Analysis of modified counter-flow cooling towers

Evaporative air cooling for human comfort and other applications, whenever possible and feasible, is less expensive than conventional air conditioning. A cooling tower is used in the centralised evaporative air cooling system. In the present study, the counter-flow cooling tower is modified to pre-cool the air at the tower inlet, either by the water after the cooling load, or the tower exit air. These two modified cooling towers are modelled and their thermal performances are compared with the conventional counter-flow cooling tower. For generality, the results are presented in terms of number of transfer units (NTU), a dimensionless number for a cooling tower indicating its size. The modified cooling towers are found to be better than the conventional one in lowering the tower approaches below about 2°C. These cooling towers seem to be distinctly advantageous when operating at low approaches, small ranges and large wet-bulb depressions, thus making them quite useful in evaporative air cooling applications.     

卷烟厂生产车间冬季供冷模式比较与应用

为给卷烟厂生产车间选择适宜的冬季供冷模式,文中对三种供冷模式即冷水机组供冷、加大空调新风比以及冷却塔供冷的特点进行了对比分析,并以杭州卷烟厂为例,通过对其生产车间冬季供冷需求和上述三种供冷模式的能耗状况进行定量模拟计算,发现冷却塔供冷是一种最为节能的冬季供冷模式。同时对杭州卷烟厂实际实施的冷却塔供冷系统的运行数据进行了监测,结果表明该系统在监测期内(2011年12月24日到2012年3月6日),与冷水机组供冷相比,总计节约电量约为69万度,节能率为61.9%,季节冷源系统能效系数达10.6。该文研究对于卷烟厂生产车间冬季供冷模式的选择具有一定的指导和参考意义。     

Wind field modifications due to an anemometer tower

Summary Variations in wind velocity and direction due to the mounting structure are studied using Gill anemometers mounted on 1.8 m long arms of a 232 m high tower. The tower ?shadowing? effect for the observed range, from 0 to 20 m/s, is in linear correlation with the velocity. The polar diagrams of the variations in wind speed and direction are presented as a function of the wind's direction. The horizontal component decreases by 15% when the anemometer is on the windward side of the tower, and by a maximum of 80% on the lee side. In the latter case the decrease is highly sensitive to wind direction. Variations in direction do not exceed 15 degrees. Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome.     

环保节水型冷却塔的研究

综合湿式冷却塔有热交换效率高且造价低而空气冷却器无水蒸发等特点,提出了环保节水型冷却塔.对该新型塔进行了理论分析,对塔内换热、气动力性能等进行了数值计算,对塔内空气换热器和填料层间的冷却负荷以及与风机性能等进行了耦合匹配,结合北方气候条件的计算分析表明新型塔确有良好的节水和环保效果.     

An empirical model for ionic wind generation by a needle-to-cylinder dc corona discharge

We present the results of an experimental study on ionic wind generation by a needle-to-cylinder dc corona discharge. A strong electrical field in the air generates air flow driven by the motion of ionized gas molecules along electric field lines. We measured the ionic wind velocity and discharge current with respect to various electrode geometries, distances between electrodes, and applied voltages. Our measurements suggest an empirical model for the ionic wind velocity as a function of the geometric factors of the collector electrode and the applied electric potential, which is useful for designing ionic wind cooling systems for small electronics.     

Quasilinear model of deformation of a stratified three-dimensionally inhomogeneous flow above a randomly inhomogeneous surface

We study the deformation of the wind velocity profile due to resonant interactions with waves radiated by the flow over a statistically homogeneous topography. The wind whose velocity vector changes its direction within a layer of finite thickness is considered. Quasilinear equations for the velocity components of the mean flow are derived under large Richardson, numbers and small Froude numbers. It is shown that the modulus of the wind velocity is constant in time and its direction angle satisfies the Riemann equation for simple waves. The flow deformation is determined by the average wave resistance force per unit square. The deformation of the wind velocity profile takes place within the layer between the Earth’s surface and the level where the wind change its direction to the opposite one. At large time scales, the wind velocity vector in this layer approaches the direction opposite to the near-surface one. Institute of Applied Physics, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 3, pp. 255–265, March 1999.     

开缝式风力机静态失速特性的研究

本文通过数值模拟的方法,研究了三种开缝方案对风力机静态失速特性的影响,模拟结果表明,开缝式风力机静态失速特性较为平坦,风力机开缝对静态失速进行控制的方法是可行的,由下风面到上风面开缝的方案在多冲角工况下有较好的静态失速特性.开缝结构的吸气口具有堵塞效应,排气口的排气会明显干涉来流的流动,因此开缝方向和开缝口处的形状对开缝效果的影响显著.     

涡轮叶片端壁槽缝气与离散气膜孔冷却特性实验研究

真实发动机涡轮叶片端壁为曲面造型,并且其冷却受槽缝气、泄漏流和离散气膜冷却多种冷却气叠加影响,同时又受到主流二次流影响,因此呈现复杂冷却特性。为研究接近真实发动机涡轮叶片端壁构型和工况下的气膜冷却特性,本文采用高速风洞(主流雷诺数为37万)及压敏漆(PSP)技术,研究了槽缝气、泄漏流以及离散气膜对曲面端壁的气膜冷却效率的影响,并针对不同冷气流量比对端壁气膜冷效的影响规律进行了对比分析。结果表明:端壁表面气膜冷效随着槽缝气流量比增大而增大,当流量比增大到1.71%时,槽缝气膜几乎可以覆盖整个端壁表面;与槽缝气相比,端壁表面的离散气膜冷气覆盖范围较为有限,端壁压力面侧下游区域气膜覆盖较差;在喉部之前,随着流量比增大,离散气膜冷效呈现下降趋势;在喉部之后,随着流量比从1.3%增大到1.9%,离散气膜冷效呈现上升趋势;与仅有离散气膜相比,包含槽缝气、泄漏流、离散气膜的全气膜覆盖更为均匀,全气膜冷效的叠加使得端壁冷效相比仅有离散气膜时整体提高了93.4%。     

高超临界雷诺数区间内二维圆柱绕流的实测研究

实测强风工况下高度167 m的徐州彭城电厂冷却塔的表面风荷载,并归纳历史上其他研究人员给出的实测结果,以丰富高超临界雷诺数(Re)区间二维圆柱绕流的试验成果.在低湍流度均匀流场和高湍流度大气边界层流场中分别开展4种风速8类粗糙度条件下的冷却塔刚性模型测压风洞试验,通过对比低雷诺数(Re=2.1×10~5—4.19×10~5)条件下的风洞试验结果和高雷诺数(Re=5.4×10~7—1×10~8)条件下的现场实测结果研究各种静动态绕流特征随雷诺数的变化规律,重点考察雷诺数无关现象的产生条件.研究结果表明,对于物表相对粗糙度在0.01以上的圆柱绕流,雷诺数不相关现象存在于很宽的雷诺数范围(2×10~5Re1×10~8)内;增大来流湍流度亦能引起的雷诺数无关现象,但此时该现象可能仅存在于一个较窄的低雷诺数范围内.     

风力发电机自循环蒸发内冷系统稳定性的研究

自循环蒸发内冷系统的冷却效率高,可以实现无泵自循环,运行安全可靠,基本免维护,因此适合在大型风力发电机中使用.蒸发内冷系统的稳定性对风力发电机的安全运行十分重要,本文基于非线性分岔理论及其数值延拓法,对自循环蒸发内冷系统应用于风力发电机的的静态稳定性进行了深入研究.获得了系统静态分岔解图,分析了系统演化特性,同时分析了系统分岔现象的参数效应.搭建了实验平台,通过实验观测到了自循环蒸发内冷系统的静态分岔现象,验证了理论计算的正确性.     

热源塔热泵系统夏季工况优化运行实验研究

由于热源塔在冬夏季工况下的换热能力存在较大差异,按冬季工况设计的热源塔热泵系统,在夏季工况下运行时存在换热能力过剩的问题,影响系统性能。为解决上述问题,本文构建了热源塔热泵系统,实验研究了其冬夏季工况的性能差异。在此基础上,对夏季工况下的优化运行进行了实验研究,结果表明,通过调节空气和溶液流量,将热源塔的逼近度和冷幅分别控制在3.5℃和4.3℃,可使得系统性能系数由3.6提升至3.9,并对其节能机理进行了分析。     

Structure of Liquid‐Sheet Sprays

Spray characteristics and their spatial distribution have been investigated experimentally for sprays generated by the breakup of thin liquid sheets in co‐flowing air streams. The spray characteristics such as droplet mean and fluctuation velocity and Sauter mean diameter have been measured by using phase Doppler anemometry under various liquid and air flow conditions at the nozzle exit. The results show that at a given spray cross section the droplet axial mean velocity has a maximum value at the spray center, and decreases towards the edge of the spray; whereas the Sauter mean diameter has a minimum value at the center and increases monotonically towards the spray periphery. Data analysis indicates that sufficiently downstream of the nozzle exit the droplet mean velocity attains a jet‐like self‐similar distribution in the transverse direction, and such universal distribution is also observed for the turbulent fluctuation velocity and turbulent intensity, although it is achieved further downstream compared to the mean velocity profile. The Sauter mean diameter at the spray center has a complex variation in the downstream direction due to secondary atomization at high air velocity near the nozzle exit and droplet entrainment, migration and possible coalescence farther downstream.     

Visualization of molten pools and invisible laser beam profiles using an ultraviolet CCD camera

Experiments were conducted on the effects of a wall distance and velocity ratio of suction flow to injection flow on the flow and heat transfer characteristics of a circular impinging jet accompanying an annular suction flow. As a result, it is found that in the case of accompanying suction flow, a higher Nusselt number can be obtained compared with in the case without suction flow, under a condition of the wall distance within eight times of injection pipe diameter from the near pipe exit edge. In addition, when the effect of velocity ratio is examined at a fixed arbitrary wall distance, it is found that there exists an optimum velocity ratio where the Nusselt number becomes the maximum. It is shown that these heat transfer characteristics are closely associated with the fluctuating velocity and the mean velocity in the two-dimensional velocity field observed by Particle Image Velocimetry (PIV).     

A numerical study of rotation effects on jets effusing from inclined holes into a cross-flow

In this work, the complexity of the flow field arising from the impact of the interaction of coolant jets with a hot cross-flow under rotation conditions was numerically simulated using large eddy simulation with artificial inflow boundary condition. The finite-volume method and the unsteady PISO (Pressure Implicit with Splitting of Operators) algorithm were applied on a non-uniform staggered grid. The simulations were performed for four different values of rotation number (Ro) of 0.0, 0.03021, 0.06042, and 0.12084, a jet Reynolds number of 4700, based on the hole width and the jet exit velocity. The air jet was injected at 30° and 90° in the streamwise direction with a density ratio of 1.04 and a velocity ratio of 0.5. The flow fields of the present study were compared with experimental data in order to validate the reliability of the LES technique. It was shown that the rotation has a strong impact on the jet trajectory behaviour and the film cooling effectiveness. The film trajectory always inclines centrifugally. Under rotating conditions, the film trajectory departs from the centreline to the left boundary. The deflection becomes greater as Ro increases. Furthermore, it was also found that the injection angle has a strong impact on separation and reattachment behaviour as well as the strength of the penetration into the cross-flow. As it increases, the distribution of the film cooling downstream the jet exit is more non-uniform and the film cooling effectiveness level slightly decreases.     

以地下土壤为冷源的空气取水实验研究

随着水资源的日益缺乏,如何获取更多的淡水资源越来越得到重视,尤其体现在一些严重干旱地区。为解决干旱地区淡水资源短缺的问题,研究并探索了一种利用沙漠中土壤与大气环境温差来实现空气取水装置。空气中含有大量的水蒸气可以利用,本文为此设计了一种新型空气取水系统,利用温度较为恒定的土壤作为冷源,整个系统使用极低的能耗,通过降温的方式达到空气取水的效果。搭建试验台进行了相关实验,发现系统的取水能力主要受空气温度的影响,通过模型实验与计算的方法确定了空气取水过程中送风速度与冷凝水量的关系式,得出最优风量为11.37 m/s,此时取水系统的取水效率最高。     

低速轴流压气机顶部微量喷气控制失速机理的数值模拟

对低速轴流压气机的转子顶部进行微量喷气已经证明可以有效的抑制旋转失速,但通过实验研究其机理比较困难。本文对该低速轴流压气机的转子顶部进行微量喷气的失速起始过程进行了数值模拟,通过非定常流场和失速起始过程同未加喷气的情况进行比较,分析了微量喷气控制失速起始的机理。计算得到的特性线和失速点流量同实验较好吻合。     

Study on generation mechanism of anomalous acoustic-gravity waves before the 2011 Beijing earthquake(M_L=3.0)

Observation results of abnormal acoustic-gravity waves before a Beijing earthquake(M_L=3.0) are presented.During this period,abnormalities of earth surface tilt variations were also recorded.The cross-correlations between the both values are high,which reach maximal values of 0.5 in the area close to the epicenter.The correlations decrease with increasing distances from the epicenter.It was proposed that generation of the anomalous waves may be associated with the pressure and wind perturbations in the air flow caused by slowly shaking mountains during slow surface motion preceding the earthquake in Beijing.Based on the wind velocity data taken from a 350 m meteorological tower in Beijing,the propagation of ducted acoustic-gravity waves in a two-layer model of the atmosphere was numerically simulated.It is shown that characteristic periods,amplitudes and velocities of the simulated phases which were assumed from non-stationary air flow relative to mountains are approximate to the observed phases.A consistency between the simulated results and observation data indicates that a slow surface motion may be a possible source of the anomalous acoustic-gravity waves observed prior to the earthquake.     

压气机抽气级静叶吸力面抽气方式的研究

本文提出了将压气机系统性抽气与改善流道内部边界层流动相结合的方法,以提高压气机抽气级的性能.以某多级轴流压气机为例,采用数值模拟的方式讨论了压气机静叶吸力面抽气的可行性.通过不同抽气流量下3个算例计算结果的比较分析,证明了通过静叶吸力面抽气改善叶片性能和流动状况是可行的.     

北京一次小震级地震前异常声-重力波产生机理的研究

观测到北京一次小震级地震(ML=3.0)前的异常声-重力波,并同时记录到异常地表倾斜信号。二者相关系数比较高,在接近震中的地区相关系数达到最大值0.5,相关系数随着远离震中的距离增大而减小。经过研究表明,异常声-重力波的产生与震前的地表缓慢活动引发的山体缓慢晃动导致的气流风速波动变化有关。基于350 m高的气象铁塔观测的风速数据,对两层大气模型传播的声-重力波进行了数值计算,得到的相对山体非平稳气流引起的声-重力波与观测信号在特征周期、幅度和速度三个参数上近似。以地表倾斜为例的模型与观测数据的一致性表明该震前声-重力波与地震存在关联性。      

Thermal optimization of high power LED arrays with a fin cooling system

In this paper, we describe an optimization process of thermal design for the light lamp which utilizes the Light Emitting Diode (LED) module as a lighting source. The thermal performance of the LED module was shown to significantly improve by the optimization process of cooling system attached with it. A wind circulating cooling system was designed for the LED arrays with the input power of 60?Watts and another heat pipe cooling system was designed for the input power of 144?Watts. The effects of design parameters such as air temperature and air velocity on the thermal performance of LED lamp were investigated. Thermal performance of the two cooling systems was compared for practical application.