3,241 research outputs found
An experimental and theoretical investigation of a wick-type solar still for water desalination
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Solar distillation using a wick-type solar still was investigated theoretically and experimentally. A tilled flat plate wick-type solar still was designed and constructed.
Charcoal cloth was used as an absorber/evaporator material and for saline water transport. A theoretical model for the performance of the wick-type solar still has been developed and analysed. It investigates the effect of various factors on the still productivity. A Fortran computer program has been developed and a finite difference technique was used to solve the main equations and to determine related parameters.
Indoor experimental testing was carried out to investigate the effect of input water flow rate and salinity on the still productivity together with the variation of the solar still efficiency with absorber temperature. The tests were conducted using the irradiance from a lamp array. Outdoor testing was carried out with and without a V-trough solar concentrator on clear days in summer and winter. Representative daily efficiencies of the still with and without the solar concentrator were about 60% and 50% respectively on clear days in summer. The solar absorptances of samples of charcoal cloth and blackened hessian cloth were determined before and after environmental exposure. The solar reflectances of samples of 3M Scotchcal Films and aluminised plastic (as potential reflecting materials for the concentrator mirrors) were investigated before and after environmental exposure and also exposure to elevated temperatures and humidities. It has been concluded that: charcoal cloth is a good material for use as an absorber/evaporator and also as a water transport medium. Increase of the input water mass flow rate leads to a reduction in the efficiency of the wick-type solar still. The still efficiency decreased linearly with Increase of salinity of the input saline water. The productivity of the still Increases linearly with absorber temperature. The best absorber-cover separation Is found to be in the range 20-25 mm. Wind speed has no significant effect (up to about 10 m/s) on the performance of a well sealed still. The transmittance of the glass cover has a strong influence on the still efficiency. Use of the solar concentrator with the inclined wick-type solar still leads to a greater fractional increase In still productivity on clear days in winter than on clear days in summer
A mathematical approach to Wick rotations
No full textIn this thesis we define Wick-rotations mathematically using pseudo-Riemannian geometry, and relate Wick-rotations to real geometric invariant theory (GIT). We discover some new results concerning the existence of Wick rotations (of various signatures). For instance we show that a Wick-rotation of a pseudo-Riemannian space (at a fixed point p) to a Riemannian space forces the space to be Riemann purely electric (RPE). We also define compatibility among representations and relate them to real GIT and Wick-rotations. The polynomial curvature invariants of pseudo-Riemannian spaces are also considered and related to Wick-rotations.
Wick-rotations of a special class of pseudo-Riemannian manifolds (M; g) are also studied; namely Lie groups G equipped with left-invariant metrics. We prove some new results concerning the existence of real slices (of Lie algebras) of certain signatures of a holomorphic inner product space (gC; gC) (on a complex Lie algebra). The definition of a Cartan involution for a semisimple Lie algebra is defined for a general Lie algebra equipped with a pseudo-inner product: (g; g), and the theorems of Cartan (concerning Cartan involutions) are generalised and proved. For instance we prove that a pseudo-Riemannian Lie group (G; g) can be Wick-rotated to a Riemannian Lie group ( ~ G; ~g) if and only if there exist a Cartan involution of the Lie algebra g
Modeling and Design Optimization of Ultra-Thin Vapor Chambers for High Heat Flux Applications
No full textPassive phase-change thermal spreaders, such as vapor chambers have been widely employed to spread the heat from small-scale high-flux heat sources to larger areas. In this paper, a numerical model for ultrathin vapor chambers has been developed, which is suitable for reliable prediction of the operation at high heat fluxes and small scales. The effects of boiling in the wick structure on the thermal performance are modeled, and the model predictions are compared with experiments on custom-fabricated vapor chamber devices. The working fluid for the vapor chamber is water and a condenser side temperature range of 293 K–333 K is considered. The model predictions agree reasonably well with experimental measurements and reveal the input parameters to which thermal resistance and vapor chamber capillary limit are most sensitive. The vapor space in the ultrathin devices offers significant thermal and flow resistances when the vapor core thickness is in the range of 0.2 mm–0.4 mm. The performance of a 1-mm-thick vapor chamber is optimized by studying the variation of thermal resistance and total flow pressure drop as functions of the wick and vapor core thicknesses. The wick thickness is varied from 0.05 to 0.25 mm. Based on the minimization of a performance cost function comprising the device thermal resistance and flow pressure drop, it is concluded that the thinnest wick structures (0.05 mm) are optimal for applications with heat fluxes below 50 W/cm2, while a moderate wick thickness of 0.1 mm performs best at higher heat flux inputs (\u3e50 W/cm2)
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0-G experiments with advanced ceramic fabric wick structures
No full textBoth Air Force and NASA future spacecraft thermal management needs span the temperature range from cryogenic to liquid metals. Many of these needs are changing and not well defined and will remain so until goals, technology, and missions converge. Nevertheless, it is certain that high-temperature (> 800 K) and medium-temperature (about 450 K) radiator systems will have to be developed that offer significant improvements over current designs. This paper discusses experiments performed in the lower temperature regime as part of a comprehensive advanced ceramic fabric (ACF) heat pipe development program. These experiments encompassed wicking tests with various ceramic fabric samples, and heat transfer tests with a 1-m long prototype ACF water heat pipe. A prototype ceramic fabric/titanium water heat pipe has been constructed and tested; it transported up to 60 W of power at about 390 K. Startup and operation both with and against gravity examined. Wick testing was begun to aid in the design and construction of an improved prototype heat pipe, with a 38-{mu}m stainless steel linear covered by a biaxially-braided Nextel (trademark of the 3M Co., St. Paul, Minnesota) sleeve that is approximately 300-{mu}m thick. Wick testing took place in 1-g; limited testing in 0-g was initiated, and results to date suggest that in 0-g, wick performance improves over that in 1-g
Pseudo-differential operators with isotropic symbols, Wick and anti-Wick operators, and hypoellipticity
No full textWe study the link between ilidos and Wick operators via the Bargmann transform. We deduce a formula for the symbol of the Wick operator in terms of the short-time Fourier transform of the Weyl symbol. This gives characterizations of Wick symbols of ilidos of Shubin type and of infinite order, and results on composition. We prove a series expansion of Wick operators in terms of anti-Wick operators which leads to a sharp Garding inequality and transition of hypoellipticity between Wick and Shubin symbols. Finally we show continuity results for anti-Wick operators, and estimates for the Wick symbols of anti-Wick operators.(c) 2022 The Author(s). Published by Elsevier Masson SAS. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Lamp Wick Raiser.
No full textPatent for a device designed to manipulate a lamp-wick in its guiding tube without cutting or injuring the wick, including illustrations
White Noise Functional Solutions for Wick-Type Stochastic Fractional Mixed KdV-mKdV Equation Using Extended G′/G-Expansion Method
No full textIn this paper, white noise functional solutions of Wick-type stochastic fractional mixed KdV-mKdV equations have been obtained by using the extended G′/G-expansion method and the Hermite transform. Firstly, the Hermite transform is used to transform Wick-type stochastic fractional mixed KdV-mKdV equations into deterministic fractional mixed KdV-mKdV equations. Secondly, the exact traveling wave solutions of deterministic fractional mixed KdV-mKdV equations are constructed by applying the extended G′/G-expansion method. Finally, a series of white noise functional solutions are obtained by the inverse Hermite transform
U.S. President Ronald Reagan addresses the Voice of America on its fortieth anniversary
No full textGift of Voice of America.Charles Wick, Director of the US Information Agency, introduces the President. Reagan complements the VOA and describes many threats to freedom in the world. He also recounts his own experiences as a radio sports broadcaster. Wick presents Reagan with a microphone commemorating his presence at the event
Rede an dem für die Jugend veranstalteten Reformationsfeste den 10. Januar 1819 bei St. Peter vorgetragen und zum gesegneten Andenken den lieben Kindern übergeben
No full textvon Jacob Wick, Diaco
UJI JENIS NUTRISI PADA SELADA HIDROPONIK SISTIM WICK: Nutrition Type Test On Hydroponic Lettuce Wick System
No full textSimple hydroponic wick system (Wicks) can be applied in overcoming the land crisis for the development of horticultural crops. Nutrients are an important part of hydroponic activities and Abmix is a standard nutrient in hydroponic farming activities. It is necessary to test the opportunities for the utilization of nutrients from POC and synthetic fertilizers. This study aims to determine the opportunities for using liquid organic fertilizers (POC) and synthetic fertilizers in hydroponic lettuce plants using the wick system. The treatment consisted of 5 types of nutrition, namely (1) AB mix (control) 50 mL per 10 liters of water (ABM); (2) NPK 10 g + Gandasil 5 g per 10 liters of water (NPG); (3) Abmix 25 mL + 5g NPK + 2.5 g Gandasil per 10 liters of water (ANG); (4) Abmix 25 mL + 400 mL POC from chicken feather waste (ABP) and (5) 5 g NPK + 2.5 g Gandasil + 400 mL POC chicken feathers per 10 liters of water (NGP). The results showed that there were differences in the growth of lettuce in the hydroponic wick system due to the type of nutrition treatment. Alternative nutrients that have the potential to be used in wick cystic hydroponic lettuce are Abmix 25ml + 5g NPK + 2.5 g Gandasil per 10 liters of water (ANG) and Abmix 25 mL+ 400 mL POC from chicken feather waste per 10 liters of water (ABP
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