made of low thermal conductivity material. A series of tests with corresponding heat transfer models has been conducted in order to clarify the heat transfer characteristics of the long pin-finned flow channel. It is assumed that heat transfer coefficients can be predicted by the linear combination of two heat transfer equations, which were separately developed for the pin fin surface and for tubes in crossflow. To confirm the suggested combined equations, experiments have been carried out, in which the aspect ratio and the thermal conductivity of the pin were the test parameters. To maintain a high heat transfer coefficient for a long pin fin under high-pressure conditions, the heat transfer was augmented by adding a turbulence promoter on the pin-finned endwall surface. A corresponding equation that describes this situation has been developed. The predicted and measured values showed good agreement. In this paper, a comprehensive study on the heat transfer of a long pin-fin array will be presented.

Heat Transfer Behavior of Silica Nanoparticles in Pool Boiling Experiment

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Denitsa Milanova ◽  
Ranganathan Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Chemical Composition ◽  
Particle Deposition ◽  
Ph Value ◽  
Pool Boiling ◽  
High Heat ◽  
Boiling Regime ◽  
High Heat Transfer ◽  
The Wire

The heat transfer characteristics of silica (SiO2) nanofluids at 0.5vol% concentration and particle sizes of 10nm and 20nm in pool boiling with a suspended heating Nichrome wire have been analyzed. The influence of acidity on heat transfer has been studied. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles and their mutual interactions toward the suspended heated wire. When there is no particle deposition on the wire, the nanofluid increases critical heat flux (CHF) by about 50% within the uncertainty limits regardless of pH of the base fluid or particle size. The extent of oxidation on the wire impacts CHF, and is influenced by the chemical composition of nanofluids in buffer solutions. The boiling regime is further extended to higher heat flux when there is agglomeration on the wire. This agglomeration allows high heat transfer through interagglomerate pores, resulting in a nearly threefold increase in burnout heat flux. This deposition occurs for the charged 10nm silica particle. The chemical composition, oxidation, and packing of the particles within the deposition on the wire are shown to be the reasons for the extension of the boiling regime and the net enhancement of the burnout heat flux.

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