Name: pool-boiling heat-transfer enhancement on cylindrical surfaces with hybrid wettable patterns
Uploaded: 2017-04-10T14:00:00
Description: Watch this Scientific Journal Video about Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns at JoVE.com

The authors gratefully acknowledge funding support from the Ministry of Science and Technology, MOST (project numbers: MOST 104-2218-E-002 -004, MOST 105-2218-E-002-019, MOST 105-2221-E-002 -107 -MY3, MOST 102-2221-E-002 -133 -MY3, and MOST 102-2221-E-002 -088 -MY3).

1. Preparation of the Modified Surfaces
<ol>
	<li>Manually polish the test piece (hollow copper cylinder with a 40-mm length (l), a 25-mm outer diameter (do), and an 18-mm inner diameter (di)) for 15 min using a &#65283;2,000 emery paper. Clean the polished surface by rinsing it with acetone followed by DI water.</li>
	<li>Place the polished test piece in an oven for 2 h at a constant temperature of 120 &#176;C.</li>
	<li>Prepare a superhydrophilic SiO2 nanopa...

<ol>
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The main goal of this investigation was to develop a pool-boiling heat sink for high heat dissipation applications, such as nuclear reactors, boilers, and heat pipes, by introducing the hybrid wettable surface, as described in the protocol section. These surfaces can produce better pool-boiling performances than homogeneous wettable surfaces (hydrophilic and hydrophobic). The improvement in the boiling heat-transfer performance is due to an increase in active nucleation sites and the easy detachment of the formed bubbles...

A high heat flux-sustaining system providing cooling in the range of 10-105 W/cm2 is required in the emerging fields of electronics, defense, avionics, and nuclear device development. Conventional cooling with air is insufficient for these applications due to the low heat-transfer coefficient (HTC) for both free- and forced-convection conditions. The phase change-based cooling techniques, such as pool boiling and flow boiling, are good enough to remove high heat fluxes on the order of 10 - 1,000 W/cm2 1. Since the two-phase heat-transfer process is isothermal, the cooled device temperature is almost constant over its surface. Due to the negligible variation of the temperature along the surface, the thermal shock of the device can be eliminated. However, the major limiting parameter in boiling heat-transfer is the critical heat flux (CHF), which causes an abnormal rise in temperature2.
In the last few decades, extensive research has been carried out to improve the CHF by using surface modification, nanofluids, and surface coatings3,4,5,6,7,8,9,10,11. Among the various methods, surface coatings are found to be the best method to improve the CHF due to the substantial increase in the surface area. Surface coatings generally increase the heat transfer by fin action, porosity effects, and surface wettability12. Surface wettability plays a significant role in boiling heat-transfer. Previous studies show that at lower heat-flux conditions, the hydrophobic surface shows better HTC due to the early nucleation. However, at higher heat flux, the detachment of the formed bubbles is slow due to the low affinity of water towards the surface. This leads to bubble coalescence and results in a lower CHF3. On the other hand, a hydrophilic surface produces a higher CHF, because of the fast detachment of the formed bubbles, but it gives a lower HTC at low heat fluxes, due to the delay in bubble nucleation13.
The hybrid structures show a remarkable enhancement in boiling heat-transfer for all heat fluxes due to the combined effect of hydrophobicity and hydrophilicity14,15,16. Hsu et al. produced heterogeneous wettable surface by coating superhydrophilic Si nanoparticles on a masked copper surface. They achieved different wettability ratios by varying the coating time. The onset of boiling occurred earlier on the heterogeneous surfaces compared to the homogeneous surface, which substantially reduced the wall superheat17. Jo et al. conducted nucleate boiling heat-transfer studies on hydrophilic, hydrophobic, and heterogeneous wetting surfaces. The heterogeneous wetting surface was composed of hydrophobic patterned dots on the hydrophilic surface. They got higher HTCs and the same CHF for the heterogeneous surface as compared to the hydrophilic surface. An improvement in boiling heat-transfer directly depends upon the number of dots on the surface and upon the boiling conditions18.
In this study, axial hybrid wettable patterns were produced on a cylindrical copper surface using the dip coating technique. Pool-boiling heat-transfer studies were conducted to determine the effects of the number of interlines and of the orientation of the hybrid wettable pattern. Boiling heat flux, HTC, and bubble dynamics were analyzed for the all coated substrates and were compared with the copper substrate.

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pool-boiling heat-transfer enhancement on cylindrical surfaces with hybrid wettable patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were conducted on a hybrid wettable cylindrical surface using the experimental setup whose schematic is shown in Figure 5. The pool-boiling experimental procedure explained in step 2 of the protocol section was successfully carried out while investigating the effect of the number of interlines and of the orientation of the hybrid wettable pattern on the pool-boiling performance. The pool-boiling performances of the different-treated ...

Watch this Scientific Journal Video about Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns at JoVE.com

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

The overall goal of this experiment is to investigate the effect of the number and orientation of axial wettable patterns on pool-boiling heat-transfer. This method can help answer key questions in the field of pool-boiling heat transfer such as the effect of hybrid variability on the boiling heat transfer coefficient and bubble dynamics. The main advantage of this technique is that it can accurately measure the pool-boiling heat-transfer coefficient and bubble dynamics of hybrid wettable surface.To begin, manually polish a hollow copper cylinder for 15 minutes using number 2, 000 emery paper. Clean the polished surface by rinsing it with acetone followed by deionized water. Place the polished test piece in an oven for two hours at a constant temperature of 120 degrees Celsius.To prepare a superhydrophilic silicon dioxide nanoparticle solution, first prepare solution A by mixing tetraethoxy silane and deionized water. Then add two drops of 37%concentrated HCl to solution A and stir for two hours. Next, make solution B by mixing ethanol and deionized water.Then mix one milliliter of solution A and 80 milliliters of solution B and stir for two hours. And 32 grams of silicon dioxide nanoparticles to the prepared solution and stir for one hour before immersing the test piece as described in the text protocol. Next, prepared two interlined hybrid patterns with different orientations along the axial direction of the test piece, by masking the area to be uncoated using the insulation tape according to the required number of interlines with the proper orientation.For the two interlined surface at a zero degree orientation adjust interlines at the center and the superhydrophilic area on the top side. Conversely, for the 180 degree orientation, adjust the superhydrophilic area at the bottom and the interlines at the center. Similarly adjust the position of the four and eight interlined surfaces with the different orientations.Next, immerse the masked test piece in the prepared solution by using a dip coating apparatus at a high dipping velocity and rise at a slow velocity of five millimeters per minute. Keep the coated test piece in an oven at 120 degrees for one hour. Finally, remove the insulation tape from the masked area to obtain the required number of interlines with the proper orientation.Using insulation tape, fix one glass tube at each circular base of the coated test piece. Horizontally fix this assembly to the chamber using silicon paste according to the required position of interlines. Place a cartridge heater with a thin film of thermal paste on the circumferential area into the hole of the test piece.Connect the cartridge heater to a direct current power supply unit. Place T-type thermocouples into the eight equally spaced one millimeter holes with alternate depths of five millimeters and seven millimeters. Then, connect them to the data logger.Insert and fix resistance temperature detectors, a reflux condenser and an auxiliary heater in the spaces provided on the top cover. Fix them over the boiling chamber. Next, fill 1.4 liters of deionized water into the pool-boiling chamber.Connect the reflux condenser to a cooling chamber that is maintained at five degrees Celsius. Prior to the experiment, vigorously boil the deionized water in the pool-boiling chamber for 30 minutes using the auxiliary heater. Keep the deionized water at the saturated boiling condition by using the auxiliary heater.Subsequently, switch on the power supply and give an initial current of 0.1 amps. Meanwhile, record the bubble dynamics for each power input by using a CCD camera that is placed in front of the pool-boiling chamber and focused on the test piece. After waiting for two minutes to reach a steady-state, increase the electric current with increments of 0.3 amps.Record the temperature at each power input by using the data logger. Continue the experiment until a maximum current of four amps is reached. Finally, perform Data Reduction as described in the text protocol.Shown here are pool-boiling performances of plain copper surface, fully superhydrophilic surface, and hybrid surfaces with different numbers of interlines at zero degree orientation. The effect of various surfaces on pool-boiling curves is shown, as well as the variation of the heat transfer coefficient, or HTC with respect to heat flux. Eight interlined surfaces show better HTC as compared to other surfaces for particular heat flux, but two and four interlined surfaces have almost the same HTC.The effect of orientation on pool-boiling curves of two interlined hybrid surfaces, four interlined hybrid surfaces, and eight interlined hybrid surfaces are shown. The leftward shift in pool-boiling curves is obtained for the two interlined surface for zero degrees, the four interlined surface at 90 degrees, and the eight interlined surface at 45 degrees. Also shown is the effect of orientation on the heat transfer coefficient for two interlined hybrid surfaces, four interlined hybrid surfaces, and eight interlined hybrid surfaces.HTC of the two interlined surface at zero degrees, the four interlined surface at 90 degrees, and the eight interlined surface at 45 degrees show the highest values. Once mastered this technique can done in ways if it is performed properly. For learning this procedure, analysis of pool-boiling heat-transfer coefficient and bubble dynamics can be performed to investigate the effect of hybrid variability on pool-boiling.Don't forget that, working with nanoparticles and chemicals can be hazardous and precautions such as wearing gloves and masks should always be taken while performing this procedure.

pool-boiling-heat-transfer-enhancement-on-cylindrical-surfaces-with

Research

JoVE Journal

Engineering

Micropunching Lithography for Generating Micro- and Submicron-patterns on Polymer Substrates

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of low weight, easy tailoring of properties and a wide spectrum of applications2,3. Due to sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature and chemical solutions), lithographic techniques present significant technical challenges when working with these materials4. For example, current photolithographic methods, such as ultra-violet (UV), are unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in these methods. In addition, current micro/nanosystems mainly have a planar form5,6. One layer of structures is built on the top surfaces of another layer of fabricated features. Multiple layers of these structures are stacked together to form numerous devices on a common substrate. The sidewall surfaces of the microstructures have not been used in constructing devices. On the other hand, sidewall patterns could be used, for example, to build 3-D circuits, modify fluidic channels and direct horizontal growth of nanowires and nanotubes.
A macropunching method has been applied in the manufacturing industry to create macropatterns in a sheet metal for over a hundred years. Motivated by this approach, we have developed a micropunching lithography method (MPL) to overcome the obstacles of patterning conducting polymers and generating sidewall patterns. Like the macropunching method, the MPL also includes two operations (Fig. 1): (i) cutting; and (ii) drawing. The "cutting" operation was applied to pattern three conducting polymers4, polypyrrole (PPy), Poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT) and polyaniline (PANI). It was also employed to create Al microstructures7. The fabricated microstructures of conducting polymers have been used as humidity8, chemical8, and glucose sensors9. Combined microstructures of Al and conducting polymers have been employed to fabricate capacitors and various heterojunctions9,10,11. The "cutting" operation was also applied to generate submicron-patterns, such as 100- and 500-nm-wide PPy lines as well as 100-nm-wide Au wires. The "drawing" operation was employed for two applications: (i) produce Au sidewall patterns on high density polyethylene (HDPE) channels which could be used for building 3D microsystems12,13,14, and (ii) fabricate polydimethylsiloxane (PDMS) micropillars on HDPE substrates to increase the contact angle of the channel15.

A micropunching lithography approach is developed to generate micro- and submicron-patterns on top, sidewall and bottom surfaces of polymer substrates. It overcomes the obstacles of patterning conducting polymers and generating sidewall patterns. This method allows rapid fabrication of multiple features and is free of aggressive chemistry.

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of ...

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

High-speed Particle Image Velocimetry Near Surfaces

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The complex nature of these flows may be studied using particle image velocimetry (PIV), a laser-based imaging technique for optically accessible flows. Though many forms of PIV exist that extend the technique beyond the original planar two-component velocity measurement capabilities, the basic PIV system consists of a light source (laser), a camera, tracer particles, and analysis algorithms. The imaging and recording parameters, the light source, and the algorithms are adjusted to optimize the recording for the flow of interest and obtain valid velocity data. 
Common PIV investigations measure two-component velocities in a plane at a few frames per second. However, recent developments in instrumentation have facilitated high-frame rate (&gt; 1 kHz) measurements capable of resolving transient flows with high temporal resolution. Therefore, high-frame rate measurements have enabled investigations on the evolution of the structure and dynamics of highly transient flows. These investigations play a critical role in understanding the fundamental physics of complex flows.
A detailed description for performing high-resolution, high-speed planar PIV to study a transient flow near the surface of a flat plate is presented here. Details for adjusting the parameter constraints such as image and recording properties, the laser sheet properties, and processing algorithms to adapt PIV for any flow of interest are included.

A procedure for studying transient flows near boundaries using high-resolution, high-speed particle image velocimetry (PIV) is described here. PIV is a non-intrusive measurement technique applicable to any optically accessible flow by optimizing several parameter constraints such as the image and recording properties, the laser sheet properties, and analysis algorithms.

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces

Here, we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. Optical property evaluation of thin films and the surfaces of bulk materials is an important step in understanding new optical material systems and their applications. The method presented can estimate thickness, refractive index, and use absorptive properties of materials for detection. This metrology system uses evanescent field-based photoacoustics (EFPA), a field of research based upon the interaction of an evanescent field with the photoacoustic effect. This interaction and its resulting family of techniques allow the technique to probe optical properties within a few hundred nanometers of the sample surface. This optical near field allows for the highly accurate estimation of material properties on the same scale as the field itself such as refractive index and film thickness. With the use of EFPA and its sub techniques such as total internal reflection photoacoustic spectroscopy (TIRPAS) and optical tunneling photoacoustic spectroscopy (OTPAS), it is possible to evaluate a material at the nanoscale in a consolidated instrument without the need for many instruments and experiments that may be cost prohibitive.

Here we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. This technique evanescent field-based photoacoustics can be used to create a photoacoustic metrology system to estimate materials&#39; thicknesses, bulk and thin film refractive indices, and explore their optical properties.

Here, we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. ...

The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, building and food industries, amongst others. Polyester and coatings containing both polyester and silica nanoparticles (SiO2NPs) have been widely used to protect steel substrata from corrosion. In this study, we utilized X-ray photoelectron spectroscopy, attenuated total reflection infrared micro-spectroscopy, water contact angle measurements, optical profiling and atomic force microscopy to provide an insight into how exposure to sunlight can cause changes in the micro- and nanoscale integrity of the coatings. No significant change in surface micro-topography was detected using optical profilometry, however, statistically significant nanoscale changes to the surface were detected using atomic force microscopy. Analysis of the X-ray photoelectron spectroscopy and attenuated total reflection infrared micro-spectroscopy data revealed that degradation of the ester groups had occurred through exposure to ultraviolet light to form COO&#903;, -H2C&#903;, -O&#903;, -CO&#903; radicals. During the degradation process, CO and CO2 were also produced.

Two types of surfaces, polyester-coated steel and polyester coated with a layer of silica nanoparticles, were studied. Both surfaces were exposed to sunlight, which was found to cause substantial changes in the chemistry and nanoscale topography of the surface.

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, ...

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer coefficient as a function of the liquid flow rate in a transparent pipe. With certain amendments, the approach is extended to gas-liquid flows, with a particular emphasis on the effect of a single elongated (Taylor) air bubble on heat transfer enhancement. A non-invasive thermography technique is applied to measure the instantaneous temperature of a thin metal foil heated electrically. The foil is glued to cover a narrow slot cut in the pipe. The thermal inertia of the foil is small enough to detect the variation in the instantaneous foil temperature. The test section can be moved along the pipe and is long enough to cover a considerable part of the growing thermal boundary layer.
At the beginning of each experimental run, a steady state with a constant water flow rate and heat flux to the foil is attained and serves as the reference. The Taylor bubble is then injected into the pipe. The heat transfer coefficient variations due to the passage of a Taylor bubble propagating in a vertical pipe is measured as function of the distance of the measuring point from the bottom of the moving Taylor bubble. Thus, the results represent the local heat transfer coefficients. Multiple independent runs preformed under identical conditions allow accumulating sufficient data to calculate reliable ensemble-averaged results on the transient convective heat transfer. In order to perform this in a frame of reference moving with the bubble, the location of the bubble along the pipe has to be known at all times. Detailed description of measurements of the length and of the translational velocity of the Taylor bubbles by optical probes is presented.

This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

Fabricating Reactive Surfaces with Brush-like and Crosslinked Films of Azlactone-Functionalized Block Co-Polymers

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl dimethyl azlactone) (PGMA-b-PVDMA), are presented. Due to the high reactivity of azlactone groups towards amine, thiol, and hydroxyl groups, PGMA-b-PVDMA surfaces can be modified with secondary molecules to create chemically or biologically functionalized interfaces for a variety of applications. Previous reports of patterned PGMA-b-PVDMA interfaces have used traditional top-down patterning techniques that generate non-uniform films and poorly controlled background chemistries. Here, we describe customized patterning techniques that enable precise deposition of highly uniform PGMA-b-PVDMA films in backgrounds that are chemically inert or that have biomolecule-repellent properties. Importantly, these methods are designed to deposit PGMA-b-PVDMA films in a manner that completely preserves azlactone functionality through each processing step. Patterned films show well-controlled thicknesses that correspond to polymer brushes (~90 nm) or to highly crosslinked structures (~1-10 &#956;m). Brush patterns are generated using either the parylene lift-off or interface directed assembly methods described and are useful for precise modulation of overall chemical surface reactivity by adjusting either the PGMA-b-PVDMA pattern density or the length of the VDMA block. In contrast, the thick, crosslinked PGMA-b-PVDMA patterns are obtained using a customized micro-contact printing technique and offer the benefit of higher loading or capture of secondary material due to higher surface area to volume ratios. Detailed experimental steps, critical film characterizations, and trouble-shooting guides for each fabrication method are discussed.

Surface fabrication methods for patterned deposition of nanometer thick brushes or micron thick, crosslinked films of an azlactone block co-polymer are reported. Critical experimental steps, representative results, and limitations of each method are discussed. These methods are useful for creating functional interfaces with tailored physical features and tunable surface reactivity.

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl ...

Uncoupling Coriolis Force and Rotating Buoyancy Effects on Full-Field Heat Transfer Properties of a Rotating Channel

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that characterize the transport phenomena in a rotating channel are identified via the parametric analysis of the momentum and energy equations referring to a rotating frame of reference. Based on these dimensionless flow equations, an experimental strategy that links the design of the test module, the experimental program and the data analysis is formulated with the attempt to reveal the isolated Coriolis-force and buoyancy effects on heat transfer performances. The effects of Coriolis force and rotating buoyancy are illustrated using the selective results measured from rotating channels with various geometries. While the Coriolis-force and rotating-buoyancy impacts share several common features among the various rotating channels, the unique heat transfer signatures are found in association with the flow direction, the channel shape and the arrangement of heat transfer enhancement devices. Regardless of the flow configurations of the rotating channels, the presented experimental method enables the development of physically consistent heat transfer correlations that permit the evaluation of isolated and interdependent Coriolis-force and rotating-buoyancy effects on the heat transfer properties of rotating channels.

Here, we present an experimental method for decoupling the interdependent Coriolis-force and rotating-buoyancy effects on full-field heat transfer distributions of a rotating channel.

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that ...