دانلود دسته: کتابخانه

دانلود پایان نامه انگلیسی آنالیز، تولید و تست یک سیستم میکروپیشرانش بر پایه میکروالکترومکانیکال سیستم ها

Various trends in the spacecraft industry are driving the development of low-thrust propulsion systems.
These may be needed for fine attitude control, or to reduce the mass of the propulsion system through the
use of small lightweight components. The nozzle converts the stored energy in a pressurized gas into kinetic
energy through an expansion. The nozzle efficiency is characterized by the amount of kinetic energy leaving
the nozzle, and is governed by the exit velocity. Because of the increase in viscous losses as scale is reduced,
it was feared that high Mach number supersonic flows could not be generated in microdevices. However, a
scaling analysis indicates that the reduction in throat area can be offset by an increase in operating pressure
to maintain a constant Reynolds number. Therefore, thrust can be decreased by reducing the nozzle scale,
and viscous losses mitigated by running at higher chamber pressures.

دانلود پایان نامه انگلیسی کارشناسی طراحی یک سیستم هیبریدی تبدیل انرژی بادی-خورشیدی کوچک

Approaching problems with global warming due to
the use of fossil fuels, means that new system
solutions have to be investigated. This report
investigates the possibility to expand an existing
photovoltaic system with a wind turbine
generator to simplify the expansion of renewable
energy sources. Through an extensive literature
study and simulation in SIMULINK the result has
been developed and tested. It shows that it is
possible to connect a wind turbine generator to
the same inverter as the PV-modules if no MPPT
algorithm for PV-modules is integrated. To protect
the inverter a dump load has to be connected.
Because of the complexity a DC-coupled system
brings, AC-coupling is advised when expanding PVmodules
with a WTG. The optimal wind turbine is
considered to be a permanent magnet
synchronous generator connected to the AC-bus
through a full-effect inverter. The turbine should
be chosen according to the intended location
based on wind conditions and desired energy
production.

دانلود پایان نامه کارشناسی ارشد آنالیز انتروپی بعنوان وسیله ای برای بهینه کردن biorefineries

The objective of this thesis is to develop entropy analysis as a possible evaluation tool
for optimization of biorefinery processes. This is a new application of entropy
analysis which is rarely discussed in the literature. The scientific basis of the entropy
analysis is described and the proposed methodology is explained. The position of
entropy analysis among other system analysis tools such as exergy analysis and life
cycle assessment is discussed along with entropy analysis earlier applications.

دانلود پایان نامه انگلیسی کارشناسی ارشد طراحی و آنالیز یک سیستم جذبی خنک کاری کمک شونده با انرژی خورشیدی و مجتمع با ذخیره کننده حرارت نهان

Air conditioning is one of the major consumers of electrical energy in many parts of the world.
The demand can be expected to increase because of the changing working times, increased
comfort expectations and global warming. With more air conditioning units, the electricity
demand has been rising thereby increasing the use of fossil fuels and nuclear energy. A drastic
change, therefore, should be implemented in the energy structure of the developed countries.
Environmentally friendly and energy efficient technologies should be introduced in which the
environmental impact of the conventional air conditioning system is minimized.
Solar radiation as a sustainable energy resource is one of the most available forms of energy on
the earth surface which could reduce the fossil fuel consumption and CO2 emission to the
atmosphere. Solar cooling is a possible technological alternative to conventional air
conditioning systems that has recently attracted a growing interest. A solar assisted absorption
cooling system as a sustainable solution for cooling systems could provide both heating and
cooling of a building. Since the solar energy is available for only a fraction of the day and its
availability depends on several factors such as latitude and sky clearness, the storage of it is an
important concern. Thermal energy storage is a practical way in conserving the solar energy as
it can reduce the discrepancy between the energy supply and demand. Latent heat storage units
(LHSU) using Phase Change Materials (PCMs) are promising candidates as heat storage media.
In this thesis, the behavior of a solar assisted single effect absorption system integrated with
LHSU was investigated. The mathematical model for the single effect absorption system and
the LHSU based on the mass and energy balances and heat transfer equations were developed.
The models were implemented in MATLAB and the numerical results were validated with the
experimental results from the literature. Based on the cooling demand of a specific building
(waiting room in Schiphol airport) the absorption system and the LHSU were designed and the
behavior of each system for different control parameters is investigated. For the designed single
effect absorption system, variation of the COP and the evaporator heat transfer rate at the
different flow rates and temperatures of the external cool water, hot water and the chilled water
were studied. The results show that the chilled, hot and cooled water temperatures have
significant effect on the performance of the absorption system. For the designed latent heat
storage, several numerical investigations were conducted. The impact of the key parameters e.g.
the mass of PCM, the number of tubes inside the PCM container and the radius of the tubes, on
the thermal performances of the latent heat storage and the melting time duration were studied.
The behavior of the designed latent heat storage unit in charging process with varying solar
collector field area was studied subsequently. The discharging process of LHSU for the
maximum cooling demand of the building was investigated. It was observed that the designed
LHSU could provide the requested hot water temperature for more than 10 hours which is
sufficient for driving the air conditioning system.

دانلود پایان نامه انگلیسی کارشناسی ارشد دربارۀ Modeling of Resin Transfer Molding of Composite Materials

The goal of this research was to develop a computer model for the treatment of
Resin Transfer Molding (RTM) of unidirectional layer stranded fabrics oriented in
various directions. The individual fabric layers contain high fiber volume fraction
strands, separated by channels, which the model includes as separate phases. A finite
difference approximation has been developed to determine the effective permeability of
the channels. This approximation is based on classical channel flow equations, and is
applied to all three directions of the channels. The axial permeability in the strands has
been measured. The transverse permeabilities in the strands are assumed to be equal, and
are fitted to the model results.
The model consists of a finite difference routine which uses cell centered grids to
approximate the geometry of the reinforcement. The moving boundary resin is treated
with as constant pressure condition. The injection and vent ports are also modeled as
constant pressure conditions.
The model has been correlated with experimental results. Simulations and
experiments have been run using a single fabric layer at 0, two layers at ±45, and three
layers at 45/0/-45 and 0/±45. The model accurately captures the flow front shape for
each case, and shows general agreement with the positions vs. time