Papers by Keyword: Exergy

Abstract: The development of eco-materials has become an important direction of materials science. Using appropriate methods to evaluate the environmental impacts caused by materials production is important for eco-materials research. For the purpose of obtaining more objective results to environment impacts, several exergy-based methods to indicate resource depletion have been established. However, no proper exergy-based evaluation methods for emissions in China have been reported. The objective of this study is to establish comprehensive exergy-based characterization model for life cycle assessment, and to apply this model to steel production.

Abstract: In this paper, for the purpose of providing a scientific reference for saving energy and improving the efficiency of diesel engine, the impact of ethanol diesel-oil alternative fuel and waste heat recovery are investigated on the basis of thermodynamic analysis. The results illustrate that, after using ethanol diesel alternative fuel, engine performance parameters are of no big change, however, the exhaust emissions are significantly reduced; Recycling the energy contained in the exhaust gas and cooling water, can achieve the purpose of energy conservation and emissions reduction, beside improving the thermal efficiency and exergy efficiency of the diesel engine.

Abstract: Air conditioning system consumes approximately 50% of the total energy consumption of buildings. Split-type air conditioner is the most widely used in residential and commercial buildings. As a result, enhancement on the performance of the air conditioners will yield a significant energy savings. The use of ejector as an expansion device on the split-type air conditioners is one method to increase the system performance. Exergy analysis on a split-type air conditioner uses an ejector as an expansion device at room and outdoor temperatures of 24 °C and 34 °C, respectively, yielded the percentage of exergy reduction up to 40.6%. Also, the exergy losses on in the compressor had the highest impact on the performance improvement of the split-type air conditioner.

Abstract: Subjected to fixed total heat transfer surface area, the distribution of surface in multiple-effect evaporator affects the performance of the evaporator. Previous studies have been concerned with optimization of surface distribution with the assumption that no fouling occurs. The present study considers a more realistic case when the last-effect vessel is subjected to fouling. It is shown that, in order to consume the minimum steam exergy to produce a given amount of evaporation, the area of the last-effect vessel must be increased as the rate of fouling increases.

Abstract: Study on environment friendly mixed refrigerant to replace R134a in vapour compression refrigeration (VCR) System. The mixed refrigerants investigated are propane (R290), butane (R600), isobutene (R600a) and R134a. Even though the ozone depletion potentials of R134a relative to CFC-11 are very low; the global warming potentials are extremely high and also expensive. For this reason, the production and use of R134a will be terminated in the near future. Hydrocarbons are free from ozone depletion potential and have negligible global warming potential. The results showed that, mixed refrigerant with charge of 80 g satisfy the required freezer air temperature when R134a with a charge of 110 g is used as refrigerant. The actual COP of refrigerator using mixed refrigerant was almost nearer that of the system using R134a as refrigerant. The coefficient of performance of the vapour compression refrigeration system using mixed refrigerant MR-3 [R134a/R290/ R600a/ R600 (20/35/40/5)] is having very close value with R134a and the Global warming potential of MR-3 is negligible when compared with R134a. Hence the mixed refrigerant MR-3 is chosen as an environmental friendly alternate refrigerant to R134a. The exergy analysis of the vapour compression refrigeration system using R134a and all the above mixtures are investigated. The effect of evaporator temperature on exergy efficiency and exergy destruction ratio of the system are experimentally studied. The exergy defect in the compressor, condenser, expansion device and evaporator are also obtained. Key words: R134a, Mixed refrigerant, Chlorofluorocarbons, Propane, Butane, Isobutene, REFPROP, COP, ODP, GWP, Exergy, VCR System.

Abstract: A pipe segment system has been used to estimate its inherent resilience properties for the variation of mass flow rate, inlet temperature and inlet pressure. Superheated steam is taken as the process fluid. The magnitude of the resilience decreases from 927.8 kJ/m³s to 43 kJ/m³s and 31.5 kJ/m³s for variation of mass flow rate, inlet pressure and inlet temperature respectively. In this work, a novel methodology has been described for quantification of inherent system resilience and resilience magnitude has been found to be highest (927.8 kJ/m³s) in case of variation of mass flow rate through the pipe segment system. A useful correlation T = T_a(1-e^-nL)+T_se^-nL has been formulated for estimation of process fluid temperature, T at any pipe length, L.

Abstract: Energy and exergy analyses were carried out on an active 42MW open cycle gas turbine power plant. Data from the power plant record book were employed in the investigation. The First and Second Laws of Thermodynamics were applied to each component of the gas power plant at ambient air temperature range of 21 - 33⁰C. Results obtained from the analyses show that the energy and exergy efficiencies decrease with increase in ambient air temperature entering the compressor. It was also shown that 66.98% of fuel input and 54.53% of chemical exergy are both lost to the environment as heat from the combustion chamber in the energy and exergy analysis respectively. The energy analysis quantified the efficiency of the plant arising from energy losses , while exergy analysis revealed the magnitude of losses in various components of the plant. Therefore a complete thermodynamic evaluation of gas turbine power plants requires the use of both analytical methods.

Abstract: Turbine Air Powered Engine (TAPE) is a new type engine which has the character of zero emission, no pollution. Mathematical models of TAPE were established by the method of exergy analysis, the overall exergy and the exergy loss after reduced pressure with throttling were simulated in this paper. The results show that the maximum exergy loss of system is 60% during the process of reduced pressure with throttling, so the type of throttling decompression is not suitable for the system of TAPE which has bigger pressure reducing ratio. The results of bench test indicate that output power increases with the increase of inlet pressure within the scope of less pressure, and the regulation is similar to the simulating result. In the hybrid system of pneumatic internal-combustion engine, the measure which the air powered system is used in low-speed stage and the internal combustion engine powered system is adopted in high-speed stage can effectively solve the problem which the fuel consumption of the internal combustion engine is too bigger at low speed.

Abstract: A novel ammonia-water power cycle is proposed, which uses low-temperature heat sources such as oceanic-thermal, biomass as well as industrial waste heats. An ejector is introduced between the turbine and the absorber. The main emphasis is placed on the energy and exergy analysis to guide the thermodynamic improvement for the cycle; parametric analysis is conducted to investigate the effects of thermodynamic parameters on the cycle performances. The result shows that the thermal efficiency can reach to 5.31% and the exergitic efficiency varies between 13.3% and 24.4% under the given condition. In addition, the generator pressure, the deflation ratio variation and the turbine outlet depressurization made by ejector have significant effects on the performance of the power cycle.

Abstract: This paper approaches the microgrid concept from a systemic and cybernetics viewpoint, as a viable sustainable energy system (SES) for supplying electricity and heat to small, rural communities in Chile. As such the microgrid may be viewed as a complex adaptive system (CAS) when connected to the grid and operating without energy storage, only with the grid as back-up power source. From an exergy and homeostatic control (HC) standpoint, one may analyze the microgrid as a socio-technical CAS when it is coupled with a set of homes and also connected to the grid; capable of supplying close to 80% of the daily residential consumer needs on average. Thus, under these conditions homes may draw inexpensive renewable electricity and heat from the microgrid if they are thrifty and efficient in their energy consumption, and they may also consume from the utility grid, yet at an expensive price. Based on this an exergy and HC approach is proposed to develop such SES for rural and remote communities in Chile and South America, aiming to enhance energy efficiency (EE) and energy sustainability (ES). Under this scheme, renewable power (RP) being a scarce resource that must be managed efficientlyis supplied only to homes which comply with a specific criterion in an effort to curtail demand to ensure ES overtime. Simulation shows as expected that indeed certain criteria produce much better results than others in incentivizing thrifty, efficient energy consumption for small-size communities without the need for expensive and sometimes polluting and forbidden energy storage systems.