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Observation and modelling of urban dewRichards, Katrina 05 1900 (has links)
Despite its relevance to many aspects of urban climate and to several practical
questions, urban dew has largely been ignored. Here, simple observations, an outof-
doors scale model, and numerical simulation are used to investigate patterns of
dewfall and surface moisture (dew + guttation) in urban environments. Observations
and modelling were undertaken in Vancouver, B.C., primarily during the summers of
1993 and 1996.
Surveys at several scales (0.02-25 km) show that the main controls on dew
are weather, location and site configuration (geometry and surface materials).
Weather effects are discussed using an empirical factor, Φw. Maximum dew
accumulation (up to ~0.2 mm per night) is seen on nights with moist air and high Φw,
i.e., cloudless conditions with light winds. Favoured sites are those with high Ψsky
and surfaces which cool rapidly after sunset, e.g., grass and well insulated roofs.
A 1/8-scale model is designed, constructed, and run at an out-of-doors site to
study dew patterns in an urban residential landscape which consists of house lots, a
street and an open grassed park. The Internal Thermal Mass (ITM) approach is used
to scale the thermal inertia of buildings. The model is validated using data from fullscale
sites in Vancouver. Patterns in the model agree with those seen at the fullscale,
i.e., dew distribution is governed by weather, site geometry and substrate
conditions. Correlation is shown between Ψsky and surface moisture accumulation.
The feasibility of using a numerical model to simulate urban dew is
investigated using a modified version of a rural dew model. Results for simple
isolated surfaces—a deciduous tree leaf and an asphalt shingle roof—show promise,
especially for built surfaces. [Scientific formulae used in this abstract could not be reproduced.]
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Observation and modelling of urban dewRichards, Katrina 05 1900 (has links)
Despite its relevance to many aspects of urban climate and to several practical
questions, urban dew has largely been ignored. Here, simple observations, an outof-
doors scale model, and numerical simulation are used to investigate patterns of
dewfall and surface moisture (dew + guttation) in urban environments. Observations
and modelling were undertaken in Vancouver, B.C., primarily during the summers of
1993 and 1996.
Surveys at several scales (0.02-25 km) show that the main controls on dew
are weather, location and site configuration (geometry and surface materials).
Weather effects are discussed using an empirical factor, Φw. Maximum dew
accumulation (up to ~0.2 mm per night) is seen on nights with moist air and high Φw,
i.e., cloudless conditions with light winds. Favoured sites are those with high Ψsky
and surfaces which cool rapidly after sunset, e.g., grass and well insulated roofs.
A 1/8-scale model is designed, constructed, and run at an out-of-doors site to
study dew patterns in an urban residential landscape which consists of house lots, a
street and an open grassed park. The Internal Thermal Mass (ITM) approach is used
to scale the thermal inertia of buildings. The model is validated using data from fullscale
sites in Vancouver. Patterns in the model agree with those seen at the fullscale,
i.e., dew distribution is governed by weather, site geometry and substrate
conditions. Correlation is shown between Ψsky and surface moisture accumulation.
The feasibility of using a numerical model to simulate urban dew is
investigated using a modified version of a rural dew model. Results for simple
isolated surfaces—a deciduous tree leaf and an asphalt shingle roof—show promise,
especially for built surfaces. [Scientific formulae used in this abstract could not be reproduced.] / Arts, Faculty of / Geography, Department of / Graduate
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Latitudinal and vertical relationships between tropospheric ozone and water vapor as measured in Project GametagRouthier, Francis Xavier 08 1900 (has links)
No description available.
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Automatic isochoric apparatus for PVT and phase equilibrium studies of natural gas mixturesZhou, Jingjun 15 May 2009 (has links)
We have developed a new automatic apparatus for the measurement of the phase equilibrium and pVT properties of natural gas mixtures in our laboratory. Based on the isochoric method, the apparatus can operate at temperature from 200 K to 500 K at pressures up to 35 MPa, and yield absolute results in fully automated operation. Temperature measurements are accurate to 10 mK and pressure measurements are accurate to 0.002 MPa. The isochoric method utilizes pressure versus temperature measurements along an isomole and detects phase boundaries by locating the change in the slope of the isochores. The experimental data from four gas samples show that cubic equations of state, such as Peng-Robinson and Soave-Redich-Kwong have 1-20% errors in predicting hydrocarbon mixture dew points. The data also show that the AGA 8-DC92 equation of state has errors as large as 0.6% when predicting hydrocarbon mixture densities when its normal composition range is extrapolated.
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Automatic isochoric apparatus for PVT and phase equilibrium studies of natural gas mixturesZhou, Jingjun 15 May 2009 (has links)
We have developed a new automatic apparatus for the measurement of the phase equilibrium and pVT properties of natural gas mixtures in our laboratory. Based on the isochoric method, the apparatus can operate at temperature from 200 K to 500 K at pressures up to 35 MPa, and yield absolute results in fully automated operation. Temperature measurements are accurate to 10 mK and pressure measurements are accurate to 0.002 MPa. The isochoric method utilizes pressure versus temperature measurements along an isomole and detects phase boundaries by locating the change in the slope of the isochores. The experimental data from four gas samples show that cubic equations of state, such as Peng-Robinson and Soave-Redich-Kwong have 1-20% errors in predicting hydrocarbon mixture dew points. The data also show that the AGA 8-DC92 equation of state has errors as large as 0.6% when predicting hydrocarbon mixture densities when its normal composition range is extrapolated.
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EXPERIMENTAL STUDY AND QUANTIFICATION OF EMISSIONS IN CONTROL ATMOPSHERE BRAZING PROCESSRenduchintala, Ajay Babu 01 January 2006 (has links)
The work explains how the dynamics of the release of water vapors from flux during the Control Atmosphere Brazing influences the process conditions important for the quality of the brazed product. The process involves sequential events such as continuous ramp-up heating, flux and filler melting, reactive flow, isothermal dwell and rapid quench solidification performed under the controlled atmosphere. During this complex process effluents are released. Some effluents are detrimental for the product quality (water vapor) and some are harmful for the environment (HF). We selected to study water vapor emissions with an objective to quantify these emissions and to consider their influence on the manufacturing process. Experiments were conducted using different fluxes. Findings are presented to compare the vapors released in each case. The objective is not necessarily to develop a metric for sustainability, but to understand the kinetics of an effluent release. A simple predictive model has been devised to approximate experimental data behavior. The data from the TGA analysis obtained from other sources, and the dew point temperature history from the controlled atmosphere brazing experiments performed in course of this work, have been used for the purpose of comparison and analysis.
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A Study of Dew Harvesting and Freezing Performance of Non-Wetting SurfacesFuller, Alexander Michael 12 July 2023 (has links)
Non-wetting surfaces offer enhanced capabilities over bare metal substrates for condensation with or without phase change. This trait can be utilized to broaden strategies in combating water scarcity in water stressed areas. Slippery lubricant infused surfaces have the ability to shed water droplets with lower nucleation times, taking advantage of more of the limited amount of time available to collect dew and fog than traditional surfaces. However, existing studies focus on short durations with scant information available on the longer-term performance or durability of the materials in application environments. To address this knowledge gap, dew harvesting studies were conducted over a 96 hour period on a lubricant infused surface vis-à-vis regular surface of the same material. Three phases of performance are identified and discussed with regard to the water harvesting potential. The second part of the thesis addresses water condensation under conditions where freezing is a potential issue. Non-wetting surfaces have been shown to be a promising method of limiting the formation of ice from sessile droplets. This study explores the effect of surface roughness on the freeze time of sessile water droplets. Superhydrophobic and hydrophobic, lubricant infused, copper surfaces were created via electrodeposition and chemical etching in conjunction with chemical treatments to achieve non-wetting surfaces of varying surface textures. Freezing characteristics on the surfaces are studied experimentally and, for the first time, computationally, wherein the surface is described using a fractal surface topography. The effect of surface engineering on the freezing dynamics and comparison between the experimental and the computational studies are elucidated. / Master of Science / The use of durable, water repelling surfaces that are also thermally conductive provide an opportunity to help alleviate strain from a growing world crisis, water scarcity. Lubricant infused surfaces shed water from their surface by providing a slippery layer for the droplets to slide on, as opposed to bare metal which water tends to cling to. This behavior makes lubricant infused surfaces attractive as a water harvesting method. However, these surfaces degrade over time and must be maintained to perform at their maximum capability, collecting water for 40 minutes more than a bare surface. This thesis focuses on the performance of these surfaces over a 96-hour operating period to characterize the effect lubricant drainage has on the water collection behavior.
Freezing water droplets, commonly referred to as icing, poses concerns for safety and operational ability in industries like renewable energy generation, where icing limits efficiency. Non-wetting surfaces have a unique ability to inherently slow down the phase change of a water droplet to ice due to the lower contact area of droplets resting on the surface. This thesis examines superhydrophobic and lubricant infused surfaces of varying degrees of roughness to explore the effect that the contact angle and different surface structures have on the freezing rate of water on the surface. The experimental results are compared to numerical simulations, which is useful in designing systems that would implement this passive icing mitigation technique.
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Dew Point Hygrometer With Constant Resistance Humidity TransducerCampbell, Curtis B. 01 May 1969 (has links)
The hygroscopic and electrical resistance characteristics of lithium chloride are investigated. Then an evaluation is made of the lithium chloride characteristics that would be suitable in development of a dew point hygrometer with measurement accuracy of + 0. 3 c.
The development of a 12 volt battery-powered hygrometer is presented with circuit details and performance characteristics. Lithium chloride phase transition hygrometers tend to oscillate under certain conditions. A damping control is presented as part of the circuit details and recordings of the response characteristics and effectiveness of damping are presented showing effective control of the oscillations with a wide range of humidity transients.
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Experimental and theoretical study of the phenomena of corrosion by carbon dioxide under dewing conditions at the top of a horizontal pipeline in the presence of a non-condensable gasVitse, Frédéric. January 2002 (has links)
Thesis (Ph.D.)--Ohio University, November, 2002. / Title from PDF t.p. Includes bibliographical references (leaves 175-177)
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A Stable Isotope Approach to Investigative Ecohydrological Processes in NamibiaKaseke, Kudzai Farai 12 1900 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Drylands cover 40% of the earth’s terrestrial surface supporting over 2 billion
people, the majority of whom reside in developing nations characterised by high population
growth rates. This imposes pressure on the already limited water resources and in some
dryland regions such as southern Africa, the origins and dynamics of rainfall are not well
understood. Research has also tended to focus on factors limiting (e.g., rainfall) than
sustaining productivity in drylands. However, non-rainfall water (NRW) e.g., fog and dew
can supplement and/or exceed rainfall in these environments and could potentially be
exploited as potable water resources. Much remains unknown in terms of NRW formation
mechanisms, origins, evolution, potability and potential impact of global climate change
on these NRW dependent ecosystems.
Using Namibia as a proxy for drylands and developing nations, this dissertation
applies stable isotopes of water (δ2H, δ18O, δ17O and d-excess), cokriging and trajectory
analysis methods to understand ecohydrological processes. Results suggest that locally
generated NRW may be a regular occurrence even in coastal areas such as the Namib
Desert, and that what may appear as a single fog event may consist of different fog types
co-occurring. These results are important because NRW responses to global climate change
is dependent on the source, groundwater vs. ocean, and being able to distinguish the two
will allow for more accurate modelling. I also demonstrate, that fog and dew formation are
controlled by different fractionation processes, paving the way for plant water use strategy
studies and modelling responses to global climate change. The study also suggests that
current NRW harvesting technologies could be improved and that the potability of this
water could raise some public health concerns related to trace metal and biological
contamination. At the same time, the dissertation concludes that global precipitation
isoscapes do not capture local isotope variations in Namibia, suggesting caution when
applied to drylands and developing nations. Finally, the dissertation also reports for the
first time, δ17O precipitation results for Namibia, novel isotope methods to differentiate synoptic from local droughts and suggests non-negligible moisture contributions from the
Atlantic Ocean due to a possible sub-tropical Atlantic Ocean dipole.
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