Micro Particle Image Velocimetry Research Articles

Oil droplet movement and micro-flow characteristics during interaction process between gas bubble and oil droplet in flotation

Flotation is an efficient pre-treatment technology for oily water. In this work, the interaction process between the moving oil droplet and the gas bubble was studied by high-speed camera and Bassset-Boussinesq-Oseen (BBO) theoretical model, and the experimental and simulation results of the oil droplet trajectory were compared. Moreover, the micro-particle image velocimetry system was utilized to observe the flow inside and outside of the moving oil droplet. The results show that the BBO model with the mobile bubble’s surface can reflect the velocity change trend of the oil droplet during the interaction process between the moving oil droplet and the gas bubble, but there are some significant differences between the experimental and simulation results. While the oil droplet is moving on the bubble’s surface, the velocity of the area near the contact point of oil droplet–gas bubble is less than that of the other areas inside the oil droplet. Meanwhile, the flow of water above the oil drop is more biased towards the gas bubble.

Scaling of Droplet Breakup in High-Pressure Homogenizer Orifices. Part I: Comparison of Velocity Profiles in Scaled Coaxial Orifices

Properties of emulsions such as stability, viscosity or color can be influenced by the droplet size distribution. High-pressure homogenization (HPH) is the method of choice for emulsions with a low to medium viscosity with a target mean droplet diameter of less than 1 µm. During HPH, the droplets of the emulsion are exposed to shear and extensional stresses, which cause them to break up. Ongoing work is focused on better understanding the mechanisms of droplet breakup and relevant parameters. Since the gap dimensions of the disruption unit (e.g., flat valve or orifice) are small (usually below 500 µm) and the droplet breakup also takes place on small spatial and time scales, the resolution limit of current measuring systems is reached. In addition, the high velocities impede time resolved measurements. Therefore, a five-fold and fifty-fold magnified optically accessible coaxial orifice were used in this study while maintaining the dimensionless numbers characteristic for the droplet breakup (Reynolds and Weber number, viscosity and density ratio). Three matching material systems are presented. In order to verify their similarity, the local velocity profiles of the emerging free jet were measured using both a microparticle image velocimetry (µ-PIV) and a particle image velocimetry (PIV) system. Furthermore, the influence of the outlet geometry on the velocity profiles is investigated. Similar relationships were found on all investigated scales. The areas with the highest velocity fluctuations were identified where droplets are exposed to the highest turbulent forces. The Reynolds number had no influence on the normalized velocity fluctuation field. The confinement of the jet started to influence the velocity field if the outlet channel diameter is smaller than 10 times the diameter of the orifice. In conclusion, the scaling approach offers advantages to study very fast processes on very small spatial scales in detail. The presented scaling approach also offers chances in the optimization of the geometry of the disruption unit. However, the results also show challenges of each size scale, which can come from the respective production, measurement technology or experimental design. Depending on the problem to be investigated, we recommend conducting experimental studies at different scales.

Effects of Shearing and Extensional Flows on the Alignment of Colloidal Rods

Cellulose nanocrystals (CNC) can be considered as model colloidal rods and have practical applications in the formation of soft materials with tailored anisotropy. Here, we employ two contrasting microfluidic devices to quantitatively elucidate the role of shearing and extensional flows on the alignment of a dilute CNC dispersion. Characterization of the flow field by micro-particle image velocimetry is coupled to flow-induced birefringence analysis to quantify the deformation rate--alignment relationship. The deformation rate required for CNC alignment is 4$\times$ smaller in extension than in shear. Alignment in extension is independent of the deformation rate magnitude, but is either 0$^\circ$ or 90$^\circ$ to the flow, depending on its sign. In shear flow the colloidal rods orientate progressively towards 0$^\circ$ as the deformation rate magnitude increases. Our results decouple the effects of shearing and extensional kinematics at aligning colloidal rods, establishing coherent guidelines for the manufacture of structured soft materials.

Molecular behavior and interaction between THSB and DPG particles at the gas/liquid interface

Particle reinforced foams have been widely investigated for enhancing oil recovery. The addition of DPG particles into THSB surfactant foam greatly enhances its stability. In this study, the interaction between the THSB surfactant and DPG particles at the gas/liquid interface was investigated by experiments and molecular simulations. The tension and the zeta potential of the DPG/THSB mixed system were measured to show the interaction between them. The effects of the addition of DPG particles on the interfacial properties were studied by microparticle image velocimetry. A molecular dynamics simulation was used to simulate the adsorption properties of THSB and DPG at the gas/liquid interface. The experimental and simulation results indicate that DPG particles and THSB were adsorbed together through electrostatic interactions and hydrophobic interactions. The aggregation of DPG particles at the interface slowed down the fluidity of the interface and surrounding liquid phase. DPG particles were brought onto the interface by the THSB surfactant, which made the interface molecules more compact, the mean square displacement of molecules and the total energy of the mixed system were reduced, and the number of bound water and trapped water in the liquid membrane increased. The addition of DPG particles slowed the movement of molecules in the liquid membrane, and water molecules were hard to diffuse; thus, a more stable liquid film was formed.

Fibrinogen and Fibrin Differentially Regulate the Local Hydrodynamic Environment in Neutrophil–Tumor Cell–Endothelial Cell Adhesion System

As cancer is one of the major fatal diseases for human beings worldwide, the metastasis of tumor cells (TCs) from a blood vessel to an adjacent organ has become a focus of research. A tumor metastasis theory named the “two-step theory” pointed out that polymorphnuclear neutrophils (PMNs) could facilitate TC adhesion on an endothelial monolayer under flow, which was regulated by shear flow and promoted by fibrinogen and fibrin. In order to further understand the role of hydrodynamics played in the “two-step theory”, we improved our side-view micro-particle imaging velocimetry (PIV) system and successfully measured the flow velocity profiles around adherent PMNs and TCs on an endothelial monolayer in the presence of soluble fibrinogen or fibrin under shear flow. Combined with a computational fluid dynamics simulation, we found that: (1) soluble fibrinogen and fibrin influenced the variations of relative shear rates above an adhered PMN and an adherent TC at different PMN-to-TC position states; (2) compared with soluble fibrinogen, soluble fibrin made the curves of relative shear rates above an adherent cell flatter. Soluble fibrin might increase the collision frequency and affect the contact time and contact area between PMNs, TCs, and endothelium cells, resulting in the enhancement of TC adhesion and retention on an endothelial monolayer.

The Complexity of Porous Media Flow Characterized in a Microfluidic Model Based on Confocal Laser Scanning Microscopy and Micro-PIV

In this study, the complexity of a steady-state flow through porous media is revealed using confocal laser scanning microscopy (CLSM). Micro-particle image velocimetry (micro-PIV) is applied to construct movies of colloidal particles. The calculated velocity vector fields from images are further utilized to obtain laminar flow streamlines. Fluid flow through a single straight channel is used to confirm that quantitative CLSM measurements can be conducted. Next, the coupling between the flow in a channel and the movement within an intersecting dead-end region is studied. Quantitative CLSM measurements confirm the numerically determined coupling parameter from earlier work of the authors. The fluid flow complexity is demonstrated using a porous medium consisting of a regular grid of pores in contact with a flowing fluid channel. The porous media structure was further used as the simulation domain for numerical modeling. Both the simulation, based on solving Stokes equations, and the experimental data show presence of non-trivial streamline trajectories across the pore structures. In view of the results, we argue that the hydrodynamic mixing is a combination of non-trivial streamline routing and Brownian motion by pore-scale diffusion. The results provide insight into challenges in upscaling hydrodynamic dispersion from pore scale to representative elementary volume (REV) scale. Furthermore, the successful quantitative validation of CLSM-based data from a microfluidic model fed by an electrical syringe pump provided a valuable benchmark for qualitative validation of computer simulation results.Graphic

Particle recirculating orbits within microvortices using microfluidics

Particle/cell separation from a mixture using a hydrodynamic vortex has been attracting much interest for the isolation of circulating tumor cells in basic biological studies and clinical applications. However, some issues regarding the particle recirculating orbits within the vortex in microcavities remain unclear. In this work, using micro-particle image velocimetry and a high-speed microscopy system, we quantitatively investigate the effects of inlet Reynolds numbers (Re) on the microcavity flow characteristics and particle recirculating behavior. The results show that due to the evolution of microcavity flow patterns (Re = 15–313), the particle orbit topology expands gradually, developing from a single small orbit (Re = 39–79) to a single semicircular orbit (98–117), then to alternating double orbits (Re = 136–215), and at last to a single large orbit (Re = 254–352). The alternating double orbits are observed for the first time. The particle orbit periods and topologies (lengths and area) have also been characterized. Moreover, the variations of the recirculating particle velocity are also quantitatively measured. The results deepen the fundamental understanding of particle recirculating behavior and could provide useful guidance for vortex-based microfluidics.

Swimming kinematics and hydrodynamics of barnacle larvae throughout development.

Changes in size strongly influence organisms' ecological performances. For aquatic organisms, they can transition from viscosity- to inertia-dominated fluid regimes as they grow. Such transitions are often associated with changes in morphology, swimming speed and kinematics. Barnacles do not fit into this norm as they have two morphologically distinct planktonic larval phases that swim differently but are of comparable sizes and operate in the same fluid regime (Reynolds number 100-101). We quantified the hydrodynamics of the rocky intertidal stalked barnacle Capitulum mitella from the nauplius II to cyprid stage and examined how kinematics and size increases affect its swimming performance. Cyprids beat their appendages in a metachronal wave to swim faster, more smoothly, and with less backwards slip per beat cycle than did all naupliar stages. Micro-particle image velocimetry showed that cyprids generated trailing viscous vortex rings that pushed water backwards for propulsion, contrary to the nauplii's forward suction current for particle capture. Our observations highlight that zooplankton swimming performance can shift via morphological and kinematic modifications without a significant size increase. The divergence in ecological functions through ontogeny in barnacles and the removal of feeding requirement likely contributed to the evolution of the specialized, taxonomically unique cyprid phase.

Haemodynamics around confined microscopic cylinders

Motivated by the recent developments in the research of untethered microrobots for performing minimally invasive procedures inside blood vessels, we have devised a novel microfluidic experiment for studying the haemodynamics around different types of cylinders confined inside a straight, long, 270×100μm channel. Two test sections are studied: flow past a confined circular cylinder and past a confined elliptic cylinder. The two cylinders cause a channel blockage of about 28%. We consider a continuous regime for the blood flow, since its pulsatile nature is barely felt in the regions of the human body further away from the heart, and Reynolds numbers (Re) in the range of 0.05–100, which allow to replicate a variety of flow conditions. Human blood is emulated using non-particulate polymer solutions with rheological properties analogue to those of the biofluid. Pressure drop measurement, micro-Particle Image Velocimetry and streak imaging techniques are employed to study the viscoelastic haemodynamics in the test sections, characterised by elasticity numbers (El) in the approximate interval of 1–30. Our findings include a striking dampening effect on the acceleration of the flow in the contractions between the elliptic cylinder and the channel walls, due to the elasticity of blood, and steeper pressure drops and longer recovery lengths measured in the test section of the elliptic obstacle, caused by a stronger shear stress field characterising this flow geometry and higher strain accumulation in its wake, respectively, compared to the circular cylinder.

Viscous flow through microfabricated axisymmetric contraction/expansion geometries

We employ a state-of-the-art microfabrication technique (selective laser-induced etching) to fabricate a set of axisymmetric microfluidic geometries featuring a 4:1 contraction followed by a 1:4 downstream expansion in the radial dimension. Three devices are fabricated: the first has a sudden contraction followed by a sudden expansion, the second features hyperbolic contraction and expansion profiles, and the third has a numerically optimized contraction/expansion profile intended to provide a constant extensional/compressional rate along the axis. We use micro-particle image velocimetry to study the creeping flow of a Newtonian fluid through the three devices and we compare the obtained velocity profiles with finite-volume numerical predictions, with good agreement. This work demonstrates the capability of this new microfabrication technique for producing accurate non-planar microfluidic geometries with complex shapes and with sufficient clarity for optical probes. The axisymmetric microfluidic geometries examined have potential to be used for the study of the extensional properties and non-linear dynamics of viscoelastic flows, and to investigate the transport and deformation dynamics of bubbles, drops, cells, and fibers.Graphic abstract

Simulating flow induced migration in vascular remodelling

Shear stress induces directed endothelial cell (EC) migration in blood vessels leading to vessel diameter increase and induction of vascular maturation. Other factors, such as EC elongation and interaction between ECs and non-vascular areas are also important. Computational models have previously been used to study collective cell migration. These models can be used to predict EC migration and its effect on vascular remodelling during embryogenesis. We combined live time-lapse imaging of the remodelling vasculature of the quail embryo yolk sac with flow quantification using a combination of micro-Particle Image Velocimetry and computational fluid dynamics. We then used the flow and remodelling data to inform a model of EC migration during remodelling. To obtain the relation between shear stress and velocity in vitro for EC cells, we developed a flow chamber to assess how confluent sheets of ECs migrate in response to shear stress. Using these data as an input, we developed a multiphase, self-propelled particles (SPP) model where individual agents are driven to migrate based on the level of shear stress while maintaining appropriate spatial relationship to nearby agents. These agents elongate, interact with each other, and with avascular agents at each time-step of the model. We compared predicted vascular shape to real vascular shape after 4 hours from our time-lapse movies and performed sensitivity analysis on the various model parameters. Our model shows that shear stress has the largest effect on the remodelling process. Importantly, however, elongation played an especially important part in remodelling. This model provides a powerful tool to study the input of different biological processes on remodelling.

Water spray heat transfer through a piezoelectric atomizer with a single-hole micronozzle

We report an experimental study on the flow and heat transfer for a single microhole of water spray impingement on an indium tin oxide (ITO) heating plate using a piezoelectric atomizer. A microhole of dj = 35 µm was used and tested with a volumetric flow rate of 0.22 cm3/min for three different spray heights of 10, 20 and 30 mm and five heater initial temperatures of 25 °C, 50 °C, 100 °C, 150 °C, and 200 °C. Through the optical measuring techniques of the microparticle image velocimetry (μPIV) as well as interferometric particle imaging (IPI) and micro laser-induced fluorescence (μLIF), the velocity field, such as spray centerline velocity, droplet impact velocity and impact crater diameter, including impinged liquid film thickness and heat transfer performance (CHF) can be measured and calculated. The effects of the spray height and initial heater temperature on the flow and thermal characteristics are presented and discussed herein. The experimental results show that both the spray centerline velocity and spray droplet impact velocity were significantly influenced by the initial surface temperature as well as by the spray height. As a result, the cooling performance would be, in turn, affected by the aforesaid two parameters.

Parameters optimization of light field micro-particle image velocimetry

The light field micro-particle image velocimetry (LF-μPIV) can record the instantaneous three-dimensional (3D) spatial position information of tracer particles in a single photographic exposure by a single camera, and thus achieve the instantaneous 3D velocity measurement of the micro-scale flow. The accuracy of the spatial positions of the reconstructed tracer particles is closely related to the spatial reconstruction resolution of the LF-μPIV system, and determines the measurement accuracy of the 3D velocity distribution. In this paper, the effects of the optical parameters of the LF-μPIV system and the spatial position of the tracer particle on the spatial resolution and reconstruction quality are numerically studied. The location of the measurement volume and the optical parameters of the LF-μPIV system are further optimized. Based on the optimized parameters, a LF-μPIV system is assembled. Finally, experiments are carried out to verify the feasibility of the optical parameters optimization from simulations and to evaluate the performance of the LF-μPIV system for three-dimensional velocity field in a micro-scale convergent channel. Results indicate that the lateral and axial reconstruction resolutions are higher in the outside and inside regions away from the focal plane, compared with those in the region near the focal plane of the objective lens, and is less affected by the microlens aperture, CCD sensor pixel size and objective lens magnification. The spatial reconstruction resolution of the LF-μPIV system at different depths is in good agreement with the simulation results, proving the effectiveness of the optical parameters optimization of the LF-μPIV system. The measurement results of 3D velocity field in a micro-scale convergent channel are consistent with the simulation results by ANSYS Fluent, further verifying the feasibility of the optimized LF-μPIV system for 3D velocity field.

Investigating the Effect of Antibody-Antigen Reactions on the Internal Convection in a Sessile Droplet via Microparticle Image Velocimetry and DLVO Analysis.

The evaporation of antigen-laden sessile droplets on antibody-immobilized PDMS substrates could be used in place of microwells for detection purposes owing to the lesser requirements of analytes and a reduced reaction time. To develop such techniques, the effects of different parameters on the reaction efficiency and on the resulting deposition patterns of antigens on the surface after evaporation need to be well understood. While the resultant deposition patterns from the evaporation of droplets of biological fluids on surfaces are being studied for various biomedical applications, systems where the analyte of interest in the droplet binds to the surface have not been investigated until now. While the effect of temperature on the internal convection within sessile droplets has been studied, the effect of the analyte (antigen in this work) concentration and the analyte-surface (antigen-antibody in this work) binding on the internal convection has not been studied until now. Therefore, to gain insight, the evaporation dynamics of sessile droplets with different concentrations of antigens along with polystyrene microspheres (used as tracers) in phosphate-buffered saline (PBS) on antibody-immobilized PDMS substrates were experimentally studied using microparticle image velocimetry (PIV). It was found that Marangoni flow due to concentration gradients and surface reactions was responsible for the observed velocity field. The antibody-antigen reaction (as compared to the control case of no surface reaction) and higher concentrations of prostate specific antigen (PSA) resulted in increased strength of Marangoni convection. To obtain further insight into the different deposition patterns obtained, the contributions of different particle-particle and particle-substrate forces were determined, and it was observed that the Marangoni forces along with surface tension and DLVO forces create a uniform deposition of the particles present within the droplet. This learning could be used to design biosensors.

Experimental fluid dynamics characterization of a novel micropump-mixer.

The application of lab-on-a-chip systems to biomedical engineering and medical biology is rapidly growing. Reciprocating micropumps show significant promise as automated bio-fluid handling systems and as active reagent-to-sample mixers. Here, we describe a thorough fluid dynamic analysis of an active micro-pump-mixer designed for applications of preclinical blood analysis and clinical diagnostics in hematology. Using high-speed flow visualization and micro-particle image velocimetry measurements, a parametric study is performed to investigate the fluid dynamics of six discrete modes of micropump operation. With this approach, we identify an actuation regime that results in optimal sample flow rates while concomitantly maximizing reagent-to-sample mixing.

Analysis of reattachment length dynamics in cavities

Recirculation zone dynamics in a cavity located in the bottom wall of a water channel with height h = 0.3 mm and width b = 0.9 mm are investigated experimentally and numerically.A microparticle image velocimetry method and instrumentation are used for the experimental determination of flow velocity distribution and reattachment pattern with Reynolds number from ReDh = 30–2000, cavity length to depth ratios of L/h1 = 10 and 16, and channel expansion ratios of H/h = 1.3, 1.5, 2, 3, and 5. Numerical simulation using commercially available Ansys Fluent software is conducted for analysis of the influence of flow regime and cavity dimensions by changing ReDh, L/h1, and H/h in the ranges of (1–105), (8–36) and (1.25–5), respectively.The experimental and numerical simulation results show that in a laminar flow regime reattachment length increases with increasing ReDh in the same manner as in flow over a backward-facing step. Reh1 and H/h are the main scaling parameters for the reattachment length. However, the results suggest that the transition to a turbulent flow regime occurs earlier due to the small channel spanwise aspect ratio AR = b/h = 3. Reh1 ≈ 500 and Reh1 ≈ 2000 are the critical values that determine the onset of flow transition from a laminar to a turbulent regime and the onset of fully developed turbulent flow, respectively. In addition, it is found that the influence degree of channel expansion ratio depends on whether H/h > 2 or H/h < 2.

Effective mixing due to oscillatory laminar flow in tubular networks of plasmodial slime moulds

The plasmodium of the unicellular slime mould Physarum polycephalum forms an extended vascular network in which protoplasm is transported through the giant cell due to peristaltic pumping. The flow in the veins is always parabolic and it performs shuttle streaming, i.e., the flow reverses its direction periodically. However, particles suspended in the protoplasm are effectively and rapidly distributed within the cell. To elucidate how an effective mixing can be achieved in such a microfluidic system with Poiseuille flow, we performed micro-particle imaging velocimetry experiments and advected virtual tracers in the determined time-dependent flow fields. Two factors were found to be crucial for effective mixing: (i) flow splitting and flow reversals occurring at junctions of veins and (ii) small delays in the reversals of flows in the veins at a junction. These factors enhance the distribution of fluid volumes and hence promote mixing due to chaotic advection. From the residence time distributions of particles at a junction, it is estimated that about 10% of the volume is effectively redistributed at a junction during one period of the shuttle streaming. We presume that the principles of mixing unravelled in P. polycephalum represent a promising approach to achieve efficient mixing in man-made microfluidic devices.

Fluid flow characterisation in randomly packed microscale porous beds with different sphere sizes using micro-particle image velocimetry

An experimental study using pressure-drop and μ-PIV measurements was undertaken to better understand the fluid flow characteristics in different flow regimes within randomly packed microscale porous beds with different sized spheres. Three sintered glass samples were made with glass spheres having a mean diameter of 170 μm, 430 μm and 710 μm by slightly sintering them between two glass slides, forming a sample with a sandwich structure. Four different regimes, pre-Darcy, Darcy, Forchheimer and turbulent were identified in each sintered glass sample using the pressure-drop measurements. The permeability increases with glass sphere size and so does the Reynolds number corresponding to each flow regime boundary. It was found that for a given Re, the pressure drop in the sample with 170 μm diameter spheres can be ten times higher than the pressure drop in the sample with 710 μm diameter spheres. Four different pore geometries were identified to be the focus of the measurement zones of the μ-PIV, which were taken across a range of Re spanning all the flow regimes identified in the pressure-drop measurements. The non-dimensional time-averaged velocity distribution was found to be similar in each flow regime for the samples with 170 μm and 430 μm diameter spheres, whereas it changed dramatically for the sample with 710 μm diameter spheres. In general the velocity profiles through the channels within the porous media were found to be near-parabolic, especially in the Darcy and Forchheimer regimes, but in the turbulent regime inertial effects such as localised jets were observed. Detailed observational and statistical analysis of the velocity distributions highlights their very strong dependency on the local geometry with highly localised regions of flow apparently in a different flow regime to that of the bulk flow. However, the global average of the fluctuations throughout the measurement zone does align well with the pressure drop measurements.

Signature of elastic turbulence of viscoelastic fluid flow in a single pore throat.

When a viscoelastic fluid, such as an aqueous polymer solution, flows through a porous medium, the fluid undergoes a repetitive expansion and contraction as it passes from one pore to the next. Above a critical flow rate, the interaction between the viscoelastic nature of the polymer and the pore configuration results in spatial and temporal flow instabilities reminiscent of turbulentlike behavior, even though the Reynolds number Re≪1. To investigate whether this is caused by many repeated pore body-pore throat sequences, or simply a consequence of the converging (diverging) nature present in a single pore throat, we performed experiments using anionic hydrolyzed polyacrylamide (HPAM) in a microfluidic flow geometry representing a single pore throat. This allows the viscoelastic fluid to be characterized at increasing flow rates using microparticle image velocimetry in combination with pressure drop measurements. The key finding is that the effect, popularly known as "elastic turbulence," occurs already in a single pore throat geometry. The critical Deborah number at which the transition in rheological flow behavior from pseudoplastic (shear thinning) to dilatant (shear thickening) strongly depends on the ionic strength, the type of cation in the anionic HPAM solution, and the nature of pore configuration. The transition towards the elastic turbulence regime was found to directly correlate with an increase in normal stresses. The topology parameter, Q_{f}, computed from the velocity distribution, suggests that the "shear thickening" regime, where much of the elastic turbulence occurs in a single pore throat, is a consequence of viscoelastic normal stresses that cause a complex flow field. This flow field consists of extensional, shear, and rotational features around the constriction, as well as upstream and downstream of the constriction. Furthermore, this elastic turbulence regime, has high-pressure fluctuations, with a power-law decay exponent of up to |-2.1| which is higher than the Kolmogorov value for turbulence of |-5/3|.

HFE-7100/HFE-7300 spray quenching via a piezoelectric atomizer with a single-hole micronozzle

The flow and thermal characteristics of spray cooling with a single-hole micronozzle via a piezoelectric (PZT) atomizer with two dielectric fluids were studied to provide a better physical insight of the flow phenomena as well as the cooling mechanism with HFE-7100 and HFE-7300 as coolants. The target/heater's surface was made of indium tin oxide (ITO)-coated glass. A microhole of dj = 35 µm was used and tested with a volumetric flow rate of 0.0838 ml/min (HFE-7100) and 0.1180 ml/min (HFE-7300), respectively, for spray heights of 10 mm, 20 mm, 30 mm, and 40 mm, with heater surface temperatures of 25 °C, 75 °C, 125 °C, 175 °C, and 225 °C. The spray velocity and droplet size were measured by microparticle image velocimetry (µPIV) and interferometric particle imaging (IPI), respectively, for the spray centerline velocity along the downstream during the spray flight and for the spray droplet impact velocity as well as the associated droplet size measurements. Quench cooling curves as well as the transient boiling curves were obtained. Boiling curve related parameters such as the onset of nucleate boiling, Leidenfrost temperature, etc. were identified. The maximum heat transfer coefficient (hmax) correlation was developed in terms of q“, Wep and Ja.