共查询到19条相似文献,搜索用时 296 毫秒
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在线性非平衡区域,对熵产率方程进行了相位拓展,建立了流动换热熵流变化与体系总熵产之间的关系。结果表明,熵产越小时熵流越大,则换热强度越大。当传热与传质均为自发过程,质量流与热流之间同相位时,两者的相位差越小,流动换热的强度越大,它反映了两个正熵产率过程间能量传递的场协同机制;当传热与传质分别为非自发及自发过程,质量流与热流之间反相位时,两者的相位差越大,流动换热的强度越大,它反映了正熵产率过程与负熵产率过程间能量转换的热力学耦合机制。质量流与热流之间由同相位到反相位,分别对应着场协同时的能量传递机制及热力学耦合时的能量转换机制,共同反映了体系流动换热时能量传递转换的最小熵产原理。 相似文献
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在线性非平衡区域,对熵产率方程进行了相位拓展,建立了流动换热熵流变化与体系总熵产之间的关系。结果表明,熵产越小时熵流越大,则换热强度越大。当传热与传质均为自发过程,质量流与热流之间同相位时,两者的相位差越小,流动换热的强度越大,它反映了两个正熵产率过程间能量传递的场协同机制;当传热与传质分别为非自发及自发过程,质量流与热流之间反相位时,两者的相位差越大,流动换热的强度越大,它反映了正熵产率过程与负熵产率过程间能量转换的热力学耦合机制。质量流与热流之间由同相位到反相位,分别对应着场协同时的能量传递机制及热力学耦合时的能量转换机制,共同反映了体系流动换热时能量传递转换的最小熵产原理。 相似文献
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非稳态流动过程能量平衡方程及其应用探讨 总被引:1,自引:1,他引:0
文章从理论推导与实际应用两方面探讨了热力学教材中存在的问题,认为国内外多种教材在非稳定流动过程能量平衡方程的推导中只考虑了物质流的非稳定性,疏忽了与物质流密不可分的状态参数、运动参数、位置参数的非稳定性. 相似文献
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文章从理论推导与实际应用两方面探讨了热力学教材中存在的问题,认为国内外多种教材在非稳定流动过程能量平衡方程的推导中只考虑了物质流的非稳定性,疏忽了与物质流密不可分的状态参数、运动参数、位置参数的非稳定性。 相似文献
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用SRK方程与PR方程求算双组分混合气体热力学性质 总被引:1,自引:0,他引:1
流体热力学性质的计算是化工热力学中的一类重要计算,立方型方程经常用于这类计算中。SRK方程与PR方程是在RK方程基础上发展而来的,具有比RK方程更好的计算精度。但现有教材中没有给出PR方程和SRK方程的剩余焓、剩余熵的计算公式,缺失了流体热力学性质计算的系统性。本文通过立方型状态方程的一般形式推导出PR方程和SRK方程的剩余焓、剩余熵的计算公式,利用Excel电子表格计算双组分混合气体的热力学性质。计算过程简捷明了,利于学生更好地理解混合物热力学性质的计算过程。 相似文献
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从热力学第二定律出发,将普适体系的熵产表达推广于降膜蒸发过程熵产分析并得到熵产计算式.引入单位熵产数并得到Reynolds数大于1450(cpμ/λ)-1.06(0.5-0.25ω)-1情况下和Reynolds数之间的定量关系,据此揭示了降膜蒸发过程熵产随降膜管内液膜厚度减小先降低再增大的规律,对应存在最小熵产数.与φ30×2×6000传热管内磷酸降膜蒸发实验数据对比结果吻合良好,表明本文熵产计算式可以根据过程的热力参数表达降膜蒸发过程的熵产规律,对过程强化和提高热力学效率具有实际指导意义. 相似文献
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管内流动传热传质的熵产分析 总被引:1,自引:0,他引:1
童钧耕 《高校化学工程学报》1991,5(1):33-37
本文基于不可逆过程热力学的基本概念,导出了管内流动热、质同时传递过程的熵产率的一般表达式,推导中考虑了由于存在传热温差、传质化学势差及流体粘性阻力造成的不可逆性。当质量传递趋于零时,由该式得到的仅考虑温差及流体粘性的不可逆性时管内流动传热过程熵产率计算式与文献[3]提供的一致。由该一般式导得了一定条件下光滑圆管内充分发展的系统与壁面进行热、质交换的熵产率计算式。通过求熵产率极小可帮助确定基于第二定律分析的优化运行条件。 相似文献
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In the present investigation, second‐law based thermodynamics analysis was applied to a new heat exchanger with helical baffles. The helical baffles are designed as quadrant ellipses and each baffle occupies one quadrant of the cross‐section of the shell side. Experimental tests were carried out with cold water in the tube side with a constant flow rate, and hot oil on the shell side with flow rate range from 4–24 m3/h. The temperatures and pressures for the inlet and outlet of both sides were measured. The heat transfer, pressure drop, entropy generation, and exergy loss of the new heat exchanger were investigated and compared with the results for a conventional shell‐and‐tube heat exchanger with segmental baffles. The computed results indicated that both the entropy generation number and exergy losses of the new heat exchanger design are lower than those of the heat exchanger with segmental baffles, which means that the novel heat exchanger has a higher efficiency than the heat exchanger with segmental baffles, from the second‐law based thermodynamics viewpoint. 相似文献
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应用雷诺应力模型对壁面绝热的旋风分离器的流场进行数值分析,对模拟结果采用熵产分析法和(火用)分析法计算分离器的(火用)损,证实了热力学第二定律研究旋风分离器能量损失的可行性。分别计算了旋风分离器内湍流熵产、黏性熵产、壁面熵产和温差传热熵产。结果表明,壁面熵产和湍流熵产占总熵产的比例分别大于56%和38%,是影响旋风分离器能耗的主要因素。分析了旋风分离器内局部熵产,结果表明,芯管附近体积占旋风分离器体积的10%,其熵产占分离器总熵产的比例高于14%,灰斗入口附近体积仅为旋风分离器体积的5.8%,其熵产占总熵产的比例高于16%,因此芯管附近和排尘口附近是旋风分离器能耗的主要区域。 相似文献
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本文介绍了一种在教学上利用热力学第二定律及理想气体的状态方程直接导出熵的简单方法,利用系统过程中环境压强与系统体积变化的乘积小于等于系统压强与系统体积变化的乘积的关系,直接导出Clausius不等式。该教学方法还可引导学生找出另外一个新的热力学状态函数。 相似文献
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《Chemical engineering science》2003,58(12):2515-2518
The paper presents an attempt to define the physical entropy of the dense phase of a fluidized bed, based on liquid-like properties of fluidized systems. The quantity U was used as the analogy of temperature in classical thermodynamics. The obtained expression for physical entropy was compared to the correlation suggested for the Kolmogorov entropy in bubbling bed. 相似文献
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The prime objective of the present communication is to examine the entropy-optimized second order velocity slip Darcy–Forchheimer hybrid nanofluid flow of viscous material between two rotating disks.Electrical conducting flow is considered and saturated through Darcy–Forchheimer relation. Both the disks are rotating with different angular frequencies and stretches with different rates. Here graphene oxide and titanium dioxide are considered for hybrid nanoparticles and water as a continuous phase liquid. Joule heating, heat generation/absorption and viscous dissipation effects are incorporated in the mathematical modeling of energy expression. Furthermore, binary chemical reaction with activation energy is considered. The total entropy rate is calculated in the presence of heat transfer irreversibility, fluid friction irreversibility,Joule heating irreversibility, porosity irreversibility and chemical reaction irreversibility through thermodynamics second law. The nonlinear governing equations are first converted into ordinary differential equations through implementation of appropriate similarity transformations and then numerical solutions are calculated through Built-in-Shooting method. Characteristics of sundry flow variables on the entropy generation rate, velocity, concentration, Bejan number, temperature are discussed graphically for both graphene oxide and titanium dioxide hybrid nanoparticles. The engineering interest like skin friction coefficient and Nusselt number are computed numerically and presented through tables. It is noticed from the obtained results that entropy generation rate and Bejan number have similar effects versus diffusion parameter. Also entropy generation rate is more against the higher Brinkman number. 相似文献
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Based on the Second Law of Thermodynamics, the entropy generation is studied for laminar forced convection flow of different nanoparticles(Al_2 O_3, CuO and SiO_2) mixed with water through a hexagon microchannel heat sink(HMCHS). The effects of different heat fluxes and Reynolds numbers on the entropy generation for different nanofluids, volume fractions and nanoparticles diameter are investigated. The heat flux is in the range of 125 to 500 kW·m~(-2) and the Reynolds numbers vary between 200 and 1500. The thermal, frictional and total entropy generations are calculated by integrating the volumetric rate components over the entire HMCHS. The results clearly show that the rise in the heat flux leads to an increase in the thermal entropy generation for nanofluids and pure water but they don't have any influence on the frictional entropy generation. Moreover, when the Reynolds number increases, the frictional entropy generation increases while the thermal entropy generation decreases. The results revealed that at low heat fluxes and high Reynolds numbers, pure water gives the lowest entropy generation, while at high heat flux the nanofluid has to be used in order to lower the overall irreversibility. 相似文献