Advanced Exergoeconomic Analysis of a Refrigeration Machine: Part 2—Improvement

In the first part of the paper, the advanced exergy-based analyses are applied to an air refrigeration machine. In this part, we demonstrate that the information obtained in the first part can be used to modify the values of the decision variables to reduce the cost of the final product (cold) of the overall system.

Influence of Vegetation Moisture on Combustion of Pyrolysis Gases in Wildland Fires

Since wildland fires occur in living vegetation, the fuel moisture content must be considered in order to correctly predict the behavior of the fire. One facet of combustion of pyrolysis gases that has not been considered in previous research is the effect of moisture on the combustion process. This effect is investigated by using CHEMKIN software to study an opposed diffusion flame model for three pyrolysis fuels relevant to wildfires. The effect of moisture on flame structure is investigated by varying the mole fraction of water vapor in the fuels, with air as oxidizer. In all cases, the flame extinguishes when the water mole fraction is between 0.55 and 0.65. O2 and H are the only components that exhibit a significant change in concentration under these conditions.

Thermal Properties of Nanotubes and Nanowires With Acoustically Stiffened Surfaces

A core-shell elasticity model is employed to investigate the effect of a nanowire and nanotube’s increased surface moduli on specific heat, ballistic thermal conductance, and thermal conductivity as a function of temperature. Phonon confinement is analyzed using approximated phonon dispersion relations that result from solutions to the frequency equation of a vibrating rod and tube. The results indicate a maximum 10% decrease in lattice thermal conductivity and ballistic thermal conductance near 160 K for a 10 nm outer diameter nanotube with an inner diameter of 5 nm when the average Young’s Modulus of both the inner and outer free surfaces is increased by a factor of 1.53. In the presence of the acoustically stiffened surfaces, the specific heat of the nanotube is found to decrease by up to 20% at 160 K. Near room temperature, changes in thermal properties are less severe. In contrast, a 10 nm outer diameter nanowire composed of similar material exhibits up to a 12% maximum increase in thermal conductivity at 600 K, a 25% increase in ballistic thermal conductance at 400 K, and a 48% increase in specific heat at 470 K when its outer free surface is acoustically stiffened to the same degree. Our simplified model may be extended to investigate the acoustic tuning of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization and coatings.

The Survival Spectrum: The Key to Transition Engineering of Complex Systems

This paper puts forward a simple idea describing the time, space and relationship scales of survival. The proposed survival spectrum concept represents a new way to think about sustainability that has clear implications for influencing engineering projects in all fields. The argument for the survival spectrum is developed sequentially, building on theory, definition, examples and history. The key idea is that sustainability can be effectively addressed by emergence of a new field, Transition Engineering. This is a parallel of safety engineering but with longer time scale, broader space scale, and more complex relationship scale. The past 100-year development of safety engineering is examined as a model for development of sustainability risk management and mitigation. The conclusion is that the new field, Transition Engineering, will emerge as the way our society will realize reduction in fossil fuel use and reduction in the detrimental social and environmental impacts of industrialization.

Performance Assessment of Single Electrode-Supported Solid Oxide Cells Operating in the Steam Electrolysis Mode

An experimental study has been conducted to assess the performance of electrode-supported solid-oxide cells operating in the steam electrolysis mode for hydrogen production. Results presented in this paper were obtained from single cells, with an active area of 16 cm2 per cell. The electrolysis cells are electrode-supported, with yttria-stabilized zirconia (YSZ) electrolytes (∼10 μm thick), nickel-YSZ steam/hydrogen electrodes (∼1400 μm thick), and modified LSM or LSCF air-side electrodes (∼90 μm thick). The purpose of the present study is to document and compare the performance and degradation rates of these cells in the fuel cell mode and in the electrolysis mode under various operating conditions. Initial performance was documented through a series of voltage-current (VI) sweeps and AC impedance spectroscopy measurements. Degradation was determined through long-term testing, first in the fuel cell mode, then in the electrolysis mode. Results generally indicate accelerated degradation rates in the electrolysis mode compared to the fuel cell mode, possibly due to electrode delamination. The paper also includes details of an improved single-cell test apparatus developed specifically for these experiments.

Macro-System Model for Hydrogen Energy Systems Analysis in Transportation

The introduction of hydrogen as an energy carrier for light-duty vehicles involves concomitant technological development of an array of infrastructure elements, such as production, delivery, and dispensing, all associated with energy consumption and emission levels. To analyze these at a system level, the suite of corresponding models developed by the United States Department of Energy and involving several national laboratories is combined in one macro-system model (MSM). The MSM uses a federated simulation framework for consistent data transfer between the component models. The framework is built to suit cross-model as well as cross-platform data exchange and involves features of “over-the-net” computation. While the MSM can address numerous hydrogen systems analysis aspects, of particular interest is the optimal deployment scenario. Depending on user-defined geographic location and hydrogen demand curve parameters, the cost-optimal succession of production/delivery/dispensing pathways undergo significant changes (the most important of these being the transition between distributed and central H2 production with delivery). Some ‘tipping’ (break-even) points are identified.

The Research of Energy Conversion and Heat Transfer in the Ceramic Foams of Solar Energy Converter

The solar energy converter in Concentrated Solar Power (CSP) system, applies the solid frame structure of the ceramic foams to receive the concentrated solar radiation, convert it into thermal energy, and heat the air flow through the ceramic foams by convection heat transfer. In this paper, first, the pressure drops in the studied ceramic foams were measured under all kinds of flow condition. Based on the experimental results, an empirical numerical model was built for the air flow through ceramic foams. Second, a 3-D numerical model was built, for the receiving and conversion of the solar energy in the ceramic foams of the solar energy converter. Third, applying two aforementioned numerical models, the numerical studies of the thermal performance were carried out, for the solar energy converter filled with the ceramic foams, and results show that the structure parameters of the ceramic foams, the effective reflective area and the solar radiation intensity of the solar concentrator, have direct impacts on the absorptivity and conversion efficiency of the solar energy in the solar energy converter. And the results of the numerical studies are found to be in reasonable agreement with the experimental measurements. This paper will provide a reference for the design and manufacture of the solar energy converter with the ceramic foams.

Performance Investigation of a Four Stroke Diesel Engine, Using Water-Based Ferrofluid as an Additive

In this experimental study, a four stroke diesel engine was conducted to investigate the effect of adding water-based ferrofluid to diesel fuel on engine performance. To our knowledge, Magnetic nanoparticles had not been used before. To this end, emulsified diesel fuels of 0, 0.4, and 0.8 water-based ferrofluid/Diesel ratios by volume were used as fuel. The ferrofluid used in this study was a handmade water-based ferrofluid prepared by the authors. The results show that adding water-based ferrofluid to diesel fuel has a perceptible effect on engine performance, increasing the brake thermal efficiency relatively up to 12%, and decreasing the brake specific fuel consumption relatively up to 11% as compared to diesel fuel. In addition, the results indicate that increasing ferrofluid concentration will magnify the results. Furthermore, it was found that magnetic nanoparticles can be collected at the engine exhaust using magnetic bar.

Renewable Hydrogen Production Using Sailing Ships

Vast ocean areas of planet Earth are exposed year-round to strong wind currents. We suggest that this untapped ocean wind power be exploited by the use of sailing ships. The availability of constantly updated meteorological information makes it possible to operate the ships in ocean areas with optimum wind power so that the propulsive ship power can be converted into electric power by means of ship-mounted hydro-power generators. Their electric power output then is fed into ship-mounted electrolyzers to convert sea water into hydrogen and oxygen. In this paper we estimate the ship size, sail area and generator size to produce a 1.5 MW electrical power output. We describe a new oscillating-wing hydro-power generator and present results of model tests obtained in a towing tank. Navier-Stokes computations are presented to provide an estimate of the power extraction efficiency and drag coefficient of such a generator which depends on a range of parameters such as foil maximum pitch angles, plunge amplitude, phase between pitch and plunge and load. Also, we present a discussion of the feasibility of sea water electrolysis and of the re-conversion of hydrogen and oxygen into electricity by means of shore-based hydrogen-oxygen power plants.

From Component to Macro Energy Systems: A Common Design and Off-Design Modeling Approach

A common approach for simulation of energy systems at design and off-design conditions is presented, which uses the same concepts and terminology independently of system dimension, complexity and detail. The paper shows that the higher the dimension of the system, the simpler is the model of each part of the system, but concepts and approach to built the model remain the same, being those commonly used in the literature. The approach consists in organizing energy systems models according to some criteria, which help enhance system models comprehension, and build them more easily. For any dimension and level of detail of the system these criteria consist in identifying the design specification from the environment surrounding the system, choosing the independent variables depending on the nature of the model, organizing them into categories, defining performance curves (characteristic maps) of each part of the system and organizing mass and energy balances into categories. Particular emphasis is given on modeling of system units behavior, which is generally described by the mathematical functions (characteristic maps) linking outflow to inflow variables. Examples of characteristic maps of the system units at each level of detail are shown, and models are then completed by mass, energy and momentum balances linking the behavior of all system units.