Performance evaluation of VIP latrines in the Upper West Region of Ghana

The prevalence of Ventilated Improved Pit (VIP) latrines in Ghana suggests that the design must have a high user acceptance. The two key factors attributed to user acceptance of a VIP latrine over an alternative latrine design, such as the basic pit latrine, are its ability to remove foul odors and maintain low fly populations; both of which are a direct result of an adequate ventilation flow rate. Adequate ventilation for odorless conditions in a VIP latrine has been defined by the United Nations Development Program (UNDP) and the World Bank, as an air flow rate equivalent to 6 air changes per hour (6 ACH) of the superstructure’s air volume. Additionally, the UNDP determined that the three primary factors that affect ventilation are: 1) wind passing over the mouth of the vent pipe, 2) wind passing into the superstructure, and 3) solar radiation on to the vent pipe. Previous studies also indicate that vent pipes with larger diameters increase flow rates, and the application of carbonaceous materials to the pit sludge reduces odor and insect prevalence. Furthermore, proper design and construction is critical for the correct functioning of VIP latrines. Under-designing could cause problems with odor and insect control; over-designing would increase costs unnecessarily, thereby making it potentially unaffordable for benefactors to independently construct, repair or replace a VIP latrine. The present study evaluated the design of VIP latrines used by rural communities in the Upper West Region of Ghana with the focus of assessing adequate ventilation for odor removal and insect control. Thirty VIP latrines from six communities in the Upper West Region of Ghana were sampled. Each VIP latrine’s ventilation flow rate and micro-environment was measured using a hot-wire anemometer probe and portable weather station for a minimum of four hours. To capture any temporal or seasonal variations in ventilation, ten of the latrines were sampled monthly over the course of three months for a minimum of 12 hours. A latrine usage survey and a cost analysis were also conducted to further assess the VIP latrine as an appropriated technology for sustainable development in the Upper West Region. It was found that the average air flow rate over the entire sample set was 11.3 m3/hr. The minimum and maximum air flow rates were 0.0 m3/hr and 48.0 m3/hr respectively. Only 1 of the 30 VIP latrines (3%) was found to have an air flow rate greater than the UNDP-defined odorless condition of 6 ACH. Furthermore, 19 VIP latrines (63%) were found to have an average air flow rate of less than half the flow rate required to achieve 6 ACH. The dominant factors affecting ventilation flow rate were wind passing over the mouth of the vent pipe and air buoyancy forces, which were the effect of differences in temperature between the substructure and the ambient environment. Of 76 usable VIP latrines found in one community, 68.4% were in actual use. The cost of a VIP latrine was found to be equivalent to approximately 12% of the mean annual household income for Upper West Region inhabitants.

Aerodynamic loads on bluff bodies under wind gusts

Esta tesis doctoral se ha centrado en el estudio de las cargas aerodinámicas no estacionario en romos cuerpos o no aerodinámicos (bluff bodies). Con este objetivo se han identificado y analizado los siguientes puntos: -Caracterización del flujo medido con diferentes tipos de tubos de Pitot y anemómetro de hilo caliente en condiciones de flujo no estacionario inestable generado por un túnel aerodinamico de ráfagas. -Diseño e integración de los montajes experimentales requeridos para medir las cargas de viento internas y externas que actúan sobre los cuerpos romos en condiciones de flujo de viento con ráfagas. -Implementación de modelos matemáticos semi-empíricos basados en flujo potencial y las teorías fenomenológicas pertinentes para simular los resultados experimentales. -En diversan condiciones de flujo con ráfagas, la identificación y el análisis de la influencia de los parámetros obtenida a partir de los modelos teóricos desarrollados. -Se proponen estimaciones empíricas para averiguar los valores adecuados de los parámetros que influyente, mediante el ajuste de los resultados experimentales y los predichos teóricamente. Los montajes experimentales se has reakizado en un tunel aerodinamico de circuito abierto, provisto de baja velocidad, cámara de ensayes cerrada, un nuevo concepto de mecanismo generador de ráfaga sinusoidal, diseñado y construido en el Instituto de Microgravedad "Ignacio Da Riva" de la Universidad Politécnica de Madrid, (IDR / UPM). La principal característica de este túnel aerodynamico es la capacidad de generar un flujo con un perfil de velocidad uniforme y una fluctuación sinusoidal en el tiempo. Se han realizado pruebas experimentales para estudiar el efecto de los flujos no estacionarios en cuerpos romos situados en el suelo. Se han propuesto dos modelos teóricos para diterminar las cargas de presión externas e internas respectivamente. Con el fin de satisfacer la necesidad de la crea ráfagas de viento sinusoidales para comprobar las predicciones de los modelos teóricos, se han obtenido velocidades de hasta 30 m/s y frecuencias ráfaga de hasta 10 Hz. La sección de la cámara de ensayos es de 0,39 m x 0,54 m, dimensiónes adecuadas para llevar a cabo experimentos con modelos de ensayos. Se muestra que en la gama de parámetros explorados los resultados experimentales están en buen acuerdo con las predicciones de los modelos teóricos. Se han realizado pruebas experimentales para estudiar los efectos del flujo no estacionario, las cuales pueden ayudar a aclarar el fenómeno de las cargas de presión externa sobre los cuerpos romos sometidos a ráfagas de viento: y tambien para determinan las cargas de presión interna, que dependen del tamaño de los orificios de ventilación de la construcción. Por último, se ha analizado la contribución de los términos provenientes del flujo no estacionario, y se han caracterizado o los saltos de presión debido a la pérdida no estacionario de presión a través de los orificios de ventilación. ABSTRACT This Doctoral dissertation has been focused to study the unsteady aerodynamic loads on bluff bodies. To this aim the following points have been identified and analyzed: -Characterization of the flow measured with different types of Pitot tubes and hot wire anemometer at unsteady flow conditions generated by a gust wind tunnel. -Design and integrating of the experimental setups required to measure the internal and external wind loads acting on bluff bodies at gusty wind flow conditions. -Implementation of semi-empirical mathematical models based on potential flow and relevant phenomenological theories to simulate the experimental results.-At various gusty flow conditions, extracting and analyzing the influence of parameters obtained from the developed theoretical models. -Empirical estimations are proposed to find out suitable values of the influencing parameters, by fitting the experimental and theoretically predicted results. The experimental setups are performed in an open circuit, closed test section, low speed wind tunnel, with a new sinusoidal gust generator mechanism concept, designed and built at the Instituto de Microgravedad “Ignacio Da Riva” of the Universidad Politécnica de Madrid, (IDR/UPM). The main characteristic of this wind tunnel is the ability to generate a flow with a uniform velocity profile and a sinusoidal time fluctuation of the speed. Experimental tests have been devoted to study the effect of unsteady flows on bluff bodies lying on the ground. Two theoretical models have been proposed to measure the external and internal pressure loads respectively. In order to meet the need of creating sinusoidal wind gusts to check the theoretical model predictions, the gust wind tunnel maximum flow speed and, gust frequency in the test section have been limited to 30 m/s and 10 Hz, respectively have been obtained. The test section is 0.39 m × 0.54 m, which is suitable to perform experiments with testing models. It is shown that, in the range of parameters explored, the experimental results are in good agreement with the theoretical model predictions. Experimental tests have been performed to study the unsteady flow effects, which can help in clarifying the phenomenon of the external pressure loads on bluff bodies under gusty winds: and also to study internal pressure loads, which depend on the size of the venting holes of the building. Finally, the contribution of the unsteady flow terms in the theoretical model has been analyzed, and the pressure jumps due to the unsteady pressure losses through the venting holes have been characterized.

Temperature measurements in turbulent pipe flow with cold wire anemometry

Passive scalars measurements in turbulent pipe flows are difficult to perform and only few experimental data are available in literature. The present thesis deals with the experimental acquisition and study of the first turbulent temperature profile inside the CICLoPE wind tunnel through cold wire anemometry technique at Reτ = 6000 and Reτ = 9500. This type of measurements provides not only useful data on temperature (and passive scalars) behaviour and statistics in turbulent pipe flows, but could be used also for temperature correction of turbulent velocity profiles. In the present work, subsequent acquisitions of temperature and velocity profiles has been performed at the same Reynolds number and in the same points, through cold wire and hot wire techniques respectively. Taking as reference data from both DNS and experimental campaigns, the activity has been carried out obtaining satisfactory results. We have verified the presence of turbulent temperature profile inside the CICLoPE wind tunnel and then studied its statistical and spectral behaviours obtaining results in agreement with existing data from Hishida, Nagano, and Ferro. Cold wire temperature data were then used to correct hot wire velocity data, obtaining a slightly improvement in the near wall region.

Effect of cold wire inclination on temperature fluctuation measurements in a heated jet

Hot-wire anemometers at low operating currents are used as fast response resistance thermometers for the study of heated turbulent flows. Simultaneous measurement of temperature and velocity is generally performed with multi-wire arrays. In order to give good spatial resolution a new layout has been tested which uses an inclined temperature wire positioned parallel to the nearest inclined velocity wire. This leads to an asymmetric wire arrangement relative to the mean flow direction. As expected, a reduction in thermal interference from the velocity wires results when compared with an array containing a temperature wire placed normal to the flow. However, measurement of higher order moments of fluctuating quantities in an axisymmetric jet shows considerable distortion of radial distributions which is traced to alteration of the temperature field sensed by the temperature wire. When inclined velocity sensitive wires contain a temperature component, the latter may be affected by the same phenomenon.

Developments in hot-filament metal oxide deposition (HFMOD)

Hot-filament metal oxide deposition (HFMOD) is a variant of conventional hot-filament chemical vapor deposition (HFCVD) recently developed in our laboratory and successfully used to obtain high-quality, uniform films of MOx WOx and VOx. The method employs the controlled oxidation of a filament of a transition metal heated to 1000 degrees C or more in a rarefied oxygen atmosphere (typically, of about 1 Pa). Metal oxide vapor formed on the surface of the filament is transported a few centimetres to deposit on a suitable substrate. Key system parameters include the choice of filament material and diameter, the applied current and the partial pressures of oxygen in the chamber. Relatively high film deposition rates, such as 31 nm min(-1) for MoOx, are obtained. The film stoichiometry depends on the exact deposition conditions. MoOx films, for example, present a mixture of MoO2 and MoO3 phases, as revealed by XPS. As determined by Li+ intercalation using an electrochemical cell, these films also show a colouration efficiency of 19.5 cm(2) C-1 at a wavelength of 700 nm. MOx and WOx films are promising in applications involving electrochromism and characteristics of their colouring/bleaching cycles are presented. The chemical composition and structure of VOx films examined using IRRAS (infrared reflection-absorption spectroscopy), RBS (Rutherford backscattering spectrometry) and XPS (X-ray photoelectron spectrometry) are also presented. (c) 2007 Elsevier B.V. All rights reserved.

Development and Automatization of a Planar Jet Wind Tunnel for the X-wire Calibration

The scope of this study is to design an automatic control system and create an automatic x-wire calibrator for a facility named Plane Air Tunnel; whose exit creates planar jet flow. The controlling power state as well as automatic speed adjustment of the inverter has been achieved. Thus, the wind tunnel can be run with respect to any desired speed and the x-wire can automatically be calibrated at that speed. To achieve that, VI programming using the LabView environment was learned, to acquire the pressure and temperature, and to calculate the velocity based on the acquisition data thanks to a pitot-static tube. Furthermore, communication with the inverter to give the commands for power on/off and speed control was also done using the LabView VI coding environment. The connection of the computer to the inverter was achieved by the proper cabling using DAQmx Analog/Digital (A/D) input/output (I/O). Moreover, the pressure profile along the streamwise direction of the plane air tunnel was studied. Pressure tappings and a multichannel pressure scanner were used to acquire the pressure values at different locations. Thanks to that, the aerodynamic efficiency of the contraction ratio was observed, and the pressure behavior was related to the velocity at the exit section. Furthermore, the control of the speed was accomplished by implementing a closed-loop PI controller on the LabView environment with and without using a pitot-static tube thanks to the pressure behavior information. The responses of the two controllers were analyzed and commented on by giving suggestions. In addition, hot wire experiments were performed to calibrate automatically and investigate the velocity profile of a turbulent planar jet. To be able to analyze the results, the physics of turbulent planar jet flow was studied. The fundamental terms, the methods used in the derivation of the equations, velocity profile, shear stress behavior, and the effect of vorticity were reviewed.

Thermal performance of sisal fiber-cement roofing tiles for rural constructions

Roofing provides the main protection against direct solar radiation in animal housing. Appropriate thermal properties of roofing materials tend to improve the thermal comfort in the inner ambient. Nonasbestos fiber-cement roofing components reinforced with cellulose pulp from sisal (Agave sisalana) were produced by slurry and dewatering techniques, with an optional addition of polypropylene fibers. Nonasbestos tiles were evaluated and compared with commercially available asbestos-cement sheets and ceramic tiles (frequently chosen as roofing materials for animal housing). Thermal conductivity and thermal diffusivity of tiles were determined by the parallel hot-wire method, along with the evaluation of the downside surface temperature. Cement-based components reinforced with sisal pulp presented better thermal performance at room temperature (25ºC), while those reinforced with sisal pulp added by polypropylene fibers presented better thermal performance at 60ºC. Non-asbestos cement tiles provided more efficient protection against radiation than asbestos corrugated sheets.

Lightweight composite concrete produced with water treatment sludge and sawdust: Thermal properties and potential application

The main objective of this study was to evaluate the potential application of a lightweight concrete produced with lightweight coarse aggregate made of the water treatment sludge and sawdust (lightweight composite), by determining the thermal properties and possible environmental impact of future residue of this concrete. Two types of concrete were prepared: concrete produced with the lightweight composite dosed with cement/sand/composite/water in a mass ratio of 1:2.5:0.67:0.6 and conventional concrete dosed with cement/sand/crushed stone/water in a mass ratio of 1:4.8:5.8:0.8. The thermal properties were determined by the hot wire parallel technique. The possible environmental impact was measured using the procedures and guidelines of the Brazilian Association of Technical Standards - ABNT. The concrete produced with the lightweight composite presented a 23% lower thermal conductivity than the conventional concrete. The concrete produced with the lightweight composite presented a set of thermal properties suitable for the application of this concrete in non-structural sealing elements. The concentration of aluminum in the solubilized extract of the concrete produced with the lightweight composite was much lower than the concentration of aluminum in the water treatment sludge, confirming the possible reduction of environmental impact of this composite for use in concrete. (C) 2010 Elsevier Ltd. All rights reserved.

Thermal diffusivity of polymers by modified angstrom method

The nature of the molecular structure of plastics makes the properties of such materials markedly temperature dependent. In addition, the continuous increase in the utilization of polymeric materials in many specific applications has demanded knowledge of their physical properties, both during their processing as raw material, as well as over the working temperature range of the final polymer product. Thermal conductivity, thermal diffusivity and specific heat, namely the thermal properties, are the three most important physical properties of a material that are needed for heat transfer calculations. Recently, among several different methods for the determination of the thermal diffusivity and thermal conductivity, transient techniques have become the preferable way for measuring thermal properties of materials. In this work, a very simple and low cost variation of the well known Angstrom method is employed in the experimental determination of the thermal diffusivity of some selected polymers. Cylindrical shaped samples 3 cm diameter and 7 cm high were prepared by cutting from long cylindrical commercial bars. The reproducibility is very good, and the results obtained were checked against results obtained by the hot wire technique, laser flash technique, and when possible, they were also compared with data found in the literature. Thermal conductivity may be then derived from the thermal diffusivity with the knowledge of the bulk density and the specific heat, easily obtained by differential scanning calorimetry. (C) 2009 Elsevier Ltd. All rights reserved.

Experimental study of a Tollmien-Schlichting wave interacting with a shallow 3D roughness element

The paper is devoted to an experimental study of the effect of a shallow 3D roughness element on the evolution of a 2D Tollmien-Schlichting wave in a Blasius boundary layer. The experiments were carried out under controlled disturbance conditions on an airfoil section which could provide a long run with zero pressure gradient flow. A pneumatically driven slit source was used to introduce the Tollmien-Schilichting wave upstream of the lower branch of the neutral stability curve. A few wavelengths downstream, the T-S wave interacts with a cylindrical roughness element. The height of the roughness was slowly oscillating in time, which allows a continuous measurement of the T-S wave response downstream the roughness. The oscillation frequency was approximately 1500 times lower than the frequency of the studied Tollmien-Schlichting wave and therefore, behaved as a steady roughness with respect to the T-S wave. Hot wire anemometry was used to measure wall normal profiles and spanwise scans close to the maximum of the eigenfunction of the T-S wave. The oscillation of the roughness and the synchronization of all-equipments permitted the use of ensemble average techniques. Two different amplitudes of T-S waves with a non-dimensional frequency of F120E-06 were studied. They show a strong amplification of the disturbances in a small spanwise wave number range. The analysis of the wall normal T-S profiles suggests the growth of oblique modes.

Characterization of turbulent jets from high-aspect-ratio rectangular nozzles

Turbulent free jets issuing from rectangular slots with various high aspect ratios (15-120) are characterized. The centerline mean and rms velocities are measured using hot-wire anemometry over a downstream distance of up to 160 slot heights at a slot-height-based Reynolds number of 10000. Experimental results suggest that a rectangular jet with sufficiently high aspect ratio (> 15) may be distinguished between three flow zones: an initial quasi-plane-jet zone, a transition zone, and a final quasi-axisymmetric-jet zone. In the quasi-plane-jet zone, the turbulent velocity field is statistically similar, but not identical, to those of a plane jet. (c) 2005 American Institute of Physics.

Sistemas geotérmicos de baixa entalpia estudos de caracterização térmica

A crescente atenção revelada pelas sociedades nos últimos anos, no que respeita à sustentabilidade energética do planeta, tornou-se o principal impulsionador para o desenvolvimento de formas de exploração de energia que contribuem para a redução dos gases com efeito de estufa. A energia geotérmica de baixa entalpia (Shallow Geothermal Energy–SGE) é um dos tipos de energia verde utilizados para aquecimento e arrefecimento de edifícios. Nas últimas décadas, tem vindo a demonstrar uma elevada eficácia energética e aplicabilidade em diversos países em todo o mundo. Aos sistemas convencionais de exploração abertos e fechados, seguiram-se os sistemas com estruturas de fundações termoactivas. A Suíça e Áustria foram os países pioneiros onde se iniciou a exploração utilizando este tipo de estruturas, primeiro com recurso a lajes de fundo e depois, em 1984, através de estacas. A utilização generalizada de fundações de forma bi-funcional poderá resultar numa compensação sustentável dos seus custos de implementação. No entanto, é necessário conhecer de forma sólida o comportamento geotécnico dos solos face à imposição das diferentes acções térmicas provocadas pelos Sistemas Geotérmicos de Baixa Entalpia. A eficácia dos Ground Energy Systems (GES) está directamente associada à capacidade que os solos apresentam para fornecer ou dissipar calor. O desempenho dos GES e a sua eficiência está ainda por avaliar relativamente às condições existentes em Portugal. As propriedades térmicas dos solos são um desses aspectos, sendo da maior relevância na avaliação do seu desempenho. Nesta dissertação são abordados os diferentes mecanismos de transferência de calor nos solos bem como propriedades térmicas necessárias para a sua caracterização. Apresenta-se também um caso prático, para o qual foi realizada caracterização térmica e posterior modelação numérica de uma estrutura termoactiva, determinando-se os campos de temperaturas máximos e mínimos e os fluxos térmicos provocados pelo seu funcionamento.

Flexible organic–inorganic hybrid layer encapsulation for organic opto-electronic devices

In this work we produce and study the flexible organic–inorganic hybrid moisture barrier layers for the protection of air sensitive organic opto-electronic devices. The inorganic amorphous silicon nitride layer (SiNx:H) and the organic PMMA [poly (methyl methacrylate)] layer are deposited alternatingly by using hot wire chemical vapor deposition (HW-CVD) and spin-coating techniques, respectively. The effect of organic–inorganic hybrid interfaces is analyzed for increasing number of interfaces. We produce highly transparent (∼80% in the visible region) hybrid structures. The morphological properties are analysed providing a good basis for understanding the variation of the water vapor transmission rate (WVTR) values. A minimum WVTR of 4.5 × 10−5g/m2day is reported at the ambient atmospheric conditions for 7 organic/inorganic interfaces. The hybrid barriers show superb mechanical flexibility which confirms their high potential for flexible applications.

Real-time monitoring of the silicidation process of tungsten filaments at high temperature used as catalysers for silane decomposition

The scope of this work is the systematic study of the silicidation process affecting tungsten filaments at high temperature (1900ºC) used for silane decomposition in the hot-wire chemical vapour deposition technique (HWCVD). The correlation between the electrical resistance evolution of the filaments, Rfil(t), and the different stages of the their silicidation process is exposed. Said stages correspond to: the rapid formation of two WSi2 fronts at the cold ends of the filaments and their further propagation towards the middle of the filaments; and, regarding the hot central portion of the filaments: a initial stage of silicon dissolution into the tungsten bulk, with a random duration for as-manufactured filaments, followed by the inhomogeneous nucleation of W5Si3 (which is later replaced by WSi2) and its further growth towards the filaments core. An electrical model is used to obtain real-time information about the current status of the filaments silicidation process by simply monitoring their Rfil(t) evolution during the HWCVD process. It is shown that implementing an annealing pre-treatment to the filaments leads to a clearly repetitive trend in the monitored Rfil(t) signatures. The influence of hydrogen dilution of silane on the filaments silicidation process is also discussed.

Study of post-deposition contamination in low-temperature deposited polysilicon films

The presence of hydrogen in polysilicon films obtained at low temperatures by hot-wire CVD and the post-deposition oxidation by air-exposure of the films are studied in this paper. The experimental results from several characterization techniques (infrared spectroscopy, X-ray photoelectron spectroscopy, secondary ion mass spectrometry and wavelength dispersive spectroscopy) showed that hydrogen and oxygen are homogeneously distributed at grain boundaries throughout the depth of the films. Hydrogen is introduced during the growth process and its concentration is higher in samples deposited at lower temperatures. Oxygen diffuses along the grain boundaries and binds to silicon atoms, mainly in Si 2O groups.