Vascularized Materials: Grids of Channels and Trees Matched Canopy to Canopy

This is a fundamental study of how to discover the optimal flow architecture to vascularize a volume so that fluid flow and function (e.g. cooling, sensing, maintenance, repair, healing) reaches every point of the material. The presentation is made by discussing flow architectures that deliver healing fluid to all the crack sites that may occur randomly through the material. Two concepts are explored. In the first, a grid of interconnected channels is built into the material, and is filled with pressurized healing fluid. When a crack forms, the pressure drops at the crack site and fluid flows from the grid into the crack. The objective is to discover the network configuration that is capable of delivering fluid to all the cracks the fastest. It is shown that the optimization of the ratio of channel diameters cuts in half the time of fluid delivery to the crack. In the second concept, one stream flows steadily through the material and bathes it volumetrically. The stream enters through one port, and distributes itself as a river delta through the volume. Later the stream reconstitutes itself as a river basin before exiting the volume through one point. This second concept is equivalent to matching two trees canopy to canopy. It is shown that the choice of tree-tree configuration has a decisive role on the global performance of the vascularized composite.

Detailed Electrochemistry and Gas Transport in a SOFC Anode Using the Lattice Boltzmann Method

A coupled electrochemical reaction and diffusion model has been developed and verified for investigation of mass transport processes in Solid Oxide Fuel Cell (SOFC) anode triple-phase boundary (TPB) regions. The coupled model utilizes a two-dimensional (2D), multi-species Lattice Boltzmann Method (LBM) to model the diffusion process. The electrochemical model is coupled through localized flux boundary conditions and is a function of applied activation overpotential and the localized hydrogen and water mole fractions. This model is designed so that the effects of the anode microstructure within TPB regions can be examined in detail. Results are provided for the independent validation of the electrochemical and diffusion sub-models, as well as for the coupled model. An analysis on a single closed pore is completed and validated with a Fick's law solution. A competition between the electrochemical reaction rate and the rate of mass transfer is observed to be dependent on inlet hydrogen mole fraction. The developed model is presented such that future studies on SOFC anode microstructures can be completed.

Development of a Performance Rating Standard for Residential Fuel Cell Systems

Fuel cell systems for residential applications are an emerging technology for which specific consumer-oriented performance standards are not well defined. This paper presents a proposed experimental procedure and rating methodology for evaluating residential fuel cell systems. In the proposed procedure, residential applications are classified as grid independent load following; grid connected constant power; grid connected thermal load following; and grid connected water heating. An experimental apparatus and procedures for steady state and simulated use tests are described for each type of system. A rating methodology is presented that uses data from these experiments in conjunction with standard residential load profiles to quantify the net effect of a fuel cell system on residential utility use. The experiments and rating procedure are illustrated using data obtained from a currently available grid connected thermally load following system.

Non-Continuum Mass Transport in Solid Oxide Fuel Cell Anodes by the Lattice Boltzmann Method

At the length scales and temperatures present in a typical SOFC, both continuum and non-continuum transport of fuel and product species are important. Fuel and product transport through a representative, microscopic, two-dimensional (2D) channel present in the porous anode of a solid oxide fuel cell (SOFC) is examined. Non-continuum transport, which can be broken down into the slip, transition and free molecular regimes, is modeled for a ternary system (H2, H2O, and N2) using the Stefan-Maxwell (SM) model, the Dusty-Gas (DG) model and the lattice Boltzmann method (LBM). Results obtained show that the LBM can provide a suitable framework for continuum as well as non-continuum transport in a SOFC up to the transition regime. LBM can also handle complex porous geometries, which are currently intractable by other modeling approaches, e.g. SM and DG. However, further work is required to extend the range of application of the present LBM to the free-molecular flow regime.

Role of Indoor Air Distribution in Performance of Heat Pump Systems in Energy-Efficient Residential Buildings

This paper demonstrates the potential impact of indoor air distribution on the energy consumption of central HVAC systems with cognizance of human thermal comfort. The study focuses on a hypothetical high-performance house incorporating a split heat pump system. The air distribution of this building incorporates high sidewall supply-air registers and near-floor, wall-mounted return-air grilles. Heating-mode stratification resulting from this prevalent configuration is a prime example of situations in which challenges regarding energy efficiency, comfort, and ventilation effectiveness emerge. These challenges underline the importance of adopting a comprehensive design strategy for high-performance buildings. Two indoor air distribution scenarios were analyzed: (1) theoretically well mixed and (2) poorly mixed, representing a realistic case. The former scenario was evaluated using an analytical approach, whereas the latter was investigated through computational fluid dynamics (CFD) simulations. For heating mode, the results indicated the presence of a pronounced thermal stratification resulting from poor air mixing. At 50% of the design heating load, for the well-mixed case, the HVAC system energy consumption was significantly higher. Considerably better air distribution performance was observed with cooling mode, in which the relative energy penalty for the well-mixed scenario was noticeably less. In real-world applications where measures must be taken to achieve near perfectly mixed indoor conditions for better comfort, the energy use is expected to be even higher. However, in the absence of such measures, the thermostat setpoint is likely to be readjusted, leading to a higher energy use without necessarily improving the overall comfort level, as demonstrated in this paper. The limitation of increasing the supply-air flow rate to enhance air mixing and diffusion is also discussed in terms of the system moisture removal capability.

Experimental Study of Transient Heat Transfer Process in a Submerged Radial Jet

A transient cooling process using a submerged radial water jet is considered. The experiment set up consists of a submerged radial jet exiting from a nozzle located over a thin plate. The plate is made out of aluminum alloy and it has two discrete heat sources located symmetrically at the opposite side of the impinging surface. The temperature variation in the plate is captured using a data acquisition system. The plate is allowed to reach a stable temperature before the radial jet system is generated. The results obtained present the temperature distribution for the plate and the heat transfer coefficient at the fluid-solid interface, for different nozzle heights and initial plate temperature.

Development of Analysis Algorithm and Computational Methodology for the Evaluation of Non-Uniform Energy Conversion System Performance: Part I — Component Analysis Modules

This paper examines the development of the individual component analysis modules applied to two selected energy conversion systems; a vapor-compression refrigeration system and a boiler heating system. The energy conversion components used in this work are the evaporator, condenser, expansion valve, mixing chamber, open feedwater heater, pipe, boiler, pump, and compressor. The developed component analysis modules are able to apply input data and specifications to estimate the corresponding thermal performance of the component. Upon investigation of the two case studies presented, it was found that the two-phase heat exchanging components such as the evaporator, condenser and boiler were the primary sources of the non-uniform system performance characteristics. As a consequence, a system connectivity matrix has been developed to evaluate the mass and energy flow characteristics of working fluids between components. The developed component analysis modules, in conjunction with the system connectivity matrix, were exclusively used to calculate the local and overall system thermal performance.

Optimization of Working Ground Heat Storage With Seasonal Regeneration

The aim of the research was an optimization of long-term heat storage with seasonal regeneration. Energy consumption for central heating during wintertime, transfererred from ground energy storage using a heat exchange device, is the operating principle of such systems. Warmed working fluid is then used in a heat pump system. However, more accurate calculations showed that over time of usage, there is a trend toward cooling at deeper round layers. Such a situation leads to a lowering of ground potential when using heat pump systems. A possible solution to this problem is the application of summer regeneration: during summer months, the working fluid is firstly warmed in solar collectors, and then forced into the same boreholes. The numerical model of a vertical, ground heat exchange device (configured as a "pipe in pipe", known as a Fields' pipe) was specially developed. Temperature distribution of the working fluid along the pipe was one of the boundary conditions, for the co-axial, time-variable, heat conduction task, which described the heat flow in energy storage. The numerical simulation of solar collectors work was based on the Hottel - Whillier - Bliss equation, in which energy flow from the solar collector is calculated, dependant on external parameters such as: insulation or ambience temperature. The combination of three computational parts- the ground heat exchange device, energy storage area and solar collectors battery- allows the target function to be defined for task optimization. The subject of optimization was an energy quantity, which can be taken from energy underground storage, and then utilized by the heat pump system. In the summarized paper, a combination of the input data, which influenced the efficiency of energy storage, was chosen. Hypothetical data were: outside diameter and length of heat exchange device, distance between pipes, fluid flow through the pipe during charge and discharge processes or temperature of inlet working fluid. The influence of individual parameters on the target function, holding all input data constant, was analyzed. A developed evolutionary numerical code known as GENOCOP I (GEnetic algorithm for Numerical Optimization for COnstrained Problems) [3] was used for optimization. After preliminary correction of boundary values of the input data, nine attempts of optimization were taken up. The research results identified optimal values of input parameters for which maximum energy could be taken from ground storage.

Economic Optimization of a Distributed Generation System for an Orifice Building

Methodologies have been developed to aid in selection of a candidate distributed generation system for use in meeting a building's electrical demand. The systems studied are comprised of a combination of microturbines and/or natural gas reciprocating engines. These systems could also be used as prime movers in a combined heat and power application. Economic optimizations have been performed in order to identify distributed generation/prime mover combinations and operating strategies that yield the lowest electrical generation cost. These optimizations take into account a finite set of operating scenarios and equipment combinations. In addition to the economic optimizations, a direct comparison of customer design considerations has been made, highlighting the advantages and disadvantages of both microturbines and reciprocating engines. In this study, the optimal system for a 9290 m2 (100,000 ft2) office building in New York City at today's natural gas prices was determined to be a combination of natural gas reciprocating engines and microturbines. This system yielded a 5% reduction in generation costs over other cases examined including all homogeneous composition systems. With an increase in natural gas prices, the optimal case changes to be comprised solely of natural gas reciprocating engines. It has been shown that many factors are important to selection of optimal equipment including the specific end use load profile, cost of fuel, and system operating strategy.

Exergy as an Indicator for Resources Scarcity: The Exergy Loss of Australian Mineral Capital — A Case Study

Over the span of the 20th century, the global demand for metals and minerals has increased dramatically. This is associated with a general trend of declining ore grades from most commodities, meaning higher quantities of ore needed to be processed and thus more energy. Hence, quantifying the loss of mineral capital in terms of mass is not enough since it does not take into account the quality of the minerals in the mine. Exergy is a better indicator than mass because it measures at the same time the three features that describe any natural resource: quantity, composition and a particular concentration. For the sake of better understanding the exergy results, they are expressed in tons of Metal equivalent, tMe, which are analogously defined to tons of oil equivalent, toe. The aim of this paper is 1) to show the methodology for obtaining the exergy loss of mineral resources throughout a certain period of time and 2) to apply it to the Australian case. From the available data of production and ore grade trends of Australian mining history, the tons of Metal equivalent lost, the cumulative exergy consumption, the exergy decrease of the economic demonstrated reserves and the estimated years until depletion of the main base-precious metals are provided, namely: for gold, copper nickel, silver lead and zinc.