49 research outputs found
INTELLIGENT DISCRIMINATION MODEL TO IDENTIFY INFLUENTIAL PARAMETERS DURING CRYSTALLISATION FOULING
Get PDFThe introduction of redundant independent variables into any function approximation model, or the neglect of important variables, may result in a correlation with poor prediction and reduced reliability. This paper demonstrates that a novel integrated model of neural networks and genetic algorithms can deal with this problem robustly with good accuracy, while be far less time-consuming compared to lengthy conventional models Furthermore, a redundant variable input was imposed to the model to discern if the approach could identify it among other important variables. Genetic algorithms were exploited as a powerful optimisation tool for the selection of best set of inputs with the help of process “prior knowledge” rules. A comprehensive databank of crystallisation fouling under subcooled flow boiling was used. The resulting model was capable of handling the data and successfully discriminated among several independent inputs if there is any redundant input. The technique may be regarded as a robust method to prevent data over-fitting as well as processes where a large number of inputs are involved such as crude oil fouling
Mitigation of crystallization fouling using projectiles in a single heated tube
Get PDFPaper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Fouling of heat exchangers is a prevalent operating
drawback in many industries. Efficient chemical inhibitors
have predominantly been used for many years to combat
deposit formation. Nevertheless new stringent
environmental legislations limit their utilization. In the
present experimental study, two spherical type projectiles of
different sizes and hardness have been used to clean the
inner surface of a single heated tube which was subjected to
the deposition of calcium sulphate. Projectiles were then
injected at different time intervals of injection of every 2, 5,
10, 15, and 30 minutes. The experimental results show that
i) the projectiles would expedite initial nucleation of
crystals even if they are soft and easy to propel inside the
tube and ii) fouling can only be mitigated if the projectiles
exert a shear force that its corresponding removal rate is
greater than the net rate the deposition.dc201
EXPERIMENTAL INVESTIGATION OF CRYSTALLIZATION FOULING ON GROOVED STAINLESS STEEL SURFACES DURING CONVECTIVE HEAT TRANSFER
Get PDFThe beneficial aspects of enhanced or extended heat transfer surfaces may be off-set if operated under fouling conditions. In the present paper, preliminary experimental results for crystallization fouling of CaSO4 solutions onto surfaces with different structures are reported. Flat stainless steel plates (50 mm x 59 mm) with \u27V\u27 shaped grooves on the side of fluid flow were used as heat transfer surfaces. Experiments were carried out both under clean and fouling conditions to discern how the same surface structures perform under such circumstances. In addition, the impact of both, the direction of grooves with respect to fluid flow (crossed, longitudinal and mixed flow grooves) and the groove dimensions has also been investigated. Fouling trends are discussed in terms of delay time and fouling rate. Significant differences have been found for the various flow conditions
Comparison of plain and finned tubes during pool boiling of CaSO4 solutions
Get PDFPaper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.One of the most severe types of fouling occurs during pool boiling heat transfer. This has led some processes such as thermal desalination units, in particular, to be operated below saturation temperature to avoid rapid and severe formation of crystallized deposits e.g. CaSO4 on heat transfer surfaces. This has been despite superiority of pool boiling to other modes of heat transfer. This study investigates experimentally the formation of deposit on the finned tubes during pool boiling of CaSO4 solutions. The structured tubes are low finned tube type with a fin density of 19 fins per inch, 1.35 mm fin pitch and Cu-Ni as substrate. Fouling runs are carried out for different heat fluxes ranging from 100 to 300 kW/m2 and different salt concentrations at atmospheric pressure. For the sake of comparison, similar runs are also conducted for plain stainless steel tubes. Experimental results show for the finned tubes, substantial reduction of fouling compared to those of the plain tube. If any deposit forms on the surface then it is only a very thin and fragile layer of crystals which differs significantly to plain tubes which is characterized with a thick layer of deposit. In addition, the finned tubes perform much better at lower heat fluxes. Finally, the cleanability of finned tubes is also examined which show good performance.dc201
Low-mass pre--main-sequence stars in the Magellanic Clouds
Full text link[Abridged] The stellar Initial Mass Function (IMF) suggests that sub-solar
stars form in very large numbers. Most attractive places for catching low-mass
star formation in the act are young stellar clusters and associations, still
(half-)embedded in star-forming regions. The low-mass stars in such regions are
still in their pre--main-sequence (PMS) evolutionary phase. The peculiar nature
of these objects and the contamination of their samples by the evolved
populations of the Galactic disk impose demanding observational techniques for
the detection of complete numbers of PMS stars in the Milky Way. The Magellanic
Clouds, the companion galaxies to our own, demonstrate an exceptional star
formation activity. The low extinction and stellar field contamination in
star-forming regions of these galaxies imply a more efficient detection of
low-mass PMS stars than in the Milky Way, but their distance from us make the
application of special detection techniques unfeasible. Nonetheless, imaging
with the Hubble Space Telescope yield the discovery of solar and sub-solar PMS
stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of
such objects are identified as the low-mass stellar content of their
star-forming regions, changing completely our picture of young stellar systems
outside the Milky Way, and extending the extragalactic stellar IMF below the
persisting threshold of a few solar masses. This review presents the recent
developments in the investigation of PMS stars in the Magellanic Clouds, with
special focus on the limitations by single-epoch photometry that can only be
circumvented by the detailed study of the observable behavior of these stars in
the color-magnitude diagram. The achieved characterization of the low-mass PMS
stars in the Magellanic Clouds allowed thus a more comprehensive understanding
of the star formation process in our neighboring galaxies.Comment: Review paper, 26 pages (in LaTeX style for Springer journals), 4
figures. Accepted for publication in Space Science Review
Validation of the use of air/water in simulating bubbly steam/water flows
Get PDFSIGLEAvailable from British Library Document Supply Centre-DSC:DXN036006 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
INVESTIGATION OF THERMOPHORESIS IMPACT ON FOAMED HEAT EXCHANGERS USING SIMULATION
No full textConcerns about emissions and desire for their reduction have resulted in
changes in automotive engine combustion systems. New developed EGR systems require high temperature and high-performance compact heat exchangers as well as capability of operating in harsh environments. Foams offer a large surface area per unit volume as well as high material thermal conductivity which would promote fluid mixing, thereby improving the overall performance of the heat exchanger. More interestingly, it is demonstrated that the foams can be cleaned easily without relying on expensive cleaning techniques. These interesting characteristics, along with recent improvements in foam fabrication methods, have resulted in several research efforts on the use of foams in compact heat exchangers, especially new EGR systems. One of the principal challenges is the deposition of particulate matter mainly as a result of thermophoresis in
non-isothermal systems. Accordingly, in the present study, to investigate the
significance of thermophoresis in open cellular metal foam, Two-Dimensional
(2D) numerical simulations of a channel partially filled with aluminium foam as
an EGR cooler were performed by ANSYS FLUENT 16.0 to solve local thermal non-equilibrium equation under clean conditions (maximum driving force of particle transport for thermophoresis mechanism). The attempted foam is made of aluminium and is embedded to the channel, meaning that the conduit is only
filled with foam partially to compensate high pressure due to blockage. Thermo-hydraulic performance for a foam with density of 20 PPI is examined under different velocities and thermal gradients. The numerical results are compared with those of experiments. Under non-isothermal conditions, the numerical results confirmed that temperature gradient would be marginal for different thicknesses of aluminium foams because thermal equilibrium has been established, especially at foam and foam-free interface. Provided that maximum driving force for thermophoresis occurs at clean conditions, it is expected that this mechanism would have minimal impact at fouling conditions where particulate matter passes through the channel
Neural network analysis of heat transfer fouling data during subcooled flow boiling of hard water
No full textInitiation of CASO<sub>4</sub> Scale Formation on Heat Transfer Surfaces under Pool Boiling Conditions
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