No description available.

Thesis (M.S.)--University of North Texas, Dec., 2008. / Title from title page display. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2000. / Typescript (photocopy). Includes bibliographical references (leaves 81-85). Also available on the World Wide Web.

An investigation was performed to demonstrate system design for the delivery of water required for evaporative cooling of a proton exchange membrane fuel cell (PEMFC). The water delivery system uses spray nozzles capable of injecting water directly and uniformly to the nickel metal foam flow-field (element for distributing the reactant gases over the surface of the electrodes) on the anode side from which water can migrate to the cathode side of the cell via electroosmotic drag. For an effective overall cooling, water distribution over the surface of the nickel foam has to be uniform to avoid creation of hotspots within the cell. A prototype PEMFC structure was constructed modeled after a 35 kW electrical output PEMFC stack. Water was sprayed on the nickel metal foam flow-field using two types of nozzle spray, giving conical fog type flow and flat fan type flow. A detailed investigation of the distribution pattern of water over the surface of the nickel metal flow field was conducted. The motive behind the investigation was to determine if design parameters such as type of water flow from nozzles, vertical location of the water nozzles above the flowfield, area of the nozzles, or operating variables such as reactant gas flow had any effect on water distribution over the surface of the Ni-metal foam flow field. It was found that the design parameters (types of flow, area and location of the nozzle) had a direct impact on the distribution of water in the nickel metal foam. However, the operating variable, reactant gas flow, showed no effect on the water distribution pattern in the Ni-foam.

Thesis (Ph. D.)--Washington State University, December 2008.. / Title from PDF title page (viewed on July 10, 2009). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 176-187).

Thesis (M.S.)--University of Wyoming, 2007. / Title from PDF title page (viewed on June 22, 2009). Includes bibliographical references (p. 72-73).

Made available in DSpace on 2014-06-11T19:35:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T19:05:51Z : No. of bitstreams: 1 camargo_jr_dr_guara.pdf: 1019492 bytes, checksum: 2297d5279bcff4ccbedcb325ccb31939 (MD5) / O resfriamento evaporativo consiste na utilização da evaporação da água através da passagem de um fluxo de ar, provocando a redução na temperatura do ar e, apesar de utilizarem tecnologia relativamente simples, ainda são pouco utilizados para o condicionamento de ar em regiões de clima úmido. Este trabalho realiza um estudo dos potenciais e limitações de sistemas de condicionamento de ar por resfriamento evaporativo e evaporativo-adsortivo quando utilizados com o objetivo de propiciar conforto térmico ao homem e reduzir o consumo de energia. Apresenta-se, inicialmente, o princípio de funcionamento de sistemas de resfriamento evaporativo e de desumidificadores por adsorção. A seguir, apresentam-se os resultados dos ensaios de desempenho realizados em um resfriador evaporativo direto e propõe-se um novo sistema a ser utilizado em regiões em que as condições de conforto não podem ser supridas pelo resfriamento evaporativo somente. Estuda-se a aplicação desses sistemas a diversas cidades, caracterizadas por diferentes condições climáticas e conclui-se que os sistemas de resfriamento evaporativo acoplados a um desumidificador adsortivo apresentam perspectivas promissoras, principalmente para aplicação em condicionamento de ar onde existem fontes de calor de baixo custo ou calor residual disponível. A análise das condições do ar de insuflamento demonstra a viabilidade da utilização do sistema proposto para conforto térmico humano em regiões de clima úmido como uma alternativa aos sistemas convencionais de condicionamento de ar, poupando energia e protegendo o meio ambiente. / Evaporative cooling consists in using water evaporation through the passage of an air flow, thus decreasing the air temperature. In spite of using simple technology, it is seldon used for air conditioning in humid climate regions. This thesis develops a methodology that can be used to establish potentials and limitations of air conditioning systems by evaporative and desiccant cooling when used for human thermal comfort and lower power consumption. Firstly, the operational principles of evaporative cooling and dehumidification by adsorption systems are presented. Next, the results of performance tests developed on a direct evaporative cooler are described. Finally, a new system to be used in regions where the thermal comfort conditions cannot be supplied only by evaporative cooling is proposed. The applications of this system in several cities, characterized by different climate conditions are studied. It concluded that evaporative cooling systems coupled to a dehumidification adsorption system present promising perspectives, mainly to low cost air conditioning applications where residual heat sources are available. The analysis of the supply air conditions shows the feasibility of the proposed system for human thermal comfort in humid climates as an alternative to conventional air conditioning systems, saving energy and protecting the environment.

An investigation was conducted to determine the feasibility of using the technique of ultrasonic nebulization of water into the anode gas stream for evaporative cooling of a Proton Exchange Membrane (PEM) fuel cell. The basic concept of this form of internal evaporative cooling of the PEM fuel cell is to introduce finely atomized liquid water into the anode gas stream, so that the finely atomized liquid water adsorbs onto the anode and then moves to the cathode via electro-osmotic drag, where this water then evaporates into the relatively dry cathode gas stream, carrying with it the waste thermal energy generated within the fuel cell. The thermal and electrical performance of a 50 cm2 PEM fuel cell utilizing this technique was compared to the performance obtained with conventional water management. Both techniques were compared over a range of humidification chamber temperatures for both the anode and cathode gas streams so as to determine the robustness of the proposed method. The proposed method produced only meager levels of evaporative cooling (at best 2 watts, for which a minimum of 30 watts was required for adequate cooling), but the average cell voltage increased considerably (as much as a 10% gain), and the technique increased the fault tolerance of the fuel cell (the Nafion™ membrane did not dry out even if cell temperature went well in excess of 70° C despite both anode and cathode humidification temperatures of 55° C). An interesting phenomena was also observed wherein the fuel cell voltage oscillated regularly with a period of tens of seconds, and that the amplitude of this oscillation corresponded inversely with the level of humidification received by the fuel cell.

A cutting edge man-portable AVMEC cooling garment was demonstrated to be able to provide sufficient cooling for personnel working at mediate activity loads. Studies were first carried out in a well controlled vacuum desiccator at room temperature to elucidate the effects of several key parameters on the performance of an AVEC device, which was similar to AVMEC except that membrane was not involved. Under the best condition, an average cooling capacity of 179 W/M2 was achieved in a period of four hours and cooling continued at a slowly declining rate for another four hours afterward. The temperature of water was maintained at approximately 12.5 oC after the pseudo steady state was established. Then, it was shown that the AVMEC cooling pads were able to provide a cooling capacity of 277.4 W/m2 in a 37 oC ambient environment (incubator). The temperature of the cooling core surface was maintained in a range of 20 – 21.8 oC in the one-hour test period. No power supply was required except for the initialization stage, which took 5 minutes. Furthermore, human subject tests with or without wearing NWBC (Nuclear Warfare Biological and Chemical) suit demonstrated that, a AVMEC garment composed of 12 cooling pads were able to maintain the core body temperature of the subjects below 38.5 oC for up to 90 minutes while the subject was walking on a treadmill at a speed of 2 miles per hour in an environment of 40 oC and 50% RH (relative humidity). These results indicate that the AVMEC garment is a promising man-portable personal cooling technology.

A cutting edge man-portable AVMEC cooling garment was demonstrated to be able to provide sufficient cooling for personnel working at mediate activity loads. Studies were first carried out in a well controlled vacuum desiccator at room temperature to elucidate the effects of several key parameters on the performance of an AVEC device, which was similar to AVMEC except that membrane was not involved. Under the best condition, an average cooling capacity of 179 W/M2 was achieved in a period of four hours and cooling continued at a slowly declining rate for another four hours afterward. The temperature of water was maintained at approximately 12.5 oC after the pseudo steady state was established. Then, it was shown that the AVMEC cooling pads were able to provide a cooling capacity of 277.4 W/m2 in a 37 oC ambient environment (incubator). The temperature of the cooling core surface was maintained in a range of 20 – 21.8 oC in the one-hour test period. No power supply was required except for the initialization stage, which took 5 minutes. Furthermore, human subject tests with or without wearing NWBC (Nuclear Warfare Biological and Chemical) suit demonstrated that, a AVMEC garment composed of 12 cooling pads were able to maintain the core body temperature of the subjects below 38.5 oC for up to 90 minutes while the subject was walking on a treadmill at a speed of 2 miles per hour in an environment of 40 oC and 50% RH (relative humidity). These results indicate that the AVMEC garment is a promising man-portable personal cooling technology.