For further improvement of PEMFC (Proton Exchange Membrane Fuel Cell) performance, an optimal design based not only on empirical knowledge but also systematic physical laws and numerical simulation is desirable. However, even basic parameters such as mass transport and thermal characteristics through layers are not completely clear. A GDL (Gas Diffusion Layer) is one of the key components of PEMFC, and its property strongly affects the temperature distribution, diffusion limitation, and flooding. Thus, we measured the diffusivity and thermal conductivity inside a GDL and at its surface boundaries. Anisotropic diffusivity was observed inside the GDL. The measured diffusivities inside the GDL were 59% lower than the value without a GDL in the thickness direction and 25% lower in plane direction. The measured diffusive resistance at the GDL surface was not considerably different from that achieved through conventional laminar analysis, although some special effects would have been observed at the GDL surface because of its high porosity. Regarding the thermal characteristics, the contact resistance at the GDL surface was measured to be as large as the resistance inside the GDL. However, the contact resistance became extremely small when the GDL contained water.

In order to prevent membrane dryout in polymer electrolyte fuel cells (PEFCs) during low humidity operation, it is essential to understand the fundamental phenomena of the water transport and reaction distribution at the anode side in an operating fuel cell. In this study, the water vapor distribution along the anode flow channel of a PEFC under low humidity conditions was quantitatively evaluated by using humidity test paper (HTP), and the effects of flow configuration and inlet humidification on the water distribution in the anode were investigated. HTP is a test paper for detecting water vapor of 20–90% RH, which is coated with a blue surface. This test paper was inserted between the anode electrode and separator in the transparent fuel cell, and the discoloration of HTP was directly visualized using a digital CCD camera. Furthermore, the temperature and current distributions in the anode electrode were measured using IR thermography and segmented cell structure concept. It was found that the water vapor concentration on the anode side increases immediately after the startup because of the back diffusion of the product water from the cathode to anode. In the case of the co-flow configuration with the dry anode and cathode inlets, the water vapor concentration increases monotonically along the anode flow channel. In addition, the anode water distribution affects the temperature and current distributions in the fuel cell largely. The local temperature and current density at the dry anode inlet are lower than those in the downstream region because of the membrane dehydration and low proton conductivity. On the other hand, in the case of the counter-flow pattern, the distributions of water concentration, temperature and current density have the maximum points in the midstream region. The counter-flow configuration is effective in improving the membrane hydration and alleviating the anode dryout.

In this study, the peak surface velocity driven by thermocapillary force in melting or welding pool irradiated by a distributed low-power-density beam is determined from a scale analysis. In view of different distances of diffusion between momentum and energy, the effects of Prandtl number on surface velocity are of interest. A low-power-density-beam heating implies no deep and narrow cavity (or keyhole) taking place in the pool. The results find that the peak surface velocity is proportional to the first power and 2/3 power of the surface tension coefficient or Marangoni number for high and low Prandtl number, respectively. The free surface velocity is determined by Prandtl and Marangoni numbers for given dimensionless beam power and Peclet numbers. The predictions agree with numerical computations.

Molecular dynamics simulation has been applied for water to compare the Wolf method to the IPS method and the Ewald sum by evaluating the diffusion coefficient and liquid structure. In our previous study, we applied the IPS method for bulk water and found notable deviation of the radial distribution function g(r). The Wolf method gives a good estimation for the potential energy and the self-diffusion coefficient at a cutoff radius, r c , greater than 2.2 nm while avoiding the notable deviation of g(r) which appeared in the case of IPS. The distance dependent Kirkwood factor G k (r) was also calculated, and the truncation of a long-range interaction of the cutofflike method (such as cutoff with or without the switch function and the reaction field) show serious shortcomings for dipole-dipole correlations in bulk water systems. This was observed by comparing the shape to that of the Ewald sum. G k (r) of the cutofflike method greatly deviates from that of the Ewald sum. However, the discrepancy of G k (r) for the Wolf method was found to be much less than that of other typical cutoff-like methods. We conclude that the Wolf method is an adequately accurate technique for estimating transport coefficients and the liquid structure of water in a homogeneous system at long cutoff distances.

Building of a model which could be used for optimization of design of nuclear waste storage, is one of biggest challenges in field of coupled processes modeling. Such a model have to take in consideration several fully-coupled processes. These processes are from field of Thermal, Hydro, Mechanical and Chemical science in short, they are described as THMC processes. Most of all, it is interaction of heat, generated by residual radiation in the waste, reacting with underground water and eventual chemical reaction in these water-solution. And all these actions being still a subject of eventual physical movements in the bedrock. In addition, model must take into consideration that values of a given process can change dramatically importance of this process characteristics for the safety of the storage. None of existing models is reaching the level of model complexity needed to address these issues. In this article is presented an object oriented model ISERIT. Model ISERIT is able to solve multidimensional task THH, where HH is for water, and water being present in 2 phases. The first phase is water vapor and the second phase is water absorbed by clay particles of the container buffer. In theoretical part of the article are defined governing equations. The governing equations are based on the conservation equations of heat and mass. The continuum equations are discretized in space by using the Galerkin finite element formulation. The time discretization is solved by implicit finite difference scheme. The main part of the article describes implementation of model ISERIT. Main structure of the model is defined with functionality of significant classes. The temperature, the water vapor concentration and the water concentration in solid phase are chosen as the three primary variables. The parameters, such as heat conductivity, heat capacity and water vapor diffusion coefficient, could be taken to be constants, or could be allowed to vary with temperature and water vapor concentration, without requiring fundamental modifications to the code. Article also describes how model can be enlarged to incorporate eventually other processes. This thanks to the fact, that model was build as object designed. At the end, article presents verification of the model against the experimental results, laboratory experiment BenchMark 1.3, as well as against full-scale experiment BenchMark 2.1.

This study is to investigate an effect of natural convection or natural circulation on a transport process by molecular diffusion in a stratified fluid layer consisting of two component gases. There are many experiments and analysis regarding natural convection in a vertical slot or natural circulation in a circular tube. However, there are few studies on natural convection or circulation with molecular diffusion in the stratified fluid layer consisting of two component gases. It is confirmed that these phenomena appear when the depressurization accident occurs in the very high temperature reactor (VHTR). Therefore it is important to evaluate the transport and mixing processes of two or more component gases during the depressurization accident of the VHTR. The experiment has been performed regarding the combined phenomena of molecular diffusion and natural convection or natural circulation in a parallel vertical slot filled with two component gases. The one vertical slot consists of the heated wall and the other side cooled wall. The other one consists of both the cooled wall. The dimension of heated wall is 500mm×200mm and thickness is 3mm. The width of the slot is 20mm and the aspect ratio of the slot is 25. Combination of nitrogen/argon is used as the two component gas system. The density change of the gas mixture and the gas temperature distribution in the slots were obtained. The mixing process of the heavier gas from the bottom side of the slot filled with the lighter gas was discussed in this paper.

We have carried out experiments on the one-directional freezing of an aqueous solution of winter flounder antifreeze protein in a narrow gap between two cover glasses. The motion of the ice/solution interface has been observed with an inverted microscope. The solution has been cooled by a Peltier device. The local change in protein concentration has been estimated from the measured intensity of fluorescence from molecules tagged to the protein. It is found that highly-concentrated regions of the protein can be observed in the bottom edge of the serrated interface. These regions interact with the interface, though most of the protein diffuses due to the concentration gradient. The diffusion velocity is much lower than the interface velocity. Thus, the protein is accumulated near the interface.

Thermal therapy, destroying tumor in situ by localized heating, is emerging as one of the treatment options for benign and localized tumors. Despite many advantages of thermal therapy, its clinical application is still limited due to the lack of a reliable intraoperative monitoring technique of the thermal lesion. To address this challenge, an intraoperative thermometry technique has been proposed using the temperature-dependent fluorescence of quantum dots (QDs). Its feasibility is recently demonstrated by monitoring the spatiotemporal temperature during gold nanoshell-mediated heating. In the present study, the effects of tissue-light interaction on the QD-mediated thermometry were investigated both experimentally and theoretically so that the technique can be extended to in vivo applications. As for experimental investigation, the QD fluorescence through tissue phantom was characterized with varying the thickness of the phantom over a temperature range relevant to thermal therapy. The results showed that the QD fluorescence through tissue phantom was still linearly correlated to the local temperature, but the slope of the correlations decreased with the phantom thickness. As for theoretical investigation, the radiative transfer equation was reduced to the diffusion approximation, and the QD fluorescence through tissue phantom was predicted by numerically solving the diffusion approximation. The results confirmed that the diffusion approximation could describe the tissue-light interaction for the QD-mediated thermometry but further research is still required to improve the accuracy of the prediction.

Simultaneous Particle Image Velocimetry (PIV) measurement and Planar Laser Induced Fluorescence (PLIF) measurement at the same position were performed to clarify the relationship between spatial structure and mass transfer in the drag reducing surfactant flow. In the drag reducing flow, mass flux is largely suppressed in the near-wall region with increasing drag reduction rate. To discuss the relationship between coherent motion and drag reduction more detail, weighted probability density function was also calculated. As a result of simultaneous measurement, diffusion of wall-normal direction is largely suppressed and this indicated that turbulent coherent structure changes and sweep and ejection which produce the skin frictional drag are suppressed.

There has been significant progress in reducing NOx and particulate emissions from diesel engines. However, many challenges remain particularly in view of the global energy issues and increasingly stringent emission regulations. Several recent efforts have focused on achieving low-temperature, premixed combustion for simultaneously reducing NOx and PM emissions, but without any detrimental effect on fuel consumption and energy density. Various strategies being explored include homogeneously charged compression ignition (HCCI), reducing flame temperature through excessive EGR, enhancing premixed combustion by controlling injection parameters, and promoting premixing by using early injection and low cetane number fuels. The present study is aimed at examining the effects of injection timing, initial gas temperature, and cylinder and piston wall temperatures on the spray processes, and thereby on the ignition, combustion and emission characteristics in a diesel engine. The reacting two-phase flow field in a 1.9L, 4-cylinder GM diesel engine is simulated using a CFD code ‘CONVERGE’, which employs an innovative cut-cell Cartesian method for grid generation, and a semi-detailed reaction mechanism for n-heptane combustion. A 51.430 sector with a single hole is considered to simulate the 7-hole common-rail injector. Results indicate that while the initial gas temperature does not affect the spray and combustion behavior qualitatively, it modifies combustion temperatures and thus NOx emissions noticeably. On the other hand, the piston and cylinder wall temperatures qualitatively influence the spray behavior and thereby the combustion and emission behavior. The injection timing has a strong influence on the spray and mixture formation processes, and thus on the combustion and emission characteristics. Delaying the start of injection (SOI) can lead to a significant reduction in NOx formation with only a moderate increase in soot formation. A detailed analysis of the spray and combustion processes indicated two main fuel consumption regions, one near the piston bowl wall and the other in the main spray near the injector. Fuel consumption in the first region mainly follows the conventional diesel combustion model involving rich premixed burning and diffusion burning, while that in the second region involves premixed combustion. As the SOI is delayed, the spray impingement on the piston bowl wall increases, causing more fuel consumption in the first region, which leads to reduction in NOx but increase in soot formation, indicating a tradeoff between NOx and soot emissions. However, with further delay in the SOI, the amount of fuel consumption in the first region increases significantly, while that in the main spray region involves lean premixed combustion. The net effect is a significant reduction in NOx with only a moderate increase in soot emission. Future studies will focus on the effects of modifying the level of premixing and the ignition delay on diesel engine combustion and emission.

To design a diesel engine adapting to future exhaust gas regulation, it is important to develop a driving mode simulator which can simulate vehicle performance and exhaust emissions including after-treatment system. The combustion model for this objective must be able to simulate heat release rate, variety of emissions necessary for after-treatment simulation, and exhaust gas temperature in very short computational time. The authors have developed a diesel combustion model based on the Hiroyasu model by adding variety of modifications to minimize optimization process of the empirical constants. It was shown that the simulation results with the improvement model were in good agreement with the experimental results. By adding Tsurushima model consisting of nine reaction steps with several intermediate species, the model became available for the both combustions of spray diffusion flame and of homogeneous charge compression ignition.

Flame structure of micro scale methane-air premixed flames is investigated experimentally. The flame is stabilized even on the burner whose diameter is 0.3 mm when it is with pilot flame. However, shape of the flame formed on the burner whose diameter is less than 1 mm is similar to micro diffusion flame. It is supposed that the flame formed on the burner whose diameter is submillimeter is dominated by the diffusion mixing of oxygen and methane from the premixture and heat and radicals from the pilot gas flow.

A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed that converts liquid biofuels, such as biodiesel or ethanol, into a substitute for natural gas. This fuel can then be burned with low emissions in virtually any combustion device in place of natural gas, providing users substantial fuel flexibility. A gas turbine utilizing the LPP combustion technology to burn biofuels creates a “dispatchable” (on-demand) renewable power generator with low criteria pollutant emissions and no net carbon emissions. Natural gas, petroleum based fuel oil #1 and #2, biodiesel and ethanol were tested in an atmospheric pressure test rig using actual gas turbine combustor hardware (designed for natural gas) and achieved natural gas level emissions. Both biodiesel and ethanol achieved natural gas level emissions for NO x , CO, SO x and particulate matter (PM). Extended lean operation was observed for all liquid fuels tested due to the wider lean flammability range for these fuels compared to natural gas. Autoignition of the fuels was controlled by the level of diluent (inerting) gas used in the vaporization process. This technology has successfully demonstrated the clean generation of green, dispatchable, renewable power on a 30kW Capstone C30 microturbine. Emissions on the vaporized derived from bio-ethanol are 3 ppm NO(x) and 18 ppm CO, improving on the baseline natural gas emissions of 3 ppm NO(x), 30 ppm CO. Performance calculations have shown that for a typical combined cycle power plant, one can expect to achieve a two percent (2%) improvement in the overall net plant heat rate when burning liquid fuel as LPP Gas™ as compared to burning the same liquid fuel in traditional spray-flame diffusion combustors. This level of heat rate improvement is quite substantial, and represents an annual fuel savings of over five million dollars for base load operation of a GE Frame 7EA combined cycle plant (126 MW). This technology provides a clean and reliable form of renewable energy using liquid biofuels that can be a primary source for power generation or be a back-up source for non-dispatchable renewable energy sources such as wind and solar. The LPP technology allows for the clean use of biofuels in combustion devices without water injection or the use of post-combustion pollution control equipment and can easily be incorporated into both new and existing gas turbine power plants. No changes are required to the DLE gas turbine combustor hardware.

A thermal gradients’ field was studied for an as cast massive roll. Three ranges within the thermal gradients field were differentiated. The thermal gradient is constant along with the second range of thermal gradients’ field. Thus, columnar into equiaxed structure transition (CET) is to be expected within the second range. This statement is in good qualitative agreement with a similar observation given by Hunt’s theory. The columnar structure formation was significantly slowed down within the second range of thermal gradients field. At beginning of the second range the liquidus isotherm tears away from columnar structure / liquid interface. The columnar structure is still formed within the time adequate to the second range of thermal gradients but its growth vanishes due to lost competition, and at the end of the second range the equiaxed structure growth dominates, exclusively. In fact, the extrapolation of the velocity of the columnar structure / liquid interface to its value equal with zero confirms the appropriate location of the end of the second range within which the CET is observed. The detailed analysis of the solidus isotherm / liquidus isotherm movements allows a development of the Space-Time-Structure Map for a solidifying massive roll. The Map shows the location of the CET in time (solidification time) and in space (along the roll radius). Moreover a proper locations of structural zones are drawn in the Map. The simulation of the thermal gradients’ field is a very useful tool in the industrial practice. The results of simulation can be used to predict the Space-Time-Structure Map (STSM) for a given massive roll or a massive ingot. Additionally, the equation for solute redistribution after back-diffusion was formulated on the basis of the new theory for microsegregation. It allows formulating the so-called macrosegregation index dealing with the whole ingot/roll volume.

The initial cavitation model, originally reported in 2000, has been successfully implemented within several CFD codes (CFD-ACE+, Fluent, ...) and applied throughout a variety of industrial applications. The objective of this study was to extend this model into cryogenic fluids and demonstrate its capability to simulate cryogenic propellant fed turbo pumps associated with liquid rocket engines. In the modeling approach described here the energy equation was modified to include the phase change effects due to cavitation. This necessitated variable physical properties, including vapor pressure, liquid density, vapor density, thermal conductivity, specific heat, fluid viscosity, surface tension, and evaporation heat for the cryogenic fluids. These properties were extracted from NIST tables which were implemented into the CFD-ACE+ computer code. Customized solution algorithm treatments were necessary to ensure robust numerical convergence as a result of the large variations in vapor pressure with respect to temperature typically present in cryogenic fluid pumping and diffusion phenomena. The Hord’s experiment was chosen for the validation as a result of its complete and comprehensive measurement set availability in the open literature. The calculated pressure and temperature profiles along a hydro foil, at different flow conditions for both nitrogen and hydrogen fluids, were compared with experimental measurements. Without any modification to the empirical constants, originally calibrated with water, the predicted results matched remarkably well with the experimental data. This effort has established a new standard compared to previous predictions for liquid nitrogen. For liquid hydrogen flows a significant improvement in the temperature recovery region compared to previous predictions is described and provides for an excellent baseline effort to improve upon.

Open-cell metal foams are of interest for a variety of thermal engineering applications because of their high surface-to-volume ratio and high convective heat transfer coefficients relative to conventional fins. The tortuous flow path through the foam promotes rapid transverse mixing, a fact that is important in heat exchanger applications. Transverse mixing acts to spread heat away from a heated surface, bringing cooler fluid to the foam elements that are in direct contact with the surface. Heat is also spread by conduction in the foam ligaments. The present work addresses fully-coupled thermal dispersion in a metal foam. Dispersion of the thermal wake of a line source was measured. A conjugate heat transfer model was developed which showed good agreement with the data. The validated model was used to examine the complementary effects of the mechanical dispersion, molecular diffusion in the gas, and conduction in the solid.

The numerical diffusion of the discretization of the convection term is investigated. The quantitative evaluation method for the numerical diffusion is proposed. The method evaluates the influence of the numerical diffusion to the shape and the thickness of the free surface by the rate of dullness and blur, respectively. High-order schemes are compared with each other using the proposed method in a two-dimensional simple flow and a two-dimensional collapsing water column. As a result, Chakravarthy-Osher (CO) method and Compressive Interface Capture Scheme for Arbitrary Meshes (CICSAM) are more accurate than other schemes in a two-dimensional simple flow. In the collapsing water column, CICSAM is more accurate than CO. CICSAM with the anti-diffusion operation is lower than CICSAM in the rate of dullness and blur. It is shown that the proposal quantitative evaluation method is able to quantify the numerical diffusion.

A microgravity environment is essential for studying the phenomenon of thermodiffusion in order to suppress the microscopic flows in the mixture. It is, however, noted that the residual micro accelerations (g-jitters) in the space laboratories is produced by several sources such as crew activities, mechanical systems, thrusters firing, spacecraft docking, etc. Such external forces lead to significant flows which can induce convection that may affect the accuracy of the experiment. Consequently, an appropriate interpretation of the space experimental results relies on theoretical and numerical studies of the g-jitter effect on the temperature and the concentration fields. In this paper, we have modeled the thermodiffusion experiment subjected to different levels of vibration when the steady gravity is assumed zero. A rectangular cavity that is subjected to a thermal gradient is filled with a binary mixture (water and isopropanol) and put under the influence of different levels of vibrations. The thermal gradient is applied perpendicular to the vibration. All physical properties including density, mass diffusion and thermodiffusion coefficients are assumed variable as function of temperature and concentration using PC-SAFT equation of state. It is found that using variable physical properties including density and diffusion coefficients make the results more realistic in comparison with the constant model especially in cases with higher Rayleigh vibrations.

Textiles maintain wearer comfort by allowing evaporated sweat to permeate through, providing thermal management and keeping skin dry. Each textile layer presents a resistance to mass transport consistent with its physical structure (i.e., thickness, porosity, and tortuosity). However, when textiles are layered, water vapor transport becomes more complex because diffusing molecules must traverse interstitial spaces between layers. Interstitial mass transport resistances of significant magnitude can reduce rates of water vapor transport through layered textile stacks. The prevailing textile mass transport resistance interrogation method is ASTM F1868: “Standard Test Method for Thermal and Evaporative Resistance of Clothing Materials Using a Sweating Hot Plate.” A self-calibrating element of this method is to measure one, two, three, and four fabric layers. Each newly added layer is prescribed to increase the stack mass transport resistance by the integer resistance presented by a single layer with no interstitial resistance consideration. Four improvements to ASTM F1868 are recommended: 1) gravimetric mass transport measurement, 2) a Stefan flow model, 3) correct accounting for apparatus mass transport resistances, and 4) recognizing and measuring interstitial mass transport resistances. These improvements were implemented and evaluated by running tests using Southern Mills Defender™ 750 fabric, the calibration standard used for ASTM F1868, on a new gravimetric experimental apparatus. The mass transport resistance of one fabric layer measured via the gravimetric method is related to the ASTM F1868 value through working fluid properties. Using the gravimetric approach, mass transport resistance for a single layer of calibration fabric was measured at 60.3 ± 14.4 s/m, which is consistent with the prescribed result from ASTM F1868 (after the conversion factor), 73.1 ± 7.3 s/m. The diffusion coefficient for water vapor in air in the fabric pores measured by gravimetric experiment, (2.02 ± 0.59) × 10 −5 m 2 /s, agrees (within experimental uncertainty) with the theoretical value for the experimental conditions, 2.54 × 10 −5 m 2 /s. However, for stacks of two or more calibration fabric layers, the gravimetric approach does not agree with the prescribed ASTM F1868 result due to interstitial mass transport resistance between fabric layers. The measured interstitial resistance value is 23.6 s/m, 39.1% of a single fabric layer, a value too significant to be ignored in engineering analysis.

Flow patterns and mixing phenomena are investigated qualitatively in a planar passive scaled-up micromixer using flow visualization over 5 ≤ Re ≤ 200. To promote molecular diffusion, the test section utilizes an uneven interdigital inlet which reduces the diffusion path and enhances mixing at the side walls. Five circular sector obstructions located along the channel length serve to divide and recombine the flow, as well as induce Dean vortex formation at high Reynolds numbers. Induced fluorescence is used to provide a quantitative estimate of mixing efficiency at certain Reynolds numbers. A decreasing-increasing trend in mixing efficiency is observed with increasing Reynolds numbers, marking the transition from mass diffusion dominance to mass advection dominance. The design operates well at higher Reynolds numbers, where the dominant mixing mechanism is mass advection.