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
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.
By performing gas flow field numerical simulations for several inlet Reynolds numbers
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.
The flow structure in tight lattice is still of great interest to nuclear industry. An accurate prediction of flow parameter in subchannels of tight lattice is likable. Unsteady Reynolds averaged Navier Stokes (URANS) is a promising approach to achieve this goal. The implementation of URANS approach will be validated by comparing computational results with the experimental data of Krauss. In this paper, the turbulent flow with different Reynolds number (5000–215000) and different pitch-to-diameter(
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, NO
The simulation model of a power generation system was developed based on EASY5 simulation platform. The performances of the power plant under the conditions of the furnace slagging and ash deposition of the heating surfaces in the boiler were simulated. The results show that the simulation model can reasonably reflect the characteristics of the power plant when each component is under fault conditions. Through fault simulation, the change of the performance parameters can be obtained, which can be used in fault diagnosis system as the diagnosis criterion for expert system.