Development of a Method to Model an Enclosed, Coaxial Carbon Nanotube Speaker with Experimental Validation

Carbon nanotube (CNT) speakers operate on heat as compared to conventional loudspeakers that operate on vibration. CNT speakers are extremely lightweight, stretchable, flexible, and have high operating temperatures. Due to these advantages, CNT speakers are being considered as a viable replacement option for conventional loudspeakers. One such application is automotive exhaust noise control. The goal of this research is to design an enclosed, coaxial CNT speaker and to develop a modeling method to model this speaker using COMSOL Multiphysics. As part of this research, an enclosed, coaxial CNT speaker was designed and manufactured for automotive exhaust noise control. The first prototype was a proof of concept that the design is feasible, and the speaker works. Two additional prototypes have been developed to improve the manufacturing feasibility and performance. The first task undertaken during the modeling method development has been to create COMSOL models that simulated the CNT film temperature oscillation and the corresponding SPL. The simulation results have been compared with a MATLAB model for a planar CNT speaker. In addition, the SPL generated by the coaxial speaker has been compared with the simulated SPL generated by the CNT speaker. In addition, the performance of the coaxial speaker has been simulated in the presence of flow. Generally, a good correlation has been observed between the experimental SPL and simulated SPL. The models can be improved with the future development of improved material properties

Numerical simulation and experimental validation of vapor compression refrigerating systems: special emphasis on natural refrigerants

The aim of this work is to study the thermal and fluid-dynamic behavior of vapor compression refrigerating systems and their constitutive elements (heat exchangers, expansion devices, compressors and connecting tubes) focused on the use of natural refrigerants (carbon dioxide, isobutane and ammonia). The specific topics analyzed throughout this thesis have arisen from the growing interest in environmentally friendly refrigerants that has led the CTTC group (Centro Tecnológico de Transferencia de Calor) to undertake significant research efforts and to take part in several projects with national and European institutions. The information reported herein represents a summary of the work carried out by the author during the last years together with the contributions provided by other members of the CTTC group. This thesis has led to the creation of some publications in International Conferences and indexed journals. The main achievement of this work has been the development of a flexible numerical tool based on several subroutines. The whole numerical infrastructure is the result of coupling the specific resolution procedures for each vapor compression refrigerating system component together with the whole system resolution algorithm. The simulations have been oriented to study the system thermodynamical characteristics as well as some relevant aspects of its particular elements. In addition to the numerical results a significant experimental work has also been carried out in the CTTC facilities due to the need for experimental validation. The author has been fully involved in data acquisition procedures and has also collaborated in the setting up of the experimental units. In general, all the studies conducted in this work have been presented following the same structure: i) numerical model and resolution procedure explanation; ii) model validation against experimental data; and iii) simulation results. The specific topics tackled within this thesis include the implementation of a two-phase numerical model to simulate the thermal and fluid-dynamic behavior of single- and two-phase flows inside ducts, the study of heat transfer coefficient empirical correlations for both cooling of carbon dioxide at transcritical conditions and evaporation of ammonia at overfeed conditions, the implementation of a numerical model to simulate capillary tubes in order to study their behavior at typical operational conditions found in household refrigerators working with isobutane, the development of a two-phase flow distribution model to simulate heat exchangers made up by manifold systems, and the study of vapor compression refrigeration cycles with special emphasis on carbon dioxide transcritical situations. The set of the numerical models implemented has demonstrated to be a flexible tool as several different aspects of refrigeration vapor compression systems have been successfully simulated and study. It has also demonstrated to be an accurate tool as the numerical results achieved have shown good agreement against experimental dataThe aim of this work is to study the thermal and fluid-dynamic behavior of vapor compression refrigerating systems and their constitutive elements (heat exchangers, expansion devices, compressors and connecting tubes) focused on the use of natural refrigerants (carbon dioxide, isobutane and ammonia). The specific topics analyzed throughout this thesis have arisen from the growing interest in environmentally friendly refrigerants that has led the CTTC group (Centro Tecnológico de Transferencia de Calor) to undertake significant research efforts and to take part in several projects with national and European institutions. The information reported herein represents a summary of the work carried out by the author during the last years together with the contributions provided by other members of the CTTC group. This thesis has led to the creation of some publications in International Conferences and indexed journals. The main achievement of this work has been the development of a flexible numerical tool based on several subroutines. The whole numerical infrastructure is the result of coupling the specific resolution procedures for each vapor compression refrigerating system component together with the whole system resolution algorithm. The simulations have been oriented to study the system thermodynamical characteristics as well as some relevant aspects of its particular elements. In addition to the numerical results a significant experimental work has also been carried out in the CTTC facilities due to the need for experimental validation. The author has been fully involved in data acquisition procedures and has also collaborated in the setting up of the experimental units. In general, all the studies conducted in this work have been presented following the same structure: i) numerical model and resolution procedure explanation; ii) model validation against experimental data; and iii) simulation results. The specific topics tackled within this thesis include the implementation of a two-phase numerical model to simulate the thermal and fluid-dynamic behavior of single- and two-phase flows inside ducts, the study of heat transfer coefficient empirical correlations for both cooling of carbon dioxide at transcritical conditions and evaporation of ammonia at overfeed conditions, the implementation of a numerical model to simulate capillary tubes in order to study their behavior at typical operational conditions found in household refrigerators working with isobutane, the development of a two-phase flow distribution model to simulate heat exchangers made up by manifold systems, and the study of vapor compression refrigeration cycles with special emphasis on carbon dioxide transcritical situations. The set of the numerical models implemented has demonstrated to be a flexible tool as several different aspects of refrigeration vapor compression systems have been successfully simulated and study. It has also demonstrated to be an accurate tool as the numerical results achieved have shown good agreement against experimental dat

Thermal Modeling and Imaging of As-built Automotive Parts

Simulation is of significant importance in the automotive industry and can be done for various applications ranging from fluid flow analysis to complex thermal management of components. This thesis describes the method and necessary requirements for thermal modeling of automotive parts. Simulation of under hood and under vehicle automotive poses several challenges, the shape and complexity of the geometry used being the first and foremost to be considered. This thesis addresses the simulation of thermal images of as-built automotive parts using the 3D meshes generated from 3D modeling tools, CAD meshes and reverse engineered meshes. Thermal modeling requires complete knowledge about the under hood and under vehicle automotive components. Many factors, both inside and outside the vehicle, affect the heat flow pattern of the vehicle under consideration. Thermal image sequences of under vehicle chassis were acquired to understand the thermal heat pattern and to serve as a basis for simulation. It was inferred that the exhaust system is the system with significant change in temperature and is at temperature close to 450 degree Celsius when the engine is operating at its full capacity. The exhaust system components, namely the catalytic converter, muffler and the exhaust pipes, were considered as the significant components for thermal modeling. The temperature curves of those components were measured with the help of an infrared thermometer to enhance the results of simulation. Application of thermal imaging in the field of threat detection is also addressed in this thesis. Simulation or thermal modeling of the automotive components was done using the software MuSES. The thermal properties and the boundary conditions were assigned to the 3D geometry used and the transient solution was carried out over a period of time. The results for the three types of meshes mentioned earlier are presented and the thermal predictions are analyzed. As-built models can be modeled as they are with the help of reverse engineering, and the temperature predictions of those components provide better simulation results close to reality. The thesis also addresses the idea of comparison between simulation results and real time experimental results

Acoustics and Noise Control in Space Crew Compartments

This book discusses the acoustics and noise control in spacecraft crew compartments, using experience and lessons learned from the Apollo, Orbiter, and ISS Programs

Updating the Lambda modes of a nuclear power reactor

[EN] Starting from a steady state configuration of a nuclear power reactor some situations arise in which the reactor configuration is perturbed. The Lambda modes are eigenfunctions associated with a given configuration of the reactor, which have successfully been used to describe unstable events in BWRs. To compute several eigenvalues and its corresponding eigenfunctions for a nuclear reactor is quite expensive from the computational point of view. Krylov subspace methods are efficient methods to compute the dominant Lambda modes associated with a given configuration of the reactor, but if the Lambda modes have to be computed for different perturbed configurations of the reactor more efficient methods can be used. In this paper, different methods for the updating Lambda modes problem will be proposed and compared by computing the dominant Lambda modes of different configurations associated with a Boron injection transient in a typical BWR reactor. (C) 2010 Elsevier Ltd. All rights reserved.This work has been partially supported by the Spanish Ministerio de Educacion y Ciencia under projects ENE2008-02669 and MTM2007-64477-AR07, the Generalitat Valenciana under project ACOMP/2009/058, and the Universidad Politecnica de Valencia under project PAID-05-09-4285.González Pintor, S.; Ginestar Peiro, D.; Verdú Martín, GJ. (2011). Updating the Lambda modes of a nuclear power reactor. Mathematical and Computer Modelling. 54(7):1796-1801. https://doi.org/10.1016/j.mcm.2010.12.013S1796180154

Waste heat recovery with Organic Rankine Cycle (ORC) in marine and commercial vehicles Diesel engine applications

Heavy and medium duty Diesel engines, for marine and commercial vehicles applications, reject more than 50-60% of the fuel energy in the form of heat, which does not contribute in terms of useful propulsion effect. Moreover, the increased attention towards the reduction of polluting emissions and fuel consumption is pushing engine manufacturers and fleet owners in the direction of increasing the overall powertrain efficiency, still considering acceptable investment and operational costs. For these reasons, waste heat recovery systems, such as Organic Rankine Cycles (ORC), are undergoing a period of intense research and development. However, in most of engine waste heat recovery studies in literature, the engine side analysis is not considered in a detailed way, even though the engine architecture and the operational behaviour strongly influence the availability of heat sources, and their characteristics, to be recovered using heat recovery systems. As an example, the use of emission reduction strategies, such as Exhaust Gas Recirculation (EGR), can introduce an additional heat source and modify the temperatures in the engine gas lines, thus leading to new possible scenarios for the exploitation of the engine wasted heat. The scope of this work is to introduce a combined engine-waste heat recovery system analysis and design methodology, which could go beyond the traditional development approach, considering both the engine and the ORC system as a synergic and integrated powertrain. For this reason, industry-standard engine gas dynamics simulation software and thermodynamic process simulation techniques have been used and developed in order to study the combined effects and performance of engine-ORC systems in the commercial vehicle and marine sectors, addressing at the same time several development issues, such as: working fluid and layout choice, powertrain thermal management, energy utilization, turbocharging and emission reduction strategies, in the direction of a co-simulation approach, which is one of the industry\u2019s main interests, to reduce development time and costs. After a detailed literature review and modelling approach explanation, four different case studies have been proposed, to show an increasing level of integration between engine and ORC system analysis, addressing also applications which are not commonly considered in literature, such as off-highway vehicles and two-stroke ships propulsion units. The combination of energy, exergy and economic analysis, allows the developer to deeply understand the thermodynamics of the combined engine-ORC systems, addressing all the energy and exergy streams available for heat recovery, highlighting the main sources of inefficiencies in the powertrain, and proposing improvements to increase the overall system efficiency at acceptable investment and operational costs. The methodology can be, in principle and with further developments, applied to any kind of engine-waste heat recovery system powertrain. Moreover, the combined use of emission reduction strategies and new technologies, such as EGR and ORC, can allow to develop clean, but at the same time efficient, propulsion units. However, while for commercial vehicles the recovery of high temperature exhaust gas and EGR heat is more beneficial in terms of compromise between performance, system costs and packaging issues, in the case of large ship propulsion units, the recovery of lower temperature heat sources, such as coolant and scavenge air, could become very interesting for future developments, because of the high amount of heat available, even if at lower temperature levels, suitable for the use of an ORC technology. The results of the proposed case studies show a fuel consumption reduction up to around 5-10% when adopting ORC systems, depending on the application, type of engine, overall system architecture and design point chosen, showing the potential of the technology in the considered sectors

Advanced Technologies for the Optimization of Internal Combustion Engines

This Special Issue puts together recent findings in advanced technologies for the optimization of internal combustion engines in order to help the scientific community address the efforts towards the development of higher-power engines with lower fuel consumption and pollutant emissions