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Heat and mass transfer of ammonia-water in falling film evaporator
Xianbiao BU, Weibin MA, Huashan LI
Front Energ. 2011, 5 (4): 358-366.
https://doi.org/10.1007/s11708-011-0161-y
To investigate the performance of heat and mass transfer of ammonia-water during the process of falling film evaporation in vertical tube evaporator, a mathematical model of evaporation process was presented, the solution of which that needed a coordinate transformation was based on stream function. The computational results from the mathematical model were validated with experimental data. Subsequently, a series of parameters, such as velocity, film thickness and concentration, etc., were obtained from the mathematical model. Calculated results show that the average velocity and the film thickness change dramatically at the entrance region when x<100 mm, while they vary slightly with the tube length in the fully developed region when x>100 mm. The average concentration of the solution reduces along the tube length because of evaporation, but the reducing tendency becomes slow. It can be concluded that there is an optimalβrelationship between the tube length and the electricity generated. The reason for the bigger concentration gradient in the y direction is that the smooth tube is chosen in the calculation. It is suggested that the roll-worked enhanced tube or other enhanced tube can reduce the concentration gradient in the film thickness direction and enhance the heat and mass transfer rate.
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Unified cycle model of a class of internal combustion engines and their optimum performance characteristics
Shiyan ZHENG
Front Energ. 2011, 5 (4): 367-375.
https://doi.org/10.1007/s11708-011-0170-x
The unified cycle model of a class of internal combustion engines is presented, in which the influence of the multi-irreversibilities mainly resulting from the adiabatic processes, finite-time processes and heat leak loss through the cylinder wall on the performance of the cycle are taken into account. Based on the thermodynamic analysis method, the mathematical expressions of the power output and efficiency of the cycle are calculated and some important characteristic curves are given. The influence of the various design parameters such as the high-low pressure ratio, the high-low temperature ratio, the compression and expansion isentropic efficiencies etc. on the performance of the cycle is analyzed. The optimum criteria of some important parameters such as the power output, efficiency and pressure ratio are derived. The results obtained from this unified cycle model are very general and useful, from which the optimal performance of the Atkinson, Otto, Diesel, Dual and Miller heat engines and some new heat engines can be directly derived.
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Availability of wind energy resource potential for power generation at Jos, Nigeria
O. O. Ajayi, R. O. Fagbenle, J. Katende, J. O. Okeniyi
Front Energ. 2011, 5 (4): 376-385.
https://doi.org/10.1007/s11708-011-0167-5
The objective of this study was to assess the potential viability of the wind resource potential in Jos, Plateau state, Nigeria for power generation. The monthly mean wind speeds that span from 1987 to 2007 were employed to statistically analyze the monthly, annual and seasonal potentials of the wind energy resources at the site. Besides, the results were employed together with two models of wind energy conversion system to simulate the likely average output power. The outcome showed that Jos was suitable as a site for wind farm projects of varying sizes and that MW·h to GW·h of electricity is likely to be produced per period of months, seasons and years. The average wind speed range at the site was also estimated to be between 6.7 and 11.8 m/s across the months, years and seasons.
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Impact of oxygen enriched combustion on the performance of a single cylinder diesel engine
K. RAJKUMAR, P. GOVINDARAJAN
Front Energ. 2011, 5 (4): 398-403.
https://doi.org/10.1007/s11708-011-0157-7
In the present experiment, a computerized single cylinder diesel engine with a data acquisition system was used to study the effects of oxygen enriched combustion technology (OECT) on the performance characteristics. The use of different levels of oxygen-enriched air was compared with respect to percentage load. Increasing the oxygen content in the air leads to faster burn rates and increases the combustibility at the same stoichiometry (oxygen-to-fuel ratio). These effects have the potential to increase the thermal efficiency and specific power output of a diesel engine. The power increases considerably with oxygen enrichment. In addition, oxygen enrichment can also be considered as a way to reduce the sudden loss in power output when the engine operates in a high load condition. Assessed high combustion temperature from the oxygen enriched combustion leads to high combustion efficiency. OECT reduces the volume of flue gases and reduces the effects of greenhouse effects. Engine tests were conducted in the above said engine for different loads and the following performance characteristics like brake power (BP), specific fuel consumption (SFC), mean effective pressure, brake thermal efficiency, mechanical efficiency, and exhaust gas temperature were studied. The objective of this paper is to address, in a systematic way, the key technical issues associated with applying OECT to single cylinder diesel engines.
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Influence of cetane number improver on performance and emissions of a common-rail diesel engine fueled with biodiesel-methanol blend
Wu YU, Gen CHEN, Zuohua HUANG
Front Energ. 2011, 5 (4): 412-418.
https://doi.org/10.1007/s11708-011-0163-9
In this paper, the effect of cetane number (CN) improver on performance and emissions, including particulate number concentration and size distribution, of a turbocharged, common-rail diesel engine fueled with biodiesel-methanol were studied. Two volume fractions (0.3% and 0.6%) of CN improver were added to BM30 (30% of methanol in the biodiesel-methanol blend) in the experiment. The results show that, compared with those of biodiesel-methanol blend, the peak value of cylinder pressure increases, the second peak of heat release rate decreases, the start of second heat release are advanced, and the fuel economy and thermal efficiency are improved when CN improver is added to biodiesel-methanol blend. Besides, CO and HC emissions decrease, NOx emission varies little and smoke emissions increase slightly. Moreover, exhaust particles of BM30 mainly distribute in nano-size range. Furthermore, particle number concentration decreases and peak of size distribution profile shifts toward large size direction.
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Review of aeroelasticity for wind turbine: Current status, research focus and future perspectives
Pinting ZHANG, Shuhong HUANG
Front Energ. 2011, 5 (4): 419-434.
https://doi.org/10.1007/s11708-011-0166-6
Aeroelasticity has become a critical issue for Multi-Megawatt wind turbine due to the longer and more flexible blade. In this paper, the development of aeroelasticity and aeroelastic codes for wind turbine is reviewed and the aeroelastic models for wind turbine blade are described, based on which, the current research focuses for large scale wind turbine are discussed, including instability problems for onshore and offshore wind turbines, effects of complex inflow, nonlinear effects of large blade deflection, smart structure technologies, and aerohydroelasticity. Finally, the future development of aeroelastic code for large scale wind turbine: aeroservoelasticity and smart rotor control; nonlinear aeroelasticity due to large blade deflection; full-scale 3D computational fluid dynamics (CFD) solution for dynamics; and aerohydroelasticity are presented.
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