| Solar energy has the advantages of clean, huge amount and extensive distribution etc. and is the world’s most promising renewable energy sources, the development of solar energy utilization technology can effectively relieve the environmental pollution and the global warming. Currently the parabolic trough solar power technology has become the world’s most mature solar thermal power technology, among which parabolic trough direct steam generation (DSG) power generation technology has the advantages of simple system, no heat-transfer medium needed and high heat transfer efficiency and so on has drawn the attention from the international scholars. However, the parabolic trough DSG power generation system with water as the cycle working fluid can only achieve higher thermal efficiency in higher heat collecting temperature, the heat loss of the collector increases remarkably, and at the same time, the cost of power generation system will also rise. Organic Rankine Cycle (ORC) technology can efficiently make use of the medium and low temperature heat energy within 300℃, and it is very suitable for the solar energy which has low energy flux density. In order to improve the efficiency of solar-powered ORC, this paper proposed parabolic trough solar direct vapor generation ORC technology. Combining with analytical methods of heat transfer, thermodynamics and fluid mechanics, the performance and optimization models of recirculation parabolic trough solar direct vapor generation ORC system with regenerator were established by using MATLAB2014b. The main research contents are as follows:(1) Performance simulation models of tubular parabolic and non-evacuated parabolic trough solar collector were established, and models have been verified by experimental data of Sandia National Laboratories (SNL). Based on the performance simulations of tubular parabolic and non-evacuated parabolic trough solar collector, the variations of useful energy and heat loss with solar irradiance, ambient temperature, outer side temperature of metal absorber tube, wind speed and pressure in annular space were discussed.(2) The select and physical properties calculation methods of organic working fluid of parabolic trough solar direct vapor generation ORC system were studied. The calculation method for thermodynamic properties of the organic working fluid by using Patel-Teja (PT) equation of state was established. Since the iteration process was needed for implicit format of equation of state, computation time was long, and it was not suitable for realizing computer programming, a method of function approximation with polynomial explicit format was proposed to calculating thermodynamic properties of the working fluid based on the thermodynamic general relations of working fluid state parameters and Taylor expansion principle of multivariate function, the physical properties calculation deviations were less than 4% or even lower by using this method, it met the requirements of calculation, was facility for realizing computer programming and had high calculation speed.(3) A flow boiling heat transfer experimental apparatus was constructed, flow boiling heat transfer of organic working fluid R123 in metal tube was studied. The measured value of flow boiling heat transfer coefficient of R123 were compared with the calculated values by using Chen equation, Gungor-Winterton equation and Liu-Winterton equation respectively, the results indicated that Liu-Winterton equation has a good calculation accuracy, the maximum deviation of it is 23.48% and the average deviation is 7.02%, which can be used for designing and simulating parabolic trough solar direct vapor generation ORC system.(4) Combining with the analytical methods of heat transfer, thermodynamics and fluid mechanics, the performance simulation model of recirculation parabolic trough solar direct vapor generation ORC system with regenerator was established by considering the effect of regenerator on system performance. The performance simulation of recirculation parabolic trough solar direct vapor generation ORC system with regenerator was conducted based on geographical location and meteorological condition in literature, and the calculated results were in good agreement with the variation tendency of simulation results in literature. The net power output, thermal efficiency and specific net work of recirculation parabolic trough solar direct vapor generation ORC system with regenerator using different working fluids were compared, the results indicated that R123, R113, hexane and n-pentane system has good cycle performance and R123 is ideal cycle working fluid; the effects of main parameters including effective solar irradiance, evaporation temperature, circulation ratio, proportion of length of superheating section to total solar collector, number of collector arrays, etc. on performance of recirculation parabolic trough solar direct vapor generation ORC system with regenerator were also studied, the results indicated that the net power output of system increase with increasing effective solar irradiance and evaporation temperature, it increase firstly and then decrease with increasing circulation ratio, proportion of length of superheating section to total solar collector and number of collector arrays. Exergy analysis of recirculation parabolic trough solar direct vapor generation ORC system with regenerator was conducted based on the second law of thermodynamics, the results indicated that the vast majority of exergy destruction in system occur in solar collector, and exergy destruction rate is 74.56%; the next were the exergy destruction occur in condenser and turbine, the exergy destruction rate is 2.77% and 2.76% respectively; system exergy efficiency is 16.47%. In the operating temperature range of ORC system, the performances of recirculation parabolic trough solar direct vapor generation ORC system with regenerator using evacuated tubular solar collector and non-evacuated solar collector were compared, the net power output and thermal efficiency of system using non-evacuated solar collector decreased smally, therefore, the non-evacuated solar collector could be used for replacing evacuated tubular solar collector in parabolic trough solar direct vapor generation ORC system.(5) Multi-parameter parallel optimization method of recirculation parabolic trough solar direct vapor generation ORC system with regenerator was proposed. Based on mathematical programming theory and genetic algorithm, the net power output was chosen as the objective function, the optimization of proportion of length of superheating section to total solar collector, number of collector arrays, circulation ratio, evaporation temperature and working fluid temperature rise in regenerator were conducted, the results showed that the optimal net power output was increased signally.
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