Abstract: The aim of the study is to improve the understanding
of latent and sensible thermal energy storage within a paraffin wax
media by an array of cylindrical tubes arranged both in in-line and
staggered layouts. An analytical and experimental study is carried out
in a horizontal shell-and-tube type system during melting process.
Pertamina paraffin-wax was used as a phase change material (PCM),
while the tubes are embedded in the PCM. From analytical study we
can obtain the useful information in designing a thermal energy
storage such as: the motion of interface, amount of material melted at
any time in the process, and the heat storage characteristic during
melting. The use of staggered tubes is proposed compared to in-line
layout in a heat exchanger as thermal storage. The experimental study
is used to verify the validity of the analytical predictions. From the
comparisons, the analytical and experimental data are in a good
agreement.
Abstract: Rapid prototyping is a new group of manufacturing
processes, which allows fabrication of physical of any complexity
using a layer by layer deposition technique directly from a computer
system. The rapid prototyping process greatly reduces the time and
cost necessary to bring a new product to market. The prototypes
made by these systems are used in a range of industrial application
including design evaluation, verification, testing, and as patterns for
casting processes. These processes employ a variety of materials and
mechanisms to build up the layers to build the part. The present work
was to build a FDM prototyping machine that could control the X-Y
motion and material deposition, to generate two-dimensional and
three-dimensional complex shapes. This study focused on the
deposition of wax material. This work was to find out the properties
of the wax materials used in this work in order to enable better
control of the FDM process. This study will look at the integration of
a computer controlled electro-mechanical system with the traditional
FDM additive prototyping process. The characteristics of the wax
were also analysed in order to optimise the model production process.
These included wax phase change temperature, wax viscosity and
wax droplet shape during processing.
Abstract: In this study, one dimensional phase change problem
(a Stefan problem) is considered and a numerical solution of this
problem is discussed. First, we use similarity transformation to
convert the governing equations into ordinary differential equations
with its boundary conditions. The solutions of ordinary differential
equation with the associated boundary conditions and interface
condition (Stefan condition) are obtained by using a numerical
approach based on operational matrix of differentiation of shifted
second kind Chebyshev wavelets. The obtained results are compared
with existing exact solution which is sufficiently accurate.
Abstract: The nanoindentation behaviour and phase
transformation of annealed single-crystal silicon wafers are examined.
The silicon specimens are annealed at temperatures of 250, 350 and
450ºC, respectively, for 15 minutes and are then indented to maximum
loads of 30, 50 and 70 mN. The phase changes induced in the indented
specimens are observed using transmission electron microscopy
(TEM) and micro-Raman scattering spectroscopy (RSS). For all
annealing temperatures, an elbow feature is observed in the unloading
curve following indentation to a maximum load of 30 mN. Under
higher loads of 50 mN and 70 mN, respectively, the elbow feature is
replaced by a pop-out event. The elbow feature reveals a complete
amorphous phase transformation within the indented zone, whereas
the pop-out event indicates the formation of Si XII and Si III phases.
The experimental results show that the formation of these crystalline
silicon phases increases with an increasing annealing temperature and
indentation load. The hardness and Young’s modulus both decrease as
the annealing temperature and indentation load are increased.
Abstract: An important problem for the CaSO4/CaSO4･1/2H2O
Chemical heat pump (CHP) is that the material is deactivated through
repetitive reaction between hydration and dehydration in which the
crystal phase of the material is transformed from III-CaSO4 to
II-CaSO4. We investigated suppression on the phase change by adding
a sulfated compound. The most effective material was MgSO4. MgSO4
doping increased the durability of CaSO4 in the actual CHP repetitive
cycle of hydration/dehydration to 3.6 times that of undoped CaSO4.
The MgSO4-doped CaSO4 showed a higher phase transition
temperature and activation energy for crystal transformation from
III-CaSO4 to II-CaSO4. MgSO4 doping decreased the crystal lattice
size of CaSO4･1/2H2O and II-CaSO4 to smaller than that of undoped
CaSO4. Modification of the crystal structure is considered to be related
to the durability change in CaSO4 resulting from MgSO4 doping.
Abstract: A numerical model has been developed to investigate the thermally triggered release kinetics for drug delivery using phase change material as shell of microcapsules. Biocompatible material n-Eicosane is used as demonstration. PCM shell of microcapsule will remain in solid form after the drug is taken, so the drug will be encapsulated by the shell, and will not be released until the target body part of lesion is exposed to external heat source, which will thermally trigger the release kinetics, leading to solid-to-liquid phase change. The findings can lead to better understanding on the key effects influencing the phase change process for drug delivery applications. The facile approach to release drug from core/shell structure of microcapsule can be well integrated with organic solvent free fabrication of microcapsules, using double emulsion as template in microfluidic aqueous two phase system.
Abstract: The thermal behavior of a large-scale, phase change material (PCM) enhanced building envelope system was studied in regard to the need for pre-fabricated construction in subtropical regions. The proposed large-scale envelope consists of a reinforced aluminum skin, insulation core, phase change material and reinforced gypsum board. The PCM impact on an energy efficiency of an enveloped room was resolved by validation of the EnergyPlus numerical scheme and optimization of a smart material location in the core. The PCM location was optimized by a minimization method of a cooling energy demand. It has been shown that there is good agreement between the test and simulation results. The optimal location of the PCM layer in Hong Kong summer conditions has been then recomputed for core thicknesses of 40, 60 and 80 mm. A non-dimensional value of the optimal PCM location was obtained to be same for all the studied cases and the considered external and internal conditions.
Abstract: A one-dimensional mathematical model was developed in order to analyze and optimize the latent heat storage wall. The governing equations for energy transport were developed by using the enthalpy method and discretized with volume control scheme. The resulting algebraic equations were next solved iteratively by using TDMA algorithm. A series of numerical investigations were conducted in order to examine the effects of the thickness of the PCM layer on the thermal behavior of the proposed heating system. Results are obtained for thermal gain and temperature fluctuation. The charging discharging process was also presented and analyzed.
Abstract: Novel compact expressions for propagation constant (γ) of SWCNT and bundled SWCNTs interconnect, in terms of physical parameters such as length, operating frequency and diameter of CNTs is proposed in this work. These simplified expressions enable physical insight and accurate estimation of signal attenuation level and its phase change at any length for a particular frequency. The proposed expressions are validated against SPICE simulated results of lumped as well as distributed equivalent electrical RLC nets of CNT interconnect. These expressions also help us to evaluate the cut off frequencies of SWCNTs for different interconnect lengths.
Abstract: In this paper the influence of a vertical plate’s thermal capacity is numerically investigated in order to evaluate the evolution of the thermal boundary layer structure, as well as the convective heat transfer coefficient and the velocity and temperature profiles. Whereas the heat flux of the heated vertical plate is evaluated under time depending boundary conditions. The main important feature of this problem is the unsteadiness of the physical phenomena. A 2D CFD model is developed with the Ansys Fluent 14.0 environment and is validated using unsteady data obtained for plasterboard studied under a dynamic temperature evolution. All the phenomena produced in the vicinity of the thermal conductive vertical plate (plasterboard) are analyzed and discussed. This work is the first stage of a holistic research on transient free convection that aims, in the future, to study the natural convection in the vicinity of a vertical plate containing Phase Change Materials (PCM).
Abstract: A new type of lightweight plaster with the thermal capacity enhanced by PCM (Phase Change Material) addition is analyzed. The basic physical characteristics, namely the bulk density, matrix density, total open porosity, and pore size distribution are measured at first. For description of mechanical properties, compressive strength measurements are done. The thermal properties are characterized by transient impulse techniques as well as by DSC analysis that enables determination of the specific heat capacity as a function of temperature. The resistivity against the liquid water ingress is described by water absorption coefficient measurement. The experimental results indicate a good capability of the designed plaster to moderate effectively the interior climate of buildings.
Abstract: In space during functioning, a satellite will be heated
up due to the behavior of its components such as power electronics.
In order to prevent problems in the satellite, this heat has to be
released in space thanks to the cooling system. This system consists
of a loop heat pipe (LHP), in which a fluid streams through an
evaporator and a condenser. In the evaporator, the fluid captures the
heat from the satellite and evaporates. Then it flows to the condenser
where it releases the heat and it condenses. In this project, the two
mains parts of a cooling system are studied: the evaporator and the
condenser. The study of the diphasic loop was done starting from
digital simulations carried out under Matlab and Femlab.
Abstract: With the long-term objective of Critical Heat Flux (CHF) prediction, a Direct Numerical Simulation (DNS) framework for simulation of subcooled and saturated nucleate pool boiling is developed. One case of saturated, and three cases of subcooled boiling at different subcooling levels are simulated. Grid refinement study is also reported. Both boiling and condensation phenomena can be computed simultaneously in the proposed numerical framework. Computed bubble detachment diameters of the saturated nucleate pool boiling cases agree well with the experiment. The flow structures around the growing bubble are presented and the accompanying physics is described. The relation between heat flux evolution from the heated wall and the bubble growth is studied, along with investigations of temperature distribution and flow field evolutions.
Abstract: Numerical parametric study is conducted to study the effects of ampoule rotation on the flows and the dopant segregation in vertical bridgman (vb) crystal growth. Calculations were performed in unsteady state. The extended darcy model, which includes the time derivative and coriolis terms, has been employed in the momentum equation. It’s found that the convection, and dopant segregation can be affected significantly by ampoule rotation, and the effect is similar to that by an axial magnetic field. Ampoule rotation decreases the intensity of convection and stretches the flow cell axially. When the convection is weak, the flow can be suppressed almost completely by moderate ampoule rotation and the dopant segregation becomes diffusion-controlled. For stronger convection, the elongated flow cell by ampoule rotation may bring dopant mixing into the bulk melt reducing axial segregation at the early stage of the growth. However, if the cellular flow cannot be suppressed completely, ampoule rotation may induce larger radial segregation due to poor mixing.
Abstract: A numerical investigation has carried out to understand the melting characteristics of phase change material (PCM) in a fin type latent heat storage with the addition of embedded aluminum spiral fillers. It is known that melting performance of PCM can be significantly improved by increasing the number of embedded metallic fins in the latent heat storage system but to certain values where only lead to small improvement in heat transfer rate. Hence, adding aluminum spiral fillers within the fin gap can be an option to improve heat transfer internally. This paper presents extensive computational visualizations on the PCM melting patterns of the proposed fin-spiral fillers configuration. The aim of this investigation is to understand the PCM-s melting behaviors by observing the natural convection currents movement and melting fronts formation. Fluent 6.3 simulation software was utilized in producing twodimensional visualizations of melting fractions, temperature distributions and flow fields to illustrate the melting process internally. The results show that adding aluminum spiral fillers in Fin type latent heat storage can promoted small but more active natural convection currents and improve melting of PCM.
Abstract: The storage of thermal energy as a latent heat of phase
change material (PCM) has created considerable interest among
researchers in recent times. Here, an attempt is made to carry out
numerical investigations to analyze the performance of latent heat
storage units (LHSU) employing phase change material. The
mathematical model developed is based on an enthalpy formulation.
Freezing time of PCM packed in three different shaped containers
viz. rectangular, cylindrical and cylindrical shell is compared. The
model is validated with the results available in the literature. Results
show that for the same mass of PCM and surface area of heat
transfer, cylindrical shell container takes the least time for freezing
the PCM and this geometric effect is more pronounced with an
increase in the thickness of the shell than that of length of the shell.
Abstract: In this paper, the melting of a semi-infinite body as a
result of a moving laser beam has been studied. Because the Fourier
heat transfer equation at short times and large dimensions does not
have sufficient accuracy; a non-Fourier form of heat transfer
equation has been used. Due to the fact that the beam is moving in x
direction, the temperature distribution and the melting pool shape are
not asymmetric. As a result, the problem is a transient threedimensional
problem. Therefore, thermophysical properties such as
heat conductivity coefficient, density and heat capacity are functions
of temperature and material states. The enthalpy technique, used for
the solution of phase change problems, has been used in an explicit
finite volume form for the hyperbolic heat transfer equation. This
technique has been used to calculate the transient temperature
distribution in the semi-infinite body and the growth rate of the melt
pool. In order to validate the numerical results, comparisons were
made with experimental data. Finally, the results of this paper were
compared with similar problem that has used the Fourier theory. The
comparison shows the influence of infinite speed of heat propagation
in Fourier theory on the temperature distribution and the melt pool
size.
Abstract: Scalability poses a severe threat to the existing
DRAM technology. The capacitors that are used for storing and
sensing charge in DRAM are generally not scaled beyond 42nm.
This is because; the capacitors must be sufficiently large for reliable
sensing and charge storage mechanism. This leaves DRAM memory
scaling in jeopardy, as charge sensing and storage mechanisms
become extremely difficult. In this paper we provide an overview of
the potential and the possibilities of using Phase Change Memory
(PCM) as an alternative for the existing DRAM technology. The
main challenges that we encounter in using PCM are, the limited
endurance, high access latencies, and higher dynamic energy
consumption than that of the conventional DRAM. We then provide
an overview of various methods, which can be employed to
overcome these drawbacks. Hybrid memories involving both PCM
and DRAM can be used, to achieve good tradeoffs in access latency
and storage density. We conclude by presenting, the results of these
methods that makes PCM a potential replacement for the current
DRAM technology.
Abstract: The development and application of wind power for
renewable energy has attracted growing interest in recent years. Renewable energy sources are attracting much alteration as they can
reduce both environmental damage and dependence on fossil fuels. With the growing need for sustainable energy supplies, a case is made
for decentralized, stand-alone power supplies (SAPS) as an alternative to power grids. In the era which traditional petroleum energy resource
decreasing and the green house affect significant increasing, the development and usage of regenerative resources is inevitable. Due to the contribution of the pioneers, the development of regenerative resources already has a remarkable achievement; however, in the view of economy and quantity, it is still a long road for regenerative energy
to replace traditional petroleum energy. In our prospective, in stead of
investigate larger regenerative energy equipment, it is much wiser to
think about the blind side and breakthrough of the current technique.
Abstract: One of the potential and effective ways of
storing thermal energy in buildings is the integration of brick with phase change materials (PCMs). This paper presents a two-dimensional model for simulating and analyzing of PCM
in order to minimize energy consumption in the buildings. The numerical approach has been used with the real weather data of a selected city of Iran (Tehran). Two kinds of brick integrated PCM are investigated and compared base on
outdoor weather conditions and the amount of energy
consumption. The results show a significant reduction in
maximum entering heat flux to building about 32.8%
depending on PCM quantity. The results are analyzed by
various temperature contour plots. The contour plots
illustrated the time dependent mechanism of entering heat flux for a brick integrated with PCM. Further analysis is developed to investigate the effect of PCM location on the inlet heat flux. The results demonstrated that to achieve maximum performance of PCM it is better to locate PCM near the outdoor.