8,481 research outputs found
Engineering calculations for the Delta S method of solving the orbital allotment problem
The method of calculating single-entry separation requirements for pairs of satellites is extended to include the interference on the top link as well as on the down link. Several heuristic models for analyzing the effects of shaped-beam antenna designs on required satellite separations are introduced and demonstrated with gain contour plots. The calculation of aggregate interference is extended to include the effects of up-link interference. The relationship between the single-entry C/I requirements, used in determining satellite separation constraints for various optimization procedures, and the aggregate C/I values of the resulting solutions is discussed
Energy non-equipartition in systems of inelastic, rough spheres
We calculate and verify with simulations the ratio between the average
translational and rotational energies of systems with rough, inelastic
particles, either forced or freely cooling. The ratio shows non-equipartition
of energy. In stationary flows, this ratio depends mainly on the particle
roughness, but in nonstationary flows, such as freely cooling granular media,
it also depends strongly on the normal dissipation. The approach presented here
unifies and simplifies different results obtained by more elaborate kinetic
theories. We observe that the boundary induced energy flux plays an important
role.Comment: 4 pages latex, 4 embedded eps figures, accepted by Phys Rev
Steps towards the development of an experimentally verified simulation of pool nucleate boiling on a silicon wafer with artificial sites
Nucleate boiling is a very effective heat transfer cooling process, used in numerous industrial applications. Despite intensive research over decades, a reliable model of nucleate pool boiling is still not available. This paper presents a numerical and experimental investigation of nucleate boiling from artificial nucleation sites.
The numerical investigation described in the first section of the paper is carried out by a hybrid mechanistic numerical code first developed at the University of Ljubljana to simulate the temperature field in a heated stainless steel plate with a large number of nucleation sites during pool boiling of water at atmospheric pressure. It is now being redeveloped to interpret experiments on pool boiling at artificial sites on a silicon plate and as a design tool to investigate different arrangements of sites to achieve high heat fluxes. The code combines full simulation of the temperature field in the solid wall with simplified models or correlations for processes in the liquid-vapour region. The current capabilities and limitations of the code are reviewed and improvements are discussed. Examples are given of the removal of computational constraints on the activation of sites in close proximity and improvements to the bubble growth model. Preliminary simulations are presented to compare the wall conditions to be used in the experiments on silicon at Edinburgh University with the conditions in current experiments on thin metal foils at Ljubljana.
An experimental rig for boiling experiments with artificial cavities on a 0.38 mm thick silicon wafer immersed in FC-72, developed at Edinburgh University, is described in the second part of the paper
What do stakeholders consider the key issues affecting the quality of foodservice provision for long-stay patients
This study aimed to elicit concerns of key stakeholders regarding food service provision to long stay hospital patients. Seventeen focus groups and four individual interviews were conducted involving six stakeholder groups: dietitians, nutrition assistants, patients, nurses, food service assistants and food service managers. Ninety-eight participants (20 male; 78 female) were recruited from public and private hospitals in New South Wales, Australia. Each of the focus groups and individual interviews was conducted in the hospital setting where free and open discussions could be digitally recorded. Transcripts were prepared from the digital recordings and QSR Nvivo 2.0™ qualitative analysis software was used to code the transcripts prior to content and thematic analysis. Themes were identified by relative frequency in the discussion, number of issues raised within each theme and the importance placed on the issues raised. Five major themes emerged from thirty seven discussion topics: the food service system, menu variety, preparation to eat/feeding assistance, packaging and portion size. Participants were particularly concerned about the increased packaging of food products, perceived lack of meal set up and feeding assistance, limited menu variety especially when considering longer stay hospital inpatients, and the increased use of cook-chill operations. These findings lend themselves well to testing in a wider sphere via quantitative means in a proposed national survey. The results of this survey may produce a position on the main barriers to effective food service provision to long stay patients in the Australian context, and enable identification of practical solutions
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Experimental pool boiling investigations of vertical coalescence for FC-72 on silicon from an isolated artificial cavity
In this study bubble growth from an isolated artificial cavity micro-fabricated on a horizontal 380 µm thick silicon wafer was investigated. The horizontally oriented boiling surface was heated by a thin resistance heater integrated on the rear of the silicon test section. The temperature was measured using an integrated micro-sensor situated on the boiling surface with the artificial cavity located in its geometrical centre. A resistive track was used as the sensor, which when calibrated, exhibited a near-linear behaviour with increasing temperature. To conduct pool boiling experiments the test section was immersed in degassed fluorinert FC-72. Bubble nucleation, growth and detachment at different pressures were observed using high-speed imaging. Coalescence was observed at the boundary between the isolated bubble and interference regimes. The occurrence of vertical coalescence was found to be more frequent, with increasing wall superheat and decreasing pressure.
The equivalent sphere volumes of two bubbles before and after coalescence were evaluated from area measurements. It was observed that the second nucleated bubble is always smaller than its predecessor. The vapour generation appears not to stop during coalescence as the volume of the merged bubble was typically 5-18% larger than the sum of the bubble volumes just before coalescence
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