Showing papers in "Thermal Science in 2008"
TL;DR: The present paper reviews the literature dealing with various aspects of cooling methods and includes papers on experimental work on analyzing cooling technique and its stability, numerical modeling, natural convection, and advanced cooling methods.
Abstract: Due to rapid growth in semiconductor technology, there is a continuous increase of the system power and the shrinkage of size. This resulted in inevitable challenges in the field of thermal management of electronics to maintain the desirable operating temperature. The present paper reviews the literature dealing with various aspects of cooling methods. Included are papers on experimental work on analyzing cooling technique and its stability, numerical modeling, natural convection, and advanced cooling methods. The issues of thermal management of electronics, development of new effective cooling schemes by using advanced materials and manufacturing methods are also enumerated in this paper. .
204 citations
TL;DR: In this article, a step still with two different depth of trays is used to improve the productivity of a basin solar still by integrating small fins in basin plate and adding sponges in the trays.
Abstract: Maintaining minimum depth in conventional basin type solar still is difficult, as the area is large. However this can be achieved in stepped solar still in which the area of the basin is minimized by having small trays. Very few works have been carried so far in stepped solar still and constant depth trays are used in the basin plate. In this work, a stepped still with two different depth of trays are used. The basin plate contains twenty five trays with 10 mm depth and twenty five trays with 5 mm depth. To improve the productivity, experiments were carried out by integrating small fins in basin plate and adding sponges in the trays. Theoretical and experimental analyses are made for fin type, sponge type, and combination of fin and sponge type stepped solar still. When the fin and sponge type stepped solar is used, the average daily water production has been found to be 80% higher than ordinary single basin solar still. The theoretical results agree well with the experimental. Also an economic analysis was made. The payback period of this setup is 400 days.
115 citations
TL;DR: In this paper, the authors present a systematic literature survey to exploit the thermophysical characteristics of nanofluids and present empirical correlation to predict the thermal conductivity of Al2O3, Cu, CuO, and TiO2 nanoparticles with water and ethylene glycol as base fluid.
Abstract: Nanofluids exhibits larger thermal conductivity due to the presence of suspended nanosized solid particles in them such as Al2O3, Cu, CuO,TiO2, etc. Varieties of models have been proposed by several authors to explain the heat transfer enhancement of fluids such as water, ethylene glycol, engine oil containing these particles. This paper presents a systematic literature survey to exploit the thermophysical characteristics of nanofluids. Based on the experimental data available in the literature empirical correlation to predict the thermal conductivity of Al2O3, Cu, CuO, and TiO2 nanoparticles with water and ethylene glycol as base fluid is developed and presented. Similarly the correlations to predict the Nusselt number under laminar and turbulent flow conditions is also developed and presented. These correlations are useful to predict the heat transfer ability of nanofluids and takes care of variations in volume fraction, nanoparticle size and fluid temperature. The improved thermophysical characteristics of a nanofluid make it excellently suitable for future heat exchange applications. .
89 citations
TL;DR: In this paper, an analysis of rice bran oil methyl ester (RBME) as a diesel fuel was conducted on a 4.4 kW, single-cylinder, naturally aspirated, direct-injection air-cooled stationary diesel engine to evaluate the feasibility of RBME and its diesel blends as alternate fuels.
Abstract: There has been a worldwide interest in searching for alternatives to petroleum-derived fuels due to their depletion as well as due to the concern for the environment. Vegetable oils have capability to solve this problem because they are renewable and lead to reduction in environmental pollution. The direct use of vegetable oils as a diesel engine fuel is possible but not preferable because of their extremely higher viscosity, strong tendency to polymerize and bad cold start properties. On the other hand, Biodiesels, which are derived from vegetable oils, have been recently recognized as a potential alternative to diesel oil. This study deals with the analysis of rice bran oil methyl ester (RBME) as a diesel fuel. RBME is derived through the transesterification process, in which the rice bran oil reacts with methanol in the presence of KOH. The properties of RBME thus obtained are comparable with ASTM biodiesel standards. Tests are conducted on a 4.4 kW, single-cylinder, naturally aspirated, direct-injection air-cooled stationary diesel engine to evaluate the feasibility of RBME and its diesel blends as alternate fuels. The ignition delay and peak heat release for RBME and its diesel blends are found to be lower than that of diesel and the ignition delay decreases with increase in RBME in the blend. Maximum heat release is found to occur earlier for RBME and its diesel blends than diesel. As the amount of RBME in the blend increases the HC, CO, and soot concentrations in the exhaust decreased when compared to mineral diesel. The NOx emissions of the RBME and its diesel blends are noted to be slightly higher than that of diesel.
68 citations
TL;DR: A thermal model has been developed to predict the performance of the still based on both, the inner and the outer glass temperatures of the solar still as discussed by the authors, and two sets of values of C and n of internal heat and mass transfer coefficients, obtained from the experimental data under Indian climatic conditions have been used.
Abstract: In this paper, expressions for water and glass temperatures, hourly yield and instantaneous efficiency for double slope solar distillation systems have been derived analytically. The analysis is based on the basic energy balance for the systems. A thermal model has been developed to predict the performance of the still based on both, the inner and the outer glass temperatures of the solar still. In the present work two sets of values of C and n of internal heat and mass transfer coefficients, obtained from the experimental data under Indian climatic conditions, have been used. It is concluded that (1) there is a significant effect of operating temperature range on the internal heat transfer coefficients and (2) by considering the inner glass cover temperature there is reasonable agreement between the experimental and predicted theoretical results.
41 citations
TL;DR: In this paper, the experimental results of rice bran oil and jatropha oil methyl ester were analyzed in the presence of homogeneous acid catalyst and optimized their operating parameters like reaction temperature, quantity of alcohol and the catalyst requirement, stirring rate and time of esterification.
Abstract: Biodiesel, a promising substitute as an alternative fuel has gained significant attention due to the finite nature of fossil energy sources and does not produce sulfur oxides and minimize the soot particulate in comparison with the existing one from petroleum diesel. The utilization of liquid fuels such as biodiesel produced from vegetable oil by transesterification process represents one of the most promising options for the use of conventional fossil fuels. In the first step of this experimental research, edible rice bran oil used as test material and converted into methyl ester and non-edible jatropha vegetable oil is converted into jatropha oil methyl ester, which are known as biodiesel and they are prepared in the presence of homogeneous acid catalyst and optimized their operating parameters like reaction temperature, quantity of alcohol and the catalyst requirement, stirring rate and time of esterification. In the second step, the physical properties such as density, flash point, kinematic viscosity, cloud point, and pour point were found out for the above vegetable oils and their methyl esters. The same characteristics study was also carried out for the diesel fuel for obtaining the baseline data for analysis. The values obtained from the rice bran oil methyl ester and jatropha oil methyl ester are closely matched with the values of conventional diesel and it can be used in the existing diesel engine without any hardware modification. In the third step the storage characteristics of biodiesel are also studied. .
37 citations
TL;DR: In this article, the influence of biodiesel on the injection, spray, and engine characteristics with the aim of reducing harmful emissions is discussed, and the results indicate that, by using biodiesel, harmful emissions can be reduced to some extent by adjusting the injection pump timing properly while keeping other engine characteristics within acceptable limits.
Abstract: This paper discusses the influence of biodiesel on the injection, spray, and engine characteristics with the aim to reduce harmful emissions. The considered engine is a bus diesel engine with injection M system. The injection, fuel spray, and engine characteristics, obtained with biodiesel, are compared to those obtained with mineral diesel under peak torque and rated conditions. The considered fuel is neat biodiesel from rapeseed oil. Its density, viscosity, surface tension, and sound velocity are determined experimentally and compared to those of mineral diesel. The experimentally obtained results are used to analyze the most important injection, fuel spray, and engine characteristics. Furthermore, the influence of biodiesel usage on lubrication is presented briefly. The results indicate that, by using biodiesel, harmful emissions (NOx, CO, HC, smoke, and PM) can be reduced to some extent by adjusting the injection pump timing properly while keeping other engine characteristics within acceptable limits. Furthermore, the results indicate better lubrication conditions when biodiesel is used.
35 citations
TL;DR: The engine-in-the-loop study of a V-8, 6l engine coupled to a virtual 4´4 off road vehicle sheds light on critical transients in a conventional powertrain and their effect on NOx and soot emissions.
Abstract: This paper describes development of a test cell setup for concurrent running of a real engine and a simulation of the vehicle system, and its use for investigating highly-dynamic engine-in-vehicle operation and its effect on diesel engine emissions. Running an engine in the test cell under conditions experienced in the vehicle enables acquiring detailed insight into dynamic interactions between power train sub-systems, and the impact of it on fuel consumption and transient emissions. This type of data may otherwise be difficult and extremely costly to obtain from a vehicle prototype test. In particular, engine system response during critical transients and the effect of transient excursions on emissions are investigated using advanced, fast-response test instrumentation and emissions analyzers. Main enablers of the work include the highly dynamic AC electric dynamometer with the accompanying computerized control system and the computationally efficient simulation of the driveline/vehicle system. The latter is developed through systematic energy-based proper modeling that tailors the virtual model to capture critical powertrain transients while running in real time. Coupling the real engine with the virtual driveline/vehicle offers a chance to easily modify vehicle parameters, and even study different power train configurations. In particular, the paper describes the engine-in-the-loop study of a V-8, 6l engine coupled to a virtual 4´4 off road vehicle. This engine is considered as a high-performance option for this truck and the real prototype of the complete vehicle does not exist yet. The results shed light on critical transients in a conventional powertrain and their effect on NOx and soot emissions. Measurements demonstrate very large spikes of particulate concentration at the initiation of vehicle acceleration events. Characterization of transients and their effect on particulate emission provides a basis for devising engine-level or vehicle level strategies, and direct guidance for developing drive-by-wire systems and/or hybrid supervisory control.
31 citations
TL;DR: In this article, a simulation code of part load and off-design operation of an organic Rankine cycle unit for combined heat and power has been developed, taking the real situation of a furniture manufacturing factory as a starting point, it is shown how all energy flows occurring all year long inside the combined heat/power plant, can be estimated on the basis of the thermal user duty time profile, the available biomass flow rate and the adopted operation strategy.
Abstract: Exploitation of low and medium temperature thermal sources, in particular those based on biomass combustion and on industrial residual heat recovery, has been increasingly investigated in the last decades, accordingly to the growing interest towards reduction in primary energy consumption and environmental issues. Organic Rankine cycle technology allows designing power plants that are less demanding in terms of auxiliaries, safety systems, maintenance and operating costs when compared to conventional water steam power plants. To support the preliminary technical and economic design of this kind of plants in different contexts, a simulation code of part load and off-design operation of an organic Rankine cycle unit for combined heat and power has been developed. In the paper, taking the real situation of a furniture manufacturing factory as a starting point, it is shown how all energy flows occurring all year long inside the combined heat and power plant, can be estimated on the basis of the thermal user duty time profile, the available biomass flow rate and the adopted operation strategy. This information is the basis in order to correctly evaluate the energetic, economic and environmental advantages of the proposed technical solution, with respect to a particular context, as it is shown in the concluding part of the paper.
30 citations
TL;DR: In this article, the utility of sewage sludge as a biomass fuel is taken as an approach to deal with global warming, and thermal characterization of this new type of fuel is a premise before it is practically used in real facilities.
Abstract: The utility of sewage sludge as a biomass fuel is taken as an approach to deal with global warming. Thermal characterization of this new type of fuel is a premise before it is practically used in real facilities. Four sludge derived fuels were examined by thermal calorimeters (TG-DTA, C80, and TAM) at temperature ramp and isothermal conditions. Heat generation at low temperature was found in some sludge species. The corresponding spontaneous ignition was measured in an adiabatic spontaneous ignition tester at 80 °C. The reason of the thermal behaviors of the sludge fuels was discussed. The critical temperature of large scale pile-up was predicted. .
27 citations
TL;DR: In this article, the crude tyre pyrolisisis oil was desulphurised and distilled to improve the properties and studied the use of it for internal combustion engines.
Abstract: Conversion of waste to energy is one of the recent trends in minimizing not only the waste disposal but also could be used as an alternate fuel for internal combustion engines. Fuels like wood pyrolysis oil, rubber pyrolysis oil are also derived through waste to energy conversion method. Early investigations report that tyre pyrolysis oil derived from vacuum pyrolysis method seemed to possess properties similar to diesel fuel. In the present work, the crude tyre pyrolisis oil was desulphurised and distilled to improve the properties and studied the use of it. Experimental studies were conducted on a single cylinder four-stroke air cooled engine fuelled with two different blends, 30% tyre pyrolysis oil and 70% diesel fuel (TPO 30) and 30% distilled tyre pyrolysis oil and 70% diesel fuel (DTPO 30). The results of the performance, emission and combustion characteristics of the engine indicated that NOx is reduced by about 8% compared to tire pyrolysis oil and by about 10% compared to diesel fuel. Hydrocarbon emission is reduced by about 2% compared to TPO 30 operation. Smoke increased for DTPO 30 compared to TPO 30 and diesel fuel.
TL;DR: In this article, an automotive air-conditioning system based on absorption refrigeration cycle has been simulated, where the water-lithium bromide pair is used as a working mixture for its favorable thermodynamic and transport properties compared to the conventional refrigerants utilized in vapor compression refrigeration applications.
Abstract: An automotive air-conditioning system based on absorption refrigeration cycle has been simulated. This waste heat driven vapor absorption refrigeration system is one alternate to the currently used vapour compression refrigeration system for automotive air-conditioning. Performance analysis of vapor absorption refrigeration system has been done by developing a steady-state simulation model to find the limitation of the proposed system. The water-lithium bromide pair is used as a working mixture for its favorable thermodynamic and transport properties compared to the conventional refrigerants utilized in vapor compression refrigeration applications. The pump power required for the proposed vapor absorption refrigeration system was found lesser than the power required to operate the compressor used in the conventional vapor compression refrigeration system. A possible arrangement of the absorption system for automobile application is proposed.
TL;DR: In this paper, a steady flow rig experiment is used to evaluate the swirl of a helical intake port design for different operating conditions, and the variable swirl plate set up of the W06DTIE2 engine was used to experimentally study the swirl variation for different openings of the valve.
Abstract: It is known that a helical port is more effective than a tangential port to attain the required swirl ratio with minimum sacrifice in the volumetric efficiency. The swirl port is designed for lesser swirl ratio to reduce emissions at higher speeds. But this condition increases the air fuel mixing time and particulate smoke emissions at lower speeds. Optimum swirl ratio is necessary according to the engine operating condition for optimum combustion and emission reduction. Hence the engine needs variable swirl to enhance the combustion in the cylinder according to its operating conditions, for example at partial load or low speed condition it requires stronger swirl, while the air quantity is more important than the swirl under very high speed or full load and maximum torque conditions. The swirl and charging quantity can easily trade off and can be controlled by the opening of the valve. Hence in this study the steady flow rig experiment is used to evaluate the swirl of a helical intake port design for different operating conditions. The variable swirl plate set up of the W06DTIE2 engine is used to experimentally study the swirl variation for different openings of the valve. The sliding of the swirl plate results in the variation of the area of inlet port entry. Therefore in this study a swirl optimized combustion system varying according to the operating conditions by a variable swirl plate mechanism is studied experimentally and compared with the computational fluid dynamics predictions. In this study the fluent computational fluid dynamics code has been used to evaluate the flow in the port-cylinder system of a DI diesel engine in a steady flow rig. The computational grid is generated directly from 3-D CAD data and in cylinder flow simulations, with inflow boundary conditions from experimental measurements, are made using the fluent computational fluid dynamics code. The results are in very good agreement with experimental results.
TL;DR: In this paper, three chemical kinetic mechanisms of methane combustion were tested and compared using the internal combustion engine model of Chemkin 4.02 and compared with the standard detailed scheme GRIMECH 3.0.
Abstract: Three chemical kinetic mechanisms of methane combustion were tested and compared using the internal combustion engine model of Chemkin 4.02 [1]: one-step global reaction mechanism, four-step mechanism, and the standard detailed scheme GRIMECH 3.0. This study shows good concordances, especially between the four-step and the detailed mechanisms in the prediction of temperature and main species profiles. But reduced schemes were incapables to predict pollutant emissions in an internal combustion engine. The four-step mechanism can only predict CO emissions but without good agreement.
TL;DR: In this paper, the heat transfer coefficients in a spiral plate heat exchanger are investigated and a new correlation for the Nusselt number which can be used for practical applications is proposed.
Abstract: In this paper, the heat transfer coefficients in a spiral plate heat exchanger are investigated. The test section consists of a plate of width 0.3150 m, thickness 0.001 m and mean hydraulic diameter of 0.01 m. The mass flow rate of hot water (hot fluid) is varying from 0.5 to 0.8 kg/s and the mass flow rate of cold water (cold fluid) varies from 0.4 to 0.7 kg/s. Experiments have been conducted by varying the mass flow rate, temperature, and pressure of cold fluid, keeping the mass flow rate of hot fluid constant. The effects of relevant parameters on spiral plate heat exchanger are investigated. The data obtained from the experimental study are compared with the theoretical data. Besides, a new correlation for the Nusselt number which can be used for practical applications is proposed.
TL;DR: In this article, a thermodynamic simulation of the ammonia-water absorption refrigeration system is carried out to investigate the effects of different operating variables on the performance of the cycle, and a computer program in C language is written for the performance analysis.
Abstract: The ammonia-water absorption refrigeration system is attracting increasing research interests, since the system can be powered by waste thermal energy, thus reducing demand on electricity supply. The development of this technology demands reliable and effective system simulations. In this work, a thermodynamic simulation of the cycle is carried out to investigate the effects of different operating variables on the performance of the cycle. A computer program in C language is written for the performance analysis of the cycle.
TL;DR: In this article, a mathematical model based on heat and mass transfer principle is developed to find the outlet condition of water and air, which is solved using iterative method Energy and exergy analysis infers that inlet air wet bulb temperature is the most important parameter than inlet water temperature and also variation in dead state properties does not affect the performance of wet cooling tower.
Abstract: Cooling tower is an open system direct contact heat exchanger, where it cools water by both convection and evaporation In this paper, a mathematical model based on heat and mass transfer principle is developed to find the outlet condition of water and air The model is solved using iterative method Energy and exergy analysis infers that inlet air wet bulb temperature is found to be the most important parameter than inlet water temperature and also variation in dead state properties does not affect the performance of wet cooling tower
TL;DR: In this article, the authors present the activities of UN-ECE working group PMP on defining the best procedure and methodology for the measurement of passenger cars diesel engines particle mass and number concentrations.
Abstract: Air pollution caused by diesel engine emissions, especially particulate matters and nitric oxides emissions, is one of the biggest problems of current transportation. In the near future the emission of diesel particulate matters will become one of the most important factors that will affect the trend of engine development. Ambient airborne particles have adverse environmental and health effects and therefore their concentration in the air is regulated. Recent medical studies showed that different particle properties are important (for example: number/concentration, active surface, chemical composition/morphology) and may take role in the responsibility for their human health impact. Thus, diesel engines are one of the most important sources of particles in the atmosphere, especially in urban areas. Studying health effects and diesel engine particulate properties, it has been concluded that they are a complex mixture of solids and liquids. Biological activity of particulate matter may be related to particle sizes and their number. The paper presents the activities of UN-ECE working group PMP on defining the best procedure and methodology for the measurement of passenger cars diesel engines particle mass and number concentrations. The results of inter-laboratory emissions testing are presented for different engine technologies with special attention on repeatability and reproducibility of measured data. .
TL;DR: In this paper, water spray cooling was modeled to investigate the influences of the droplet size, injected velocity, the pressure and velocity of the superheated steam on the evaporation of the cooling water.
Abstract: Spray cooling of the superheated steam occurs with the interaction of many complex physical processes, such as initial droplet formation, collision, coalescence, secondary break up, evaporation, turbulence generation, and modulation, as well as turbulent mixing, heat, mass and momentum transfer in a highly non-uniform two-phase environment. While it is extremely difficult to systematically study particular effects in this complex interaction in a well defined physical experiment, the interaction is well suited for numerical studies based on advanced detailed models of all the processes involved. This paper presents results of such a numerical experiment. Cooling of the superheated steam can be applied in order to decrease the temperature of superheated steam in power plants. By spraying the cooling water into the superheated steam, the temperature of the superheated steam can be controlled. In this work, water spray cooling was modeled to investigate the influences of the droplet size, injected velocity, the pressure and velocity of the superheated steam on the evaporation of the cooling water. The results show that by increasing the diameter of the droplets, the pressure and velocity of the superheated steam, the amount of evaporation of cooling water increases. .
TL;DR: In this article, the combined effect of the tumble flow and combustion chamber geometry layout variations on flame front shape and its propagation through homogenous mixture of isooctane and air are presented.
Abstract: In this paper some results concerning the combined effect of the tumble flow and combustion chamber geometry layout variations on flame front shape and its propagation through homogenous mixture of isooctane and air are presented. Spatial distributions of NO in different combustion chamber geometries are presented as well. The basic combustion chamber geometry layout considered consists of the flat head with two vertical valves and a cylindrical bowl subjected to variations of depth and squish area. All results presented were obtained by dint of multidimensional modeling of reactive flows in arbitrary geometry with moving objects and boundaries with modified KIVA3 and KIVA3V source codes. Two additional computer codes were applied to generate boundary conditions for KIVA3V calculations with moving valves. The AVL TYCON code was used for the calculation of valve lift profiles, and AVL BOOST code was used for the calculation of relevant data set in the valve regions. Different combustion chamber geometry layouts generate different levels of squish, and the combustion effects in essence depend on the interaction of that flow with tumble. It was found that for particular combustion chamber shapes with different diameter/depth aspect ratios entirely different flame front shapes and propagation velocities were encountered primarily due to variations of fluid flow patterns in the vicinity of top dead center.
TL;DR: In this article, an experimental investigation of the airflow through inlet port of a standard production direct injection diesel engine is presented, which comprises mass flow rate and pressure drop measurements at fixed valve lifts, and spatial distributions of mean and r.m.s. velocity components around the port/valve annulus measured under steady flow conditions by special designed miniature hot-wire anemometer X probe.
Abstract: An experimental investigation of the airflow through inlet port of a standard production direct injection diesel engine is presented. The investigation comprises mass flow rate and pressure drop measurements at fixed valve lifts, and spatial distributions of mean and r.m.s. velocity components around the port/valve annulus measured under steady flow conditions by special designed miniature hot-wire anemometer X probe. The results show that the velocity field is distributed non-uniformly across the valve gap and around valve periphery. Nonuniformity is more expressed at higher valve lifts. Flow instability in a jet leaving the port (jet flapping) is also evident since the skewness and kurtosis of the velocity probability distribution function depart from the Gaussian form. The presented experimental method, based on the application of miniature multiple hot-wire probes, makes possible investigation of flow performances of an inlet port and poppet valve assembly of a production engine head without any modification for ensuring an optical access within the port/cylinder.
TL;DR: In this article, the authors show that the limitations of traditional first-law analysis, based upon thermodynamic performance of process unit coupled with mass and energy balances, are not a serious limitation when dealing with familiar systems.
Abstract: Limitations of traditional first-law analysis, based upon thermodynamic performance of process unit coupled with mass and energy balances, are not a serious limitation when dealing with familiar systems. However, when dealing with more uncongenial, complex ones, it provides incomplete insight for such evaluation. These limitations came from the fact that first-law analysis does not indicate the sources or magnitudes of entropy production, which is, by the second law, essential criterion for scaling losses. An evaluation of plant performance will usually require a comparison of the thermodynamic performance of process units with available data from existing plants. Therefore, exergy analysis is more than useful, providing information about magnitudes of losses and their distribution throughout the system as well. Such analysis is very thankful at the level of process units but applied on higher system levels e.g. the comparison of overall plant performance (total system) or the performance of subsystems, represents the valuable method for indicating where research resources can be directed to best advantage.
TL;DR: In this article, the authors discuss the need for better understanding of the complex problems in implementing incentives and disincentives aimed at achieving intermodal balance, and provide a summary of lessons and guidelines for the future.
Abstract: The 20th century witnessed revolutionary developments in transportation technology with major impacts on the form and character of cities. Progress in increasing mobility has brought many benefits as well as serious problems, particularly in deterioration of livability and sustainability. Increase in auto ownership led to serious problems of chronic traffic congestion. Attempts to rebuild cities to provide full accommodation of private cars have led to serious problems of auto dependency and deterioration of cities. Experiences from recent decades have shown that urban transportation is much more complex than usually realized. Livable and sustainable cities require policies that lead to creation of a transportation system consisting of coordinated public transit and private cars, and encourages pedestrian environment and efficient, sustainable development. Great need for better understanding of the complex problems in implementing incentives and disincentives aimed at achieving intermodal balance is emphasized. Brief descriptions of cities which lead in achieving such livable conditions is followed by a summary of lessons and guidelines for the future.
TL;DR: In this paper, an experimental study on the replacement of CFC12 and HFC134a by the new R290/R600a refrigerant mixture as drop-in replacement refrigerant with and without the effect of magnetic field.
Abstract: This paper presents an experimental study on the replacement of CFC12 and HFC134a by the new R290/R600a refrigerant mixture as drop-in replacement refrigerant with and without the effect of magnetic field. Without any modification to the system components drop-in experimental tests were performed on a vapour compression refrigeration system with a reciprocating compressor, which was originally designed to operate with CFC12.The test results with no magnets showed that the refrigerant R290/R600a had 19.9-50.1% higher refrigerating capacity than R12 and 28.6-87.2% than R134a. The mixture R290/R600a consumed 6.8- -17.4% more energy than R12. The coefficient of performance of R290/R600a mixture increases from 3.9-25.1% than R12 at lower evaporating temperatures and 11.8-17.6% at higher evaporating temperatures. The effect of magnetic field force reduced the compressor energy consumption by 1.5-2.5% than with no magnets. The coefficient of performance of the system was higher in the range 1.5-2.4% with the effect of magnetic field force. The R290/600a (68/32 by wt.%) mixture can be considered as an excellent alternative refrigerant for CFC12 and HFC134a systems.
TL;DR: In this paper, the authors argue that if we are to provide a sustainable secure environment and prosperity for next generations, we have to act now at least with developments in particular in the direction of clean, cheap, and renewable energy sources with an emphasis on basic, curiosity driven research which through scientific breakthroughs, is the only realistic solution to solving world's energy requirements.
Abstract: According to the Lisbon declaration from 2000 the goal of European Union is to become by 2010 the most competitive and dynamic knowledge-driven economy and by 2025 a sustainable knowledge society. The EU however faces some strong challenges on the road toward these goals and is evidently lagging behind both USA and Japan. Our analysis is based on six dimensions of these challenges, including the economic challenge, the demographic challenge, the scientific challenge, the challenge of higher education, the challenge of European governance and identity/system of values, and the environmental/ecotechnological challenge. We argue that if we are to provide a sustainable secure environment and prosperity for next generations, we have to act now at least with developments in particular in the direction of clean, cheap, and renewable energy sources with an emphasis on basic, curiosity driven research which through scientific breakthroughs, is the only realistic solution to solving world's energy requirements. Such an action could for example facilitate the transition from fossil fuels to solar power in a relatively short time of about two decades, and help EU achieve its declared sustainability targets.
TL;DR: In this article, the advantages of CO2 utilization in prospective automotive heat pump systems are discussed. But, the authors focus on the benefits of using CO2 as a refrigerant.
Abstract: Based on Kyoto Protocol and the decisions of European Commission R134a refrigerant, currently dominantly used in mobile air conditioning systems, needs to be phased-out. At present automotive industry looks at carbon dioxide (CO2; R744) as the refrigerant of the future. Apart from the environmental benefits discussed are the technical characteristics of carbon dioxide refrigeration cycle and mobile air-conditioning systems in comparison to R134a refrigerant. Analyzed are challenges emerged from the use of CO2 as refrigerant and improvement opportunities in regards to increase of the system performance and efficiency. Particular attention is dedicated to the advantages of CO2 utilization in prospective automotive heat pump systems.
TL;DR: In this paper, an implicit finite difference method and the Gauss elimination technique have been used to solve the governing partial differential equations of motion (Navier Stocks equations) for two-dimensional model.
Abstract: The problem of the laminar upward mixed convection heat transfer for thermally developing air flow in the entrance region of a vertical circular cylinder under buoyancy effect and wall heat flux boundary condition has been numerically investigated. An implicit finite difference method and the Gauss elimination technique have been used to solve the governing partial differential equations of motion (Navier Stocks equations) for two-dimensional model. This investigation covers Reynolds number range from 400 to 1600, heat flux is varied from 70 W/m2 to 400 W/m2. The results present the dimensionless temperature profile, dimensionless velocity profile, dimensionless surface temperature along the cylinder, and the local Nusselt number variation with the dimensionless axial distance Z+. The dimensionless velocity and temperature profile results have revealed that the secondary flow created by natural convection have a significant effect on the heat transfer process. The results have also shown an increase in the Nusselt number values as the heat flux increases. The results have been compared with the available experimental study and with the available analytical solution for pure forced convection in terms of the local Nusselt number. The comparison has shown satisfactory agreement. .
TL;DR: In this article, the results of the development and of the tests of an experimental demonstrative boiler burning small bales of soya straw have been presented in the boiler, the combustion has been organized on the 'cigarette burning' principle, and fuel feeding has been done by gravity.
Abstract: There is a growing need for the use of alternative and renewable energy sources, in terms of sustainable energy development. One of the potentially biggest renewable energy sources in Serbia is agricultural biomass, quite available and cheap at the moment. For many years, the Vinca Institute of Nuclear Sciences, Laboratory for Thermal Engineering and Energy, has been working on the development of clean technologies for efficient utilization of biomass, and as a result utilities and equipment (boilers and furnaces) with wide range of use have been developed. These devices have complete combustion control and primarily burn baled biomass with no adequate utilization. The results of the development and of the tests of an experimental demonstrativel boiler burning small bales of soya straw have been presented in this paper. In the boiler, the combustion has been organized on the 'cigarette burning' principle, and fuel feeding has been done by gravity. The technical scheme of the boiler and the results of preliminary tests carried out in real operation conditions have been given.
TL;DR: In this article, three independent biodiesel samples were subjected to a series of experiments, including a thermogravimetry-differential thermal analysis, a differential scanning calorimetry analysis and a modified wire basket test.
Abstract: The spontaneous ignition of biodiesel was for the first time suspected to be the cause of a recent fire in Japan. We herein present experimental evidence implying this potential risk of biodiesel. Thus, three independent biodiesel samples were subjected to a series of experiments, including a thermogravimetry-differential thermal analysis, a differential scanning calorimetry analysis and a modified wire basket test. The results were comparatively evaluated with reference to vegetable oils, of which spontaneous ignition has been well reported as a cause of fires. The heat onset temperature of biodiesel samples was determined to be ~100 °C, which was ~45 °C lower than those of vegetable oils. Furthermore, under the isothermal condition at 100 °C, the inner temperature of biodiesel samples rose rapidly with the generation of smoke after short induction periods owing to their exothermal decomposition, whereas for vegetable oils neither change in the inside temperature nor generation of smoke was observed even after 10 hours. It was therefore concluded that biodiesel possesses the higher risk of spontaneous ignition than vegetable oils. This is very important information to minimize the fire risk in biodiesel production facilities and so on. .
TL;DR: In this article, a simplified procedure of an internal combustion engine in-cylinder pressure record analysis has been presented, which is based on the consideration proposed by Hohenberg and Killman, but enhances the approach by involving the rate of heat transferred to the walls that was omitted in the original approach.
Abstract: In this paper a simplified procedure of an internal combustion engine in-cylinder pressure record analysis has been presented. The method is very easy for programming and provides quick evaluation of the gas temperature and the rate of combustion. It is based on the consideration proposed by Hohenberg and Killman, but enhances the approach by involving the rate of heat transferred to the walls that was omitted in the original approach. It enables the evaluation of the complete rate of heat released by combustion (often designated as “gross heat release rate” or “fuel chemical energy release rate”), not only the rate of heat transferred to the gas (which is often designated as “net heat release rate”). The accuracy of the method has been also analyzed and it is shown that the errors caused by the simplifications in the model are very small, particularly if the crank angle step is also small. A several practical applications on recorded pressure diagrams taken from both spark ignition and compression ignition engine are presented as well.