包含7种热机模型的普适不可逆热机循环火用经济性能优化

用有限时间热力学方法分析了热漏、热阻和其他不可逆效应对工作在两恒温热源之间的普适定常流不可逆热机循环性能的影响,导出了由两个绝热过程、两个等热容加热过程以及两个等热容放热过程组成的循环的功率、效率和利润率的特性关系．并由数值计算分析了循环过程对循环性能的影响特点。所得结果包含了内可逆和不可逆Carnot、Diesel、Otto、Atkinson、Brayton、Dual、Miller循环的有限时 [火用]经济性能。     

一类广义不可逆普适热机循环的生态学性能

用有限时间热力学的方法分析了热漏、热阻和其它不可逆效应对一类定常流普适热机循环模型性能的影响,导出了由两个绝热过程、两个等热容加热过程以及两个等热容放热过程组成的循环的功率、效率和生态学性能,并由数值计算分析了循环过程对循环性能的影响特点。所得结果包含了存在热阻、热漏和内不可逆损失的Diesel、Otto、Brayton、Atkinson、Dual和Miller循环的特性。     

具有热阻、热漏和补燃的卡诺和朗肯联合热机循环性能分析

在原有的联合循环模型的基础上,建立了一个存在热阻、热漏和补燃的卡诺和朗肯联合循环热机模型。研究其在补燃作用下的功率、效率特性并对其进行优化,导出功率、效率的基本优化关系,分析补燃对最优性能的影响。     

具有热阻_热漏和内不可逆性的联合热机性能

建立一类存在热阻、热漏和内不可逆性的定常态流联合热机循环模型,并研究其性能优化,导出功率、效率优化关系,最大功率及其相应效率,和最大效率及其相应功率。     

热漏对热机功率效率特性的影响

本研究热漏对热机最优性能的影响,导出存在热阻和热漏损失的定常态流不可逆热机的最佳功率、效率关系,所得结果不同于仅存在热阻损失的内可逆热机的功率效率特性关系,且与实际热机特性较为一致,由此指出了一些献的“不可逆循环”模型的不完备之处。     

具有热阻、热漏、内不可逆性和补燃的联合卡诺型热机有限时间火用经济性分析

在原有的不可逆联合动力循环模型的基础上,建立了一个存在热阻、热漏、内不可逆性和补燃的不可逆定常流联合热机模型。研究其在傅立叶导热定律下循环的火用经济性,并对其进行优化,导出最佳纯利润功率、效率的解析式和基本优化关系,讨论了价格比和补燃系数对纯利润功率的影响。     

燃气-蒸汽联合循环的生态学优化

建立了具有热阻、热漏的定常流布雷顿一朗肯联合循环模型,分析了联合循环功率、效率和生态学指标性能,并对其进行了优化;通过数值计算分析了功率、效率和生态学之间的优化关系,并讨论了热漏对联合循环优化性能的影响.结果表明:最大生态学指标下的效率十分接近联合循环可达到的最大效率,布雷顿一朗肯循环是燃气一蒸汽联合循环的一个特例.分析研究结果为燃气一蒸汽联合循环热机的设计提供了一定的依据.     

导热规律服用q∞（△T）^n广义不可逆卡诺热机的最优性能

考虑工质与热源间热阻损失,用一常数项表示热漏损失和常系数项表示循环中除热阻和热漏外其余不可逆性，建立不可逆卡诺热机模型。基于另一类较为普遍的导热规律Q∞（△T）^n，导出热机的功率和效率最佳特性关系，由详细数值计算分析了热漏、内不可逆性和导热规律的影响特点。     

太阳能驱动的联合卡诺热机循环生态学性能研究

用有限时间热力学的理论分析一个由太阳能驱动的具有热阻、热漏、内不可逆性和补燃的定常流联合卡诺型热机循环;研究其在补燃作用下功率、效率和生态学指标的性能,利用不可逆因子表征循环的内不可逆性,并在傅立叶导热定律下对其进行优化;得到功率、效率和生态学指标之间的优化关系。结果表明:以最大生态学指标为目标对模型进行优化,可比以功率为优化目标时获得更高的效率和更小的熵产率。     

导热规律服用q∝(ΔT)n广义不可逆卡诺热机的最优性能

考虑工质与热源间热阻损失 ,用一常数项表示热漏损失和常系数项表示循环中除热阻和热漏外其余不可逆性 ,建立不可逆卡诺热机模型。基于另一类较为普遍的导热规律Q ∝ (ΔT) n,导出热机的功率和效率最佳特性关系 ,由详细数值计算分析了热漏、内不可逆性和导热规律的影响特点     

集中供热热电联产

“集中供热 ,热电联产”是我国节能技术政策的一项重要内容。在国家计委、国家经贸委、国家科技局颁布实行的《中国节能技术政策大纲》中明确指出 :“2 0 0 0年实现城市集中供热普及率 2 5 %～30 % ,重点城市达到 4 5 %～ 5 0 %”“大力发展热电联产、区域锅炉房供热 ,合理选择集中供热方式 ,取代分散、小型工业锅炉供热 ,提高热电比重”。目前我国大约有 4 0万台小型工业锅炉在运行 ,我省约有 6 0 0 0台。集中供热是取代分散小锅炉 ,并在现有热负荷的基础上 ,建设区域性的集中供热。集中供热以高效、大容量的集中锅炉房取代小容量、低效的…     

Mass and heat transfer enhancement of chemical heat pumps

An inert additive, expanded graphite (EG), has been prepared and used to enhance the heat and mass transfer process of chemical heat pumps. The effects of mixing ratio and mixing method on the chemical reaction time are investigated.     

Numerical studies on flow and heat transfer in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger

The flow and heat transfer characteristics of synthesis gas (syngas) in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger under different operating pressures, inlet velocities and pitches are investigated numerically. The three-dimensional governing equations for mass, momentum and heat transfer are solved using a control volume finite difference method. The realizable k-ε model is adopted to simulate the turbulent flow and heat transfer in heat exchangers. There flows syngas in the channels consisting of the membrane helical coils or membrane serpentine tubes, where the operating pressure varies from 0.5 to 3.0 MPa. The numerically obtained heat transfer coefficients for heat exchangers are in good agreement with experimental values. The results show that the syngas tangential flow in the channel consisting of membrane helical coils is significant to the heat transfer enhancement to lead to the higher average heat transfer coefficient of membrane helical-coil heat exchanger compared to membrane serpentine-tube heat exchanger. The syngas tangential velocity in the membrane helical-coil heat exchanger increases along the axial direction, and it is independent of the gas pressure, increasing with the axial velocity and axial pitch rise and decreasing with the radial pitch rise.     

Boiling heat transfer and critical heat flux in liquid films falling on vertically-mounted heat sources

Boiling heat transfer measurements were obtained for an inert fluorocarbon (FC-72) liquid film injected over a vertical heated wall. Flow visualization revealed that vigorous boiling prior to burnout ruptured the liquid continuum, causing most of the film to separate from the heated wall leaving a thin liquid subfilm which maintained contact with the wall. The critical heat flux (CHF) was accompanied by dryout of the subfilm after total separation of the liquid near the upstream edge of the heater. A higher CHF was achieved by increasing the film velocity or by utilizing a shorter heater. Experimental data correlated favorably with predictions of a CHF model based on the Helmholtz instability and subfilm dryout.     

石墨烯-PFA复合材料换热器与金属换热器的传热性能对比

氟塑料换热器以其耐腐蚀、耐磨损等优点而备受关注,但氟塑料热导率较低,换热能力差,限制了其广泛应用。石墨烯-PFA复合材料兼具石墨烯优异的导热性和可熔性聚四氟乙烯(PFA)良好的耐酸碱腐蚀性,是新一代的换热器材料。搭建了余热回收测试实验台,对石墨烯-PFA复合材料换热器和金属换热器的传热性能进行对比。研究了不同烟气流速、不同进口烟气温度以及不同石墨烯配比对复合材料传热性能的影响。结果表明:对于金属换热器和复合材料换热器,当烟气流速从2.0增加到4.0 m/s时,传热系数分别增加到原来的1.19和1.34倍;随着进口烟温的升高,两种材质的传热系数分别降低了15.6%和14.7%;随着石墨烯含量增加,复合材料的导热系数以及传热系数均增加。     

“制冷、制热、卫生热水”型空气源热泵系统及分析

提出一种小型中央空调用“制冷、制热、卫生热水”型空气源热泵系统设计方案,能够利用空调部分冷凝热提供生活用卫生热水,该系统可与家用中央热水系统连接。     

Temperature Distribution and Heat Saturating Time of Regenerative Heat Transfer

In this paper, heat transfer of the ceramic honeycomb regenerator was numerically simulated based on the computational fluid dynamics numerical analysis software CFX5. The longitudinal temperature distribution of regenerator and gas were obtained. The variation of temperature with time was discussed. In addition, the effects of some parameters such as switching time, gas temperature at the inlet of regenerator, height of regenerator and specific heat of the regenerative materials on heat saturating time were discussed. It provided primarily theoretic basis for further study of regenerative heat transfer mechanism.     

Comparison of heat storage systems employing sensible and latent heat

This study makes an evaluation of the performances of heat storage systems destined for power plants with a discontinuous power source such as nuclear fusion. Two classes of heat storage systems are investigated: heat storage systems based on first sensible heat storage and second latent heat storage. Both classes of heat storage systems are evaluated both from a thermodynamic point of view, inquiring whether the irreversibility of the system stays limited or not, and from an economic point of view, examining whether the system makes proper use of the heat storage capacity present. It is shown that an unambiguous conclusion that one is superior to the other is not possible and that the operating conditions and the configuration of the phase‐changing materials play an important role. Copyright © 1999 John Wiley & Sons, Ltd.     

Fluid flow and heat transfer characteristics of cross-cut heat sinks

In this study, effects of cross-cuts on the thermal performance of heat sinks under the parallel flow condition are experimentally studied. To find effects of the length, position, and number of cross-cuts, heat sinks with one or several cross-cuts ranging from 0.5 mm to 10 mm were fabricated. The pressure drop and the thermal resistance of the heat sinks are obtained in the range of 0.01 W<P_p < 1 W. Experimental results show that among the many cross-cut design parameters, the cross-cut length has the most significant influence on the thermal performance of heat sinks. The results also show that heat sinks with a cross-cut are superior to heat sinks containing several cross-cuts in the thermal performance. Based on experimental results, the friction factor and Nusselt number correlations for heat sinks with a cross-cut are suggested. Using the proposed correlations, thermal performances of cross-cut heat sinks are compared to those of optimized plate-fin and square pin-fin heat sinks under the constant pumping power condition. This comparison yields a contour map that suggests an optimum type of heat sink under the constraint of the fixed pumping power and fixed heat sink volume. The contour map shows that an optimized cross-cut heat sink outperforms optimized plate-fin and square pin-fin heat sinks when 0.04 < log L1 < 1.