Abstract: A numerical study of natural convection heat transfer
in water filled cavity has been examined in 3-Dfor single phase liquid
cooling system by using an array of parallel plate fins mounted to one
wall of a cavity. The heat generated by a heat source represents a
computer CPU with dimensions of 37.5∗37.5mm mounted on
substrate. A cold plate is used as a heat sink installed on the opposite
vertical end of the enclosure. The air flow inside the computer case is
created by an exhaust fan. A turbulent air flow is assumed and k-ε
model is applied. The fins are installed on the substrate to enhance
the heat transfer. The applied power energy range used is between 15
- 40W. In order to determine the thermal behaviour of the cooling
system, the effect of the heat input and the number of the parallel
plate fins are investigated. The results illustrate that as the fin number
increases the maximum heat source temperature decreases. However,
when the fin number increases to critical value the temperature start
to increase due to the fins are too closely spaced and that cause the
obstruction of water flow. The introduction of parallel plate fins
reduces the maximum heat source temperature by 10% compared to
the case without fins. The cooling system maintains the maximum
chip temperature at 64.68°C when the heat input was at 40W that is
much lower than the recommended computer chips limit temperature
of no more than 85°C and hence the performance of the CPU is
enhanced.
Abstract: This paper presents a model predictive control (MPC)
of a utility interactive (UI) single phase inverter (SPI) for a
photovoltaic (PV) system at residential/distribution level. The
proposed model uses single-phase phase locked loop (PLL) to
synchronize SPI with the grid and performs MPC control in a dq
reference frame. SPI model consists of boost converter (BC),
maximum power point tracking (MPPT) control, and a full bridge
(FB) voltage source inverter (VSI). No PI regulators to tune and
carrier and modulating waves are required to produce switching
sequence. Instead, the operational model of VSI is used to synthesize
sinusoidal current and track the reference. Model is validated using a
three kW PV system at the input of UI-SPI in Matlab/Simulink.
Implementation and results demonstrate simplicity and accuracy, as
well as reliability of the model.
Abstract: The article presents the concept of an electromagnetic
circuit generator with permanent magnets mounted on the surface
rotor core designed for single phase work. Computation field-circuit
model was shown. The spectrum of time course of voltages in the
idle work was presented. The cross section with graphically
presentation of magnetic induction in particular parts of
electromagnetic circuits was presented. Distribution of magnetic
induction at the rated load point for each phase was shown. The time
course of voltages and currents for each phases for rated power were
displayed. An analysis of laboratory results and measurement of load
characteristics of the generator was discussed. The work deals with
three electromagnetic circuits of generators with permanent magnet
where output voltage characteristics versus rated power were
expressed.
Abstract: Multilevel inverter is a promising inverter topology for high voltage and high power applications. This inverter synthesizes several different levels of DC voltages to produce a stepped AC output that approaches the pure sine waveform. The three different topologies, diode-clamped inverter, capacitor-clamped inverter and cascaded h-bridge multilevel inverter are widely used in these multilevel inverters. Among the three topologies, cascaded h-bridge multilevel inverter is more suitable for photovoltaic applications since each PV array can act as a separate dc source for each h-bridge module. This research especially focus on photovoltaic power source as input to the system and shows the potential of a Single Phase Cascaded H-bridge Eleven level inverter governed by the fuzzy logic controller to improve the power quality by reducing the total harmonic distortion at the output voltage. Hence the efficiency of the system will be improved. Simulation using MATLAB/SIMULINK has been done to verify the performance of cascaded h-bridge eleven level inverter using sinusoidal pulse width modulation technique. The simulated output shows very favorable result.
Abstract: Thyristor based firing angle controlled voltage regulators are extensively used for speed control of single phase induction motors. This leads to power saving but the applied voltage and current waveforms become non-sinusoidal. These non-sinusoidal waveforms increase voltage and thermal stresses which result into accelerated insulation aging, thus reducing the motor life. Life models that allow predicting the capability of insulation under such multi-stress situations tend to be very complex and somewhat impractical. This paper presents the fuzzy logic application to investigate the synergic effect of voltage and thermal stresses on intrinsic aging of induction motor insulation. A fuzzy expert system is developed to estimate the life of induction motor insulation under multiple stresses. Three insulation degradation parameters, viz. peak modification factor, wave shape modification factor and thermal loss are experimentally obtained for different firing angles. Fuzzy expert system consists of fuzzyfication of the insulation degradation parameters, algorithms based on inverse power law to estimate the life and defuzzyficaton process to output the life. An electro-thermal life model is developed from the results of fuzzy expert system. This fuzzy logic based electro-thermal life model can be used for life estimation of induction motors operated with non-sinusoidal voltage and current waveforms.
Abstract: Various studies have showed that about 90% of single line to ground faults occurred on High voltage transmission lines have transient nature. This type of faults is cleared by temporary outage (by the single phase auto-reclosure). The interval between opening and reclosing of the faulted phase circuit breakers is named “Dead Time” that is varying about several hundred milliseconds. For adjustment of traditional single phase auto-reclosures that usually are not intelligent, it is necessary to calculate the dead time in the off-line condition precisely. If the dead time used in adjustment of single phase auto-reclosure is less than the real dead time, the reclosing of circuit breakers threats the power systems seriously. So in this paper a novel approach for precise calculation of dead time in power transmission lines based on the network equivalencing in time domain is presented. This approach has extremely higher precision in comparison with the traditional method based on Thevenin equivalent circuit. For comparison between the proposed approach in this paper and the traditional method, a comprehensive simulation by EMTP-ATP is performed on an extensive power network.
Abstract: The numerical simulation of fully developed gas–solid flow in a horizontal pipe is done using the eulerian-eulerian approach, also known as two fluids modeling as both phases are treated as continuum and inter-penetrating continua. The solid phase stresses are modeled using kinetic theory of granular flow (KTGF). The computed results for velocity profiles and pressure drop are compared with the experimental data. We observe that the convection and diffusion terms in the granular temperature cannot be neglected in gas solid flow simulation along a horizontal pipe. The particle-wall collision and lift also play important role in eulerian modeling. We also investigated the effect of flow parameters like gas velocity, particle properties and particle loading on pressure drop prediction in different pipe diameters. Pressure drop increases with gas velocity and particle loading. The gas velocity has the same effect ((proportional toU2 ) as single phase flow on pressure drop prediction. With respect to particle diameter, pressure drop first increases, reaches a peak and then decreases. The peak is a strong function of pipe bore.
Abstract: An experimental investigation was conducted to study the effect of surface roughness on friction factor and heat transfer characteristics in single-phase fluid flow in a stainless steel micro-tube having diameter of 0.85 mm and average internal surface roughness of 1.7 μm with relative surface roughness of 0.002. Distilled water and R134a liquids were used as the working fluids and testing was conducted with Reynolds numbers ranging from 100 to 10,000 covering laminar, transition and turbulent flow conditions. The experiments were conducted with the micro-tube oriented horizontally with uniform heat fluxes applied at the test section. The results indicated that the friction factor of both water and R134a can be predicted by the Hagen-Poiseuille equation for laminar flow and the modified Miller correlation for turbulent flow and early transition from laminar to turbulent flows. The heat transfer results of water and R134a were in good agreement with the conventional theory in the laminar flow region and lower than the Adam’s correlation for turbulent flow region which deviates from conventional theory.
Abstract: An optimal control strategy based on simple model, a
single phase unity power factor boost converter is presented with an
evaluation of first order differential equations. This paper presents an
evaluation of single phase boost converter having power factor
correction. The simple discrete model of boost converter is formed
and optimal control is obtained, digital PI is adopted to adjust control
error. The method of instantaneous current control is proposed in this
paper for its good tracking performance of dynamic response. The
simulation and experimental results verified our design.
Abstract: Harmonic pollution and low power factor in power
systems caused by power converters have been of great concern. To
overcome these problems several converter topologies using
advanced semiconductor devices and control schemes have been
proposed. This investigation is to identify a low cost, small size,
efficient and reliable ac to dc converter to meet the input performance
index of UPS. The performance of single phase and three phase ac to
dc converter along with various control techniques are studied and
compared. The half bridge converter topology with linear current
control is identified as most suitable. It is simple, energy efficient
because of single switch power loss and transformer-less operation of
UPS. The results are validated practically using a prototype built
using IGBT and analog controller. The performance for both single
and three-phase system is verified. Digital implementation of closed
loop control achieves higher reliability. Its cost largely depends on
chosen bit precision. The minimal bit precision for optimum
converter performance is identified as 16-bit with fixed-point
operation. From the investigation and practical implementation it is
concluded that half bridge ac – dc converter along with digital linear
controller meets the performance index of UPS for single and three
phase systems.
Abstract: This paper presents a new approach for the protection
of Thyristor-Controlled Series Compensator (TCSC) line using
Support Vector Machine (SVM). One SVM is trained for fault
classification and another for section identification. This method use
three phase current measurement that results in better speed and
accuracy than other SVM based methods which used single phase
current measurement. This makes it suitable for real-time protection.
The method was tested on 10,000 data instances with a very wide
variation in system conditions such as compensation level, source
impedance, location of fault, fault inception angle, load angle at
source bus and fault resistance. The proposed method requires only
local current measurement.
Abstract: This study examines the design and construction of AC Electronics load surge protection in order to carry electric surge load arisen from faults in low voltage electricity system (single phase/220V) by using the principle of electronics load clamping voltage during induction period so that electric voltage could go through to safe load and continue to work. The qualification of the designed device could prevent both transient over voltage and voltage swell. Both will work in cooperation, resulting in the ability to improve and modify the quality of electrical power in Thailand electricity distribution system more effective than the past and help increase the lifetime of electric appliances, electric devices, and electricity protection equipments.
Abstract: The most common cause of power transformer failures
is mechanical defect brought about by excessive vibration, which is
formed by the combination of multiples of a frequency of 120 Hz. In
this paper, the types of mechanical exciting forces applied to the
power transformer were classified, and the mechanical damage
mechanism of the power transformer was identified using the
vibration transfer route to the machine or structure. The general
effects of 120 Hz-vibration on the enclosure, bushing, Buchholz
relay, pressure release valve and tap changer of the transformer were
also examined.
Abstract: The objective of the present work is to conduct
investigations leading to a more complete explanation of single phase
natural convective heat transfer in an enclosure with fin utilizing
nano fluids. The nano fluid used, which is composed of Aluminum
oxide nano particles in suspension of Ethylene glycol, is provided at
various volume fractions. The study is carried out numerically for a
range of Rayleigh numbers, fin heights and aspect ratio. The flow and
temperature distributions are taken to be two-dimensional. Regions
with the same velocity and temperature distributions are identified as
symmetry of sections. One half of such a rectangular region is chosen
as the computational domain taking into account the symmetry about
the fin. Transport equations are modeled by a stream functionvorticity
formulation and are solved numerically by finite-difference
schemes. Comparisons with previously published works on the basis
of special cases are done. Results are presented in the form of
streamline, vector and isotherm plots as well as the variation of local
Nusselt number along the fin under different conditions.
Abstract: Fluids are used for heat transfer in many engineering
equipments. Water, ethylene glycol and propylene glycol are some
of the common heat transfer fluids. Over the years, in an attempt to
reduce the size of the equipment and/or efficiency of the process,
various techniques have been employed to improve the heat transfer
rate of these fluids. Surface modification, use of inserts and
increased fluid velocity are some examples of heat transfer
enhancement techniques. Addition of milli or micro sized particles
to the heat transfer fluid is another way of improving heat transfer
rate. Though this looks simple, this method has practical problems
such as high pressure loss, clogging and erosion of the material of
construction. These problems can be overcome by using nanofluids,
which is a dispersion of nanosized particles in a base fluid.
Nanoparticles increase the thermal conductivity of the base fluid
manifold which in turn increases the heat transfer rate. In this work,
the heat transfer enhancement using aluminium oxide nanofluid has
been studied by computational fluid dynamic modeling of the
nanofluid flow adopting the single phase approach.
Abstract: Addition of milli or micro sized particles to the heat
transfer fluid is one of the many techniques employed for improving
heat transfer rate. Though this looks simple, this method has
practical problems such as high pressure loss, clogging and erosion
of the material of construction. These problems can be overcome by
using nanofluids, which is a dispersion of nanosized particles in a
base fluid. Nanoparticles increase the thermal conductivity of the
base fluid manifold which in turn increases the heat transfer rate.
Nanoparticles also increase the viscosity of the basefluid resulting in
higher pressure drop for the nanofluid compared to the base fluid. So
it is imperative that the Reynolds number (Re) and the volume
fraction have to be optimum for better thermal hydraulic
effectiveness. In this work, the heat transfer enhancement using
aluminium oxide nanofluid using low and high volume fraction
nanofluids in turbulent pipe flow with constant wall temperature has
been studied by computational fluid dynamic modeling of the
nanofluid flow adopting the single phase approach. Nanofluid, up till
a volume fraction of 1% is found to be an effective heat transfer
enhancement technique. The Nusselt number (Nu) and friction factor
predictions for the low volume fractions (i.e. 0.02%, 0.1 and 0.5%)
agree very well with the experimental values of Sundar and Sharma
(2010). While, predictions for the high volume fraction nanofluids
(i.e. 1%, 4% and 6%) are found to have reasonable agreement with
both experimental and numerical results available in the literature.
So the computationally inexpensive single phase approach can be
used for heat transfer and pressure drop prediction of new nanofluids.
Abstract: In designing of condensers, the prediction of pressure
drop is as important as the prediction of heat transfer coefficient.
Modeling of two phase flow, particularly liquid – vapor flow under
diabatic conditions inside a horizontal tube using CFD analysis is
difficult with the available two phase models in FLUENT due to
continuously changing flow patterns. In the present analysis, CFD
analysis of two phase flow of refrigerants inside a horizontal tube of
inner diameter, 0.0085 m and 1.2 m length is carried out using
homogeneous model under adiabatic conditions. The refrigerants
considered are R22, R134a and R407C. The analysis is performed at
different saturation temperatures and at different flow rates to
evaluate the local frictional pressure drop. Using Homogeneous
model, average properties are obtained for each of the refrigerants
that is considered as single phase pseudo fluid. The so obtained
pressure drop data is compared with the separated flow models
available in literature.
Abstract: Induction motors are being used in greater numbers
throughout a wide variety of industrial and commercial applications
because it provides many benefits and reliable device to convert the
electrical energy into mechanical motion. In some application it-s
desired to control the speed of the induction motor. Because of the
physics of the induction motor the preferred method of controlling its
speed is to vary the frequency of the AC voltage driving the motor. In
recent years, with the microcontroller incorporated into an appliance
it becomes possible to use it to generate the variable frequency AC
voltage to control the speed of the induction motor.
This study investigates the microcontroller based variable
frequency power inverter. the microcontroller is provide the variable
frequency pulse width modulation (PWM) signal that control the
applied voltage on the gate drive, which is provides the required
PWM frequency with less harmonics at the output of the power
inverter.
The fully controlled bridge voltage source inverter has been
implemented with semiconductors power devices isolated gate
bipolar transistor (IGBT), and the PWM technique has been
employed in this inverter to supply the motor with AC voltage.
The proposed drive system for three & single phase power inverter
is simulated using Matlab/Simulink. The Matlab Simulation Results
for the proposed system were achieved with different SPWM. From
the result a stable variable frequency inverter over wide range has
been obtained and a good agreement has been found between the
simulation and hardware of a microcontroller based single phase
inverter.
Abstract: In this paper, Zinc Oxide (ZnO) thin films are deposited on glass substrate by sol-gel method. The ZnO thin films with well defined orientation were acquired by spin coating of zinc acetate dehydrate monoethanolamine (MEA), de-ionized water and isopropanol alcohol. These films were pre-heated at 275°C for 10 min and then annealed at 350°C, 450°C and 550°C for 80 min. The effect of annealing temperature and different thickness on structure and surface morphology of the thin films were verified by Atomic Force Microscopy (AFM). It was found that there was a significant effect of annealing temperature on the structural parameters of the films such as roughness exponent, fractal dimension and interface width. Thin films also were characterizied by X-ray Diffractometery (XRD) method. XRD analysis revealed that the annealed ZnO thin films consist of single phase ZnO with wurtzite structure and show the c-axis grain orientation. Increasing annealing temperature increased the crystallite size and the c-axis orientation of the film after 450°C. Also In this study, ZnO thin films in different thickness have been prepared by sol-gel method on the glass substrate at room temperature. The thicknesses of films are 100, 150 and 250 nm. Using fractal analysis, morphological characteristics of surface films thickness in amorphous state were investigated. The results show that with increasing thickness, surface roughness (RMS) and lateral correlation length (ξ) are decreased. Also, the roughness exponent (α) and growth exponent (β) were determined to be 0.74±0.02 and 0.11±0.02, respectively.
Abstract: This paper presents the impact study of GTO Controlled Series Capacitor (GCSC) parameters on measured impedance (Zseen) by MHO distance relays for single transmission line high voltage 220 kV in the presence of single phase to earth fault with fault resistance (RF). The study deals with a 220 kV single electrical transmission line of Eastern Algerian transmission networks at Group Sonelgaz (Algerian Company of Electrical and Gas) compensated by series Flexible AC Transmission System (FACTS) i.e. GCSC connected at midpoint of the transmission line. The transmitted active and reactive powers are controlled by three GCSC-s. The effects of maximum reactive power injected as well as injected maximum voltage by GCSC on distance relays measured impedance is treated. The simulations results investigate the effects of GCSC injected parameters: variable reactance (XGCSC), variable voltage (VGCSC) and reactive power injected (QGCSC) on measured resistance and reactance in the presence of earth fault with resistance fault varied between 5 to 50 Ω for three cases study.