The Effect of Roughness on the Impact Dynamics and Heat Transfer of Cryogen Droplets Impinging Onto Indented Skin Phantoms

2005 ◽  
Author(s):  
Jie Liu ◽  
Walfre Franco ◽  
Guillermo Aguilar
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Human Skin ◽  
Spray Deposition ◽  
Skin Surface ◽  
Therapeutic Modality ◽  
Impact Dynamics ◽  
Large Momentum ◽  
Superficial Skin ◽  
The Impact

Laser dermatological surgery (LDS) is the preferred therapeutic modality for various dermatoses, including port wine stain (PWS) birthmarks. LDS is commonly used in conjunction with cryogen spray cooling, which is an auxiliary procedure that pre-cools the superficial skin layer (epidermis) prior to laser irradiation to avoid non-specific and excessive epidermal heating. Clinical observations show that skin indents markedly during spray deposition due to the large momentum of cryogen droplets. Furthermore, the human skin surface is far from smooth. Therefore, with the objective to provide some insight into the interaction between cryogen sprays and the rough and deformable human skin surface, the impingement dynamics and heat transfer induced by single cryogen droplets falling on rough and indented skin phantoms are present in this paper. Epoxy skin phantoms with a constant semispherical indentation of depth and radius of 2.44 mm and 6.34 mm, respectively, were used to simulate indented skin. Each phantom had a different surface roughnesses varying from 0.5 μm to 50μm. The experiments were carried out within a pressurized chamber to control or eliminate droplet evaporation. A high-speed camera and the temperature sensors placed on the upper surface of the skin phantoms were synchronized to record the impact dynamics and temperature changes as cryogen droplets fell on them. The results show that the surface roughness affects the impact dynamics and heat transfer during single droplet impingement. As the surface roughness (Ra) increasing, the heat flux decrease.

Effect of Surface Roughness on Single Cryogen Droplet Spreading

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Jie Liu ◽  
Walfre Franco ◽  
Guillermo Aguilar
Keyword(s):  
Surface Roughness ◽  
Human Skin ◽  
Droplet Diameter ◽  
Skin Surface ◽  
Skin Layer ◽  
Droplet Spreading ◽  
Viscous Boundary Layer ◽  
Superficial Skin ◽  
The Impact ◽  
Effect Of Surface

Cryogen spray cooling is an auxiliary procedure to dermatologic laser surgery, which consists of precooling the superficial skin layer (epidermis) during laser irradiation of subsurface targets to avoid nonspecific epidermal thermal damage. While previous studies have investigated the interaction of cryogen sprays with microscopically smooth human skin models, it is important to recognize that real human skin surface is far from smooth. With the objective to provide physical insight into the interaction between cryogen sprays and human skin, we study the effect of surface roughness on the impact dynamics of single cryogen droplets falling on skin models of various roughnesses (0.5–70μm). We first develop a theoretical model to predict the maximum spread diameter (Dm) following droplet impingement based on a similarity approximation to the solution of a viscous boundary layer that incorporates friction as the major source of viscous dissipation on a rough surface. Then, we measure the droplet diameter, impact velocity, and Dm of cryogen droplets falling by gravity onto skin models. Experimental data prove that the proposed model predicts Dm with good accuracy, suggesting that the effects of surface roughness and friction on Dm are properly taken into account for the range of surface roughness studied herein.

A Study on Evolution of Splat Radius and Temperature in Thermal Spray Process

2018 ◽  
Author(s):  
Manpreet Dash ◽  
Sangharsh Kumar ◽  
Partha Pratim Bandyopadhyay ◽  
Anandaroop Bhattacharya
Keyword(s):  
Heat Transfer ◽  
Thermal Spray ◽  
Molten Metal ◽  
Spray Deposition ◽  
Substrate Surface ◽  
Metal Droplet ◽  
Droplet Impingement ◽  
Impact Process ◽  
The Impact ◽  
Maximum Spreading

The impact process of a molten metal droplet impinging on a solid substrate surface is encountered in several technological applications such as ink-jet printing, spray cooling, coating processes, spray deposition of metal alloys, thermal spray coatings, manufacturing processes and fabrication and in industrial applications concerning thermal spray processes. Deposition of a molten material or metal in form of a droplet on a substrate surface by propelling it towards it forms the core of the spraying process. During the impact process, the molten metal droplet spreads radially and simultaneously starts losing heat due to heat transfer to the substrate surface. The associated heat transfer influences impingement behavior. The physics of droplet impingement is not only related to the fluid dynamics, but also to the respective interfacial properties of solid and liquid. For most applications, maximum spreading diameter of the splat is considered to be an important factor for droplet impingement on solid surfaces. In the present study, we have developed a model for droplet impingement based on energy conservation principle to predict the maximum spreading radius and the radius as a function of time. Further, we have used the radius as a function of time in the heat transfer equations and to study the evolution of splat-temperature and predict the spreading factor and the spreading time and mathematically correlate them to the spraying parameters and material properties.

Buoyancy Effects on Human Skin Tissue Thermoregulation due to Environmental Influence

2020 ◽  
Vol 401 ◽  
pp. 107-116
Author(s):  
Lawal Hamid Adeola ◽  
Oluwole Daniel Makinde
Keyword(s):  
Heat Transfer ◽  
Blood Flow ◽  
Human Skin ◽  
Environmental Influence ◽  
Saturated Porous Medium ◽  
Skin Tissue ◽  
Bioheat Equation ◽  
Biophysical Parameters ◽  
Thermal Buoyancy ◽  
The Impact

This paper theoretically examines the impact of thermal buoyancy on human skin tissue’s blood flow, heat exchange and their interaction with the surrounding environment using a two phase mathematical model that relies on continuity, momentum and energy conservation equations in continuum mechanics. The tissue blood flows and heat transfer characteristics are determined numerically based on Darcy’s Brinkman model for a saturated porous medium coupled with modified Pennes bioheat equation while analytical approach is employed to tackle the model of interacting surrounding environmental buoyancy driven air flow with heat sink. The influence of embedded biophysical parameters on the skin tissue’s blood flow rate and temperature distribution together with friction coefficient at skin tissue surface and Nusselt number are display graphically and discussed quantitatively. It is found that a boost in thermal buoyancy enhances skin tissue heat transfer and blood flow rates.

Stable channel flow with spanwise heterogeneous surface temperature

2022 ◽  
Vol 933 ◽  
Author(s):  
T. Bon ◽  
J. Meyers
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Friction Coefficient ◽  
Surface Temperature ◽  
Channel Flow ◽  
Secondary Flows ◽  
Heterogeneous Surface ◽  
Length Scale ◽  
Mean Flow ◽  
The Impact

Recent studies have demonstrated that large secondary motions are excited by surface roughness with dominant spanwise length scales of the order of the flow's outer length scale. Inspired by this, we explore the effect of spanwise heterogeneous surface temperature in weakly to strongly stratified closed channel flow (at $Ri_\tau =120$ , 960; $Re_\tau = 180$ , 550) with direct numerical simulations. The configuration consists of equally sized strips of high and low temperature at the lower and upper boundaries, while an overall stable stratification is induced by imposing an average temperature difference between the top and bottom. We consider the influence of the width of the strips ( ${\rm \pi} /8 \leq \lambda /h \leq 4{\rm \pi} $ ), Reynolds number, stability and upper boundary condition on the mean flow structure, skin friction and heat transfer. Results indicate that secondary flows are excited, with alternating high- and low-momentum pathways and vortices, similar to the patterns induced by spanwise heterogeneous surface roughness. We find that the impact of the surface heterogeneity on the outer layer depends strongly on the spanwise heterogeneity length scale of the surface temperature. Comparison to stable channel flow with uniform temperature reveals that the heterogeneous surface temperature increases the global friction coefficient and reduces the global Nusselt number in most cases. However, for the high-Reynolds cases with $\lambda /h \geq {\rm \pi} /2$ , we find a reduction of the friction coefficient. At stronger stability, the vertical extent of the vortices is reduced and the impact of the heterogeneous temperature on momentum and heat transfer is smaller.

CFD Modelling Strategies for the Simulation of Roughness Effects on Friction and Heat Transfer in Additive Manufactured Components

2020 ◽  
Author(s):  
Lorenzo Mazzei ◽  
Riccardo Da Soghe ◽  
Cosimo Bianchini
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Thermal Performance ◽  
Accurate Estimation ◽  
Real Surface ◽  
Cfd Modelling ◽  
Roughness Effects ◽  
Modelling Strategies ◽  
The Impact ◽  
Grain Roughness

Abstract It is well-known from the literature that surface roughness affects significantly friction and heat transfer. This is even more evident for additive manufactured (AM) components, which are taking an increasingly important role in the gas turbine field. However, the exploitation of numerical approaches to improve their design is hindered by the lack of dedicated correlations and CFD model developed for such high roughness conditions. Usually the additive manufactured components are simulated considering the surfaces as smooth or applying an equivalent sand-grain roughness (ks) that results in a velocity shift in the boundary layer. However, determining a priori the most appropriate value of ks is challenging, as dozens of correlations are available, returning scattered and uncertain results. The aim of this work is to benchmark some existing modelling strategies (among which the equivalent sand grain roughness) and test a numerical approach capable of narrowing the existing gap between simulated and tested thermal performance of additive manufactured devices. The technology enabler is represented by higher-fidelity CFD simulations accounting for the impact of real surface roughness on pressure drop and heat transfer. At this purpose, an existing literature model for rough walls has been implemented in ANSYS Fluent and tested on a variety of AM mini-channels so as to determine the best-fitting values of ks and corrected wetted surface ratio Scorr that match the experimental data in terms of friction factor and Nusselt number. Knowing also the measured roughness descriptors of each component, it has been possible to derive valuable guidelines for an effective exploitation of CFD on additive manufactured components, thus allowing a more accurate estimation of the thermal performance in additive manufactured components.

Relationship between dermal birefringence and the skin surface roughness of photoaged human skin

2009 ◽  
Vol 14 (4) ◽  
pp. 044032 ◽  
Author(s):  
Shingo Sakai ◽  
Noriaki Nakagawa ◽  
Masahiro Yamanari ◽  
Arata Miyazawa ◽  
Yoshiaki Yasuno ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Human Skin ◽  
Skin Surface ◽  
Skin Surface Roughness

Development of a Biomimetic Vibrotactile Sensor for Dynamic Deformation With an Array of Polymer Structures

2015 ◽  
Author(s):  
Jae Young Choi ◽  
Baek Chul Kim ◽  
Ja Choon Koo
Keyword(s):  
Surface Roughness ◽  
Human Skin ◽  
Dynamic Deformation ◽  
Skin Surface ◽  
Electrical Signal ◽  
Point Of View ◽  
Static Deformation ◽  
Skin Deformation ◽  
Vibration Sensing ◽  
Finger Skin

Humans can discriminate surface roughness using fingertip’s touch. It is believed that surface roughness is perceived by static and dynamic deformation of human skin. Recent findings have shown that subcutaneous slowly adapting mechanoreceptor (SA) detect static deformation of finger skin. However, there are difficulties to infinitely increase density of SA in limited skin space. [1] So, we focused on dynamic deformation is related with rapidly adapting mechanoreceptor (RA). In the process of scanning surface of objects with fingertips, RA detects vibrations induced by skin deformation. In this study, we suggest that sensors mimicking roles of RA can detect surface roughness. We used a polymer having similar characteristics of skin surface that transduce physical vibrations into electrical signal. And an array of polymer structures discriminates surface roughness. In other researches, they were tried to use one mechanoreceptor to acquire total range of vibrations. From the point of view which RAs have different vibration sensing ranges, we divided range of vibration through polymer structures and analyzed frequency element.

The impact of piston thermal barrier coating roughness on high-load diesel operation

2019 ◽  
pp. 146808741989348 ◽  
Author(s):  
Eric Gingrich ◽  
Michael Tess ◽  
Vamshi Korivi ◽  
Peter Schihl ◽  
John Saputo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Thermal Barrier Coating ◽  
Engine Performance ◽  
Operating Conditions ◽  
Thermal Barrier ◽  
Engine Operation ◽  
Barrier Coating ◽  
The Impact ◽  
High Output

Thermal barrier coatings of various thickness and surface roughness were applied to the piston crown of a single-cylinder research engine and tested over a range of high-output diesel operating conditions, some near 30 bar gross indicated mean effective pressure. Three yttria-stabilized zirconia coated pistons were compared to a baseline metal piston. At each operating condition, a start-of-injection sweep was conducted to generate efficiency trends and find the optimal combustion phasing. Three variations of pistons coated with a graded-layer thermal barrier coating were tested: (1) 0.185 mm coating thickness with a surface roughness of approximately Ra = 11.8 µm, (2) 0.325 mm thickness with Ra = 11.8 µm, and (3) 0.325 mm thickness with Ra = 6.0 µm. Both coated pistons with Ra = 11.8 µm did not show any statistically significant improvement to engine performance when compared to the metal baseline piston, but did produce higher filter smoke numbers. The coated piston with Ra = 6.0 µm and 0.325 mm showed an increase of gross indicated thermal efficiency of up to 3.5% (relative) compared to the metal baseline piston for operating conditions comparable to standard engine operation and a reduction of filter smoke number back to the metal baseline. The increase in efficiency was found to correlate with additional late-cycle apparent heat release and a reduction in in-cylinder heat transfer. The very high-output conditions showed statistically insignificant changes in performance or heat transfer, which may have been related to the long injection duration used for these cases targeting outside of the piston bowl.

scholarly journals Sensitivity Study of Ice Accretion Simulation to Roughness Thermal Correction Model

Aerospace ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 84
Author(s):  
Kevin Ignatowicz ◽  
François Morency ◽  
Héloïse Beaugendre
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Sensitivity Study ◽  
Correction Coefficient ◽  
Ice Accretion ◽  
Roughness Parameters ◽  
Thermal Correction ◽  
The Impact

The effects of atmospheric icing can be anticipated by Computational Fluid Dynamics (CFD). Past studies show that the convective heat transfer influences the ice accretion and is itself a function of surface roughness. Uncertainty quantification (UQ) could help quantify the impact of surface roughness parameters on the reliability of ice accretion prediction. This paper aims to quantify ice accretion uncertainties and identify the key surface roughness correction parameters contributing the most to the uncertainties in a Reynolds-Averaged Navier-Stokes (RANS) formulation. Ice accretion simulations over a rough flat plate using two thermal correction models are used to construct a RANS database. Non-Intrusive Polynomial Chaos Expansion (NIPCE) metamodels are developed to predict the convective heat transfer and icing characteristics of the RANS database. The metamodels allow for the computation of the 95% confidence intervals of the output probability distribution (PDF) and of the sensitivity indexes of the roughness parameters according to their level of influence on the outputs. For one of the thermal correction models, the most influential parameter is the roughness height, whereas for the second model it is the surface correction coefficient. In addition, the uncertainty on the freestream temperature has a minor impact on the ice accretion sensitivity compared to the uncertainty on the roughness parameters.

Enzymatic Determination of Hydroxysteroids in Human Skin Surface Lipids1

1963 ◽  
Vol 41 (5) ◽  
pp. 265-268 ◽  
Author(s):  
Thomas J Cook ◽  
Allan L Lorincz ◽  
Alan R Spector
Keyword(s):  
Human Skin ◽  
Skin Surface ◽  
Enzymatic Determination
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