163,675 research outputs found
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)
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
Lamp Wick.
No full textPatent for a new and improved wick for oil lamps. This design "consists in forming the lamp-wick of one or more layers of mineral wool inclosed in a textile material, the whole being sewed together by a series of parallel longitudinal stitches" (lines 18-22). Employing textile material represents an improvement in capillarity over previous wicks made with refractory cement
Wick Regulator for Lamps.
No full textPatent for "an improvement in those lamp-wick regulators which consists of a threaded rod operated by a nut and connected to the wick, whereby the wick may be raised or lowered by operating the nut; and the invention lies in an improved connection between the wick and rod, by which the wick can be raised with more uniformity and ease." (Lines 8-15) Includes instructions and illustrations
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
Phase-change heat transfer of sintered-particle wick in downward facing orientation: Particle size and wick thickness effects
No full textClick on the DOI link to access the article (may not be free).Two-phase cooling systems using wicks offer reliable and high heat flux cooling capability, however, the maximum heat removal capacity is related to capillary pumping limit and wick superheat. In this study, non-uniform wicks are examined to simultaneously enhance the capillary pumping limit and minimize wick superheat. The non-uniform wick consists of a thin evaporation wick for reducing the wick superheat and a thick coolant supply wick for enhancing the coolant supply. Also, it has a phase-separating wick attached to the coolant supply wick to ensure the vapor escape channels. The thin wick is fabricated using sintered-copper particles with 30–200 μm spherical particles, while the post and phase-separating wicks are constructed using 10 and 3 layers of 200 μm copper particles, respectively. To minimize the gravity-driven liquid supply, the liquid reservoir is placed below the wick structure, i.e., downward facing orientation. The heat flux is measured as a function of the wick superheat using different particles sizes and thicknesses of the thin wick, i.e., 30, 60, 100, 200, 60/200, and 100/200 μm with 1–3 layers. The results show that 60 μm particles result in the minimal wick superheat at q < 100 W/cm2 for 1 and 2 layers of the wick, while the 100/200 μm particles with 3 layers leads to the maximum heat flux of 223 W/cm2, which is ~48% enhancement compared to the bare copper surface at the wick superheat of 38.6 °C. Also, it is found that the 2 and 3 layer wicks substantially decrease the wick superheat compared to the single layer wick, although the wick thickness (conductive thermal resistance) is larger. This is attributed to the 2 and 3 layer wick enhance the liquid supply, by increasing the cross-section area of the wick, thus, delaying the surface dryout
Marvin Stone with Charles Wick, Dir. of USIA
No full textMarvin Stone with Charles Wick, Dir. of USIA, col. back reads: Nov. 1985 w/Charles Wick (Wick was Director of USIA, U.S. Information Agency).https://mds.marshall.edu/marvin_stone_collection/1023/thumbnail.jp
On the essential self-adjointness of Wick powers of relativistic fields and of fields unitary equivalent to random fields
No full textThe essential self-adjointness on a natural domain of the sharp-time Wick powers of the relativistic free field in two space-time dimension is proven. Other results on Wick powers are reviewed and discussed
Lee–Wick theories at high temperature
No full textAbstractAn extension of the standard model, the Lee–Wick standard model, based on ideas of Lee and Wick was recently introduced. It does not contain quadratic divergences in the Higgs mass and hence solves the hierarchy puzzle. The Lee–Wick standard model contains new heavy Lee–Wick resonances at the TeV scale that decay to ordinary particles. In this Letter we examine the behavior of Lee–Wick resonances at high temperature. We argue that they contribute negatively to the energy density ρ and pressure p and at temperatures much greater than their mass M their O(T4) contributions to ρ and p cancel against those of the ordinary (light) particles. The remaining O(M2T2) contributions are positive and result in an equation of state that approaches w=1 from below as T→∞
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