Showing papers in "International journal of ambient energy in 2010"
TL;DR: In this article, a survey was conducted to assess attitudes of the public towards renewable energy and the information gathered was analyzed for respondents attitudes towards issues such as, knowledge of renewable energy sources and power generation, encouragement by government as well as at a personal level.
Abstract: SYNOPSIS A survey was conducted to assess attitudes of the public towards renewable energy. The information gathered was analysed for respondents attitudes towards issues such as, knowledge of renewable energy sources and power generation, encouragement by government as well as at a personal level, comparison of fossil fuels use and renewable power, opinions for encouragement, leads for encouraging renewable energy growth with financial incentives, global warming problem and renewable energy as an option and public financial contribution towards lowering global warming. It was observed that the public has considerable awareness of the sources of the energy. It confirms from the data that the public understands mostly that renewable energy is the non polluting source and going for utilisation of renewable energy is a very good idea. It was also clear that people knew about wind and atomic energy generation systems. Among the renewable energy sources it was found that public opinion supported wind energy as...
26 citations
TL;DR: In this article, a complete transient simulation model of a solar heating and cooling plant is presented based on the coupling of evacuated solar collectors with a single-stage LiBr-H2O absorption chiller.
Abstract: SYNOPSIS In this paper, a complete transient simulation model of a solar heating and cooling plant is presented. The system under analysis is based on the coupling of evacuated solar collectors with a single-stage LiBr-H2O absorption chiller. An auxiliary heater, circulation pumps, storage tanks, feedback controller, mixers, diverters, ON/OFF hysteresis controller, single lumped capacitance building and controllers are also included. The simulation was performed using the TRNSYS environment. This software also includes a detailed database with weather parameters for several cities all over the world. The system was simulated using specially designed control strategies and varying the main design variables. In particular, a variable speed pump on the solar collector was implemented, in order to maximise the tank temperature and minimise heat losses. A cost model was also developed in order to calculate operating and capital costs. A case study is presented and discussed, aiming at determining the performan...
17 citations
TL;DR: In this article, the optimal configuration of the expansion process of a heated working fluid with convective-radiative heat transfer law was determined, i.e. q ∞ Δ(T) + Δ (T4) is, determined.
Abstract: SYNOPSIS The optimal configuration of the expansion process of a heated working fluid with convective-radiative heat transfer law, i.e. q ∞ Δ(T) + Δ(T4)is, determined. The optimal processes that maximise the work output of the working fluid with and without given final internal energy constraints are obtained, respectively, using optimal-control theory and the method of eliminating the volume variable V(t). It is shown that all the optimal processes consist of, at most, three stages, including an initial adiabatic branch, one intermediate Euler-Lagrange arc and a final adiabatic branch. The solutions of all state variables are obtained. Numerical examples of the optimal configurations are provided. The obtained results are compared with those obtained with Newtonian and radiative heat transfer laws.
13 citations
TL;DR: In this article, to decrease the viscosity of raw cottonseed oil, cottonseed methyl ester is obtained by transesterification process, which is a promising alternative fuel for diesel engines as it has several advantages.
Abstract: SYNOPSIS The scarce and rapidly depleting conventional petroleum resources have promoted research for alternative fuels for internal combustion engines. In view of this, vegetable oil is a promising alternative fuel for diesel engines as it has several advantages. The high viscosity causes some problems in atomisation of injector systems and combustion in cylinders of diesel engines. In present research, to decrease viscosity of raw cottonseed oil, cottonseed methyl ester is obtained by transesterification process. The fuel properties of cottonseed methyl ester such as kinematic viscosity, calorific value, flash point, fire point, carbon residue and density were determined. Experiments were carried out using a single cylinder, four stroke, constant speed, water cooled, direct injection diesel engine. The acquired data were analysed for various parameters such as brake thermal efficiency, specific fuel consumption and exhaust gas temperature. Results indicated that Diesel with 25% esterified cottonseed oil...
11 citations
TL;DR: In this paper, the effects of variable specific heat ratio of the working fluid on the performance of a Diesel cycle, with considerations of heat transfer and friction-like term losses, are investigated by using finite time thermodynamics.
Abstract: SYNOPSIS The effects of the variable specific heat ratio of the working fluid on the performance of a Diesel cycle, with considerations of heat transfer and friction-like term losses, are investigated by using finite time thermodynamics in this paper. The relationships between power output and compression ratio, between thermal efficiency and compression ratio, as well as the optimal relationship between power output and efficiency of the cycle, are derived by detailed numerical examples. The results obtained herein show that the effects of variable specific heat ratio of working fluid on the power output and thermal efficiency of the cycle are significant and should be considered in the design of practical Diesel engines.
10 citations
TL;DR: In this paper, the optimal motion of a model internal combustion engine with a piston fitted inside a cylinder containing an ideal gas is examined, where the gas is heated at a given rate f(t) and coupled to a heat bath with linear phenomenological heat transfer law q ∝ Δ(T−1) for a finite amount of time.
Abstract: SYNOPSIS The optimal motion of a model internal combustion engine with a piston fitted inside a cylinder containing an ideal gas is examined. The gas is heated at a given rate f(t) and coupled to a heat bath with linear phenomenological heat transfer law q ∝ Δ(T−1) for a finite amount of time. The optimal motion of the model internal combustion engine with linear phenomenological heat transfer law and maximum power output objective is obtained, as well as the optimal motion of the model internal combustion engine with linear phenomenological heat transfer law, fixed power output and maximum useful work output objective. The maximum useful work output per cycle, the maximum power output and the corresponding efficiency are obtained. Numerical examples are provided and the obtained results are compared with those obtained with Newton's heat transfer law. The results presented herein can provide the basis for both determination of optimal operating conditions and design of real systems operating with linear ...
10 citations
TL;DR: In this article, a general cycle model of a class of typical irreversible heat engines with temperature-dependent heat capacities of the working substance is established and expressions for work output and efficiency of the heat engines are derived.
Abstract: SYNOPSIS A general cycle model of a class of typical irreversible heat engines with temperature-dependent heat capacities of the working substance is established. The expressions for work output and efficiency of the heat engines are derived. The influence of variable heat capacities of the working substance, heat leak losses, compression and expansion efficiencies and other parameters on the optimal performance of the cycle is investigated. The optimum criteria of some important parameters are obtained and the optimal operating regions of the heat engines are determined. The optimum performance of several typical heat engines is directly derived. The results obtained may provide some theoretical guidance for the performance improvement and optimal design of real heat engines.
10 citations
TL;DR: In this article, the performance of environmentally-friendly refrigerant mixtures in an organic Rankine Cycle (ORC) for power generation has been compared at low and medium waste heat temperatures to other organic and nonorganic fluids.
Abstract: SYNOPSIS This paper presents and discusses the performance of environmentally-friendly refrigerant mixtures in an Organic Rankine Cycle (ORC) for power generation. The performance has been compared at low and medium waste heat temperatures to other organic and non-organic fluids. The refrigerant mixtures boil at extremely low temperatures and are capable of efficiently capturing waste heat at temperatures less than 27°C (80°F). The quaternary mixtures are fully HFCs and their compositions can be varied to best recover heat at temperatures up to 482°C (900°F). In this paper, energy and exergy analysis have been presented for the behaviour of the quaternary refrigerant mixtures and compared to other commonly used fluids. Results showed that at this range of heat source temperatures the refrigerant mixtures efficiently recover waste heat and produce power at efficiencies significantly higher than with other working fluids. The results also showed that other low temperature applications are possible and econo...
10 citations
TL;DR: In this article, a proprietary heatpipe Evacuated tube solar water heater manifold was inclined at 1° to the horizontal, reverse fluid flow was observed for 69% of the monitored diurnal periods.
Abstract: A proprietary heat-pipe Evacuated Tube Solar Water Heater (ETSWH) originally designed for collection of solar energy using forced fluid circulation was operated using thermosyphon fluid circulation. The thermal performance of this solar water heating system was monitored from October 2006 to June 2007. The ETSWH array was inclined with the expected collector outlet at a higher datum level than the expected collector inlet to provide a hydrostatic pressure differential across the manifold. During the monitoring period it was observed that thermosyphon flow was not always in the expected direction, with flow reversal occurring when the collector inlet temperature was greater than that of the outlet. When the evacuated tube solar water heater manifold was inclined at 1° to the horizontal, reverse fluid flow was observed to occur for 69% of the monitored diurnal periods. Diurnal reverse circulation lowers system efficiency by reducing thermal stratification in the hot water storage tank via convective entrainment and mixing. The thermal performance of the ETSWH was monitored continuously from January 2007 to June 2007 with the manifold inclined at 5° to the horizontal. Over this time period it was found that fluid flow reversal arose for 22% of the diurnal periods considered, resulting in a 47% improvement in diurnal storage efficiency compared to when the system had its manifold inclined at 1°. The long term diurnal storage efficiency of the optimised system inclined at 5” was measured as 66%.
10 citations
TL;DR: In this article, a modified analysis of a counterflow plate heat exchanger that takes into account a heat source, which is assumed to be volumetrically uniform in the hot fluid, is presented.
Abstract: SYNOPSIS A modified analysis is presented of a counterflow plate heat exchanger that takes into account a heat source, which is assumed to be volumetrically uniform in the hot fluid. New expressions for the number of transfer units (NTU) and effectiveness of the heat exchanger are derived. These expressions are verified against the conventional effectiveness-NTU relationships in the limit of zero heat source rate. Such heat exchanger with heat source in the hot fluid is of interest in applications to ammonia-water absorption heat exchanger where a heat of absorption source term arises in the solution side. The model studies two cases based on the minimum and maximum heat capacities of the hot fluid. The results show that the number of heat transfer units and the effectiveness of the heat exchanger are not the same for both cases. The analysis is applied to an absorber heat exchanger. Effectiveness-NTU relationships are also given for a parallel flow heat exchanger with a heat source in the hot fluid.
6 citations
TL;DR: In this paper, the performance of photogalvanic cells for solar energy conversion and storage has been studied in a previously unexplored system containing Brilliant Cresyl Blue as photosensitiser with D-Xylose as reductant and Sodium Lauryl Sulphate (NaLS) as surfactant.
Abstract: SYNOPSIS The performance of photogalvanic cells for solar energy conversion and storage has been studied in a previously unexplored photogalvanic system containing Brilliant Cresyl Blue as photosensitiser with D-Xylose as reductant and Sodium Lauryl Sulphate (NaLS) as surfactant. The observed value of the photogeneration of photopotential was 940.0 mV and photocurrent was 440.0 μA. The maximum power of the cell was 413.16 μW whereas the observed power at the power point was 115.00 μW. The conversion efficiency was 1.1057%. A fill factor of 0.2408 was experimentally determined at the power point of the photogalvanic cell. The rate of initial generation of current is 53.33 μA min-1. The photogalvanic cell so developed can work for 140.0 minutes in the dark if it is irradiated for 150.0 minutes, i.e. the storage capacity of the photogalvanic cell is 93.33%. Performance values exceed those reported in previous works.
TL;DR: In this article, a comparative study between two types of absorption cooling systems with identical cold output is carried out, accounting for both energy and exergy considerations, and simulation results were used to study the influence of various operating parameters on the coefficient of performance (COP), exergy efficiency and the total exergy destruction of the two systems.
Abstract: SYNOPSIS Air conditioning systems have a major impact on energy demand. With fossil fuels fast depleting, it is imperative to look for cooling systems that require less high-grade energy for their operation. In this context, absorption cooling systems have become increasingly popular in recent years from the viewpoints of energy and the environment. Two types of absorption chillers, single effect and half-effect cycles, can operate using low temperature hot water. In this paper a comparative study between these two systems with identical cold output is carried out. An efficiency analysis, accounting for both energy and exergy considerations is presented. Simulation results were used to study the influence of the various operating parameters on the coefficient of performance (COP), exergy efficiency and the total exergy destruction of the two systems. The COP of the half-effect system is approximately half the COP of the single effect system but the exergy efficiency of the latter is slightly lower. In thi...
TL;DR: In this paper, the effect of incomplete conversions in chemical reactions was analyzed for steady-state solid oxide fuel cells and a general approach was developed that attributes lowering of the cell voltage below its reversible value to polarisations and imperfect chemical conversions.
Abstract: This research continues the thermodynamic analysis of steady-state solid oxide fuel cells initiated in Sieniutycz (Sieniutycz, S., 2010, Thermodynamic aspects of power generation in imperfect fuel cells: part I. International Journal of Ambient Energy, 31 (4), 195–202). This analysis focuses on the effect of incomplete conversions in chemical reactions. A general approach is developed that attributes lowering of the cell voltage below its reversible value to polarisations and imperfect chemical conversions. Relevant model, appropriate for systems with complete conversions, is extended to imperfect cases. The performance curves of a fuel cell and the effect of typical design and operating parameters on the cell behaviour are analysed. A general result is obtained for power limits of fuel cells propelled by linear transport phenomena.
TL;DR: In this paper, a prototype battery powered electric vehicle using a solar photovoltaic array (10 kWp) was installed at a monastery situated at Achkout (Lebanon) with a total agricultural area of 50 hectares, 10 hectares of which was under viticulture.
Abstract: SYNOPSIS Hilly and remote areas in the Southern Mediterranean region suffer a high cost of diesel fuel, problematic supply, poor or non-existent grid connections and lack of maintenance technicians to service farm grid generation systems and machinery. A prototype battery powered electric vehicle using a solar photovoltaic array (10 kWp) was installed at a monastery situated at Achkout (Lebanon) with a total agricultural area of 50 hectares, 10 hectares of which was under viticulture. The monastery and associated farmland previously relied on a diesel powered generator (35 kVA) and a diesel fuelled tractor (20 kW) for meeting electrical loads and motive power. This prototype battery powered electric vehicle or Renewable Energy Agricultural Multipurpose System (RAMseS) for Farmers has been developed under the European Union's FP6 programme to investigate the potential for the cleaner production of power, hence reducing the use of diesel fuels in agriculture. Data collected from the test site is presented. ...
TL;DR: In this article, two non-imaging CPC solar collectors with an identical cavity profile were fabricated in house, the only discernable difference between these was that one utilised a heat-pipe absorber whereas the other used a simple direct flow absorber.
Abstract: For northern maritime climates with a high diffuse component of solar radiation, non-imaging CPC solar collectors with concentration ratios of up to 2 can be used to concentrate direct as well as diffuse incident solar radiation without tracking. Due to the concentrated solar flux incident on the absorber these systems can produce temperatures in the excess of those produced by conventional solar water heaters thus reducing the auxiliary energy demand. Additionally a smaller absorber area is required reducing the cost of the solar collector making these systems more economically attractive. Two CPC solar collectors with an identical cavity profile were fabricated in house, the only discernable difference between these was that one utilised a heat-pipe absorber whereas the other used a simple direct flow absorber. These were both tested under steady state operating conditions at inlet temperatures of 20°C, 30°C 40°C and 50°C to simulate the conditions experienced by a typical domestic solar water heater. It was found that the direct flow CPC performed better at higher solar intensities and lower inlet temperatures as the heat-pipe CPC had a much higher absorber plate temperature. Thus for domestic applications simple direct flow CPC systems would be preferred due to their higher efficiency and lower cost.
TL;DR: In this article, the authors presented the characteristics of a novel heat pump system with a flash tank coupled with a scroll compressor and its improved system; the proposed apparatus has been named the heat pump systems with flash reservoir.
Abstract: SYNOPSIS A heat pump system with a flash tank is suitable to use as the thermodynamic cycle in the compact air-source heat pump for cold climate regions This paper presents the characteristics of a novel heat pump system with a flash tank coupled with a scroll compressor and its improved system; the proposed apparatus has been named the heat pump system with flash reservoir With the aid of an analytical model based on the first law of thermodynamics and experimental data, the performance of the two systems are predicted in detail The calculated results show that the two systems can improve the heating capacity efficiently when run under the conditions of low climate temperature, and the intermediate pressure evaluated between 8 bar and 10 bar is favourable for the two systems
TL;DR: In this paper, a hybrid renewable energy system, consisting of a 1.27 kWp solar photovoltaic generator, a 15 kWe biomass gasification system and a 7.28 kWh battery backup, has been designed for the electrification of a representative village, namely Chhouk Ksach in Cambodia, which is not currently connected to the electrical power grid and where car batteries are used for electrification.
Abstract: SYNOPSIS A hybrid renewable energy system, consisting of a 1.27 kWp solar photovoltaic generator, a 15 kWe biomass gasification system and a 7.28 kWh battery backup, has been designed for the electrification of a representative village, namely Chhouk Ksach in Cambodia, which is not currently connected to the electrical power grid and where car batteries are used for electrification. The hybrid system is designed to ensure that the load demand is supplied for 24 hours a day throughout the year. The photovoltaic generator allows the gasification system to shut down when the load demand is small during daytime hours. The system has an electrical generation capacity of 34,376 kWh per year of which 4% is generated by the photovoltaic system and 96% by the biomass gasification system. The annual load demand is 24,518 kWh, of which 90% is taken directly from the biomass gasification system, 3% is taken directly from the photovoltaic system and 7% is taken from the backup battery. The annual net loss is estimated...
TL;DR: In this paper, the authors analyzed theoretically the heat transfer characteristics of fin-and-tube evaporators with R22 and R407C/R290/R600a (M20) refrigerant mixture using existing correlations from published literature.
Abstract: SYNOPSIS This paper analyses theoretically the heat transfer characteristics of fin-and-tube evaporators with R22 and R407C/R290/R600a (M20) refrigerant mixture. The heat transfer coefficient and the pressure drop of refrigerant for two-phase flow are calculated using existing correlations from published literature. The simulation algorithm is based on the ϵ-NTU section-by-section method. The tube is divided into an equal number of finite segments and the analysis is performed sequentially along the direction of the refrigerant flow. For each segment the temperature difference between refrigerant and air, outlet temperature of refrigerant and air and heat transfer rate in the flow direction are calculated using a discrete pattern to simulate the continuous variation found in actual fin-and-tube evaporators. The model results are compared with the experimental results of R22 and M20 refrigerant mixture reported in previous studies. The simulated temperature differences of the M20 refrigerant mixture are hi...