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Graduate

Microchannels have been used in electronics cooling and in air conditioning applications as condensers. Little study has been made in the application of microchannels in automotive heat exchangers, particularly the radiator. The presented research captures the need for the design improvement of radiator heat exchangers in heavy-duty vehicles in order to reduce aerodynamic drag and improve fuel economy. A method for analyzing an existing radiator is set forth including the needed parameters for effective comparisons of alternative designs. An investigation of microchannels was presented and it was determined that microchannels can improve the overall heat transfer of a radiator but this alone will not decrease the dimensions of the radiator. Investigations into improving the air-side heat transfer were considered and an improved fin design was found which allows a reduction in frontal area while maintaining heat transfer. The overall heat transfer of the design was improved from the original design by 7% well as 52% decrease in frontal area but at the cost of 300% increase in auxiliary power. The energy saved by a reduction in frontal area is not substantial enough to justify the increase of auxiliary power. The findings were verified through a computational fluid dynamic model to demonstrate the heat transfer and pressure drop of microchannel tubes. The results confirmed that heat transfer of microchannels does improve the thermal performance of the radiator but the pressure drop is such that the net benefit does not outweigh the operating cost. An additional CFD study of the new fin geometry and air-side heat transfer predictions was conducted. The results of the study confirmed the theoretical calculations for the fin geometry.

The replacement of copperlbrass radiators in the automotive industry with radiators made from aluminium components provided the basis of this research. Since aluminium is more susceptible to corrosion than either copper or brass, factors that contribute to its corrosion are of major interest and importance, and have been investigated. Three different aluminium alloys were selected for study because of a special interest in their corrosive behaviour by the automotive industry. These are the aluminium alloy AA 3003 (samples A and B) and two supplier specific alloys (sample D containing Zn and sample E containing Cu and Mg). The various joining operations used in the automotive manufacturing process dictated the preparation of the aluminium alloys used for corrosion studies. Mechanically Assembled (MA) aluminium radiators use alloy samples as supplied by the aluminium industry and hence suitable experiments were carried out on the 'as-supplied' (AS) samples used for both finstock and tubestock material. The development of Composite Deposition (CD) Technology to braze together finstock and tubestock material introduced new challenges to corrosion research. To gain an insight into the corrosion of a Brazed aluminium radiator, all samples were subjected to a thermal profile identical to that experienced industrially under a Controlled Atmosphere Brazing (CAB) furnace. Two cases of interest emerged. Firstly the 'heat-treated' (HT) samples were used to evaluate the effect ofheat treatment on the alloy's resistance to corrosion. Secondly, alloy samples treated with a Composite Powder Coating (CPC) and then subjected to the thermal profile provided a surface of an AI-Si melt which represented the brazed joint. Experiments on these samples yielded information on the AI-Si melt and the likely corrosion in a brazed joint. The resulting corrosion of the AS, HT and CPC samples immersed in various corrosive electrolyte solutions for 60 minutes was examined using two microscopic techniques. Firstly, the actual surface pitting was examined using a Scanning Electron Microscope (SEM), and secondly, cross-sections of the samples mounted in a resin, then suitably polished and etched were examined using an optical microscope to further reveal the nature of corrosion of the samples. The nature of corrosion was best revealed in an acidified chloride solution. The AS samples showed delocalised crystallographic pitting consisting of coalesced pits at localised regions of the surface. The HT samples showed IV localised crystallographic pIttIng consIstIng of many individual pits and intergranular corrosion both at and below the surface. Intergranular corrosion was most severe for HT sample E containing Cu and Mg. The CPC samples showed total corrosion of the surface layer and eutectic AI-Si melt, some crystallographic pitting of the a-AI filler metal, and crystallographic pitting including intergranular corrosion of the base alloy. The extent of corrosion was found to depend on the chemical composition of the aluminium alloys, the presence of Zn, Cu and Mg causing more severe corrosion of the aluminium alloys, with the effect ofZn being most severe. The electrochemical investigation involved the measurement of two fundamentally important parameters. Firstly, the open circuit potentials (OCP) of the alloy samples immersed in the various corrosive electrolyte solutions were measured as a function of time. Secondly, the pitting potentials (Bp) of the alloy samples were measured using anodic polarisation techniques by extrapolation of the resulting log i vs E plots. The OCP and Bp of the AS samples were found to be influenced by the chemical composition of the aluminium alloys. Heat treatment of the AS samples was found to change their microstructure and solid solution composition which in turn affected the electrochemical results. The effect of the Composite melt layer on the electrochemistry of the CPC samples is discussed. Micrographic and electrochemical results were used to assess the best combination of finstock and tubestock material that would yield an aluminium radiator most resistant to corrosion. The likely corrosion of the components in these combinations was assessed and these results were compared with the actual results obtained industrially using the SWAAT exposure test. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.

"Theoretical modeling, design, assembly, and measurement of a novel integrated phased array radiator are presented. The droopy bowtie turnstile radiator with quad line feed meets challenging radar requirements and uses low cost manufacturing and assembly techniques. This thesis develops the complete theoretical model (antenna, balun, feeding network) of a broadband phased array radiator: the droopy bowtie turnstile radiator. A novel quad line balun feed is developed that provides a low loss, high isolation, and coincident phase-center feeding network for the droopy bowtie. The radiator and feed design combines broadband RF performance and high-isolation dual-linear polarization in a low profile, compact package that enables wide scan volume performance versus frequency. This thesis develops low-cost manufacturing and assembly techniques applied to the droopy bowtie radiator with the quad line feed. The new radiator design would utilize low cost fabrication techniques such as injection molding and 3-D printing, and also leverages automated assembly techniques. Measurement prototypes and array prototypes of droopy bowtie radiators with the quad line feed are developed for L- and X-bands. The measurements demonstrate broadband RF performance in a low profile compact package viable for wide-scale phased array applications."

Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, June 1990. / Thesis Advisor(s): Kraus, Allan D. Second Reader: Brown, Sue. "June 1990." Description based on signature page. DTIC Identifier(s): Radiators (heating and cooling), radiative transfer, heat transfer (radiation). Author(s) subject terms: Radiative heat transfer, longitudinal fins, free space and non-free space. Includes bibliographical references (p. 147-148). Also available online.

A variety of open and closed multi-layered nanoparticle structures have been considered analytically and numerically for their use as scatterers and radiators. These include metamaterial-inspired structures based on dielectrics and metals excited by either plane waves or electric Hertzian dipoles at optical frequencies. Both passive and active (gain impregnated dielectric) materials have been considered. Enhanced and mitigated scattering and radiating effects have been modeled. Nano-antenna and nano-amplifier configurations for optical applications have been emphasized. A review of these modeling efforts will be presented.

Switched and adaptive parasitic monopole array radiating structures are investigated. Antenna design is orientated toward increasing practicability for implementation in terrestrial wireless communication systems. A number of antennas are designed with the aid of optimization and commercial simulation software. Simulation procedure was verified with the experimental manufacture and measurement of the arrays. The antennas presented in this thesis comprise an active monopole surrounded by a ring of parasitic monopoles. Parasitic radiators are constructed with static loading to enable simple experimental realization. Beam positions of an electrically steered equivalent antenna are thus simulated. Antenna symmetry ensures the beam can be reproduced throughout the azimuth. Complex antenna geometries require antenna design through optimization. A genetic algorithm is employed with HFSS and NEC for electromagnetic analysis. The robust optimization method couples with simulation software flexibility to provide an effective design tool for arbitrary structures. The genetic algorithm is employed strictly for design and not complete structural optimization. Dual band, five and six element switched parasitic antennas are presented. Lumped elemental loading along the radiators provide resonance and directed radiation at two GSM frequencies. Load value, radiator dimension and spacing are incorporated as design parameters. Experimentally built, 10dB return loss bandwidths of 17.2% and 9.6% and front to back ratios of 12.6dB and 8.4dB at 900MHz and 1900MHz respectively are measured. To reduce the ground requirements of monopole arrays, a skirted ground structure for switched parasitic antennas is analyzed. A six element switched parasitic monopole array with conductive ground skirt exhibits a front to back ratio of 10.7dB and main lobe gain of 6.4dBi at 1.575GHz. Radiation is not elevated despite lateral ground terminating at the parasitic elements. Skirt height is observed to linearly control radiation elevation, depressing the principal lobe through 40 degrees from 23 degrees above the horizontal. The Electronically Steerable Passive Array Radiator or ESPAR antenna is an adaptive parasitic monopole array. An ESPAR radiating structure incorporating a conductive ground skirt is designed for operation at 2.4GHz. Utility is confirmed with a frequency sensitivity analysis showing consistent electrical characteristics over an 8.1% bandwidth. The antenna design is improved with optimization to reduce average principal lobe elevation from 25 degrees to 9.7 degrees.

Business valuation of micro trading company LIPOVICA trade s.r.o; main business activity of the company is selling and distribution of aluminum radiators on the markets in the Czech and Slovak republic. The valuation is based on discounted cash flows method, economic value added method, capitalization of profits method and simple liquidation method.

A simple method is described to record the radiated sound of musical instruments and to extrapolate the sound field to distances further away from the source. This is achieved by considering instruments as complex point sources. It is demonstrated that this simplification method yields plausible results not only for small instruments like the shakuhachi but also for larger instruments such as the double bass: The amplitude decays in a given manner and calculated interaural signal differences reaching the listener decrease with increasing distance to the source. The method can be applied to analyze the sound radiation characteristics as well as the radiated sound field in a listening region regardless of room acoustical influences. Implementations in terms of room acoustical simulations, spatial additive synthesis and sound field synthesis are discussed.