Development of a mN level Meso-Scale Thruster

This dissertation focuses on the practical application of heat recirculating combustors as thrust chambers for micro-spacecraft systems, including: design, development, stability and operational characteristics of the thruster in both the steady state and pulsed configurations. Stable combustion was realized with partially premixed methanol/steam/oxygen, non-premixed methanol/steam/oxygen, and nonpremixed kerosene/steam/oxygen. The steam oxygen mixture is a surrogate for the decomposition products of hydrogen peroxide. The effect of channel geometry on the stability and thermal performance has also been conducted in addition to qualitative and quantitative comparisons of fuel/oxidizer injection configurations. In general it was found that non-premixed combustion is favorable in terms of both thermal performance and flame stability due to the predictable extinction characteristics at low flow rates and the absence of lean blow off at high flow rates. A quantitative extinction criterion was developed to predict extinction at the rich extinction limit. Additionally, nozzle discharge characteristics at low Reynolds number were studied and a correlation developed to predict the discharge coefficient from the Reynolds number for both cold and hot flow scenarios. It was found the discharge coefficient decays more rapidly for high temperature flows than low temperature flows due to the effects of temperature and viscosity on the boundary layer displacement thickness. Additionally, a milli-Newton level thrust stand was developed to indirectly measure the thrust level without allowing the thruster to translate, the thrust stand resolution was found to be <1mN. Using this device a study of the thrust characteristics was carried out in both the steady state and pulsed modes. Measurements of the specific impulse efficiency indicate that the conversion efficiency is high and any loss in thermal efficiency from the adiabatic scenario is due to wall heat losses and not incomplete combustion. Experiments conducted with hydrogen peroxide decomposed in the inlet channel of the combustor were used to validate the results taken with the steam/oxygen as the oxidizer and demonstrated that heat recirculation from the products to the exhaust is sufficient to promote efficient decomposition of the hydrogen peroxide

Thin-film calorimetric gas sensors for hydrogen peroxide monitoring in aseptic food processes

The sterilisation of the packaging material is the essential step in aseptic food processes to ensure safely packed products, which are microbiologically stable throughout their shelf life. Today, gaseous hydrogen peroxide (H2O2) in the range of several volume percent and at elevated temperature is the preferred sterilant due to its strong microbicidal efficiency and its decomposition in environment-friendly products, namely water vapour and oxygen. In order to obtain a high degree of sterility, the initial H2O2 concentration has to be high enough and uniformly distributed over the package's inner surface. To ensure that the packaging surface is thoroughly treated by H2O2, a gas sensor is required that detects the present H2O2 concentration on selected locations of the package's surface while it is sterilised. The present thesis describes the realisation and characterisation of thin-film gas sensors based on an “on chip” differential set-up for monitoring the H2O2 gas concentration during the sterilisation of the packaging material. The differential set-up contains a catalytically active sensor segment, where H2O2 decomposes in an exothermic reaction causing a temperature increase towards a passive sensor segment, where a surface reaction is inhibited. In a first sensor arrangement, thin-film thermopiles have been fabricated on a single silicon chip, respectively, and their response behaviour has been characterised in H2O2 atmosphere. In a further arrangement, thin-film resistances have been built up as temperature-sensitive transducer platform on a silicon chip. On this platform, different catalytically active materials – platinum black, palladium and manganese oxide – have been tested with regard to their response against H2O2, wherein all of them showed a linear response characteristic, but manganese oxide posseses the highest sensitivity. Furthermore, three temperature-stable polymeric materials – fluorinated ethylene propylene, perfluoralkoxy and epoxy-based SU-8 photoresist – have been tested for the encapsulation of the sensor surface in terms of their chemical inertness against H2O2. Therein, all of them have shown a high resistivity against H2O2 underlining their suitability for sensor passivation. Within the frame of this work, the sensor set-up has further been realised on a thin polyimide foil because of its high temperature endurance, its chemical stability and particularly, its low thermal conductivity allowing an improved thermal separation of the active and passive sensor segment. As a result, the sensitivity of the polyimide-based sensor was strongly increased compared to the concentration-dependent response of the silicon-based sensors. Microbiological experiments with bacterial spores of Bacillus atrophaeus have demonstrated that the microbicidal effectiveness of the sterilisation process depends on the present H2O2 concentration in first order as well as on the contact time between the item that has to be sterilised and the gaseous H2O2. By means of sensor measurements conducted at the same time, a correlation model between the microbial inactivation kinetics and the sensor response was established that allows to use the sensor not only for concentration measurements, but also for the quantification and control of the degree of the package's sterility. In order to determine the present H2O2 concentration spatially resolved over the package surface during the short sterilisation cycle, a wireless sensor electronic based on the industrial ZigBee standard was developed. The sensor electronic contains a remote unit, which is connected to one of the calorimetric gas sensors fixed on a test package, and an external base unit connected to a laptop computer. For real-time measurements, a novel sensor read-out strategy was established, wherein the sensor response is measured within the short sterilisation time and correlated with both the present H2O2 concentration as well as the microbicidal effectiveness. As a result, this kind of “intelligent” package represents a novel instrumentation to monitor the package sterilisation in aseptic food processes under real-time conditions

The NASA SBIR product catalog

The purpose of this catalog is to assist small business firms in making the community aware of products emerging from their efforts in the Small Business Innovation Research (SBIR) program. It contains descriptions of some products that have advanced into Phase 3 and others that are identified as prospective products. Both lists of products in this catalog are based on information supplied by NASA SBIR contractors in responding to an invitation to be represented in this document. Generally, all products suggested by the small firms were included in order to meet the goals of information exchange for SBIR results. Of the 444 SBIR contractors NASA queried, 137 provided information on 219 products. The catalog presents the product information in the technology areas listed in the table of contents. Within each area, the products are listed in alphabetical order by product name and are given identifying numbers. Also included is an alphabetical listing of the companies that have products described. This listing cross-references the product list and provides information on the business activity of each firm. In addition, there are three indexes: one a list of firms by states, one that lists the products according to NASA Centers that managed the SBIR projects, and one that lists the products by the relevant Technical Topics utilized in NASA's annual program solicitation under which each SBIR project was selected

An air-breathing, portable thermoelectric power generator based on a microfabricated silicon combustor

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections."February 2011." Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 224-237).The global consumer demand for portable electronic devices is increasing. The emphasis on reducing size and weight has put increased pressure on the power density of available power storage and generation options, which have been dominated by batteries. The energy densities of many hydrocarbon fuels exceed those of conventional batteries by several orders of magnitude, and this gap motivates research efforts into alternative portable power generation devices based on hydrocarbon fuels. Combustion-based power generation strategies have the potential to achieve significant advances in the energy density of a generator, and thermoelectric power generation is particularly attractive due to the moderate temperatures which are required. In this work, a portable-scale thermoelectric power generator was designed, fabricated, and tested. The basis of the system was a mesoscale silicon reactor for the combustion of butane over an alumina-supported platinum catalyst. The system was integrated with commercial bismuth telluride thermoelectric modules to produce 5.8 W of electrical power with a chemical-to-electrical conversion efficiency of 2.5% (based on lower heating value). The energy and power densities of the demonstrated system were 321 Wh/kg and 17 W/kg, respectively. The pressure drop through the system was 258 Pa for a flow of 15 liters per minute of air, and so the parasitic power requirement for air-pressurization was very low. The demonstration represents an order-of-magnitude improvement in portable-scale electrical power from thermoelectrics and hydrocarbon fuels, and a notable increase in the conversion efficiency compared with other published works. The system was also integrated with thermoelectric-mimicking heat sinks, which imitated the performance of high-heat-flux modules. The combustor provided a heat source of 206 to 362 W to the heat sinks at conditions suitable for a portable, air-breathing TE power generator. The combustor efficiency when integrated with the heat sinks was as high as 76%. Assuming a TE power conversion efficiency of 5%, the design point operation would result in thermoelectric power generation of 14 W, with an overall chemical-to-electrical conversion efficiency of 3.8%.by Christopher Henry Marton.Ph.D

Design and Analysis of a Low Temperature Co-Fired Ceramic Micro Combustor

This thesis details the design and construction of a Low Temperature Co-Fired Ceramic (LTCC) micro combustion system. The design of the combustor requires a detailed analysis of the flame’s operational properties and stability. To this end, an analytic model was created to address these concerns. These results were used in conjunction with a detailed numerical analysis to determine the stable operating range of the combustors. The combustion of gaseous fuels requires a device with a lower bound on the channel feature size. This lower limit for combustion corresponds to the minimum quenching distance of the specific fuel being used and usually corresponds to the upper end of silicon MEMs processing techniques and the lower end of meso-scale production processes. This millimeter size range represents the normal feature size range for the LTCC tape system. A potential material imposed restriction to using LTCC is the relatively low temperature operating range when compared to the adiabatic flame temperatures encountered in the combustion of gaseous fuels. To address this concern an analytic model of the heat transfer from a simple straight channel device is presented. This model allows for the analysis of the thermal loads in the substrate as well as provides insight into the effects of the channel geometry on the stability of the flame. Several experimental devices were designed and tested in accordance with the predictions of the analytic model. These devices have similar geometric configurations with different characteristic lengths to explore the feasible operating regimes of the LTCC micro combustor. This allows for the validation of the flame stability margins and heat transfer properties predicted by the analytic model. Infrared imaging allows for the mapping of the device surface temperature and provides a correlation mechanism to the analytic model. The results of the experimental testing show the same trending characteristics predicted by the analytic analysis. However, a detailed numerical analysis is needed to fully capture the quantitive power production capabilities of the device

Distributed generation: prospects for fuel cells based micro-cogeneration systems

Distributed generation can be an option to reduce energy consumption and facilitate the introduction of bigger amount of electricity produced with renewable energy sources. In the first part of the thesis an overview on fossil fuels power plants and primary movers for distributed micro-cogeneration systems is given. Then, the effect of renewable energy sources on the operation of the European power plants and grid is discussed. In the second part of the thesis generators based on PEM fuel cells are considered and analyzed from a theoretical and experimental point of view to what concerns performance and life span. Experimental data on a micro generator are presented. Control complexity and performance degradation over time are, in particular, studied. Degradation is also studied considering the effect of load cycles profile over performance. The research is completed with the analysis of the energy saving achievable by fuel cell micro-cogeneration systemsLa generazione distribuita di energia \ue8 da molti considerata una delle soluzioni per ridurre i consumi energetici e per agevolare l\u2019introduzione di quote sempre pi\uf9 importanti di elettricit\ue0 provenienti da fonti rinnovabili di energia. Nella prima parte della tesi viene fatta una panoramica sulle tecnologie oggi pi\uf9 adatte alla generazione distribuita e viene fatta un\u2019analisi su alcune delle problematiche che la massiccia introduzione di elettricit\ue0 da fonti rinnovabili sta comportando nella gestione della rete di distribuzione e delle centrali di produzione, a livello europeo. Nella seconda parte delle tesi, si va ad analizzare un particolare tipo di impianto per la micro-cogenerazione distribuita: i generatori elettrici basati su celle a combustibile ad elettrolita polimerico. Si vanno ad analizzare, sia dal punto di vista teorico che sperimentale, le prestazioni, la vita utile ed alcune delle problematiche relative al degrado funzionale nel tempo. Si presentano dei dati sperimentali su un micro-cogeneratore di piccola taglia e se ne evidenziano le problematiche di controllo e di degrado delle prestazioni nel tempo. In particolare, a questo riguardo, vengono riportati alcuni dati sperimentali atti a valutare l\u2019effetto dei cicli di carico sul degrado delle prestazioni delle celle. La ricerca si completa con la presentazione di una metodologia per il calcolo del risparmio energetico in funzione delle caratteristiche del generatore e delle scelte di gestione dello stess

NASA SBIR abstracts of 1990 phase 1 projects

The research objectives of the 280 projects placed under contract in the National Aeronautics and Space Administration (NASA) 1990 Small Business Innovation Research (SBIR) Phase 1 program are described. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses in response to NASA's 1990 SBIR Phase 1 Program Solicitation. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 280, in order of its appearance in the body of the report. The document also includes Appendixes to provide additional information about the SBIR program and permit cross-reference in the 1990 Phase 1 projects by company name, location by state, principal investigator, NASA field center responsible for management of each project, and NASA contract number