scholarly journals Estimating the Maximum Splat Diameter of a Solidifying Droplet

1999 ◽  
Author(s):  
Nicolas G. Hadjiconstantinou
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Contact Angle ◽  
Simple Model ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Simple Analytical Model ◽  
Droplet Spreading ◽  
Isothermal Model ◽  
High Reynolds

Abstract We present a simple analytical model for the estimation of the maximum splat diameter of an impacting droplet on a subcooled target. This work is an extension of the isothermal model of Pasandideh-Fard et al. (1996). The model uses an energy conservation argument, applied between the initial and final drop configurations, to approximately capture the dynamics of spreading. The effects of viscous dissipation, surface tension, and contact angle are taken into account. Tests against limited experimental data at high Reynolds and Weber numbers indicate that an accuracy of the order of 5% is achieved with no adjustable parameters required. Agreement with experimental data in the limit We → ∞ is also very good. We additionally propose a simple model for the estimation of the thickness of the freezing layer developed at the droplet-substrate contact during droplet spreading. This model accounts for the effect of thermal contact resistance and its predictions compare favorably with experimental data.

Numerical Study on Substrate Remelting, Flow, and Resolidification in Microcasting

Volume 3 ◽  
2004 ◽  
Author(s):  
F. J. Hong ◽  
H.-H. Qiu
Keyword(s):  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Numerical Study ◽  
Thermal Contact ◽  
Spreading Factor ◽  
Droplet Spreading ◽  
Molten Droplet ◽  
Front Shape ◽  
Complex Fluid

A large and highly superheated molten droplet impacting onto the substrate during the microcasting was studied numerically. In this study, same material for both the droplet and the substrate was considered. Numerical model including the complex fluid dynamics of droplet, interfacial thermal contact resistance, and substrate remelting, as well as the flow in the substrate has been developed. Numerical simulations of a microcasting experiment were conducted with the different thermal contact resistances. The results of simulations show that the spreading factor and substrate remelting agreed well with the experimental data under the assumption of an appropriate thermal contact resistance. It is also found that the thermal contact resistance plays an important role not only in droplet spreading arrest but also in the determination of substrate remelting volume and remelting front shape. The effects of droplet impacting velocity, superheat and substrate temperature were also investigated.

scholarly journals Droplet spreading and permeating on the hybrid-wettability porous substrates: a lattice Boltzmann method study

Open Physics ◽  
2016 ◽  
Vol 14 (1) ◽  
pp. 483-491 ◽  
Author(s):  
Wen-Kai Ge ◽  
Gui Lu ◽  
Xin Xu ◽  
Xiao-Dong Wang
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Droplet Spreading ◽  
Small Surface ◽  
Pore Sizes ◽  
Fluid Properties ◽  
Boltzmann Method ◽  
Porous Substrates

AbstractThe spreading and permeation of droplets on porous substrates is a fundamental process in a variety of applications, such as coating, dyeing, and printing. The spreading and permeating usually occur synchronously but play different roles in the practical applications. The mechanisms of the competition between spreading and permeation is significant but still unclear. A lattice Boltzmann method is used to study the spreading and permeation of droplets on hybrid-wettability porous substrates, with different wettability on the surface and the inside pores. The competition between the spreading and the permeation processes is studied in this work from the effects of the substrate and the fluid properties, including the substrate wettability, the porous parameters, as well as the fluid surface tension and viscosity. The results show that increasing the surfacewettability and the porosity contact angle both inhibit the spreading and the permeation processes. When the inside porosity contact angle is larger than 90° (hydrophobic), the permeation process does not occur. The droplets suspend on substrates with Cassie state. The droplets are more easily to permeate into substrates with a small inside porosity contact angle (hydrophilic), as well as large pore sizes. Otherwise, the droplets are more easily to spread on substrate surfaces with small surface contact angle (hydrophilic) and smaller pore sizes. The competition between droplet spreading and permeation is also related to the fluid properties. The permeation process is enhanced by increasing of surface tension, leading to a smaller droplet lifetime. The goals of this study are to provide methods to manipulate the spreading and permeation separately, which are of practical interest in many industrial applications.

Effect of Thermal Contact Resistance on Alumina Molten Particle Impacting onto a Metal Substrate

2012 ◽  
Vol 326-328 ◽  
pp. 482-487 ◽  
Author(s):  
S. Oukach ◽  
Bernard Pateyron ◽  
H. Hamdi ◽  
M. El Ganaoui
Keyword(s):  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Droplet Diameter ◽  
Thermal Contact ◽  
Thermal Spraying ◽  
Droplet Spreading ◽  
Element Analysis ◽  
Molten Droplet ◽  
Molten Droplets ◽  
Droplet Sizes

In this paper, a Finite Element Analysis is carried out in order to simulate the process of spreading and solidification of a micrometric molten droplet impinging onto a cold substrate. This process is a crucial key to have a good understanding of coatings obtained by means of thermal spraying. The effect of thermal contact resistance (TCR) on the droplet spreading and solidification was investigated using different values of TCR and different droplet sizes. The solidification time was found to be a linear function of the droplet diameter square. Viscous dissipation, wettability and surface tension effects are taken into account. The Level Set method was employed to explicitly track the free surface of molten droplets.

Surface Chemistry and Characteristics Based Model for the Thermal Contact Resistance of Fluidic Interstitial Thermal Interface Materials

2001 ◽  
Vol 123 (5) ◽  
pp. 969-975 ◽  
Author(s):  
Ravi S. Prasher
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Thermal Interface Materials ◽  
Heat Spreader ◽  
Thermal Interface ◽  
Thermal Solution ◽  
Interface Materials

Microprocessor powers are increasing at a phenomenal rate, which requires very small thermal resistance between the die (chip) and the ambient, if the current economical methods of conduction and convection cooling are to be utilized. A typical thermal solution in flip chip technology utilizes two levels of thermal interface materials: between the die and the heat spreader, and between the heat spreader and the heat sink. Phase change materials and thermal greases are among the most prominent interstitial thermal interface materials (TIM) used in electronic packaging. These TIMs are typically polymeric matrix loaded with highly conducting filler particles. The dwindling thermal budget has necessitated a better understanding of the thermal resistance of each component of the thermal solution. Thermal conductivity of these particle-laden materials is better understood than their contact resistance. A careful review of the literature reveals the lack of analytical models for the prediction of contact resistance of these types of interstitial materials, which possess fluidic properties. This paper introduces an analytical model for the thermal contact resistance of these types of interstitial materials. This model is compared with the experimental data obtained on the contact resistance of these TIMs. The model, which depends on parameters such as, surface tension, contact angle, thermal conductivity, roughness and pressure matches very well with the experimental data at low pressures and is still within the error bars at higher pressures.

scholarly journals Surface tension of liquid Ti with adsorbed oxygen and a simple associate model for its prediction

2020 ◽  
Vol 49 (1-2) ◽  
pp. 89-105 ◽  
Author(s):  
J. BRILLO ◽  
J. WESSING ◽  
H. KOBATAKE ◽  
H. FUKUYAMA
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Simple Model ◽  
Chemical Analysis ◽  
Mole Fraction ◽  
Tio2 Powder ◽  
Bulk Oxygen ◽  
Electromagnetically Levitated ◽  
Oxygen Mole Fraction ◽  
Good Agreement

Surface tensions of electromagnetically levitated liquid Ti-samples were measured under the influence of oxygen. For this purpose, Ti-O samples were prepared by adding different amounts of TiO2 powder to pure Ti. The surface tension was found to strongly depend on the bulk oxygen mole fraction determined by chemical analysis. The results could be described by a simple model presented in the present work. In this model the Butler equation is applied and the formation of TiO2 – associates are taken into account. Non-ideal interactions ΔH≠0 between titanium and the associates also need to be taken into account. Good agreement with the experimental data is evident and also with a different model developed earlier by us.

scholarly journals Does the Use of Adjuvants Alter Surface Tension and Contact Angle of Herbicide Spray Droplets on Leaves of Sida spp.?

2019 ◽  
Vol 37 ◽  
Author(s):  
R.T.S. SANTOS ◽  
M.C. FERREIRA ◽  
R.G. VIANA
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Contact Angles ◽  
Control Surface ◽  
Droplet Spreading ◽  
Spray Solution ◽  
Randomized Design ◽  
Plant Surfaces ◽  
Sida Rhombifolia ◽  
Lower Contact

ABSTRACT: Droplet spreading on plant surfaces may indicate greater efficiency in herbicide application. The aim of this study was to evaluate surface tension and contact angle of the aminopyralid + fluroxypir herbicide droplets associated with adjuvants on the leaf surface of three species of the genus Sida. The experiment was carried out in a completely randomized design, in a 4x2+1 factorial arrangement, with four replications. Four treatments containing two rates of the herbicide (0.04 + 0.08 kg a.i. ha-1 and 0.08+0.16 kg a.i. ha-1) were evaluated, associated or not with the adjuvants vegetable oil, mineral oil and lecthin; and water was used as a control. Surface tension and contact angle of the syringes were measured with a tensiometer. Surface tension was evaluated at 5, 15 and 25 seconds after droplet formation. Contact angle was measured at 5, 15 and 25 seconds after droplet deposition on the adaxial and abaxial surfaces of Sida rhombifolia, S. glaziovii and S. cordifolia. The results were submitted to analysis of variance by the F-test and the means of the treatments were compared by Tukey’s test (p>0.05). There was no interaction between the factors for surface tension. The contact angles of S. cordifolia and S. glaziovii were lower after addition of lecthin on the adaxial face. The addition of the adjuvants to the spray solution provided lower contact angles at the rate of 0.04 + 0.08 kg a.i. ha-1, except for S. rhombifolia, whose contact angle was lower with the spray solution without adjuvant.

Review of Thermal Joint Resistance Models for Nonconforming Rough Surfaces

2006 ◽  
Vol 59 (1) ◽  
pp. 1-12 ◽  
Author(s):  
M. Bahrami ◽  
J. R. Culham ◽  
M. M. Yananovich ◽  
G. E. Schneider
Keyword(s):  
Experimental Data ◽  
Flux Tube ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Thermal Analyses ◽  
Theoretical Models ◽  
Empirical Correlations ◽  
Data Points ◽  
The Mean ◽  
Circular Heat

The thermal contact resistance (TCR) in a vacuum is studied. The TCR problem is divided into three different parts: geometrical, mechanical, and thermal. Each problem includes a macro- and microscale subproblem; existing theories and models for each part are reviewed. Empirical correlations for microhardness, and the equivalent (sum) rough surface approximation, are discussed. Suggested correlations for estimating the mean absolute surface slope are summarized and compared with experimental data. The most common assumptions of existing thermal analyses are summarized. As basic elements of thermal analyses, spreading resistance of a circular heat source on a half-space and flux tube are reviewed; also existing flux tube correlations are compared. More than 400 TCR data points collected by different researchers during the last 40years are grouped into two limiting cases: conforming rough and elastoconstriction. Existing TCR models are reviewed and compared with the experimental data at these two limits. It is shown that the existing theoretical models do not cover both of the above-mentioned limiting cases. This review article cites 58 references.

Numerical Simulation of Droplet Impact on an Isothermal Micro-Grooved Solid Surface

2010 ◽  
Author(s):  
Yujia Tao ◽  
Xiulan Huai ◽  
Zhigang Li
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Solid Surface ◽  
Initial Velocity ◽  
Surface Tension Coefficient ◽  
Liquid Region ◽  
Spreading Factor ◽  
Droplet Spreading ◽  
Droplet Dynamics ◽  
The Impact

The process of a micro droplet of distilled water impact on an isothermal micro-grooved solid surface is numerical simulated in this paper. To accurately represent the droplet dynamics, special attention is given to the variation of the droplet pressure and velocity, the movement of the free surface between two fluids and the deforming of the droplet after impact. The Volume Of Fluid method is used to track the position and the shape of the liquid region. The PISO algorithm is selected to solve the pressure-velocity coupling. The influences of the droplet initial velocity, the contact angle for water on the surface perpendicular to the groove direction and the surface tension coefficient on the impact process are discussed in detail. The results show that the droplet spreading factor improves notably with the increase of the initial velocity, and reduces with the increase of the contact angle. When the surface tension coefficient increases, the spreading factor reduces greatly. The spreading factor is the largest and the time elapsing is the longest in the case of σ = 0.038 N/m.

scholarly journals Effect of Compression on the Effective Thermal Conductivity and Thermal Contact Resistance in PEM Fuel Cell Gas Diffusion Layers

2010 ◽  
Author(s):  
Ehsan Sadeghi ◽  
Ned Djilali ◽  
Majid Bahrami
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Fuel Cell ◽  
Contact Resistance ◽  
Effective Thermal Conductivity ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Analytical Models

Heat transfer through the gas diffusion layer (GDL) of a PEM fuel cell is a key process in the design and operation a PEM fuel cell. The analysis of this process requires determination of the effective thermal conductivity as well as the thermal contact resistance between the GDL and adjacent surfaces/layers. In the present study, a guarded-hot-plate apparatus has been designed and built to measure the effective thermal conductivity and thermal contact resistance in GDLs under vacuum and atmospheric pressure. Toray carbon papers with the porosity of 78% and different thicknesses are used in the experiments under a wide range of compressive loads. Moreover, novel analytical models are developed for the effective thermal conductivity and thermal contact resistance and compared against the present experimental data. Results show good agreements between the experimental data and the analytical models. It is observed that the thermal contact resistance is the dominant component of the total thermal resistance and neglecting this phenomenon may result in enormous errors.

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