Transport in a Methanol Steam Reformer as the Fuel Processor for Fuel Cell Systems

An experimental and analytical study of the reacting flow in a catalytic reactor is presented. Methanol-steam reforming may be utilized in the fuel processing system for hydrogen fuel cells. Understanding the flow and transport phenomena as well as the reaction mechanisms is essential for improving the efficiency of the reforming process as well as the quality of the processed fuel. Utilizing the results obtained, optimized conditions for fuel processing are discussed.

Parallelization of the Lattice Boltzmann Method in Simulating Buoyancy-Driven Convection Heat Transfer

The main objective of the current work is to utilize Lattice Boltzmann Method (LBM) for simulating buoyancy-driven flow considering the hybrid thermal lattice Boltzmann equation (HTLBE). After deriving the required formulations, they are validated against a wide range of Rayleigh numbers in buoyancy-driven square cavity problem. The performance of the method is investigated on parallel machines using Message Passing Interface (MPI) library and implementing domain decomposition technique to solve problems with large order of computations. The achieved results show that the code is highly efficient to solve large scale problems with excellent speedup.

Optimal Integration of a Microturbine-Absorption Chiller Cooling, Heating and Power System for Highest Overall CHP System Value

System level integration of an electrical power generating prime mover with a waste heat recovery thermally activated cooling technology is analyzed. Component and system level metrics for quantifying efficiency, performance and value are defined. Trades between component level metrics and system level metrics are performed and optimal integrated cooling, heating and power configuration characteristics and value sensitivity to integration parameters are quantified. Methods developed are extensible to other integrated prime mover and thermally activated technology system approaches.

Permeability and Effective Pore Radius Measurements for Heat Pipe and Fuel Cell Applications

Permeability and effective pore radius of sintered metal powder and carbon paper samples, with specific application to fuel cells and heat pipes, were measured using the rate-of-rise test. The performance of wicks in heat pipes is characterized by effective pore radius and permeability, while the permeability measurement by itself is useful for modeling in-plane phenomena of gas diffusion layers in fuel cells. The rate-of-rise measurement technique is characterized by its simplicity and non-intrusiveness, but previous results have been considered inaccurate. In this study the amount of liquid in the samples was measured by sight for some samples but also by weight change for other samples, which is a new adaptation of the rate-of-rise test. Data is analyzed using an equation resulting from a simple model of the rising meniscus. Knowing the behavior of the equation is important when reducing data in order to obtain more accurate results. The methods used in experimentation and data reduction demonstrate the wider use and increased accuracy of the rate-of-rise test.

Optical and Heat Transfer Characteristics in a Rapid Thermal Annealing System for LCD Manufacturing Procedures

The objectives of this article are to suggest a way to evaluate the quality of polycrystalline silicon film from the thin film optics analysis and also to investigate the heat transfer characteristics in a rapid thermal annealing system for LCD manufacturing. The characteristic transmission matrix method is used to calculate the transmittance, and the predictions are compared with the experimental data for two different samples. The transient and one-dimensional conductive and radiative heat transfer equations are additionally solved to predict the surface temperatures of thin films. The two-flux method is also used for radiation and the ray-tracing method is utilized to consider the wave interference. As the film thickness increases, the peak transmittance increases and the wavelength for the peak becomes longer due to wave interferences. These characteristics can be used for in-situ and practical estimation of the silicon film quality during the crystallization process. From thermal analysis, it is shown that the selective heating in the multilayer film structure acts as an important mechanism during the annealing of silicon film deposited on the glass.

Evaluation of the Temperature Oscillation Technique to Calculate Thermal Conductivity of Water and Systematic Measurement of the Thermal Conductivity of Aluminum Oxide – Water Nanofluid

A nanofluid is a fluid containing suspended solid particles, with sizes of the order of nanometers. The nanofluids are better conductors of heat than the base fluid itself. Therefore it is of interest to measure the effective thermal conductivity of such a nanofluid. We use temperature oscillation technique to measure the thermal conductivity of the nanofluid. However, first we evaluate the temperature oscillation technique as a tool to measure thermal conductivity of water. Then we validate our experimental setup by measuring the thermal conductivity of the aluminum oxide-water nanofluid and comparing our results with previously published work. Finally, we do a systematic series of measurements of the thermal conductivities of aluminum oxide-water nanofluids at various temperatures and explain the reasons behind the dependence of the enhancement in thermal conductivity of the nanofluid on temperature.

The Effect of Gravity on Heat Transfer by Rayleigh Streaming in Pulse Tubes and Thermal Buffer Tubes

Thermoacoustic engines and refrigerators use the interaction between heat and sound to produce acoustic energy or to transport thermal energy. Heat leaks in thermal buffer tubes and pulse tubes, components in thermoacoustic devices that separate heat exchangers at different temperatures, reduce the efficiency of these systems. At high acoustic amplitudes, Rayleigh mass streaming can become the dominat means for undesirable heat leak. Gravity affects the streaming flow patterns and influences streaming-induced heat convection. A simplified analytical model is constructed that shows gravity can reduce the streaming heat leak dramatically.

Spectral Radiative Heat Transfer Analysis of the Planar SOFC

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict the temperature fields within the stack, especially near the interfaces. Because of elevated operating temperatures (of the order of 1000 K or even higher), radiation heat transfer could become a dominant mode of heat transfer in the SOFCs. In this study, we extend our recent work on radiative effects in solid oxide fuel cells (Journal of Power Sources, Vol. 124, No. 2, pp. 453–458) by accounting for the spectral dependence of the radiative properties of the electrolyte material. The measurements of spectral radiative properties of the polycrystalline yttria-stabilized zirconia (YSZ) electrolyte we performed indicate that an optically thin approximation can be used for treatment of radiative heat transfer. To this end, the Schuster-Schwartzchild two-flux approximation is used to solve the radiative transfer equation (RTE) for the spectral radiative heat flux, which is then integrated over the entire spectrum using an N-band approximation to obtain the total heat flux due to thermal radiation. The divergence of the total radiative heat flux is then incorporated as a heat sink into a 3-D thermo-fluid model of a SOFC through the user-defined function utility in the commercial FLUENT CFD software. The results of sample calculations are reported and compared against the baseline cases when no radiation effects are included and when the spectrally gray approximation is used for treatment of radiative heat transfer.

Performance Prediction of a Novel Design for Turbine Vane Film Cooling With Low Aerodynamic Loss and High Effectiveness

A new film-cooling scheme for the suction surface of a gas turbine vane in a transonic cascade is studied numerically. The concept of the present design is to inject a substantial amount of coolant at a very small angle, approaching a “wall-jet,” through a single row of relatively few, large holes near the vane leading edge. The near-match of the coolant stream and mainstream momentums, coupled with the low coolant trajectory, theoretically results in low aerodynamic losses due to mixing. A minimal effect of the film cooling on the vane loading is also important to realize, as well as good coolant coverage and high adiabatic effectiveness. A systematic computational methodology, developed in the Advanced Computational Research Laboratory (ACRL) and tested numerous times on film-cooling applications, is applied in the present work. For validation purposes, predictions from two previous turbine airfoil film-cooling studies, both employing this same numerical method, are presented and compared to experimental data. Simulations of the new film-cooling configuration are performed for two blowing ratios, M=0.90 and M=1.04, and the density ratio of the coolant to the mainstream flow is unity in both cases. A solid vane with no film cooling is also studied as a reference case in the evaluation of losses. The unstructured numerical mesh contains about 5.5 million finite-volumes, after solution-based adaption. Grid resolution is such that the full boundary layer and all passage shocks are resolved. The Renormalization Group (RNG) k-ε turbulence model is used to close the Reynolds-averaged Navier-Stokes equations. Predictions indicate that the new film-cooling scheme meets design intent and has negligible impact on the total pressure losses through the vane cascade. Additionally, excellent coolant coverage is observed all the way to the trailing edge, resulting in high far-field effectiveness. Keeping the design environment in mind, this work represents the power of validated computational methods to provide a rapid and reasonably cost-effective analysis of innovative turbine airfoil cooling.

Experimental and Analytical Investigation of Compact Liquid Cooled Heat Sinks

Compact, liquid cooled heat sinks are used in applications where high heat fluxes and boundary resistance preclude the use of more traditional air cooling techniques. Four different liquid cooled heat sink designs, whose core geometry is formed by overlapped ribbed plates, are examined. The objective of this analysis is to develop models that can be used as design tools for the prediction of overall heat transfer and pressure drop of heat sinks. Models are validated for Reynolds numbers between 300 and 5000 using experimental tests. The agreement between the experiments and the models ranges from 2.35% to 15.3% RMS.