共查询到16条相似文献,搜索用时 187 毫秒
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用有限时间热力学理论和方法分析空气标准矩形循环,由数值计算给出了存在传热损失和工质变比热时循环功与压缩比、效率与压缩比以及功和效率的特性关系,并分析了传热损失和工质变比热对循环性能的影响特点,通过分析可知传热和变比热特性对矩形循环性能有较大影响。 相似文献
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考虑摩擦时Otto循环功率效率特性新析 总被引:3,自引:0,他引:3
对有摩擦时的 Otto循环进行了有限时间热力学分析。建立了一种新的模型 ,以循环的活塞平均速度和摩擦系数为基准求得了摩擦损失功率以及功率和压缩比、效率和压缩比的关系 ,进而得到了功率与效率关系 ,并进行了计算和讨论。结果表明 ,与实际热机循环的性能特性一致。 相似文献
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应用有限时间热力学理论,建立了包含多变过程的内可逆往复式Brayton循环模型,由数值计算得到了多变指数n取不同值时的循环输出功率与压缩比、效率与压缩比、输出功率与效率之间的特性关系,分析了多变指数对循环性能的影响。结果表明:随着n的增加,当n k (k为绝热指数)时,γ_(P(opt))(最大输出功率对应的最佳压缩比)和P_η(最大效率对应的循环输出功率)减小,γ_(η(opt))(最大效率对应的最佳压缩比)和η_P(最大输出功率对应的循环效率)增加;当n k时,γ_(P(opt))和γ_(η(opt))减小,η_P和P_η减小。选取适当的多变指数,调整压缩比在γ_(P(opt))≤γ≤γ_(η(opt))范围内可得循环最优性能区域。 相似文献
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Thermodynamic Analysis and Comparison of Performances of Air Standard Atkinson,Otto, and Diesel Cycles with Heat Transfer Considerations
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This paper focuses on the overall performances of Otto, Atkinson, and Diesel air standard cycles. This study compares performance of these cycles with regard to parameters such as variable specific heat ratio, heat transfer loss, frictional loss, and internal irreversibility based on finite‐time thermodynamics. The relationship between thermal efficiency and compression ratio, and between power output and compression ratio of these cycles are obtained by numerical examples. In this study, it is assumed that during the combustion process, the heat transfer occurs only through the cylinder wall. The heat transfer is affected by the average temperature of both the cylinder wall and the working fluid. The results show that for each cycle, with the increase of the compression ratio in the specific mean piston speed, power output and thermal efficiency first increase and after reaching their maximum value, start to decrease. The results also indicate that maximum power output and maximum thermal efficiency of an Atkinson cycle could be higher than the values of these parameters in Diesel cycle and Otto cycle in the same operating conditions. The maximum power output and the maximum thermal efficiency of the Otto cycle have the lowest value among studied cycles. By increasing the mean piston speed, power output and thermal efficiency of Atkinson, Diesel, and Otto cycles start to decrease. The results of this study provide guidance for the performance analysis and show the improvement areas of practical Otto, Atkinson, and Diesel engines. 相似文献
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《International Communications in Heat and Mass Transfer》2005,32(8):1045-1056
The performance of an air standard Miller cycle with heat transfer loss and friction-like term loss was analyzed by using finite-time thermodynamics. The relation between the power output and the compression ratio, between the thermal efficiency and the compression ratio as well as the optimal relation between the power output and the efficiency of the cycle are derived. Moreover, the influences of heat transfer loss and friction loss on the cycle performance are analyzed by detailed numerical examples. The results obtained herein include the performance characteristics of different cycles in given conditions, which have universal guidance. 相似文献
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Reciprocating heat-engine cycles 总被引:4,自引:0,他引:4
The performance of a generalized irreversible reciprocating heat-engine cycle model consisting of two heating branches, two cooling branches and two adiabatic branches with heat-transfer loss and friction-like term loss was analyzed using finite-time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the efficiency of the cycle are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of the cycle process on the performances of the cycles using numerical examples. The results obtained herein include the performance characteristics of irreversible reciprocating Diesel, Otto, Atkinson, Brayton, Dual and Miller cycles. 相似文献
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Shawki M. Eldighidy 《Solar Energy》1993,51(3)
The optimum solar collector outlet temperature for maximizing the work output for an Otto air-standard cycle with ideal regeneration is investigated. A mathematical model for the energy balance on the solar collector along with the useful work output and the thermal efficiency of the Otto air-standard cycle with ideal regeneration is developed. The optimum solar collector outlet temperature for maximum work output is determined. The effect of radiative and convective heat losses from the solar collector, on the optimum outlet temperature is presented. The results reveal that the highest solar collector outlet temperature and, therefore, greatest Otto cycle efficiency and work output can be attained with the lowest values of radiative and convective heat losses. Moreover, high cycle work output (as a fraction of absorbed solar energy) and high efficiency of an Otto heat engine with ideal regeneration, driven by a solar collector system, can be attained with low compression ratio. 相似文献