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Understanding of impact dynamics of droplets on oblique plane is relevant for applications like pesticides spraying and internal combustion engines. Experiments were performed using three test fluids to investigate the effect of viscosity and surface tension properties on the elongation factor of droplets impacting on oblique planes. The temporal variation of elongation factor primarily depends upon the surface inclination and surface tension. For a given Weber number, emission of secondary droplet takes place at the earliest time for surfactant solution due to reduction of interfacial energy.

Experimental investigations were carried out to elucidate the roles of surface wettability and inclination on the post-impact dynamics of droplets. The maximum spreading diameter and spreading time were found to decrease with increasing inclination angle and normal Weber number (We n ) for superhydrophobic (SH) surfaces. The experiments on SH surfaces were found to be in excellent agreement with an existing analytical model, albeit with the incorporation of modifications for the oblique impact conditions. The energy ratios and elongation factors were also determined for different inclination angles. On inclined SH surfaces, different features like arrest of secondary droplet formation, reduced pinch-off at the contact line and inclination dependent elongation behavior were observed. On the contrary, the hydrophilic surfaces show opposite trends of maximum spreading factor and spreading time with inclination angle and We n , respectively. This is caused by the dominance of tangential kinetic energy over adhesion energy and gravitational potential at higher inclination angles. Further, the influence of the surface tension (using surfactant solutions, without significantly changing the viscosity) and viscosity (using colloids, without significantly changing the surface tension) for impact on SH and hydrophilic surfaces are probed. The exercise allows better insight on the exact hydrodynamic mechanisms at play during the impact events. Overall, the article provides a comprehensive picture of post-impact dynamics of droplets on inclined surfaces, encompassing a broad spectrum of governing parameters like Reynolds number (Re), Weber number (We), degree of inclination and surface wettability.

In this present article, we have investigated the magnetohydrodynamics of ferrofluid droplets impacting on different wettability surfaces, in the presence of a vertical magnetic field. The spreading dynamics was studied for a wide spectrum of magnetic Bond number (Bom), Hartmann number (Ha) and Weber number (We). In absence of any magnetic field, the droplets exhibited secondary droplet pinch-off during rebound. In the presence of magnetic field, the field modulated Rayleigh-Plateau instability delays the droplet pinch off as Bom increases. For a fixed We, the rebound of the droplet was suppressed on a superhydrophobic (SH) surface for varying the magnetic field strength (manifested through Bom). An analytical model based on the principle of conservation of energy was formulated to explain the magnetic field modulated droplet pinch-off. We have also investigated the influence of Bom on the temporal spreading dynamics of different Ha ferrofluid droplets impacting on hydrophilic and SH surfaces. With an increase in Bom, the magneto-visco-capillarity of high Ha droplets inhibits the capillary waves and motion of the contact line after impingement onto hydrophilic surface, compared to low Ha ferrofluid drops. Instead, the droplet rim fragments into secondary droplets during retraction event, leading to the onset of rim instability for low Ha ferrofluid drops with an increase in the magnetic field strength. We have also proposed a theoretical formulation based on energy conservation principle to predict the experimentally measured maximum spreading diameters under influence of magnetic field. The findings may hold significance in ferrofluid based droplet microfluidics systems with magnetic control or actuation.

In this article, we report the experimental and semi-analytical findings to elucidate the electrohydrodynamics (EHD) of a dielectric liquid droplet impact on superhydrophobic (SH) and hydrophilic surfaces. A wide range of Weber numbers (We) and electro-capillary numbers (Cae) are covered to explore the various regimes of droplet impact EHD. We show that for a fixed We ∼ 60, droplet rebound on a SH surface is suppressed with increase in electric field intensity (increase in Cae). At high Cae, instead of the usual uniform radial contraction, the droplets retract faster in an orthogonal direction to the electric field and spread along the direction of the electric field, inducing large electrical stresses at the liquid rim facing the electrodes. This prevents the accumulation of sufficient kinetic energy to achieve the droplet rebound phenomena. For certain values of We and Ohnesorge number (Oh), droplets exhibit somersault-like motion during rebound. Subsequently, we propose a semi-analytical model to explain the field induced rebound phenomenon on SH surfaces. Above a critical Cae ∼ 4.5, EHD instability causes a fingering pattern via evolution of a spire at the rim. Further, the spreading EHD on both hydrophilic and SH surfaces is discussed. On both wettability surfaces and for a fixed We, the spreading factor shows an increasing trend with increase in Cae. We have formulated an analytical model based on energy conservation to predict the maximum spreading diameter. The model predictions hold reasonably good agreement with the experimental observations. Finally, a phase map was developed to explain the post impact droplet dynamics on SH surfaces for a wide range of We and Cae.

The study reports the aspects of post-impact hydrodynamics of ferrofluid droplets on superhydrophobic (SH) surfaces in the presence of a horizontal magnetic field. A wide gamut of dynamics was observed by varying the impact Weber number (We), the magnetic field strength (manifested through the magnetic Bond number (Bom), which is defined as the ratio of magnetic force to surface tension force), and the Hartmann number (Ha), defined as the ratio of magnetic force to the viscous force. For a fixed We ∼ 60, we observed that at moderately low Bom ∼300, droplet rebound off the SH surface is suppressed. The noted We is chosen to observe various impact outcomes and to reveal the consequent ferrohydrodynamic mechanisms. We also show that ferrohydrodynamic interactions lead to asymmetric spreading due to variation in magnitude of the Lorentz force, and the droplet spreads preferentially in a direction orthogonal to the magnetic field lines. We show analytically that during the retraction regime, the kinetic energy of the droplet is distributed unequally in the transverse (orthogonal to the external horizontal magnetic field) and longitudinal (along the direction of the magnetic field) directions. This ultimately leads to the suppression of droplet rebound. We studied the role of Bom at fixed We ∼ 60 and observed that the liquid lamella becomes unstable at the onset of retraction phase, through nucleation of holes, their proliferation and rupture after reaching a critical thickness only on SH surfaces, but is absent on hydrophilic surfaces. We propose an analytical model to predict the onset of instability at a critical Bom. The model shows that the critical Bom is a function of the impact We, and the critical Bom decreases with increasing We. We illustrate a phase map encompassing all the post-impact ferrohydrodynamic phenomena on SH surfaces for a wide range of We and Bom.

Post impingement morphology and dynamics of water droplets on convex cylindrical surfaces has been explored experimentally. Droplet impact and post-impact feature studies have been conducted on hydrophillic and superhydrophobic cylindrical surfaces. Effects of the impact Weber number and target-to-drop diameter ratio have been studied. The post-impact hydrodynamics have been quantified using the wetting fraction, the spreading factor and nondimensional film thickness at the north pole of the target. The observations reveal that the wetting fraction and spread factor increases with an increase in the impact We and decrease in the target to drop diameter ratio. An opposite trend is noted for nondimensional film thickness at the targets north pole. It is also deduced that the spread factor is independent of the target wettability. The lamella dynamics post spreading has also been observed to be a strong function of the wettability, impact We and the diameter ratio. An analytical expression for temporal evolution of film thickness at north pole of the cylinderical target is derieved. Another theoretical model based on energy conservation for predicting the maximum wetting fraction for variant cylindrical targets in terms of the governing We and Capillary number and the experimental measurements are in good agreement with the theoretical predictions.

Comprehending the mechanism of thermal transport through biological tissues is an important factor for optimal ablation of cancerous tissues and minimising collateral tissue damage. The present study reports detailed mapping of the rise in internal temperature within the tissue mimics due to NIR (1064 nm) laser irradiation, both for bare mimics and with gold nanostructures infused. Gold nanostructures such as mesoflowers and nanospheres have been synthesised and used as photothermal converters to enhance the temperature rise, resulting in achieving the desired degradation of malignant tissue in targeted region. Thermal history was observed experimentally and simulated considering non-Fourier dual phase lag (DPL) model incorporated Pennes bio-heat transfer equation using COMSOL Multiphysics software. The gross deviation in temperature i.e. rise from the classical Fourier model for bio-heat conduction suggests additional effects of temperature rise on the secondary structures and morphological and physico-chemical changes to the collagen ultrastructures building the tissue mass. The observed thermal denaturation in the collagen fibril morphologies have been explained based on the physico-chemical structure of collagen and its response to thermal radiation. The large shift in frequency of amides A and B is pronounced at a depth of maximum temperature rise compared with other positions in tissue phantom. Observations for change in band of amide I, amide II, and amide III are found to be responsible for damage to collagen ultra-structure. Variation in the concentration of gold nanostructures shows the potentiality of localised hyperthermia treatment subjected to NIR radiation through a proposed free radical mechanism.

The present study emphasizes on various machinability aspects using different cutting fluids. The effect of cutting fluids on various machining forces, tool flank wear and chip thickness are carried out using the minimal quantity lubrication technique (MQL). This method predicts minimal health risks and economical aspect compared to other techniques. It is experimentally observed that depth of cut and speed was the principal cutting parameter affecting the cutting force and feed force and speed as the principal cutting parameter for the radial force for compressed air and water soluble coolant. Instead, depth of cut, feed and speed were the principal cutting parameters influencing cutting force, feed force and radial force, respectively using nanofluid. In the flank wear analysis, nanofluid performed the best followed by water soluble coolant and compressed air. Finally the mathematical models were developed for the machining forces with 95% confidence level using Minitab 16 which is frequently used for statistical data analysis. ANOVA analysis, Anderson-Darling test and normal probability plot was used to inspect the effectiveness, adequacy, authenticity and statistical significance of the developed model.

Photothermal therapy using (Near Infrared) NIR region of EM spectrum is a fast emerging technology for cancer therapy. Different types of nanoparticles may be used for enhancing the treatment. Though the treatment protocols are developed based on experience driven estimated temperature increase in the tissue, it is not really known what spatiotemporal thermal behavior in the tissue is. In this work, this thermal behavior of tissue models is investigated with and without using nanoparticles. An increased temperature inside tissue compared to surface is observed which is counter intuitive from the present state of knowledge. It is shown from fiber level microstructure that this increased temperature leads to enhanced damage at the deeper parts of biomaterials. Nanoparticles can be utilized to control this temperature increase spatially. A multiple scattering based physical model is proposed to explain this counterintuitive temperature rise inside tissue. The results show promising future for better understanding and standardizing the protocols for photothermal therapy. Copyright � 2014 American Scientific Publishers.

In this study, the spreading characteristics of water droplets impacted on a solid spherical target have been investigated experimentally and theoretically. Droplet impact and postimpact feature studies have been conducted on hydrophilic and superhydrophobic spherical surfaces. Effects of the impact Weber number and target-to-drop diameter ratio on the spreading hydrodynamics have been discussed. Postcollision dynamics are explored with side and top views of impaction phenomenon using a high speed imaging technique. The morphological outcome of this impingement process has been quantitatively discussed with three geometric parameters, namely, liquid film thickness at the north-pole of the target surface, spread factor, and the maximum spread angle. Observations revel that spread factor and the maximum spread angle increases with the decrease in the size of the spherical target, whereas opposite of this is true for liquid film thickness at the north-pole of the target surface. Temporal variations of liquid film thickness at the north pole of the target have been plotted and found in agreement with the theoretical predictions made in the earlier studies. Finally, a mathematical model based on the energy balance principle has been proposed to predict the maximum spread angle on spherical targets. The theoretical values are found in good agreement with the experimental results for a wide range of spherical diameters studied. The findings may have implications toward a better understanding of fluid wetting, spraying, and coating behavior of complex shapes and geometries.

Bacteriological analysis of 1,551 stool/rectal swabs from all age groups of diarrhea patients of different hospitals of Orissa from January 2004 to December 2006 was carried out using standard procedures. Among all enteropathogens isolated in 886 culture-positive samples, Escherichia coli constituted 75.5%, including 13.2% pathogenic E. coli; Vibrio cholerae O1 constituted 17.3%; V. cholerae O139, 1%; Shigella spp., 4.5% (Shigella flexneri type 6, 2.9%, S. dysenteriae type I, 0.7%, S. sonnei, 0.6%, and S. boydii, 0.3%); Salmonella spp., 0.7%; and Aeromonas spp., only 2.0%. The isolation of bacterial enteropathogens was highest during July, 2005, followed by September, 2006. The prevalence of shigellosis in this region was relatively low. Cholera cases were more frequent during the rainy seasons. The dominance of V. cholerae O1 Inaba over Ogawa serotypes was observed in 2005, whereas this trend was reversed in 2006. The resistance profile of V. cholerae O1 was co-trimoxazole (Co), furazolidone (Fr), and nalidixic acid (Na); for Aeromonas spp., it was ampicillin (A), Fr, ciprofloxacin (Cf), Na, norfloxacin (Nx), and Co. Pathogenic E. coli strains were resistant to A, Fr, Co, streptomycin (S), Cf, Na, Nx, and neomycin (N); Shigella spp. were resistant to Fr, Na, Co, and S; and Salmonella spp. were resistant to A and Fr. Active surveillance should be continued among diarrhea patients to look for different enteropathogens and to define the shifting antibiogram patterns in this region.