Abstract: A three-dimensional numerical model of
thermoelectric generator (TEG) modules attached to a large chimney
plate is proposed and solved numerically using a control volume based
finite difference formulation. The TEG module consists of a
thermoelectric generator, an elliptical pin-fin heat sink, and a cold
plate for water cooling. In the chimney, the temperature of flue gases is
450-650K. Although the TEG hot-side temperature and thus the
electric power output can be increased by inserting an elliptical pin-fin
heat sink into the chimney tunnel to increase the heat transfer area, the
pin fin heat sink would cause extra pumping power at the same time.
The main purpose of this study is to analyze the effects of geometrical
parameters on the electric power output and chimney pressure drop
characteristics. The effects of different operating conditions, including
various inlet velocities (Vin= 1, 3, 5 m/s), inlet temperatures (Tgas = 450,
550, 650K) and different fin height (0 to 150 mm) are discussed in
detail. The predicted numerical data for the power vs. current (P-I)
curve are in good agreement (within 11%) with the experimental data.
Abstract: Water spray cooling is a technique typically used in
heat treatment and other metallurgical processes where controlled
temperature regimes are required. Water spray cooling is used in
static (without movement) or dynamic (with movement of the steel
plate) regimes. The static regime is notable for the fixed position of
the hot steel plate and fixed spray nozzle. This regime is typical for
quenching systems focused on heat treatment of the steel plate. The
second application of spray cooling is the dynamic regime. The
dynamic regime is notable for its static section cooling system and
moving steel plate. This regime is used in rolling and finishing mills.
The fixed position of cooling sections with nozzles and the
movement of the steel plate produce nonhomogeneous water
distribution on the steel plate. The length of cooling sections and
placement of water nozzles in combination with the nonhomogeneity
of water distribution lead to discontinued or interrupted cooling
conditions. The impact of static and dynamic regimes on cooling
intensity and the heat transfer coefficient during the cooling process
of steel plates is an important issue.
Heat treatment of steel is accompanied by oxide scale growth. The
oxide scale layers can significantly modify the cooling properties and
intensity during the cooling. The combination of static and dynamic
(section) regimes with the variable thickness of the oxide scale layer
on the steel surface impact the final cooling intensity. The study of
the influence of the oxide scale layers with different cooling regimes
was carried out using experimental measurements and numerical
analysis. The experimental measurements compared both types of
cooling regimes and the cooling of scale-free surfaces and oxidized
surfaces. A numerical analysis was prepared to simulate the cooling
process with different conditions of the section and samples with
different oxide scale layers.
Abstract: This research focuses on the optimization of glazed
surfaces and the assessment of possible solar gains in industrial
buildings. Existing window rating methods for single windows were
evaluated and a new method for a simple analysis of energy gains and
losses by single windows was introduced. Furthermore extensive
transient building simulations were carried out to appraise the
performance of low cost polycarbonate multi-cell sheets in
interaction with typical buildings for industrial applications. Mainly
energy saving potential was determined by optimizing the orientation
and area of such glazing systems in dependency on their thermal
qualities. Moreover the impact on critical aspects such as summer
overheating and daylight illumination was considered to ensure the
user comfort and avoid additional energy demand for lighting or
cooling. Hereby the simulated heating demand could be reduced by
up to 1/3 compared to traditional architecture of industrial halls using
mainly skylights.
Abstract: It is known that residual welding deformations give
negative effect to processability and operational quality of welded
structures, complicating their assembly and reducing strength.
Therefore, selection of optimal technology, ensuring minimum
welding deformations, is one of the main goals in developing a
technology for manufacturing of welded structures.
Through years, JSC SSTC has been developing a theory for
estimation of welding deformations and practical activities for
reducing and compensating such deformations during welding
process. During long time a methodology was used, based on analytic
dependence. This methodology allowed defining volumetric changes
of metal due to welding heating and subsequent cooling. However,
dependences for definition of structures deformations, arising as a
result of volumetric changes of metal in the weld area, allowed
performing calculations only for simple structures, such as units, flat
sections and sections with small curvature. In case of complex 3D
structures, estimations on the base of analytic dependences gave
significant errors.
To eliminate this shortage, it was suggested to use finite elements
method for resolving of deformation problem. Here, one shall first
calculate volumes of longitudinal and transversal shortenings of
welding joints using method of analytic dependences and further,
with obtained shortenings, calculate forces, which action is
equivalent to the action of active welding stresses. Further, a finiteelements
model of the structure is developed and equivalent forces
are added to this model. Having results of calculations, an optimal
sequence of assembly and welding is selected and special measures to
reduce and compensate welding deformations are developed and
taken.
Abstract: In this work, we made anumerical study of the thermal and dynamic behavior of air in a horizontal channel with electronic components.The influenceto use baffles on the profiles of velocity and temperature is discussed.The finite volume method and the algorithm Simple are used for solving the equations of conservation of mass, momentum and energy.The results found show that baffles improve heat transfer between the cooling air and electronic components. The velocity will increase from 3 times per rapport of the initial velocity.
Abstract: The effect of Yttrium addition on the microstructure and mechanical properties of Sn-Zn eutectic alloy, which has been attracting intensive focus as a Pb-free solder material, was investigated in this study. Phase equilibrium has been calculated by using FactSage® to evaluate the composition and fraction of equilibrium intermetallic compounds and construct a phase diagram. In the case of Sn-8.8Zn eutectic alloy, the as-cast microstructure was typical lamellar. With addition of 0.25wt.%Y, a large amount of pro-eutectic a phase have been observed and various YZnx intermetallic compounds were expected to successively form during cooling. Hardness of Sn-8.8Zn alloy was not affected by Y-addition and both alloys could be rolled by 90% at room temperature.
Abstract: Developments in turbine cooling technology play an important role in increasing the thermal efficiency and the power output of recent gas turbines, in particular the turbojets.
Advanced turbojets operate at high temperatures to improve thermal efficiency and power output. These temperatures are far above the permissible metal temperatures. Therefore, there is a critical need to cool the blades in order to give theirs a maximum life period for safe operation.
The focused objective of this work is to calculate the turbojet performances, as well as the calculation of turbine blades cooling.
The developed application able the calculation of turbojet performances to different altitudes in order to find a point of optimal use making possible to maintain the turbine blades at an acceptable maximum temperature and to limit the local variations in temperatures in order to guarantee their integrity during all the lifespan of the engine.
Abstract: Slag sample from copper smelting operation in a
water jacket furnace from DRC plant was used. The study intends to
determine the effect of cooling in the extraction of base metals. The
cooling methods investigated were water quenching, air cooling and
furnace cooling. The latter cooling ways were compared to the
original as received slag. It was observed that, the cooling rate of the
slag affected the leaching of base metals as it changed the phase
distribution in the slag and the base metals distribution within the
phases. It was also found that fast cooling of slag prevented
crystallization and produced an amorphous phase that encloses the
base metals. The amorphous slags from the slag dumps were more
leachable in acidic medium (HNO3) which leached 46%Cu, 95% Co,
85% Zn, 92% Pb and 79% Fe with no selectivity at pH0, than in
basic medium (NH4OH). The leachability was vice versa for the
modified slags by quenching in water which leached 89%Cu with a
high selectivity as metal extractions are less than 1% for Co, Zn, Pb
and Fe at ambient temperature and pH12. For the crystallized slags,
leaching of base metals increased with the increase of temperature
from ambient temperature to 60°C and decreased at the higher
temperature of 80°C due to the evaporation of the ammonia solution
used for basic leaching, the total amounts of base metals that were
leached in slow cooled slags were very low compared to the
quenched slag samples.
Abstract: This study presents a systematic analysis of wetted region due to cooling of aluminum plate by water spray impingement with respect to different water flow rates, spray nozzle heights, and subcooling. Unlike jet impingement, the wetting is not commenced upon spray impingement and there is a delay in wetness of hot test surface. After initiation, the wetting (black zone) progresses gradually to cover all test plate and provides efficient cooling in nucleate boiling regime. Generally, spray cooling is found function of spray flow rate, spray-to-surface distance and water subcooling. Wetting delay is decreasing by increasing of spray flow rate until spray impact area is not become bigger that test surface. Otherwise, higher spray flow rate is not practically accelerated start of wetting. Very fast wetting due to spray cooling can be obtained by dense spray (high floe rate) discharged from adjacent nozzle to the test surface. Highly subcooling water spray also triggers earlier wetting of hot aluminum plate.
Abstract: Among the various cooling processes in industrial
applications such as: electronic devices, heat exchangers, gas
turbines, etc. Gas turbine blades cooling is the most challenging one.
One of the most common practices is using ribbed wall because of
the boundary layer excitation and therefore making the ultimate
cooling. Vortex formation between rib and channel wall will result in
a complicated behavior of flow regime. At the other hand, selecting
the most efficient method for capturing the best results comparing to
experimental works would be a fascinating issue. In this paper 4
common methods in turbulence modeling: standard k-e, rationalized
k-e with enhanced wall boundary layer treatment, k-w and RSM
(Reynolds stress model) are employed to a square ribbed channel to
investigate the separation and thermal behavior of the flow in the
channel. Finally all results from different methods which are used in
this paper will be compared with experimental data available in
literature to ensure the numerical method accuracy.
Abstract: Spray chilling using air-mist nozzles has received
much attention in the food processing industry because of the
benefits it has shown over forced air convection. These benefits
include an increase in the heat transfer coefficient and a reduction in
the water loss by the product during cooling. However, few studies
have simulated the heat transfer and aerodynamics phenomena of the
air-mist chilling process for optimal operating conditions. The study
provides insight into the optimal conditions for spray impaction, heat
transfer efficiency and control of surface flooding. A computational
fluid dynamics model using a two-phase flow composed of water
droplets injected with air is developed to simulate the air-mist
chilling of food products. The model takes into consideration
droplet-to-surface interaction, water-film accumulation and surface
runoff. The results of this study lead to a better understanding of the
heat transfer enhancement, water conservation, and to a clear
direction for the optimal design of air-mist chilling systems that can
be used in commercial applications in the food and meat processing
industries.
Abstract: Turbine blade cooling is considered as the most
effective way of maintaining high operating temperature making use
of the available materials, and turbine systems with wet compression
have a potential for future power generation because of high efficiency
and high specific power with a relatively low cost. In this paper
performance analysis of wet-compression gas turbine cycle with
turbine blade cooling is carried out. The wet compression process is
analytically modeled based on non-equilibrium droplet evaporation.
Special attention is paid for the effects of pressure ratio and water
injection ratio on the important system variables such as ratio of
coolant fluid flow, fuel consumption, thermal efficiency and specific
power. Parametric studies show that wet compression leads to
insignificant improvement in thermal efficiency but significant
enhancement of specific power in gas turbine systems with turbine
blade cooling.
Abstract: Heat pipes are used to control the thermal problem for
electronic cooling. It is especially difficult to dissipate heat to a heat
sink in an environment in space compared to earth. For solving this
problem, in this study, the Poiseuille (Po) number, which is the main
measure of the performance of a heat pipe, is studied by CFD; then, the
heat pipe performance is verified with experimental results. A heat
pipe is then fabricated for a spatial environment, and an in-house code
is developed. Further, a heat pipe subsystem, which consists of a heat
pipe, MLI (Multi Layer Insulator), SSM (Second Surface Mirror), and
radiator, is tested and correlated with the TMM (Thermal
Mathematical Model) through a commercial code. The correlation
results satisfy the 3K requirement, and the generated thermal model is
verified for application to a spatial environment.
Abstract: Double-diffusive natural convection in an open top
square cavity and heated from the side is studied numerically.
Constant temperatures and concentration are imposed along the right
and left walls while the heat balance at the surface is assumed to obey
Newton-s law of cooling. The finite difference method is used to
solve the dimensionless governing equations. The numerical results
are reported for the effect of Marangoni number, Biot number and
Prandtl number on the contours of streamlines, temperature and
concentration. The predicted results for the average Nusselt number
and Sherwood number are presented for various parametric
conditions. The parameters involved are as follows; the thermal
Marangoni number, 0 ≤ MaT ≤1000 , the solutal Marangoni number,
0 1000 c ≤ Ma ≤ , the Biot number, 0 ≤ Bi ≤ 6 , Grashof number,
5 Gr = 10 and aspect ratio 1. The study focused on both flows; thermal
dominated, N = 0.8 , and compositional dominated, N = 1.3 .
Abstract: Gas turbine air inlet cooling is a useful method for
increasing output for regions where significant power demand and
highest electricity prices occur during the warm months. Inlet air
cooling increases the power output by taking advantage of the gas
turbine-s feature of higher mass flow rate when the compressor inlet
temperature decreases. Different methods are available for reducing
gas turbine inlet temperature. There are two basic systems currently
available for inlet cooling. The first and most cost-effective system is
evaporative cooling. Evaporative coolers make use of the evaporation
of water to reduce the gas turbine-s inlet air temperature. The second
system employs various ways to chill the inlet air. In this method, the
cooling medium flows through a heat exchanger located in the inlet
duct to remove heat from the inlet air. However, the evaporative
cooling is limited by wet-bulb temperature while the chilling can cool
the inlet air to temperatures that are lower than the wet bulb
temperature. In the present work, a thermodynamic model of a gas
turbine is built to calculate heat rate, power output and thermal
efficiency at different inlet air temperature conditions. Computational
results are compared with ISO conditions herein called "base-case".
Therefore, the two cooling methods are implemented and solved for
different inlet conditions (inlet temperature and relative humidity).
Evaporative cooler and absorption chiller systems results show that
when the ambient temperature is extremely high with low relative
humidity (requiring a large temperature reduction) the chiller is the
more suitable cooling solution. The net increment in the power output
as a function of the temperature decrease for each cooling method is
also obtained.
Abstract: The performance of mortar subjected to high
temperature and cooled in normal ambient temperature was examined
in the laboratory to comply with the situation of burning & cooling of
a structure. Four series of cubical (5 X 5 X 5 cm) mortar specimens
were made from OPC, and partial replacement (10, 15, 20, 25 &
30%) of OPC by Rice Husk Ash (RHA) produced in the uncontrolled
environment. These specimens were heated in electric furnace to 200,
300, 400, 500 and 7000C. The specimens were kept in normal room
temperature for cooling. They were then tested for mechanical
properties and the results shows that particular 20% RHA mixed
mortar shows better fire performance.
Abstract: This paper proposes the numerical simulation of the
investment casting of gold jewelry. It aims to study the behavior of
fluid flow during mould filling and solidification and to optimize the
process parameters, which lead to predict and control casting defects
such as gas porosity and shrinkage porosity. A finite difference
method, computer simulation software FLOW-3D was used to
simulate the jewelry casting process. The simplified model was
designed for both numerical simulation and real casting production.
A set of sensor acquisitions were allocated on the different positions
of the wax tree of the model to detect filling times, while a set of
thermocouples were allocated to detect the temperature during
casting and cooling. Those detected data were applied to validate the
results of the numerical simulation to the results of the real casting.
The resulting comparisons signify that the numerical simulation can
be used as an effective tool in investment-casting-process
optimization and casting-defect prediction.