OPTICAL MEASUREMENT OF MICROSCALE TRANSPORT PROCESSES IN DROPWISE CONDENSATION

Abstract Shockless explosion combustor (SEC) is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous auto-ignition that induces a moderate rise in pressure. Since the ignition is not triggered by an external source but driven primarily by chemical kinetics, the homogeneity of the auto-ignition is very sensitive to local perturbations in equivalence ratio, temperature, and pressure that produce undesired local premature ignition. Therefore, the precise injection of a well-defined fuel profile into a convecting air flow is crucial to ensure a quasi-homogeneous ignition of the entire mixture. The objective of this work is to demonstrate that the injected fuel profile is preserved throughout the entire measurement section. For this, two different control trajectories are investigated. Optical measurement techniques are used to illustrate the effect of turbulent transport and dispersion caused by boundary layer effects on the fuel concentration profile. Results from line-of-sight measurements by tunable diode laser absorption spectroscopy indicate that the transport of the fuel-air mixture is dominated by turbulent diffusion. However, comparisons to numerical calculations reveal the effect of dispersion toward the bounds of the fuel concentration profile. The spatially resolved distributions of the fuel concentration inside the combustor gained from acetone planar laser induced fluorescence (PLIF) replicates a typical velocity distribution of turbulent pipe flow in radial direction visualizing boundary layer effects. Comparing both methods provides deep insights into the transport processes that have an impact on the operation of the SEC.

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An X-Ray Tomography Based Lattice Boltzmann Simulation Study on Gas Diffusion Layers of Polymer Electrolyte Fuel Cells

Journal of Fuel Cell Science and Technology ◽

10.1115/1.3211096 ◽

2010 ◽

Vol 7 (3) ◽

Cited By ~ 30

Author(s):

Pratap Rama ◽

Yu Liu ◽

Rui Chen ◽

Hossein Ostadi ◽

Kyle Jiang ◽

...

Keyword(s):

Fuel Cell ◽

Polymer Electrolyte ◽

Lattice Boltzmann ◽

Gas Diffusion ◽

Transport Processes ◽

Polymer Electrolyte Fuel Cell ◽

Absolute Permeability ◽

Carbon Paper ◽

X Ray ◽

Microscale Transport

This work reports a feasibility study into the combined full morphological reconstruction of fuel cell structures using X-ray computed micro- and nanotomography and lattice Boltzmann modeling to simulate fluid flow at pore scale in porous materials. This work provides a description of how the two techniques have been adapted to simulate gas movement through a carbon paper gas diffusion layer (GDL). The validation work demonstrates that the difference between the simulated and measured absolute permeability of air is 3%. The current study elucidates the potential to enable improvements in GDL design, material composition, and cell design to be realized through a greater understanding of the nano- and microscale transport processes occurring within the polymer electrolyte fuel cell.

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Investigation of the Fuel Distribution in a Shockless Explosion Combustor

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2020-16210 ◽

2020 ◽

Author(s):

Fatma Cansu Yücel ◽

Fabian Habicht ◽

Alexander Jaeschke ◽

Finn Lückoff ◽

Kilian Oberleithner ◽

...

Keyword(s):

Boundary Layer ◽

Concentration Profile ◽

Optical Measurement ◽

Turbulent Transport ◽

Measurement Techniques ◽

Transport Processes ◽

Turbulent Pipe Flow ◽

Tunable Diode Laser ◽

Fuel Concentration ◽

Fuel Profile

Abstract Shockless explosion combustion is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous autoignition that induces a moderate rise in pressure. By this, considerable losses due to entropy generation by inherent shock waves of detonation-based concepts can be avoided. Since the ignition is not triggered by an external source but driven by chemical kinetics only, the homogeneity of the autoignition is very sensitive to local perturbations in equivalence ratio, temperature, and pressure that produce undesired local premature ignition. Therefore, the precise injection of a well-defined fuel profile into an convecting air flow is crucial to ensure a quasi-homogeneous ignition of the entire flammable mixture. The objective of this work is to demonstrate that the injected fuel profile is preserved throughout the entire measurement section. For this, two different control trajectories are investigated. Optical measurement techniques are used to illustrate the effect of turbulent transport and dispersion caused by boundary layer effects on the fuel concentration profile inside the combustor. Results from line-of-sight measurements by tunable diode laser absorption spectroscopy indicate that the transport of the fuel-air mixture is dominated by turbulent diffusion. However, comparisons to numerical calculations reveal the effect of dispersion towards the bounds of the fuel concentration profile. The spatially resolved distributions of the fuel concentration inside the combustor gained from acetone planar laser induced fluorescence replicates a typical velocity distribution of turbulent pipe flow in radial direction visualizing boundary layer effects. Comparing both methods provide deep insights into the transport processes that have an impact on the operation of the shockless explosion combustor.

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Experimental Study of Microscale Bubble Growth and Departure Dynamic Over a Surface With Constant Heat Flux Boundary Condition

Heat Transfer: Volume 2 ◽

10.1115/ht2003-47240 ◽

2003 ◽

Author(s):

Saeed Moghaddam ◽

Kenneth T. Kiger

Keyword(s):

Heat Transfer ◽

Boiling Heat Transfer ◽

Bubble Diameter ◽

Nucleate Boiling ◽

Constant Heat Flux ◽

Transport Processes ◽

Flux Boundary Condition ◽

Boiling Heat Transfer Coefficient ◽

Competing Models ◽

Microscale Transport

Boiling heat transfer has been the subject of research for many years, with a substantial amount of effort devoted to understanding the microscale transport processes of nucleate boiling. This information is essential to determine appropriate expressions for the boiling heat transfer coefficient. As a result, several different competing models based on the bubbling dynamics and its associated heat transfer mechanisms have been hypothesized to account for the sensible and latent heat transport and liquid motion adjacent to the heat transfer surface. Many of the early models were based on the assumptions that growth, departure and the associated pumping action of the bubbles are responsible for heat transfer during nucleate boiling. Jakob [1] and Rohsenow [2] were apparently the first to postulate that the process of growth and departure of the bubble is responsible for the induced motion of the liquid adjacent to the heat transfer, as in any single-phase convection process. Rohsenow [2] modeled the heat transfer by using bubble diameter as a characteristic length to determine a Nusselt number based on a defined Reynolds and Prandtl number. Even with the same line of reasoning, Rohsenow’s analysis resulted in a different formulation compared to Froster and Zober [3], who implemented an alternate hypothesis for the velocity of the bubble interface used in defining the Reynolds number. Other models of this nature were also proposed by Forster and Greif [4] and Zuber [5].

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Optical Evaluation of the Effect of Curvature and Apparent Contact Angle in Droplet Condensate Removal

Journal of Heat Transfer ◽

10.1115/1.1466460 ◽

2002 ◽

Vol 124 (4) ◽

pp. 729-738 ◽

Cited By ~ 3

Author(s):

Ying-Xin Wang ◽

Ling Zheng ◽

Joel L. Plawsky ◽

Peter C. Wayner,

Keyword(s):

Contact Angle ◽

Sessile Drop ◽

Removal Rate ◽

Contact Angles ◽

Transport Processes ◽

Force Balance ◽

Pressure Fields ◽

Concave Corner ◽

Microscale Transport ◽

Droplet Condensation

The microscale transport processes in droplet condensation and removal due to interfacial phenomena were studied. In particular, this paper concerns the movement of a condensed ethanol sessile drop into a concave liquid film in the corner. An improved image analyzing procedure was used to evaluate the curvatures and contact angles for both the drop and the concave corner meniscus at different condensation rates. The experimental results demonstrated that the condensate removal rate was a function of the curvature and contact angle, which self-adjust to give the necessary force field. The use of a dimensionless, shape dependent, force balance was demonstrated. For small drops, the intermolecular force was found to be much larger than the gravitational force and dominated droplet removal. Microscale pressure fields can be experimentally measured whereas interfacial temperature differences cannot.

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Microfluidics and Microscale Transport Processes

10.1201/b12976 ◽

2012 ◽

Cited By ~ 2

Keyword(s):

Transport Processes ◽

Microscale Transport

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3D imaging of porous media using laser scanning confocal microscopy with application to microscale transport processes

Physics and Chemistry of the Earth Part A Solid Earth and Geodesy ◽

10.1016/s1464-1895(99)00079-4 ◽

1999 ◽

Vol 24 (7) ◽

pp. 551-561 ◽

Cited By ~ 96

Author(s):

J.T. Fredrich

Keyword(s):

Porous Media ◽

Confocal Microscopy ◽

Laser Scanning ◽

3D Imaging ◽

Laser Scanning Confocal Microscopy ◽

Transport Processes ◽

Scanning Confocal Microscopy ◽

Microscale Transport

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A Review of Microscale Transport in the Thermal Processing of New and Emerging Advanced Materials

Journal of Heat Transfer ◽

10.1115/1.4003512 ◽

2011 ◽

Vol 133 (6) ◽

Cited By ~ 10

Author(s):

Yogesh Jaluria ◽

Jing Yang

Keyword(s):

Optical Fibers ◽

Thermal Processing ◽

High Pressures ◽

Numerical Models ◽

Chemical Vapor ◽

Transport Processes ◽

Advanced Materials ◽

Thin Film Fabrication ◽

Microscale Transport ◽

Good Agreement

This paper reviews the microscale transport processes that arise in the fabrication of advanced materials. In many cases, the dimensions of the device being fabricated are in the micrometer length scale and, in others, underlying transformations that determine product quality and characteristics are at micro- or nanoscale levels. The basic considerations in these transport phenomena are outlined. A few important materials processing circumstances are considered in detail. These include the fabrication of multilayer and hollow optical fibers, as well as those where micro- and nanoscale dopants are added to achieve desired optical characteristics, thin film fabrication by chemical vapor deposition, and microscale coating of fibers and devices. It is shown that major challenges are posed by the simulation and experimentation, as compared with those for engineering or macroscale dimensions. These include accurate simulation to capture large gradients and variations over relatively small dimensions, simulating high pressures and viscous dissipation effects in microchannels, modeling effects such as surface tension that become dominant at microscale dimensions, and coupling micro- and nanoscale mechanisms with boundary conditions imposed at the macroscale. Similarly, measurements over microscale dimensions are much more involved than those over macro- or industrial scales because of difficult access to the regions of interest, relatively small effects such as tension, buoyancy effects, viscous rupture, bubble entrapment, and other mechanisms that are difficult to measure and that can make the process infeasible. It thus becomes difficult to achieve desired accuracy for validating the mathematical and numerical models. This paper reviews some of the approaches that have been adopted to overcome these difficulties. Comparisons between experimental and numerical results are included to show fairly good agreement, indicating the validity of the modeling of transport.

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