The Effect of Nano-Structured Surfaces on Droplet Impingement Heat Transfer

2011 ◽  
Author(s):  
Gary Rosengarten ◽  
Anggito Tetuko ◽  
Ka Kit Li ◽  
Alex Wu ◽  
Robert Lamb
Keyword(s):  
Heat Transfer ◽  
Surface Properties ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
High Speed ◽  
Liquid Droplet ◽  
Droplet Impingement ◽  
Cooling Effectiveness ◽  
Structured Surfaces ◽  
The Impact

Droplet impingement is a fundamental process for many applications particularly those involving heat transfer. While there has been considerable work over many years on understanding the flow and heat transfer processes, we have only recently been able to fabricate controllable nanostructured surfaces. Surface structure can have a massive impact on the droplet impact process dynamics and the associated convective heat transfer from the liquid droplet to the surface. In this paper we examine the impact dynamics and heat transfer using simultaneous high speed thermal imaging of the liquid from below, and high speed video camera images from the side for different surfaces, ranging from hydrophilic to superhydrophobic. In this way we characterize the heat transfer process as a function of the droplet dynamics and the surface properties. We show that the heat transfer rate is primarily affected by the contact line dynamics and the wetted area. Due to the superhydrophobic roughness scale being relatively small, the interface resistance offered by the trapped air has only a small effect on the heat transfer rate, and only in the inertia dominated region before maximum spreading diameter. Finally we show that the overall cooling effectiveness of as single impinging droplet is very dependent on the surface properties with hydrophilic surfaces offering the highest cooling effectiveness.

Ferro-nanofluid squeeze film lubrication with heat transfer

2021 ◽  
pp. 135065012110276
Author(s):  
Manimegalai Kavarthalai ◽  
Vimala Ponnuswamy
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Contact Time ◽  
Transfer Rate ◽  
Fluid Layer ◽  
Darcy Law ◽  
Squeeze Film ◽  
Mean Temperature ◽  
Special Cases ◽  
The Impact

A theoretical study of a squeezing ferro-nanofluid flow including thermal effects is carried out with application to bearings and articular cartilages. A representational geometry of the thin layer of a ferro-nanofluid squeezed between a flat rigid disk and a thin porous bed is considered. The flow behaviours and heat transfer in the fluid and porous regions are investigated. The mathematical problem is formulated based on the Neuringer–Rosensweig model for ferro-nanofluids in the fluid region including an external magnetic field, Darcy law for the porous region and Beavers–Joseph slip condition at the fluid–porous interface. The expressions for velocity, fluid film thickness, contact time, fluid flux, streamlines, pathlines, mean temperature and heat transfer rate in the fluid and porous regions are obtained by using a perturbation method. An asymptotic solution for the fluid layer thickness is also presented. The problem is also solved by a numerical method and the results by asymptotic analysis, perturbation and numerical methods are obtained assuming a constant force squeezing state and are compared. It is shown that the results obtained by all the methods agree well with each other. The effects of various parameters such as Darcy number, Beavers–Joseph constant and magnetization parameter on the flow behaviours, contact time, mean temperature and heat transfer rate are investigated. The novel results showing the impact of using ferro-nanofluids in the two applications under consideration are presented. The results under special cases are further compared with the existing results in the literature and are found to agree well.

Finite Element Analysis about the Influence that High-Speed Motorized Spindle Spindle System Material has on its Temperature Field

2013 ◽  
Vol 712-715 ◽  
pp. 1209-1212 ◽  
Author(s):  
Ke Zhang ◽  
Xiang Nan Ma ◽  
Li Xiu Zhang ◽  
Wen Da Yu ◽  
Yu Hou Wu
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Temperature Field ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
High Speed ◽  
Ceramic Materials ◽  
Motorized Spindle ◽  
Element Analysis ◽  
Finite Element Software

The article has analyzed the changes of temperature of different materials of the spindle, and considered 170SD30 Ceramic Motorized Spindle and the same model Metal Motorized Spindle as the research objects, analyzed the inside heat source and heat transfer mechanism of the high-speed motorized spindle; used finite element software to set up the model of the motorized spindle, and did simulation and analysis. Verified by simulation, heat transfer rate of ceramic materials is slower than the metallic materials, in actual operation of the process, due to different materials have different heat transfer rate, so the temperature distribution of the different materials of motorized spindle are different. This conclusion provides the basis to solve motorized spindle temperature field distribution.

Effect of Superhydrophobicity on Impinging Droplet Heat Transfer

2010 ◽  
Author(s):  
Gary Rosengarten ◽  
Rita Tschaut
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
High Speed ◽  
Cold Water ◽  
Preliminary Investigation ◽  
Infrared Camera ◽  
Contact Angles ◽  
Superhydrophobic Surfaces ◽  
Droplet Shape

In this study we present a preliminary investigation into the effect of hydrophobicity on the heat transfer rate due to the impingement of cold water droplets on heated flat surfaces. Two extreme contact angles were compared; hydrophilic (∼20°) and superhydrophobic (∼160°) using different surface coatings on a thin metal substrates. Images of the droplet impingement were simultaneously recorded by a high speed camera and a high speed, high resolution infrared camera so we could correlate droplet shape and dynamics to the heat transfer rate. There is a large effect on both the droplet fluid dynamics and heat transfer between hydrophilic and superhydrophobic surfaces. The heat transfer difference between the superhydrophobic and hydrophilic cases is a complex interplay between the increased droplet contact line velocity due to induced slip and the insulating properties of the air gap. Overall we have shown significant reductions in both the instantaneous heat transfer rates and the overall cooling effect of droplets impinging on superhydrophobic surfaces relative to those for hydrophilic surfaces. In the range of droplet velocities varied (We = 50 to 190) there was little dependency of the heat transfer or fluid flow with impact velocity, due to the dominance of inertial forces.

Alumina nanoparticle flow within a channel with permeable walls

2020 ◽  
Vol 31 (04) ◽  
pp. 2050050 ◽  
Author(s):  
Tran Dinh Manh ◽  
Nguyen Dang Nam ◽  
Gihad Keyany Abdulrahman ◽  
R. Moradi ◽  
Houman Babazadeh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Power Law ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Expansion Ratio ◽  
Hydrodynamic Characteristics ◽  
Stream Velocity ◽  
Main Stream ◽  
The Impact

The application of the nanoparticles for the heat transfer augmentation has extensively increased in the scientific and industrial applications. In this research, semi-analytic method is used to disclose the heat transmission and flow feature of the fluid with nanoparticles among the two parallel sheets. In our model, one plate is warmed with specific heat flux while fluid is streamed from another plate which extends over times. Nanoparticles of Al2O3 are applied in the main fluid to obtain nanofluid flow. To obtained viscosity coefficient and heat conductivity of the base fluid with nanoparticles, Koo–Kleinstreuer–Li (KKL) formula is applied as reliable approach. Comprehensive investigations on different factors are done to disclose the impact of important aspects such as volume fraction of the nanoparticles, main stream velocity and expansion ratio on the main thermal and hydrodynamic characteristics of the nanofluid. It was found that the rate of the Nusselt number upsurges when the velocity of main stream, volume portion of the nanoparticles and power law index is increased. However, the increasing of the expansion ratio declines the heat transfer rate in our model. Our findings disclose that heat transfer rate is directly proportional with velocity of nanofluid as index of power law equals to zero.

scholarly journals High-speed flow with discontinuous surface catalysis

2000 ◽  
Vol 420 ◽  
pp. 325-359 ◽  
Author(s):  
S. R. AMARATUNGA ◽  
O. R. TUTTY ◽  
G. T. ROBERTS
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Phase ◽  
Heat Transfer Rate ◽  
Recombination Rate ◽  
Transfer Rate ◽  
High Speed ◽  
Speed Flow ◽  
Surface Catalysis ◽  
Catalytic Recombination

In a reacting gas flow both gas-phase chemical activity and surface catalysis can increase the rate of heat transfer from the gas to a solid surface. In particular, when there is a discontinuous change in the catalytic properties of the surface, there can be a very large increase in the local heat transfer rate. In this study numerical simulations have been performed for the laminar high-speed flow of a high-temperature, non-equilibrium reacting gas mixture over a flat plate. The surface of the plate is partly catalytic, with the leading region non-catalytic, and a discontinuous change in the catalytic properties of the surface at the catalytic junction. The surface is assumed to be isothermal, and cold relative to the free stream. The gas is assumed to be a mixture of molecular and atomic forms of a diatomic gas in an inert gas forming a thermal bath, giving a three-species mixture with dissociation and recombination of the reactive species. The calculations are performed for a gas with atomic and molecular oxygen in an argon bath, but a full range of gas-phase chemical and surface catalytic effects is considered. Kinetic schemes with frozen gas-phase chemistry, and partial or full recombination of atomic oxygen in the boundary layer are investigated. The catalytic nature of the surface material is given by a catalytic recombination rate coeffcient, which varies from zero (non-catalytic) to one (fully catalytic), and the effects on the flow and the surface heat transfer of materials which are non-, partially, or fully catalytic are considered. A self-similar thin-layer analytical model of the change in the gas composition downstream of the catalytic junction is developed. For physically realistic (O(10−2)) values of the catalytic recombination rate coeffcient, the predictions from this model of the surface values of the atomic oxygen mass fraction and the catalytic surface heat transfer rate are excellent when the only change in the composition of the gas comes from the surface catalysis, and reasonable when there is partial recombination of the gas in the boundary layer due to the gas-phase chemistry. In contrast, when the surface is fully catalytic, the streamwise diffusion terms play a significant role, and the model is not valid. These results should apply to other situations with an attached boundary layer with recombination reactions. A comparison is made between the calculated and experimental measurements of the heat transfer rate at the catalytic junction. With a kinetic scheme which allows partial recombination in the boundary layer, good agreement is found between the experimental and predicted values for surface materials which are essentially non-catalytic. For a catalytic material (platinum), the experimental and numerical heat transfer rates are matched to estimate the value of the catalytic recombination rate coeffcient. The values obtained show a considerable amount of scatter, but are consistent with those found in the literature.

scholarly journals Origin of spray formation during impact on heated surfaces

Soft Matter ◽  
2017 ◽  
Vol 13 (41) ◽  
pp. 7514-7520 ◽  
Author(s):  
Michiel A. J. van Limbeek ◽  
Paul B. J. Hoefnagels ◽  
Chao Sun ◽  
Detlef Lohse
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Plate Thickness ◽  
Heated Plate ◽  
Spray Formation ◽  
Impact Process ◽  
The Impact

In many applications, it is crucial to control the heat transfer rate of impacting drops on a heated plate. Here we study how limited heat transfer, such as the plate thickness or low conductivity, affects the impact process.

Experimental Study and High Speed Visualization of Flow Boiling Characteristics in Silicon Microgap Heat Sink

2012 ◽  
Author(s):  
Tamanna Alam ◽  
Poh Seng Lee ◽  
Christopher R. Yap ◽  
Liwen Jin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Rate ◽  
Heat Sink ◽  
Transfer Rate ◽  
High Speed ◽  
Flow Boiling ◽  
Gap Size

Flow boiling in microgap heat sink is very attractive for high-performance electronics cooling due to its high heat transfer rate and easy fabrication process. In absence of thermal interface material between the active electronic component and a microgap cold plate, significant reduction in interface thermal resistance and enhancement in heat transfer rate can be achieved. In earlier studies by these authors, encouraging results have been obtained using microgap heat sink as it can potentially mitigate flow instabilities, flow reversal and maintain uniform wall temperatures over the heated surface. So, more work should be carried out to advance the fundamental understanding of the two-phase flow heat transfer associated with microgap heat sink and the underlying mechanisms. In this study, local flow boiling phenomena in different microgap sizes have been investigated experimentally. Experiments are performed in silicon based microgap heat sink having microgap depth ranging from 80 μm to 500 μm, using deionized water with 10 °C subcooled inlet temperature. The effects of mass flux and heat flux on heat transfer coefficient and pressure drop characteristics are examined by using different mass fluxes ranging from 400 kg/m2s to 1000 kg/m2s and effective heat flux varying from 0 to 100 W/cm2. Apart from these experimental investigations, simultaneous high speed visualizations are conducted to observe and explore the mechanism of flow boiling in microgap. Confined slug and annular boiling are observed as the two main heat transfer mechanisms in microgap. Moreover, experimental results show that flow boiling heat transfer coefficients are dependent on gap size, and the lower the gap size, higher the heat transfer coefficient.

scholarly journals Impact of Smoluchowski Temperature and Maxwell Velocity Slip Conditions on Axisymmetric Rotated Flow of Hybrid Nanofluid past a Porous Moving Rotating Disk

Nanomaterials ◽  
2022 ◽  
Vol 12 (2) ◽  
pp. 276
Author(s):  
Umair Khan ◽  
Aurang Zaib ◽  
Iskandar Waini ◽  
Anuar Ishak ◽  
El-Sayed M. Sherif ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Radial Direction ◽  
Velocity Slip ◽  
Hybrid Nanofluid ◽  
Al2o3 Nanoparticles ◽  
Suction Parameter ◽  
The Impact

Colloidal suspensions of regular fluids and nanoparticles are known as nanofluids. They have a variety of applications in the medical field, including cell separation, drug targeting, destruction of tumor tissue, and so on. On the other hand, the dispersion of multiple nanoparticles into a regular fluid is referred to as a hybrid nanofluid. It has a variety of innovative applications such as microfluidics, heat dissipation, dynamic sealing, damping, and so on. Because of these numerous applications of nanofluids in minds, therefore, the objective of the current exploration divulged the axisymmetric radiative flow and heat transfer induced by hybrid nanofluid impinging on a porous stretchable/shrinkable rotating disc. In addition, the impact of Smoluchowski temperature and Maxwell velocity slip boundary conditions are also invoked. The hybrid nanofluid was formed by mixing the copper (Cu) and alumina (Al2O3) nanoparticles scattered in the regular (viscous) base fluid (H2O). Similarity variables are used to procure the similarity equations, and the numerical outcomes are achieved using bvp4c in MATLAB software. According to the findings, double solutions are feasible for stretching (λ>0) and shrinking cases (λ<0). The heat transfer rate is accelerated as the hybrid nanoparticles increases. The suction parameter enhances the friction factors as well as heat transfer rate. Moreover, the friction factor in the radial direction and heat transfer enrich for the first solution and moderate for the second outcome due to the augmentation δ1, while the trend of the friction factor in the radial direction is changed only in the case of stretching for both branches.

The Study of Droplet Impact Behavior on Flat Surface with Different Surface Properties

2010 ◽  
Vol 297-301 ◽  
pp. 19-24
Author(s):  
Ku Zilati Ku Shaari ◽  
Richard Turton
Keyword(s):  
Surface Properties ◽  
High Speed ◽  
Liquid Droplet ◽  
Film Coating ◽  
Silicon Surfaces ◽  
Impact Behavior ◽  
Spreading Factor ◽  
Pharmaceutical Tablets ◽  
Coating Uniformity ◽  
The Impact

The impact behavior of a liquid droplet on solid surface is a complex phenomenon and yet is a basic component of various industrial processes particularly in the pharmaceutical industry. In this industry, film coating technique is used in tablet coating, in which coating uniformity is important especially if the coating is for functional purposes. Coating uniformity on a tablet could be affected by several factors, one of which is the impingements of droplets on its surface. In this work, the maximum spreading diameter and the initial impact behavior of a single droplet on pharmaceutical tablet surfaces and metal surfaces having different surface properties are investigated. A Charged-Coupled-Device (CCD) high-speed camera with framing rate of 2,000, attached to a 10X microscope, was used to capture the phenomena. The results show that the initial impact behavior of a droplet is not affected by the porosity of a surface. The results on the pharmaceutical tablets, stainless steel and etched silicon surfaces show that the rougher the surface the lower the spreading factor. The droplets on all surfaces demonstrate that a droplet that produces higher spreading factor gives a lower bouncing factor.

scholarly journals Numerical Simulation of Single-Droplet Dynamics, Vaporization, and Heat Transfer from Impingement onto Static and Vibrating Surfaces

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 188
Author(s):  
J. Thalackottore Jose ◽  
J. F. Dunne
Keyword(s):  
Heat Transfer ◽  
Impact Velocity ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Droplet Evaporation ◽  
Time Interval ◽  
Initial Contact ◽  
Droplet Impingement ◽  
The Impact ◽  
Minimum Impact

A numerical study is presented to examine the behavior of a single liquid droplet initially passing through air or steam, followed by impingement onto a static or vibrating surface. The fluid dynamic equations are solved using the Volume of Fluid method, which includes both viscous and surface tension effects, and the possibility of droplet evaporation when the impact surface is hot. Initially, dynamic behavior is examined for isothermal impingement of a droplet moving through air, first without and then with boundary vibration. Isothermal simulations are used to establish how droplet rebound conditions and the time interval between initial contact to detachment vary with droplet diameter for droplet impingement onto a stationary boundary. Heat transfer is then assessed for a liquid droplet initially at saturation temperature passing through steam, followed by contact with a hot vibrating boundary, in which droplet evaporation commences. The paper shows that, for droplet impingement onto a static boundary, the minimum impact velocity for rebound reduces linearly with droplet diameter, whereas the time interval between initial contact and detachment appears to increase linearly with droplet diameter. With the introduction of a vibrating surface, the minimum relative impact velocity for isothermal rebound is found to be higher than the minimum impact velocity for static boundary droplet rebound. For impingement onto a hot surface, in which droplet evaporation commences, it is shown that large-amplitude surface vibration reduces heat transfer, whereas low-amplitude high-frequency vibration appears to increase heat transfer.

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