Enhancement of Heat Transfer by an Electric Field for a Drop Translating at Intermediate Reynolds Number

2005 ◽  
Vol 127 (10) ◽  
pp. 1087-1095 ◽  
Author(s):  
Rajkumar Subramanian ◽  
M. A. Jog
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Steady State ◽  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Continuous Phase ◽  
Dispersed Phase ◽  
Enhancement Of Heat Transfer

The enhancement of heat transfer by an electric field to a spherical droplet translating at intermediate Reynolds number is numerically investigated using a finite volume method. Two heat transfer limits are considered. The first limit is the external problem where the bulk of the resistance is assumed to be in the continuous phase. Results show that the external Nusselt number significantly increases with electric field strength at all Reynolds numbers. Also, the drag coefficient increases with electric field strength. The enhancement in heat transfer is higher with lower ratio of viscosity of the dispersed phase to the viscosity of the continuous phase. The second heat transfer limit is the internal problem where the bulk of the resistance is assumed to be in the dispersed phase. Results show that the steady state Nusselt number for a combined electrically induced and translational flow is substantially greater than that for purely translational flow. Furthermore, for a drop moving at intermediate Reynolds number, the maximum steady state Nusselt number for a combined electrically induced and translational flow is slightly greater than that for a purely electric field driven motion in a suspended drop.

Enhancement of Heat Transfer of Rectangular Saw Tooth Shaped Micro Channel Heat Sink with Water Nano Fluid/Aluminium Oxide

2015 ◽  
Vol 813-814 ◽  
pp. 685-689
Author(s):  
M. Vijay Anand Marimuthu ◽  
B. Venkatraman ◽  
S. Kandhasamy
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Heat Sink ◽  
Micro Channel ◽  
Performance Curve ◽  
Theoretical Level ◽  
Enhancement Of Heat Transfer ◽  
Nano Fluid

This paper investigates the performance and characteristics of saw tooth shape micro channel in the theoretical level. If the conduct area of the nano fluid increases the heat transfer also increases. The performance curve has drawn Reynolds number against nusselt number, heat transfer co efficient. Pressure drop plays an important role in this device. If pressure drop is high the heat transfer increases. The result in this experiment shows clearly that the heat transfer is optimized.

Visualization of a Single Boiling Bubble in a DC Electric Field

2011 ◽  
Author(s):  
Feng Chen ◽  
Dong Liu ◽  
Yaozu Song ◽  
Yao Peng
Keyword(s):  
Heat Transfer ◽  
Life Cycle ◽  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Wall Temperature ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Nucleate Boiling ◽  
Dc Electric Field

The application of electric field has been demonstrated as an effective way to enhance pool boiling heat transfer. In past studies, adiabatic experiments were often conducted to simulate the dynamics of nucleate bubbles in the presence of an electric field, where gas bubbles were injected from an orifice, to avoid complexities involved in the nucleate boiling experiments. While adiabatic studies yield useful information of the bubble dynamics, further studies about bubble dynamics during nucleate boiling heat transfer are still necessary for a full understanding of the effects of applied electric field on the liquid-vapor phase change heat transfer. In this paper, the dynamics of a single boiling bubble in a direct current (DC) electric field was studied experimentally employing R113 as the working fluid. The life cycle of the boiling bubble was visualized using high-speed photography and was compared with that of an injected nitrogen bubble. Under the same electric field, a more appreciable elongation along the field direction was observed for the boiling bubble. A modified relationship between the bubble deformation and the electrical Weber number was proposed for the boiling bubble. As the electric field strength increases, it was found that, although the growth time of the boiling bubble increases, the waiting period decreases. However, it was also found that, the change of the whole life cycle with electric field strength increasing is relevant to the wall temperature. In this work, the wall temperature measured in the vicinity of the nucleation site upon the bubble departure decreases when the electric field is applied.

Soft poly(2-chloroaniline)/pectin hydrogel and its electromechanical properties

2017 ◽  
Vol 32 (6) ◽  
pp. 788-799 ◽  
Author(s):  
Wanar Kongkaew ◽  
Watchara Sangwan ◽  
Wanchai Lerdwijitjarud ◽  
Anuvat Sirivat
Keyword(s):  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Storage Modulus ◽  
Dispersed Phase ◽  
Electromechanical Properties ◽  
Soft Actuator ◽  
High Storage

Pectin hydrogels were successfully fabricated with various physical crosslinkers and concentrations for soft actuator applications. A small amount of synthesized P2ClAn was added as a dispersed phase into the pectin matrix. The electromechanical properties of the pectin hydrogels and blends were investigated under the effects of electric field strength, ionic crosslinker type and concentration, and P2ClAn concentration. The electromechanical properties of the pectin hydrogel as crosslinked by Fe2+ were superior to other pectin hydrogels. The pristine pectin hydrogel and the P2ClAn/Pectin hydrogel blended with 0.10%v/v P2ClAn provided the high storage modulus sensitivity values of 8.61 and 14.01, respectively, under the electric field strength of 800 V/mm. The P2ClAn/Pectin hydrogel blend responded to the electric field with higher dielectrophoretic forces, but lower deflections relative to the pristine pectin hydrogel due to the additional P2ClAn polarization and the latter lower rigidity.

scholarly journals LBM Analysis of Micro-Convection in MHD Nanofluid Flow

2017 ◽  
Vol 63 (7-8) ◽  
pp. 426 ◽  
Author(s):  
Arjun Kozhikkatil Sunil ◽  
Rakesh Kumar
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Temperature Jump ◽  
Volume Fraction ◽  
Slip Coefficient

The lattice Boltzmann-Bhatnagar-Gross-Krook method was used to simulate Al2O3-water nanofluid to find the effects of Reynolds, Rayleigh and Hartmann numbers, slip coefficient, nanoparticle volume fraction and axial distance on forced convection heat transfer in MATLAB. The ranges of studied Reynolds number, Rayleigh number, magnetic field strength, nanoparticle volume concentration and slip coefficient include 200 ≤ Re ≤ 4000; 103 ≤ Ra ≤ 106; 0 ≤ Ha 90; 0 ≤ φ ≤ 2%; 0.005 ≤ B ≤ 0.02, respectively. The results show that increasing Reynolds number and nanoparticle volume fractions improve heat transfer in the 2D microtube under laminar, turbulent, slip and temperature jump boundary conditions. Decreasing the values of slip coefficient decreases the temperature jump and enhances the Nusselt number. A critical value for the Rayleigh number (105) and magnetic field strength (Ha 10) exists, at which the impacts of the solid volume fraction and slip coefficient effects are the most pronounced. The pressure drop shows a similar type of enhancement in magnitude, as observed in the case of the Nusselt number. However, application of nanofluids for low Reynolds numbers is more beneficial, and the effect of volume fractions are more pronounced in comparison to slip coefficient, though the effects are marginal.

Heat-Transfer Mechanisms in an In-Line Tube Bundle Subject to a Particulate Cross Flow

1992 ◽  
Vol 206 (5) ◽  
pp. 317-326
Author(s):  
D C Sterritt ◽  
D B Murray
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Tube Bundle ◽  
Cross Flow ◽  
Thermal Capacity ◽  
Solid Particles ◽  
Enhancement Of Heat Transfer ◽  
Tube Arrays ◽  
Loading Ratio

The effect of solid particles in suspension on heat transfer for tubes located within a square tube bundle of pitch-diameter ratio 1.75 has been investigated. Tests conducted at a Reynolds number of 6000 with mean particle diameters of 58 and 127 μm at a mass loading ratio of 0.5 kg particles/kg air indicate that heat transfer is enhanced at all locations by the presence of the particles. However, at a Reynolds number of 12 000 there is a net decrease in the mean Nusselt number at all positions, with the exception of the first row. Assessment of the main mechanisms by which particles modify heat transfer in in-line tube arrays suggests that the enhancement of heat transfer is a consequence of the increased thermal capacity of the suspension, whereas the reduction in Nusselt number is considered to result from a change in the flow structure and turbulence within the array.

Visualization of a Single Boiling Bubble in a DC Electric Field

2012 ◽  
Author(s):  
Feng Chen ◽  
Dong Liu ◽  
Yaozu Song
Keyword(s):  
Heat Transfer ◽  
Life Cycle ◽  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Wall Temperature ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Nucleate Boiling ◽  
Dc Electric Field

The application of electric field has been demonstrated as an effective way to enhance pool boiling heat transfer. In past studies, adiabatic experiments were often conducted to simulate the dynamics of nucleate bubbles in the presence of an electric field, where gas bubbles were injected from an orifice, to avoid complexities involved in the nucleate boiling experiments. While adiabatic studies yield useful information of the bubble dynamics, further studies about bubble dynamics during nucleate boiling heat transfer are still necessary for a full understanding of the effects of applied electric field on the liquid-vapor phase change heat transfer. In this paper, the dynamics of a single boiling bubble in a direct current (DC) electric field was studied experimentally employing R113 as the working fluid. The life cycle of the boiling bubble was visualized using high-speed photography and was compared with that of an injected nitrogen bubble. Under the same electric field, a more appreciable elongation along the field direction was observed for the boiling bubble. A modified relationship between the bubble deformation and the electrical Weber number was proposed for the boiling bubble. As the electric field strength increases, it was found that, although the growth time of the boiling bubble increases, the waiting period decreases. However, it was also found that, the change of the whole life cycle with electric field strength increasing is relevant to the wall temperature. In this work, the wall temperature measured in the vicinity of the nucleation site upon the bubble departure decreases when the electric field is applied.

High field kinetic processes in anodic oxide films on aluminium. I. Current transients for linearly changing electric field strength

1968 ◽  
Vol 46 (4) ◽  
pp. 535-548 ◽  
Author(s):  
M. J. Dlgnam ◽  
P. J. Ryan
Keyword(s):  
Steady State ◽  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
High Field ◽  
Oxide Films ◽  
Anodic Oxide ◽  
Anodic Oxide Films ◽  
Differential Field ◽  
Field Coefficient

Anodic oxide films were formed on high purity aluminium (99.996 %) under steady-state conditions (current and field strength constant) in a glycol–borate electrolyte until the film reached a predetermined thickness at which point the anodic overpotential was changed rapidly and in a linear manner. As little film growth occurred during these linear sweeps, the conditions corresponded to linearly changing field strength. From these data, the transient differential field coefficient, β1, defined by[Formula: see text]where i and E are the ion current density and electric field strength and Es the steady-state formation field strength, was determined β1 was found to vary linearly with Es in the manner [Formula: see text] with [Formula: see text] A recent theory proposed by one of us (M. J. D.) predicts that the parameter [Formula: see text] should have the same value as that deduced from the field dependence of the steady-state differential field coefficient,[Formula: see text]Such agreement was indeed found, two independently determined 'steady-state' values of [Formula: see text] being 3.53 ± 11% and 3.11 ± 14% ÅV−1. A direct comparison of the present results with previous steady-state results gave βs/β1 = μs/μ1 = 3.09. More complex features of the transients were also found to be in accord with the above theory, but could be accounted for almost as well by an earlier theory, the so-called high field Frenkel defect theory.Dielectric constant values determined from the current discontinuity appearing upon application of the linearly increasing field gave K1 = 8.35 ± .1 for transients commencing from steady-state conditions and K1 = 8.85 ± .2 for films formed then 'aged' at E = 0 before measurement. Certain anomalies with regard to the charging current were apparent.

Analysis of Steady State Conjugate Heat Transfer in a Circular Microtube Inside a Substrate

2004 ◽  
Author(s):  
P. Sharath C. Rao ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Stainless Steel ◽  
Nusselt Number ◽  
Steady State ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Thermal Conductivity Ratio ◽  
Interface Temperature ◽  
Outlet Temperature

The steady state heat transfer for laminar flow inside a circular microtube within a rectangular substrate has been investigated. Silicon, Silicon Carbide, and Stainless Steel were the substrates used and Water and FC-72 were the coolants employed. Equations governing the conservation of mass, momentum, and energy were solved in the fluid region. Within the solid wafer, the heat conduction was solved. A thorough investigation for velocity and temperature distributions for different substrates and coolants was performed by varying geometrical dimensions and Reynolds number. At a constant diameter and Reynolds number, for combinations comprising same coolant but different substrates, one with the lowest solid to fluid thermal conductivity ratio (ks/kf) attains the highest local peripheral average interface temperature. It was found that the Nusselt number is more for a system with Silicon as the substrate and FC-72 as the working fluid and the least for a system with Stainless Steel as the substrate and Water as the working fluid. The lower ks/kf ratio of Stainless Steel-Water combination is the main reason for the lower Nusselt number. With the increase in hydraulic diameter and Reynolds number, the average Nusselt number increased. It was also observed that the maximum temperature of the substrate and hence the outlet temperature of the fluid increased as the Reynolds number decreased.

A Numerical Investigation of the Effect of Inlet Velocity Oscillation on Heat Transfer in a Two-Dimensional Laminar Jet Impinging on an Isothermal Surface

2016 ◽  
Author(s):  
Johnny Issa ◽  
Najib Saliba ◽  
Bchara Sidnawi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Steady State ◽  
Strouhal Number ◽  
Average Nusselt Number ◽  
Inlet Velocity ◽  
Isothermal Surface ◽  
The Right ◽  
State Case

Heat transfer in a laminar confined oscillating slot jet impinging on an isothermal surface is numerically investigated. A uniform inlet velocity profile, oscillating with an angle φ, is used at the jet exit. The angle φ changes in a sinusoidal form. The height-to-jet width ratio is fixed at 5. The working fluid is air with constant physical properties corresponding to Prandtl number, Pr, equal to 0.74 at ambient conditions. Reynolds number, Re, is defined based on the jet hydraulic diameter and is varied in the self-stable range between 100 and 400. Strouhal number, St, is also varied between 0.05 and 0.75. Oscillating the jet at Reynolds number equal to 100 showed no heat transfer improvement over the steady state case, regardless of the used Strouhal number values. The vortices generated by the oscillation were too weak and could barely reach the wall. The flow showed a high vulnerability to severe oscillations which drastically reduced the jet heat removal ability. The vorticity contours showed a perfect symmetry which resulted in instantaneous and average Nusselt number distributions that are symmetric about the center of the isothermal surface at x = 0. The average stagnation Nusselt number, Nu0, decreased by about 1.25% as Strouhal number is increased from 0.4 to 0.625 then dipped by 44.1% as St is further increased to 0.75, a fact that was attributed to reduction in the bulk momentum by the relatively high frequency. With Reynolds number at 250, the lowest two frequencies corresponding to St of 0.05 and 0.1, resulted in a flow field that is more developed to the right side of the channel, a phenomenon that was linked to the direction of the first jet swing. The corresponding average Nusselt number distributions were consequently asymmetric, with a significant shift to the right. This asymmetric behavior gradually disappeared as the frequency is increased. At St of 0.4 and 0.5, the average stagnation Nusselt number Nu0, showed a 2.2% increase over the steady jet case. As Strouhal number is further increased beyond 0.5, the average Nu0 gradually decreased, since the oscillation period became too short for a vortex to be strong enough to reach the wall. For Reynolds number set at 400, the oscillating condition at the inlet engaged the jet into flapping. The jet showed a tendency to a permanent lean towards one side of the channel, for all used frequencies. Flapping was more one-sided which led to a shift in the average Nusselt number distribution at low frequencies. As Strouhal number is increased to 0.75, flapping became more stable and the generated vortices were expectedly weaker due to the higher frequency. Also, at this Strouhal number value, the average Nu distribution showed the best symmetry with a 2.45% improvement of the average stagnation Nusselt number, over that of the steady state case.

Enhancement of Heat Transfer over Spatial Stationary and Moving Sinusoidal Wavy Wall: A Numerical Analysis

2012 ◽  
Vol 326-328 ◽  
pp. 341-347 ◽  
Author(s):  
Prashant Kumar ◽  
Frédéric Topin ◽  
Lounes Tadrist
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Numerical Analysis ◽  
Pressure Drop ◽  
Standing Waves ◽  
Wavy Wall ◽  
Transfer Enhancement ◽  
Enhancement Of Heat Transfer ◽  
Stationary Wall

Heat transfer phenomena are numerically studied with standing waves inside the tubes for stationary and moving sinusoidal wavy walls. Effects of spatial wavelengths (= 1/2, 2/3, 1 and 2 mm), Reynolds number (1-120), frequency (0-60 Hz) and amplitude (1%-20% of tube diameter, d) on heat transfer and pressure drop are studied. For stationary wall case, upon increasing the number of sine waves, the Nusselt number starts to decrease; the associated pressure drop and friction factor increases very rapidly at highest value of amplitude. Heat transfer enhancement characteristics on a moving sinusoidal wavy-walled tube with imposed frequency (0

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