Abstract: The present work deals with optimization of cascade refrigeration system using eco friendly refrigerants pair R507A and R23. R507A is azeotropic mixture composed of HFC refrigerants R125/R143a (50%/50% by wt.). R23 is a single component HFC refrigerant used as replacement to CFC refrigerant R13 in low temperature applications. These refrigerants have zero ozone depletion potential and are non-flammable. Optimization of R507AR23 cascade refrigeration system performance parameters such as minimum work required, refrigeration effect, coefficient of performance and exergetic efficiency was carried out in terms of eight operating parameters- combinations using Genetic Algorithm tool. The eight operating parameters include (1) low side evaporator temperature (2) high side condenser temperature (3) temperature difference in the cascade heat exchanger (4) low side condenser temperature (5) low side degree of subcooling (6) high side degree of subcooling (7) low side degree of superheating (8) high side degree of superheating. Results show that for minimum work system should operate at high temperature in low side evaporator, low temperature in high side condenser, low temperature difference in cascade condenser, high temperature in low side condenser and low degree of subcooling and superheating in both side. For maximum refrigeration effect system should operate at high temperature in low side evaporator, high temperature in high side condenser, high temperature difference in cascade condenser, low temperature in low side condenser and higher degree of subcooling in LT and HT side. For maximum coefficient of performance and exergetic efficiency, system should operate at high temperature in low side evaporator, low temperature in high side condenser, low temperature difference in cascade condenser, high temperature in low side condenser and higher degree of subcooling and superheating in low side of the system.
Abstract: Attempt was made to improve certain characteristics of bio-oil derived from palm kernel pyrolysis by blending it with diesel fuel and alcohols. Two types of alcohol, ethanol or butanol, was used as cosolvent to stabilize the phase of ternary systems. Phase behaviors and basic fuel properties of palm kernel bio-oildiesel- alcohol systems were investigated in this study. Alcohol types showed a significant influence on the phase characteristics with palm kernel bio-oil-diesel-butanol system giving larger soluble area than that of palm kernel bio-oil-diesel-ethanol system. For fuel properties, blended fuels showed superior properties including lower values of density (~860 kg/m3 at 25°C), viscosity (~4.12 mm2/s at 40°C), carbon residue (1.02-2.53 wt%), ash (0.018-0.034 wt%) and pour point (
Abstract: The production and consumption of natural gas is on
the rise throughout the world as a result of its wide availability, ease
of transportation, use and clean-burning characteristics. The chief use
of ethane is in the chemical industry in the production of Ethene
(ethylene) by steam cracking. In this simulation, obtained ethane
recovery percent based on Gas sub-cooled process (GSP) is 99.9 by
mole that is included 32.1% by using de-methanizer column and
67.8% by de-ethanizer tower. The outstanding feature of this process
is the novel split-vapor concept that employs to generate reflux for
de-methanizer column. Remain amount of ethane in export gas cause
rise in gross heating value up to 36.66 MJ/Nm3 in order to use in
industrial and household consumptions.
Abstract: A pilot plant for continuous flow microwave-assisted
chemical reaction combined with microreactors was developed and
water heating tests were conducted for evaluation of the developed
plant. We developed a microwave apparatus having a single
microwave generator that can heat reaction solutions in four reaction
fields simultaneously in order to increase throughput. We also
designed a four-branch waveguide using electromagnetic simulation,
and found that the transmission efficiency at 99%. Finally, we
developed the pilot plant using the developed microwave apparatus
and conducted water heating tests. The temperatures in the respective
reaction fields were controlled within ±1.1 K at 353.2 K. Moreover,
the energy absorption rates by the water were about 90% in the
respective reaction fields, whereas the energy absorption rate was
about 40% when 100 cm3 of water was heated by a commercially
available multimode microwave chemical reactor.
Abstract: Cellular automata have been used for design of cryptosystems. Recently some secret sharing schemes based on linear memory cellular automata have been introduced which are used for both text and image. In this paper, we illustrate that these secret sharing schemes are vulnerable to dishonest participants- collusion. We propose a cheating model for the secret sharing schemes based on linear memory cellular automata. For this purpose we present a novel uniform model for representation of all secret sharing schemes based on cellular automata. Participants can cheat by means of sending bogus shares or bogus transition rules. Cheaters can cooperate to corrupt a shared secret and compute a cheating value added to it. Honest participants are not aware of cheating and suppose the incorrect secret as the valid one. We prove that cheaters can recover valid secret by removing the cheating value form the corrupted secret. We provide methods of calculating the cheating value.
Abstract: The concerns about clean environment and high oil
prices driving forces for the research on alternative fuels. The
research efforts directed towards improving the performance of C.I
engines using vegetable oil as fuel. The paper deals results of
performance of a four stroke, single cylinder C.I. engine by preheated
neat Karanja oil is done from 30
o
C to 100
o
C. The performance of the
engine was studied for a speed range between 1500 to 4000 rpm, with
the engine operated under full load conditions. The performance
parameters considered for comparing are brake specific fuel
consumption, thermal efficiency, brake power, Nox emission of the
engine. The engine offers lower thermal efficiency when it is
powered by preheated neat Karanja oil at higher speed. The power
developed and Nox emission increase with the increase in the fuel
inlet temperature and the specific fuel consumption is higher than
diesel fuel operation at all elevated fuel inlet temperature.
Abstract: This paper aims to study decomposition behavior in
pyrolytic environment of four lignocellulosic biomass (oil palm shell,
oil palm frond, rice husk and paddy straw), and two commercial
components of biomass (pure cellulose and lignin), performed in a
thermogravimetry analyzer (TGA). The unit which consists of a
microbalance and a furnace flowed with 100 cc (STP) min-1 Nitrogen,
N2 as inert. Heating rate was set at 20⁰C min-1 and temperature
started from 50 to 900⁰C. Hydrogen gas production during the
pyrolysis was observed using Agilent Gas Chromatography Analyzer
7890A. Oil palm shell, oil palm frond, paddy straw and rice husk
were found to be reactive enough in a pyrolytic environment of up to
900°C since pyrolysis of these biomass starts at temperature as low as
200°C and maximum value of weight loss is achieved at about
500°C. Since there was not much different in the cellulose,
hemicelluloses and lignin fractions between oil palm shell, oil palm
frond, paddy straw and rice husk, the T-50 and R-50 values obtained
are almost similar. H2 productions started rapidly at this temperature
as well due to the decompositions of biomass inside the TGA.
Biomass with more lignin content such as oil palm shell was found to
have longer duration of H2 production compared to materials of high
cellulose and hemicelluloses contents.
Abstract: This paper deals with the problem of thermal and
mechanical shocks, which rising during operation, mostly at
interrupted cut. Here will be solved their impact on the cutting edge
tool life, the impact of coating technology on resistance to shocks
and experimental determination of tool life in heating flame.
Resistance of removable cutting edges against thermal and
mechanical shock is an important indicator of quality as well as its
abrasion resistance. Breach of the edge or its crumble may occur due
to cyclic loading. We can observe it not only during the interrupted
cutting (milling, turning areas abandoned hole or slot), but also in
continuous cutting. This is due to the volatility of cutting force on
cutting. Frequency of the volatility in this case depends on the type
of rising chips (chip size element). For difficult-to-machine materials
such as austenitic steel particularly happened at higher cutting speeds
for the localization of plastic deformation in the shear plane and for
the inception of separate elements substantially continuous chips.
This leads to variations of cutting forces substantially greater than for
other types of steel.
Abstract: In this paper, the energy performance of a selected
UHDE Ammonia plant is optimized by conducting heat integration through waste heat recovery and the synthesis of a heat exchange
network (HEN). Minimum hot and cold utility requirements were estimated through IChemE spreadsheet. Supporting simulation was
carried out using HYSYS software. The results showed that there is
no need for heating utility while the required cold utility was found to
be around 268,714 kW. Hence a threshold pinch case was faced. Then, the hot and cold streams were matched appropriately. Also,
waste heat recovered resulted with savings in HP and LP steams of
approximately 51.0% and 99.6%, respectively. An economic analysis
on proposed HEN showed very attractive overall payback period not
exceeding 3 years. In general, a net saving approaching 35% was
achieved in implementing heat optimization of current studied UHDE Ammonia process.
Abstract: As the fossil fuels kept on depleting, intense research in developing hydrogen (H2) as the alternative fuel has been done to cater our tremendous demand for fuel. The potential of H2 as the ultimate clean fuel differs with the fossil fuel that releases significant amounts of carbon dioxide (CO2) into the surrounding and leads to the global warming. The experimental work was carried out to study the production of H2 from palm kernel shell steam gasification at different variables such as heating rate, steam to biomass ratio and adsorbent to biomass ratio. Maximum H2 composition which is 61% (volume basis) was obtained at heating rate of 100oCmin-1, steam/biomass of 2:1 ratio, and adsorbent/biomass of 1:1 ratio. The commercial adsorbent had been modified by utilizing the alcoholwater mixture. Characteristics of both adsorbents were investigated and it is concluded that flowability and floodability of modified CaO is significantly improved.
Abstract: The use of neural networks is popular in various
building applications such as prediction of heating load, ventilation
rate and indoor temperature. Significant is, that only few papers deal
with indoor carbon dioxide (CO2) prediction which is a very good
indicator of indoor air quality (IAQ). In this study, a data-driven
modelling method based on multilayer perceptron network for indoor
air carbon dioxide in an apartment building is developed.
Temperature and humidity measurements are used as input variables
to the network. Motivation for this study derives from the following
issues. First, measuring carbon dioxide is expensive and sensors
power consumptions is high and secondly, this leads to short
operating times of battery-powered sensors. The results show that
predicting CO2 concentration based on relative humidity and
temperature measurements, is difficult. Therefore, more additional
information is needed.
Abstract: In this paper, we have proposed a novel FinFET with
extended body under the poly gate, which is called EB-FinFET, and
its characteristic is demonstrated by using three-dimensional (3-D)
numerical simulation. We have analyzed and compared it with
conventional FinFET. The extended body height dependence on the
drain induced barrier lowering (DIBL) and subthreshold swing (S.S)
have been also investigated. According to the 3-D numerical
simulation, the proposed structure has a firm structure, an acceptable
short channel effect (SCE), a reduced series resistance, an increased
on state drain current (I
on) and a large normalized I
DS. Furthermore,
the structure can also improve corner effect and reduce self-heating
effect due to the extended body. Our results show that the EBFinFET
is excellent for nanoscale device.
Abstract: Auckland has a temperate climate with comfortable
warm, dry summers and mild, wet winters. An Auckland school
normally does not need air conditioning for cooling during the
summer and only need heating during the winter. The space hating
energy is the major portion of winter school energy consumption and
the winter energy consumption is major portion of annual school
energy consumption. School building thermal design should focus
on the winter thermal performance for reducing the space heating
energy. A number of Auckland schools- design data and energy
consumption data are used for this study. This pilot study
investigates the relationships between their energy consumption data
and school building design data to improve future school design for
energy efficiency.
Abstract: Manufacturing components of fiber-reinforced
thermoplastics requires three steps: heating the matrix, forming and
consolidation of the composite and terminal cooling the matrix. For
the heating process a pre-determined temperature distribution through
the layers and the thickness of the pre-consolidated sheets is
recommended to enable forming mechanism. Thus, a design for the
heating process for forming composites with thermoplastic matrices
is necessary. To obtain a constant temperature through thickness and
width of the sheet, the heating process was analyzed by the help of
the finite element method. The simulation models were validated by
experiments with resistance thermometers as well as with an infrared
camera. Based on the finite element simulation, heating methods for
infrared radiators have been developed. Using the numeric
simulation many iteration loops are required to determine the process
parameters. Hence, the initiation of a model for calculating relevant
process parameters started applying regression functions.
Abstract: This paper presents the experimental as well as the
simulated performance studies on the transcritical CO2 heat pumps
for simultaneous water cooling and heating; effects of water mass
flow rates and water inlet temperatures of both evaporator and gas
cooler on the cooling and heating capacities, system COP and water
outlets temperatures are investigated. Study shows that both the
water mass flow rate and inlet temperature have significant effect on
system performances. Test results show that the effect of evaporator
water mass flow rate on the system performances and water outlet
temperatures is more pronounced (COP increases 0.6 for 1 kg/min)
compared to the gas cooler water mass flow rate (COP increases 0.4
for 1 kg/min) and the effect of gas cooler water inlet temperature is
more significant (COP decreases 0.48 for given ranges) compared to
the evaporator water inlet temperature (COP increases 0.43 for given
ranges). Comparisons of experimental values with simulated results
show the maximum deviation of 5% for cooling capacity, 10% for
heating capacity, 16% for system COP. This study offers useful
guidelines for selecting appropriate water mass flow rate to obtain
required system performance.
Abstract: Vibration characteristics of subcooled flow boiling on
thin and long structures such as a heating rod were recently
investigated by the author. The results show that the intensity of the
subcooled boiling-induced vibration (SBIV) was influenced strongly
by the conditions of the subcooling temperature, linear power density
and flow velocity. Implosive bubble formation and collapse are the
main nature of subcooled boiling, and their behaviors are the only
sources to originate from SBIV. Therefore, in order to explain the
phenomenon of SBIV, it is essential to obtain reliable information
about bubble behavior in subcooled boiling conditions. This was
investigated at different conditions of coolant subcooling
temperatures of 25 to 75°C, coolant flow velocities of 0.16 to
0.53m/s, and linear power densities of 100 to 600 W/cm. High speed
photography at 13,500 frames per second was performed at these
conditions. The results show that even at the highest subcooling
condition, the absolute majority of bubbles collapse very close to the
surface after detaching from the heating surface. Based on these
observations, a simple model of surface tension and momentum
change is introduced to offer a rough quantitative estimate of the
force exerted on the heating surface during the bubble ebullition. The
formation of a typical bubble in subcooled boiling is predicted to
exert an excitation force in the order of 10-4 N.
Abstract: Axial Flux Permanent Magnet (AFPM) Machines require effective cooling due to their high power density. The detrimental effects of overheating such as degradation of the insulation materials, magnets demagnetization, and increase of Joule losses are well known. This paper describes the CFD simulations performed on a test rig model of an air cooled Axial Flux Permanent Magnet (AFPM) generator built at Durham University to identify the temperatures and heat transfer coefficient on the stator. The Reynolds Averaged Navier-Stokes and the Energy equations are solved and the flow pattern and heat transfer developing inside the machine are described. The Nusselt number on the stator surfaces has been found. The dependency of the heat transfer on the flow field is described temperature field obtained. Tests on an experimental are undergoing in order to validate the CFD results.
Abstract: Due to the low heavy metal concentrations, the
bottom ash from a 32 MW municipal district heating plant was
determined to be a potential forest fertilizer as such. However,
additional Ca would be needed, because its Ca concentration of 1.9-
% (d.w.) was lower than the statutory Finnish minimum limit value
of 6.0-% (d.w.) for Ca in forest fertilizer. Due to the elevated As
concentration (53.0 mg/kg; d.w.) in the fly ash from the 32 MW
municipal district heating plant, and Cr concentration (620 mg/kg;
d.w.) in the ash fraction (i.e. mixture of the bottom ash and fly ash)
from the 6 MW municipal district heating plant, which exceed the
limit values of 30 mg/kg (d.w.) and 300 mg/kg (d.w.) for As and Cr,
respectively, these residues are not suitable as forest fertilizers.
Although these ash fractions cannot be used as a forest fertilizer as
such, they can be used for the landscaping of landfills or in industrial
and other areas that are closed to the public. However, an
environmental permit is then needed.
Abstract: The investigation results of high-density hydrogen
heating by high-current electric arc are presented at initial pressure
from 5 MPa to 160 MPa with current amplitude up to 1.6 MA and
current rate of rise 109-1011 A/s. When changing the initial pressure
and current rate of rise, channel temperature varies from several
electronvolts to hundreds electronvolts. Arc channel radius is several
millimeters. But the radius of the discharge chamber greater than the
radius of the arc channel on approximately order of magnitude. High
efficiency of gas heating is caused by radiation absorption of
hydrogen surrounding the arc. Current channel consist from vapor of
the initiating wire. At current rate of rise of 109 A/s and relatively
small current amplitude gas heating occurs due to radiation
absorption in the band transparency of hydrogen by the wire vapours
with photon energies less than 13.6 eV. At current rate of rise of
1011 A/s gas heating is due to hydrogen absorption of soft X-rays
from discharge channel.
Abstract: This article deals with the numerical simulation of the
floor heating convector in 3D. Presented convector can operate in
two modes – cooling mode and heating mode. This initial numerical
simulation is focused on cooling mode of the convector. Models with
different temperature of the fins are compared and three various
shapes of the fins are examined as well. The objective of the work is
to predict air flow and heat transfer inside convector for further
optimalization of these devices. For the numerical simulation was
used commercial software Ansys Fluent.