冷凝器流程布置的数值模拟研究(2):计算结果与分析

运用分布参数模型对2~4排管冷凝器的流程布置方式进行了模拟计算,并对其换热和流动特性进行了分析和研究。研究结果表明,单回路冷凝器中,逆流布置换热效果最好,叉流其次,顺流最差;多排管冷凝器应尽可能采用分流方式,以减小压降,增强换热;布置冷凝器流程时,重力的影响不可忽略;当风量不变时,必然存在一最佳制冷剂流量使冷凝器性能达到最佳;当制冷剂流量保持不变时,也相应存在一个最佳风量使冷凝器性能最佳。     

冷凝器流程布置对高温热泵性能影响的实验研究

本文进行了以HFC125为工质的高温热泵热力性能的实验研究,分析了有、无回热循环工况下,冷凝器不同流程布置形式对系统COP的影响。实验结果表明:无回热循环情况下,冷凝器串并联混合布置形式具有较好的效果,系统COP实测均值达3.0,且和理论值接近度达80%以上。本文研究结果为高温热泵系统的性能优化提供了依据。     

蒸发式冷凝器热质传递模型的建立与分析

本文根据热力学和传热学理论,考虑因水蒸发或凝结而引起的喷淋水量和空气含湿量沿蒸发式冷凝器高度的变化,建立蒸发式冷凝器的热质传递数学模型,并对模型进行了合理简化,推导出描述这一热质传递过程常微分方程组的分析解。所得分析解给出了蒸发式冷凝器高度上空气含湿量、比焓、温度和水温等各参数的分布情况,并讨论了空气质量流量、喷淋水量等参数对蒸发式冷凝器换热性能的影响。蒸发式冷凝器数学模型的解析解可用于蒸发式冷凝器传热传质性能的理论分析及设计校核计算,具有较高的理论及应用价值。     

窗式空调器平行流冷凝器流程和扁管的优化分析

选择百叶窗肋片及小通道内流体传热流动的经验关联式,采用效能-传热单元数法建立了平行流冷凝器的稳态仿真模型.对不同流程数和扁管数方案的冷凝热和制冷剂压降进行了模拟分析,得出了扁管总数为39时的优化方案.     

基于Therm的门窗热工性能分析与数值模拟

结合现行国家标准和计算规程分析了建筑门窗的热工特性,采用有限单元法用国内外通用的Therm软件模拟了隔热断桥铝合金窗的传热系数.结合ISO标准和我国的计算规程,考虑了玻璃与型材接缝处线传热系数的影响,给出了线传热系数的详细计算公式和教值模拟方法,较好地解决了我国计算规程和ISO标准不协调的问题.结果表明,提出的计算方法其计算结果与试验值吻合较好,且能很好地满足我国规范要求,为建筑门窗的热工性能分析提供一种方法.     

廊载空调翅片管冷凝器空气侧传热数值模拟研究

机场环境对廊载空调换热器性能影响复杂,目前尚缺乏对其翅片管冷凝器空气侧流动传热特性影响的研究。本文采用计算流体力学(CFD)方法对廊载空调翅片管冷凝器空气侧流动传热特性进行数值模拟,综合考虑不同入口速度、不同翅片间距和不同管径对空气侧性能的影响,并结合换热器空气侧综合性能评价指标进行分析。结果表明,适当增大入口速度、减小翅片间距及增大热管直径可以有效提高换热性能,且换热器空气侧综合性能随着雷诺数的增大而提高。     

地下水流与水质联合数值模拟应用研究

随着社会的不断发展,工业、农业和人类生活中的废弃物很多,特别是城市工业废水的大量排放,农药化肥的广泛应用,致使许多地区的地下水受到不同程度的污染。基于水动力弥散的水质模型,采用多单元均衡法（MEB）,利用VC++语言编写地下水流与水质数值模拟联合通用程序,实现程序可视化。结合实际算例,利用该程序对地下水流与水质的输运机理进行数值模拟研究,发现该程序人机对话良好,可操控性高;为地下水资源的合理开发、保护和利用进行数值模拟提供了依据。     

地铁列车空调冷凝器热回流的数值模拟研究

以我国某地铁车站为研究对象,采用STESS软件和PHOENICS软件进行模拟计算,分别对开启/关闭车站排热系统时列车在停站期间的冷凝器热回流问题进行研究.通过研究发现:冷凝器的进风温度中间高两端低,说明中间位置的冷凝器排风热回流最严重,越向两端越弱;在关闭车站排热系统时,冷凝器进风平均热回流比例为64％,在开启车站排热...     

超薄玻璃生产线堆垛区的布置与流程设计

<正>0引言堆垛区的功能主要是对合格玻璃板进行取片、堆垛、加纸、包装、外运,以期达到玻璃入库的要求。堆垛又可以分为主线堆垛和支线堆垛两种方式,我们所设计的超薄玻璃生产线采用机械手自动取片、支线堆垛方式,堆垛区的布置和     

双柱面网壳并列布置风致干扰的数值模拟研究

对一典型三心圆柱面网壳进行了计算流体动力学(CFD)数值模拟,并与风洞试验进行比较,结果显示数值模拟能较准确反映实际情况,数值误差可以接受.在此基础上,将两个柱面网壳并列布置,在不同风向角及不同间距的情形下进行了详细数值模拟分析,发现此类风致干扰的主要影响因素在于遮挡效应,指出了当受扰体完全被施扰体的尾流所包裹时,遮挡效应最为严重。本文提出了柱面网壳并列布置相互干扰影响的风压分布规律和合理性建议,可指导实际工程应用。     

活性污泥数学模型ASM1在工程设计中的应用(中)

对于活性污泥数学模型(ASM1)在污水处理生物反应器设计上的应用方法进行了探讨，并列举设计实例对应用方法作了介绍，以指导试验研究、工程设计或运行管理。     

Numerical simulation of flow past a square cylinder using Partially-Averaged Navier-Stokes model

In this study, we carry out a two-stage partially averaged Navier-Stokes (PANS) simulation past a square cylinder to examine the effect of a grid system on the predicted results. The important focus in PANS is how the control parameter which is the ratio of unresolved-to-total turbulent kinetic energy is determined in the flow field. In this work, the parameter is evaluated by using an equation that we propose. The model equation utilizes the turbulent length scale, the Kolmogorov length scale and the cut-off grid length. We first perform RANS simulation to approximately evaluate the turbulent length scale and the Kolmogorov length scale. Then we construct five different grid systems based on these length scales and perform PANS simulation in which the length scales to determine control parameter are also updated as the simulation proceeds. Simulation results are compared with experimental data and the other LES and DES results. The comparison suggests that PANS approach is very effective in simulating separated turbulent flows in the sense that accurate predictions can be obtained by using a much coarser grid system than is required for LES. We then suggest the grid spacing requirements for a proper PANS simulation.     

Numerical simulation of fire-induced flow through a stairwell

Smoke movement and ambient airflow in a stairwell under fire scenarios are studied numerically using large eddy simulation. Numerical investigation is performed on a typical two-storey confined stairwell, with an open door on the top floor and a fire source on the ground floor. Results show the existence of fairly distinct layers of hot smoke and ambient air under different fire scenarios. It is found that heat release rate has a remarkable effect on distributions of smoke temperature, velocity and oxygen concentration. This paper indicates that detailed patterns of velocity, temperature and species concentration and their evolutions can be predicted by numerical simulation of a stairwell during a fire.     

Energy simulation and analysis of the heat recovery variable refrigerant flow system in winter

Heat recovery variable refrigerant flow (HR-VRF) system can supply cooling and heating for the building simultaneously and make good use of the indoor cooling and heating capacity efficiently. This system has a good energy performance and can meet the emerging requirements of modern buildings. In order to evaluate the energy features of the system, a new energy simulation module is developed and embedded in the dynamic energy simulation program, EnergyPlus. Using the program with the newly developed module, the dynamic energy simulation is performed for a simplified typical commercial building. The indoor thermal comfort of the building in winter and the setting temperature of the system are analyzed. Based on the simulation results, the energy characteristics of the system are investigated, and it is indicated that different methods of the temperature control and the percentage of the heat recovery have influence on the relative ratio of the energy saving. If the HR-VRF system adopts the same temperature control method as the heat pump VRF (HP-VRF) system, the HR-VRF system promises 15-17% energy-saving potential, when compared to the HP-VRF system.     

Numerical simulation of wind flow near a forest edge

This paper presents a computational fluid dynamics (CFD) model to simulate wind flow near a forest edge for the purpose of wind energy applications. The model uses a porous media analogy combined with a modified k–ε turbulence model to simulate momentum losses and turbulence generation within the forest. The momentum losses are represented by a drag coefficient and a leaf area density. Two directions were investigated: wind flow entering and wind flow leaving the forest. A fully developed solution with original boundary conditions was used as the inlet boundary condition in the two-dimensional CFD model for wind flow leaving the forest. Original boundary conditions were also proposed for the ground boundary within the forest. The model was solved using FLUENT 6.2 and validated against field measurements from three different authors. A sensitivity analysis was performed on two key parameters: drag coefficient and leaf area density. The results obtained using the proposed method show good agreement with the wind velocity and turbulence intensity measured experimentally.     

Numerical simulation of transient flow development in a naturally ventilated room

Numerical simulations were conducted to model the transient flow development in a naturally ventilated space containing a centrally located localized source of heat. The simulations were compared with a series of small-scale laboratory experiments and existing theoretical models. The aim of the work was to benchmark CFD models for time-dependent buoyancy-driven natural ventilation against previously published experimental results and theoretical models. The simulations agree well with experimental results during the initial development of the room stratification. The CFD results accurately predict the maximum depth of the hot buoyant layer at the top of the room as well as the steady-state interface height which separates the warm upper buoyant layer from the cooler air below. The simulations also predict well the time taken for the buoyant upper layer to reach its maximum depth. However, at longer times the results diverge. This may be due to thermal diffusion and mixing at the interface between the upper and lower layers due to the inflow from the floor level vents.     

室内火灾开口流动的FDS模拟

以Steckler开口流动实验数据作为参考,对比FDS模拟室内火灾开口流动的准确性及其影响因素.结果表明,在保证网格精度和正确的边界条件下,FDS对门洞开口质量流量的计算较为准确,而对窗户开口质量流量的预测误差较大;热释放速率的辐射分数和着火房间的压力升高都对模拟结果有一定的影响,对模型进行前期设置时应予以考虑.     

建筑能耗分析用逐时降雨模型(1):降雨判断

通过分析降雨日与非降雨日气象参数的差异,应用判断分析方法,由实测气象数据建立日降雨判断方程和逐时降雨判断方程,用得到的方程对模拟气象数据按月先进行日降雨判断再对降雨日进行降雨时刻判断,为降水量的分配确定了时间对象。