2,075 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
Asymptotic equivalence of fluctuation fields for reversible exclusion processes with speed change
No full textInhalant deaths in south Australia - A 20-year retrospective autopsy study
No full textA 20-year retrospective study of inhalant deaths in South Australia, autopsied at Forensic Science SA, was undertaken from January 1983 to December 2002. Thirty-nine cases were identified from an autopsy pool of 18,880 cases, with a male to female ratio of 12:1. Sixty-four percent of the victims (N = 25) died during voluntary inhalation of volatile substances and 28% (N = 11) committed suicide utilizing a volatile substance or gas. The remaining 3 cases involved a workplace accident (N = 1) and 2 cases of autoerotic death where inhalants were being used to augment solitary sexual activity. The mean age of the 28 victims of accidental inhalant death of 21 years (range, 13-45 years) was considerably less than that of the 11 suicide victims of 31.5 years (range, 17-48 years). No homicides were found. Approximately one quarter of the victims were Aboriginal (N = 11), 10 of whom had died as a result of gasoline inhalation ("petrol sniffing"). Other common substances of abuse were aliphatic hydrocarbons such as butane. The study has shown that those most at risk for accidental or suicidal inhalant deaths were young males, with 92% of victims overall being male, and with 77% of victims being under 31 years of age. Gasoline inhalation remains a significant problem in Aboriginal communities in South Australia.Regula Wick, John D. Gilbert, Peter Felgate, and Roger W. Byar
Corrigenda : "stabilization in H∞R(D)"
No full textIn this corrigenda we outline the necessary changes to the paper [3] so that the main result in that paper is made correct. The mistake the author made in the previous version was that the condition that f1 being positive on the zeros of f2 was not strong enough ∞ to guarantee the existence of the logarithm in HR (D)
Heat and Mass Transport in Heat Pipe Wick Structures
No full textAnovel experimental approach is developed for characterizing the performance of heat pipe wick structures. This approach simulates the actual operation of wick structures in a heat pipe. Open, partially submerged, sintered copper wicks of varying pore size are studied under the partially saturated conditions found in normal heat pipe operation. A vertical wick orientation, where the capillary lift is in opposition to gravity, is selected to test the wicks under the most demanding conditions. Mass transport measurements of the working fluid, in addition to the temperature field, are obtained for the porous wicks under the action of a discrete heat source (evaporator) mounted on one end. The working fluid, supplied from a condenser pool, evaporates from the wick surface primarily in the evaporator region and is condensed and collected into a container separate from the pool, to yield mass flow rates. Thus the liquid-pumping capability of the wick, coupled with flow impedance, is measured as a function of applied heat flux. Repeatable results with low uncertainty are obtained.Acareful analysis of the transport paths for heat and mass transfer in the wick structure confirms that mass transfer due to vaporization of the working fluid is the largest contributor to heat dissipation from the wick. The expected and measured values of evaporation rate are in good agreement. Results are also presented in terms of overall effective conductance based on measured temperatures
Corrigenda : "stabilization in H∞R(D)"
No full textIn this corrigenda we outline the necessary changes to the paper [3] so that the main result in that paper is made correct. The mistake the author made in the previous version was that the condition that f1 being positive on the zeros of f2 was not strong enough ∞ to guarantee the existence of the logarithm in HR (D)
Wick-Malliavin approximation to nonlinear stochastic partial differential equations: Analysis and simulations
No full textApproximating nonlinearities in stochastic partial differential equations (SPDEs) via the Wick product has often been used in quantum field theory and stochastic analysis. The main benefit is simplification of the equations but at the expense of introducing modelling errors. In this paper, we study the accuracy and computational efficiency of Wick-type approximations to SPDEs and demonstrate that the Wick propagator, i.e. the system of equations for the coefficients of the polynomial chaos expansion of the solution, has a sparse lower triangular structure that is seemingly universal, i.e. independent of the type of noise. We also introduce new higher-order stochastic approximations via Wick-Malliavin series expansions for Gaussian and uniformly distributed noises, and demonstrate convergence as the number of expansion terms increases. Our results are for diffusion, Burgers and Navier-Stokes equations, but the same approach can be readily adopted for other nonlinear SPDEs and more general noises. © 2013 The Author(s)
An invariance principle for reversible Markov Processes with application to random motion in random environment
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