Spelling suggestions: "subject:"heat transfer mechanisms"" "subject:"meat transfer mechanisms""
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Dynamic Modeling and Control of Distributed Heat Transfer Mechanisms: Application to a Membrane Distillation ModuleEleiwi, Fadi 12 1900 (has links)
Sustainable desalination technologies are the smart solution for producing fresh water
and preserve the environment and energy by using sustainable renewable energy
sources. Membrane distillation (MD) is an emerging technology which can be driven
by renewable energy. It is an innovative method for desalinating seawater and brackish
water with high quality production, and the gratitude is to its interesting potentials.
MD includes a transfer of water vapor from a feed solution to a permeate
solution through a micro-porous hydrophobic membrane, rejecting other non-volatile
constituents present in the influent water. The process is driven by the temperature
difference along the membrane boundaries. Different control applications and
supervision techniques would improve the performance and the efficiency of the MD
process, however controlling the MD process requires comprehensive mathematical
model for the distributed heat transfer mechanisms inside the process. Our objective
is to propose a dynamic mathematical model that accounts for the time evolution of
the involved heat transfer mechanisms in the process, and to be capable of hosting
intermittent energy supplies, besides managing the production rate of the process,
and optimizing its energy consumption. Therefore, we propose the 2D Advection-Diffusion Equation model to account for the heat diffusion and the heat convection mechanisms inside the process. Furthermore, experimental validations have proved
high agreement between model simulations and experiments with less than 5% relative
error. Enhancing the MD production is an anticipated goal, therefore, two main
control strategies are proposed. Consequently, we propose a nonlinear controller for
a semi-discretized version of the dynamic model to achieve an asymptotic tracking
for a desired temperature difference. Similarly, an observer-based feedback control
is used to track sufficient temperature difference for better productivity. The second
control strategy seeks for optimizing the trade-o between the maximum permeate flux production for a given set of inlet temperatures of the feed and the permeate solutions,
and the minimum of the energy consumed by the pump
ow rates of the feed
and the permeate solutions. Accordingly, Extremum Seeking Control is proposed for
this optimization, where the pump
flow rates of the feed and the permeate solutions
are the manipulated control input.
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ON HEAT TRANSFER MECHANISMS IN SECONDARY COOLING OF CONTINUOUS CASTING OF STEEL SLABHaibo Ma (11173431) 23 July 2021 (has links)
<p>Secondary cooling during continuous casting is a delicate
process because the cooling rate of water spray directly affects the slab
surface and internal quality. Undercooling may lead to slab surface bulging or
even breakout, whereas overcooling can cause deformation and crack of slabs due
to excessive thermal residual stresses and strains. Any slab which does not
meet the required quality will be downgraded or scrapped and remelted. In order to remain competitive and continuously
produce high-quality and high-strength steel at the maximum production rate,
the secondary cooling process must be carefully designed and controlled. Efficient
and uniform heat removal without deforming or crack the slab is a significant
challenge during secondary cooling. In the meantime, the on-site thermal
measurement techniques are limited due to the harsh environment. In contrast, experimental measurements
are only valid for the tested conditions, and the measurement process is not
only labor-intensive, but the result might be inapplicable when changes in the
process occur. On the other hand, the high-performance computing (HPC)-powered
computational fluid dynamics (CFD) approach has become a powerful tool to gain
insights into complex fluid flow and heat transfer problems. Yet, few
successful numerical models for heat transfer phenomena during secondary
cooling have been reported, primarily due to complex phenomena. </p>
<p> </p>
<p>Therefore, the current study has proposed two
three-dimensional continuum numerical models and a three-step coupling
procedure for the transport of mass, momentum, and energy during the secondary
cooling process. The first numerical model features the simulation of water
spray impingement heat and mass transfer on the surface of a moving slab considering
atomization, droplet dispersion, droplet-air interaction, droplet-droplet
interaction, droplet-wall impingement, the effect of vapor film, and droplet
boiling. The model has been validated against five benchmark experiments in
terms of droplet size prior to impingement, droplet impingement pressure, and
heat transfer coefficient (HTC) on the slab surface. The validated model has
been applied to a series of numerical simulations to investigate the effects of
spray nozzle type, spray flow rate, standoff distance, spray direction, casting
speed, nozzle-to-nozzle distance, row-to-row distance, arrangement of nozzles,
roll and roll pitch, spray angle, spray water temperature, slab surface
temperature, and spray cooling on the narrow face. Furthermore, the simulation
results have been used to generate a mathematically simple HTC correlation,
expressed as a function of nine essential operating parameters. A graphic user
interface (GUI) has been developed to facilitate the application of
correlations. The calculated two-dimensional HTC distribution is stored in the universal
comma-separated values (csv) format, and it can be directly applied as a boundary
condition to on-site off-line/on-line solidification calculation at steel mills.
The proposed numerical model and the generic methodology for HTC correlations should
benefit the steel industry by expediting the development process of HTC
correlations, achieving real-time dynamic spray cooling control, supporting
nozzle selection, troubleshooting malfunctioning nozzles, and can further
improve the accuracy of the existing casting control systems.</p>
<p> </p>
<p>In the second numerical model, the volume-averaged
Enthalpy-Porosity method has been extended to include the slurry effect at low
solid fractions through a switching function. With the HTC distribution on the
slab surface as the thermal boundary condition, the model has been used to
investigate the fluid flow, heat transfer, and solidification inside a slab
during the secondary cooling process. The model has been validated against the
analytical solution for a stationary thin solidifying body and the simulation
for a moving thin solidifying body. The effects of secondary dendrite arm
spacing, critical solid fraction, crystal constant, switching function
constant, cooling rate, rolls, nozzle-to-nozzle distance, and arrangement of
nozzles have been evaluated using the validated model. In addition, <a>the solidification model has been coupled with the
predictions from the HTC correlations, and the results have demonstrated the availability
of the correlations other than on-site continuous casting control. </a>Moreover,
the model, along with
the three-step coupling procedure, has been applied to simulate the initial
solidification process in continuous casting, where a sufficient cooling rate
is required to maintain a proper solidification rate. Otherwise, bulging or
breakout might occur. The prediction is in good agreement with the
measured shell thickness, which was obtained from a breakout incident. With the help of
HPC, such comprehensive simulations will continue to serve as a powerful tool
for troubleshooting and optimization.</p>
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Testování částí oděvu pomocí tepelného manekýna / Measurement of clothing sets by means of thermal manikinHanzlík, Martin January 2017 (has links)
This diploma thesis is focused on the experimental determination of thermal resistance of the gloves and their combination in the layering system. The measurement was based on procedure specified in the standard ČSN EN 511 by means of thermal manikin. The thesis begins with the description of heat transfer mechanisms, description of glove materials and measurement methodology. The body of paper consists of the measured data analysis and equation design for determination of the glove layering system thermal resistance. At the end of the thesis, these equations are evaluated and it has been shown, that the thermal resistance of glove layering system cannot be precisely determined by the calculation, and it is necessary to measure the whole three-layer system.
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Étude de l'ébullition sur plaque plane en microgravité, application aux réservoirs cryogéniques des fusées Ariane V / Study of nucleate boiling in microgravity conditions, aplicated to the ArineV cryogenics tanksKannengieser, Olivier 18 December 2009 (has links)
Ce rapport de thèse porte sur une étude expérimentale et théorique de l'ébullition en microgravité. Les expériences furent réalisées en condition de gravité terrestre, en vol parabolique et en fusée-sonde. Les expériences en vol parabolique ont montré l'influence de divers paramètres sur le transfert thermique et ont mis en évidence les mécanismes contrôlant le transfert thermique. De l'écriture des équations gouvernant ces mécanismes et de l'identification des échelles caractéristiques, une corrélation permettant d'estimer le transfert de chaleur lors de l'ébullition en microgravité pour une large gamme de fluide est bâtie. L'expérience en fusée-sonde a permis d'étudier l'influence des gaz incondensables et notamment de la convection Marangoni sur le comportement de l'ébullition et sur le transfert thermique. / Between the different propulsion phases, the Ariane V rocket passes through microgravity periods and solar radiation can induce boiling in its cryogenics tanks. Experiments were performed during 6 parabolic flights and in a sounding rocket to study pool boiling in microgravity. In the parabolic flight experiments, the influence of pressure, subcooling and surface roughness was studied. It is showed that subcooling has a weak effect on microgravity boiling heat transfer, and that roughness is an important factor also in microgravity. Detailed results on the behavior of bubbles and on the superheated liquid layer show that the heat transfer mechanisms can be divided in two groups : the primary mechanisms which directly take energy from the wall and the secondary mechanisms which transport the energy stored in the fluid by the primary mechanisms, from the vicinity of the wall to the bulk liquid. The secondary mechanisms appear not to limit primary mechanism heat transfer which explains the weak influence of gravity on heat transfer. From the study of equations governing primary mechanisms and the definition of new scales, a correlation is built to predict heat transfer in microgravity for a wide variety of fluids. In the sounding rocket experiment, the influence of non-condensable gases was studied. The existence of two regimes of boiling heat transfer with non-condensable gas is established. The temperature in the primary bubble is directly measured and the influences of both Marangoni convection and non-condensable gas on both heat transfer and bubble growth are also considered.
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