Heat transfer in boundary layer stagnation-point flow towards a shrinking sheet with non-uniform heat flux

In this paper, the effect of non-uniform heat flux on heat transfer in boundary layer stagnation-point flow over a shrinking sheet is studied. The variable boundary heat fluxes are considered of two types： direct power-law variation with the distance along the sheet and inverse power-law variation with the distance. The governing partial differential equations （PDEs） are transformed into non linear self-similar ordinary differential equations （ODEs） by similarity transformations, and then those are solved using very efficient shooting method. The direct variation and inverse variation of heat flux along the sheet have completely different effects on the temperature distribution. Moreover, the heat transfer characteristics in the presence of non-uniform heat flux for several values of physical parameters are also found to be interesting.

Effect of particle loading on heat transfer enhancement in a gas-solid suspension cross flow

Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (M s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number was derived from experimental data. In addition, the k-ε two-equation model and the Fluctuation-Spectrum- Random-Trajectory Model (FSRT Model) are used to simulate the flow field and heat transfer of the gas-phase and the solid-phase, respectively. Through coupling of the two phases the model can predict the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement due to particles loading the model predictions agreed well with experimental data.

Boundary Layer Flow of an Unsteady Dusty Fluid and Heat Transfer Over a Stretching Sheet with Non-Uniform Heat Source/Sink

An analysis has been carried out to study the effect of hydrodynamic laminar boundary layer flow and heat transfer of a dusty fluid over an unsteady stretching surface in the presence of non-uniform heat source/sink. Heat transfer characteristics are examined for two different kinds of boundary conditions, namely 1) variable wall temperature and 2) variable heat flux. The governing partial differential equations are transformed to system of ordinary differential equations. These equations are solved numerically by applying RKF-45 method. The effects of various physical parameters such as magnetic parameter, dust interaction parameter, number density, Prandtl number, Eckert number, heat source/sink parameter and unsteadiness parameter on velocity and temperature profiles are studied.

Effect of viscous dissipation and heat source on flow and heat transfer of dusty fluid over unsteady stretching sheet

This paper investigates the problem of hydrodynamic boundary layer flow and heat transfer of a dusty fluid over an unsteady stretching surface. The study considers the effects of frictional heating （viscous dissipation） and internal heat generation or ab- sorption. The basic equations governing the flow and heat transfer are reduced to a set of non-linear ordinary differential equations by applying suitable similarity transformations. The transformed equations are numerically solved by the Runge-Kutta-Fehlberg-45 order method. An analysis is carried out for two different cases of heating processes, namely, variable wall temperature （VWT） and variable heat flux （VHF）. The effects of various physical parameters such as the magnetic parameter, the fluid-particle interaction pa- rameter, the unsteady parameter, the Prandtl number, the Eckert number, the number density of dust particles, and the heat source/sink parameter on velocity and temperature profiles are shown in several plots. The effects of the wall temperature gradient function and the wall temperature function are tabulated and discussed.

循环流化床锅炉快速变负荷调节技术研究进展

在“碳达峰”与“碳中和”背景下,煤电是我国目前可再生能源大规模消纳的最经济调节电源。循环流化床燃烧技术因具有低负荷稳燃能力强、污染物控制成本低、负荷调节范围宽等独特优势在煤电深度灵活调峰中担当重要角色,但其独特的燃烧方式导致变负荷速率慢,无法满足未来可再生能源大规模并网的调节需求。该文结合循环流化床锅炉的燃烧原理及应用场景,深入分析制约循环流化床锅炉变负荷速率的关键影响因素,包括循环灰的流动惯性、燃料的反应惯性、床料与耐火耐磨材料的传热惯性、污染物排放等。此外,对可行的循环流化床快速变负荷调节技术进行探讨与分析,可为我国燃煤循环流化床锅炉深度与快速灵活调节技术的工业应用提供一定参考。

基于热负荷均匀分配原则的直接空冷系统轴流风机转速灵活调节策略

在直接空冷电站中,轴流风机功耗占厂用电比例较高。为获得更为高效的风机运行调整策略,以某典型2´600 MW直接空冷机组为例,基于热负荷均匀分配原则,采用数值模拟方法,研究轴流风机转速灵活调节策略。获得不同环境温度和风速条件下,各轴流风机转速分布规律以及通过空冷凝汽器单元的冷却空气质量流量分布规律。最终,计算得到不同环境气象条件下不同轴流风机转速调节策略风机总功耗变化规律。结果表明,基于热负荷均匀分配原则的轴流风机转速灵活调整策略明显优于轴流风机转速整体调节策略,结果可为直接空冷机组优化运行和深层次节能提供参考。

日光温室主动蓄放热系统热过程模拟与参数优化研究

为进一步提高日光温室太阳能利用效率,降低加温成本,在当前日光温室主动式水循环蓄放热系统的基础上,构建了系统运行数学模型,利用该模型对系统参数(循环水流量与蓄热水箱体积)进行优化设计。研究结果表明:在兰州地区冬季日光温室生产条件下,当系统循环水流量为0.23 m^(3)·h^(-1),蓄热水箱体积为0.13 m^(3)时,系统性能最优,集、放热效率达到70.62%与98.38%,集/放热单元夜间平均热流密度达到237.84 W·m^(-2)。利用优化后参数,为兰州地区EPS装配式日光温室设计了一套太阳能主动蓄放热加温方案:集放/热单元(高2.05 m,宽1.105 m,厚3 cm)为50个,循环水泵流量为11.5 m^(3)·h^(-1),蓄热水箱体积为6.5 m^(3)。该方案可满足日光温室越冬生产,较优化前节约2个集/放热单元,8.5 m^(3)蓄水池体积,降低了加温成本。

电机冷却水热时间常数模型分析及影响因素研究

为保证半导体精密运动设备内精密温度控制模块的精度及稳定性,建立了负载电机冷却水热时间常数理论计算模型,用于计算电机工作时的最大热负荷梯度,为精密温度控制模块选型提供依据。理论模型表明冷却水热时间常数主要受电机结构、材料热物性和冷却水流量影响。仿真结果表明,电机冷却水温度随时间变化基本符合时间常数理论模型,冷却水时间常数与电机热功率无关,但随着电机冷却水流量的减小而增大,仿真值与理论模型计算差值为27%。实验结果与仿真结果基本一致,相同工况下仿真与实验得到的冷却水时间常数最大差值为7%。

煤电机组宽负荷脱硝改造路线的选择与应用

为解决深度调峰工况下,燃煤机组存在脱硝系统入口烟气温度偏低而无法满足脱硝系统催化剂安全运行温度的要求,对比分析了6种常见的宽负荷脱硝技术的优缺点,对应用结果进行核算分析,探讨其适用条件。结果表明:(1)烟气旁路改造方案,采用多烟道抽取高温烟气的方式,能够缩小旁路烟道挡板尺寸,可大幅降低烟气旁路漏量,同时改善烟气旁路调节的灵活性;(2)省煤器分级技术方案,对锅炉效率影响较小,但需注意满负荷烟气温度超限运行和低负荷一二次风温度降低影响低负荷稳燃的问题;(3)烟气旁路或省煤器流量置换改造方案,对于欠温幅度大于30℃的亚临界机组建议采用该方案,无启动循环泵的超(超)临界机组可以结合干湿态转换需求同步增加炉水循环泵来实现机组宽负荷脱硝,不建议开展基于省煤器出口热水循环至省煤器入口的流量置换(或复合热水再循环)改造;(4)直接调节尾部烟气挡板方案,对于尾部双烟道布置且省煤器单侧布置的机组,可通过直接调节尾部烟气挡板来实现20%以上负荷宽负荷脱硝。综合对比,除省煤器分级改造方案以外,其他通过提高脱硝系统入口烟气温度的方案均会增加机组能耗,脱硝入口烟温每提高1℃,导致锅炉效率约降低0.02%。所述改造方案可以为煤电机组开展相关工作提供参考。

凝汽器清洁系数对机组出力的影响规律研究

介绍了凝汽器总体传热系数和实际清洁系数的计算方法。以某核电机组为例,计算并研究了在不同冷却水温度、冷却水流量、凝汽器热负荷条件下凝汽器清洁系数对机组出力的影响。结果表明:在南方地区或带基本负荷的核电机组上,应尽量提高凝汽器清洁系数;在评估大修后的凝汽器性能时,应注意冷却水温度的变化及方向。

Analysis of one-dimensional consolidation of soft soils with non-Darcian flow caused by non-Newtonian liquid

Based on non-Darcian flow caused by non-Newtonian liquid, the theory of one-dimensional (1D) consolidation was modified to consider variation in the total vertical stress with depth and time. The finite difference method (FDM) was adopted to obtain numerical solutions for excess pore water pressure and average degree of consolidation. When non-Darcian flow is degenerated into Darcian flow, a comparison between numerical solutions and analytical solutions was made to verify reliability of finite difference solutions. Finally, taking into account the ramp time-dependent loading, consolidation behaviors with non-Darcian flow under various parameters were analyzed. Thus, a comprehensive analysis of 1D consolidation combined with non-Darcian flow caused by non-Newtonian liquid was conducted in this paper.

循环流化床锅炉负荷快速调节技术现状及发展趋势

在碳达峰、碳中和目标背景下,我国正加快构建新能源占比逐渐提高的新型电力系统,目前煤电正是消纳可再生能源大规模并网的最经济调节电源。循环流化床锅炉机组因自身天然优势在煤电深度灵活调峰中担任重要角色,但其独特的结构和运行方式导致变负荷速率偏低,消纳高比例新能源并网的能力亟待提高。分析了制约循环流化床锅炉变负荷速率的影响因素,包括气固两相流动的惯性、炉侧水侧传热的惯性、固体颗粒燃烧的惯性、水动力安全性、机炉动态匹配问题等,并解释了产生惯性的物理机制。归纳了提高循环流化床机组快速变负荷能力的关键技术,通过加快流动参数、提高传热系数、减小炉侧热容、增强炉侧水侧间的传热、强化燃烧反应、优化控制策略等方法,考虑工业尺寸锅炉的可行性,提出了一套综合优化技术方案,即“智能吞吐”系统的设想。在1台135 MW循环流化床锅炉上进行验证,结果表明,锅炉平均变负荷变化率可提升16%,最大负荷变化率短时间内可持续达到4%/min左右。在此基础上,对宽负荷灵活运行的循环流化床锅炉机组的设计思路进行展望,用数据驱动热力系统动态模型,融合创新技术的热力系统多时空匹配运行技术,构建“三自一体”的先进协同控制系统,并参考成熟的煤粉炉蓄能利用技术,为将来实际工业应用提供理论指导。

低温堆供热控制研究

核能作为清洁、高效的能源,可以取代燃煤用于冬季供暖,从而实现供暖过程中“减污降碳”的目标。针对热网提出的供热需求指标,本文基于MATLAB/Simulink仿真平台,建立了池式低温堆全厂主系统模型,并提出了可用于反应堆功率调节的供热控制方案。文中主要针对功率定值调节过程和热网事故小扰动工况反应堆响应过程作了详细分析。仿真研究结果显示,该控制方案能够根据热网对负荷的需求,调整反应堆功率,调节过程中反应堆各温度参数都在安全限值以内,并能够将用户室内温度维持在一个相对稳定的范围内。同时,该控制方案具有一定的抗事故工况负荷小扰动能力。在热网管网断裂等事故造成的负荷阶跃小扰动时,能够维持反应堆功率不变,使各回路温度在安全允许的范围内缓慢改变并重新达到稳定,且用户室内温度稍微变化后即可重新稳定。因此,该供热控制方案具有一定的设计参考价值。

计及用户行为差异性和配电网潮流的电采暖负荷群优化调度策略研究

电采暖负荷作为一种优质的需求响应资源,可通过集群优化调度改善配网运行。为了实现合理调度电采暖负荷,提出一种计及用户行为差异性和配电网潮流的电采暖负荷群优化调度策略。首先对电采暖负荷可控容量预测机理进行分析。其次根据用户需求响应行为影响因素,将用户整合为多个电采暖负荷聚合体,并对各群体进行了热舒适度设计及可控容量求解。然后考虑配电网潮流约束,建立以负荷波动最小为目标的电采暖负荷群优化调度模型。最后算例分析表明,该优化调度模型可以提高电采暖负荷响应预测的准确度,改善配电网的削峰填谷效果,有利于系统经济安全运行。

基于末端负荷监测的变压差控制方法研究

由于空调水系统大部分时间在部分负荷下运行,提出了一种能够满足最不利热力末端需求的外网变压差控制策略,可以通过实时监测负荷调控末端的流量与压差。以某区域供冷供热系统为例进行研究,调研得到各末端用户的控制温差,实验测试确定了热力稳定时间。搭建了案例的环状管网水力模型,对比了定压差控制策略与变压差控制策略。结果表明,变压差控制策略使得末端用户阀门开度保持在90%左右,相较于定压差供回水温差提升了1℃,水泵的输配能耗减少了24.8%,有效实现了节能减排。

超短期热负荷预测在发电机组厂级供热调度的应用

对于火力发电厂的综合能源应用,存在供热蒸汽调度控制和管道延迟导致的供热蒸汽不能及时满足供热用户需求的问题。根据所延时的时间长度提出采用对供热用户需求的预测值取代实时供热需求值作为供热调度的约束条件,基于Informer建立一个热负荷多步时序预测模型。构建的Informer模型采用的概率稀疏自注意力机制能够有效获取热负荷时序数据中的信息,并建立热负荷与相关气象因素之间的非线性关系,进而提高热负荷预测精确度。通过实际现场数据验证表明,建立的基于Informer的热负荷多步时序预测模型能够与未来一段时间内的热负荷有很强的拟合度,并满足实际调度控制延迟对热负荷的需求。

Comparison of space cooling/heating load under non-uniform indoor environment with convective heat gain/loss from envelope

The indoor parameters are generally non-uniform distributed.Consequently,it is important to study the space cooling/heating load oriented to local requirements.Though the influence of indoor set point,heat sources,and ambient temperature of convective thermal boundary on cooling/heating load has been investigated in the uniform environment in previous research,the influence of these factors,particularly the convective heat gain/loss through a building envelope,on cooling/heating load of non-uniform environment has not yet been investigated.Therefore,based on the explicit expression of indoor temperature under the convective boundary condition,the expression of space cooling/heating load with convective heat transfer from the building envelope is derived and compared through case studies.The results can be summarized as follows.(1)The convective heat transferred through the building envelope is significantly related to the airflow patterns:the heating load in the case with ceiling supply air,where the supply air has a smaller contribution to the local zone,is 24%higher than that in the case with bottom supply air.(2)The degree of influence from each thermal boundary to the local zone of space cooling cases is close to that of a uniform environment,while the influence of each factor,particularly that of supply air,is non-uniformly distributed in space heating.(3)It is possible to enhance the influence of supply air and heat source with a reasonable airflow pattern to reduce the space heating load.In general,the findings of this study can be used to guide the energy savings of rooms with non-uniform environments for space cooling/heating.

海底管道预热方案优化研究

海底管道预热是高含蜡原油在投产或再启动前的重要流动安全保障措施,预热方案优化对油田提高生产时效和节能降耗具有重要意义。利用OLGA软件构建了双层管中管保温海底管道预热模型,模拟研究了不同热水流量、不同加热负荷条件下管道沿线温度变化趋势以及“三耗”(耗时、耗水和耗能)变化规律,并考察了末端温度对关键参数的敏感性。结果表明:适度提高预热流量可显著节省预热时间和能耗,而不会显著增加水量消耗;适度降低加热负荷能进一步节省预热能耗,并不会显著延长预热时间;提高预热流量和降低加热负荷应以管道末端平衡温度高于预热目标温度为边界。

高超声速飞行器防热瓦结构的变厚度轻量化设计方法

针对非均匀气动加热条件下三维复杂防热瓦结构的轻量化需求,基于变厚度设计理念,发展了一种基于网格变形技术(ASD)和热固耦合分析相结合的防热瓦结构优化方法。优化结果表明,基于网格变形技术能够快速有效地解决优化过程中的网格自动更新问题,避免了网格重新划分的耗费及复杂结构网格重构的困难,并得到了光滑柔顺的厚度形状曲线;相比等厚设计,变厚度设计可以有效考虑载荷的非均匀效应,并极大地减轻结构重量;优化后可以更充分发挥防热瓦结构各层材料的承载能力。

非均匀气动加热下隔热层结构的优化设计

为获得非均匀气动加热条件下高超声速飞行器不同部位的合适的热防护系统厚度,发展了一种基于网格变形技术(ASD)的隔热层结构优化方法。以高超声速飞行器的复合材料隔热层结构为研究对象,采用有限元法在局部均布热流载荷、三角形均变热流载荷和二次函数热流载荷等作用条件下建立隔热层结构的热固耦合分析模型,提出了基于ASD技术与热固耦合分析相结合的结构轻量化设计方法。结果表明,基于网格变形技术能够快速有效地解决优化过程中的网格自动更新问题,并得到了光滑柔顺的厚度形状曲线,优化后更充分发挥了隔热层结构各层材料的承载能力。