Experimental Study on the Resistance and Splash Performances of Water Collecting Devices for Mechanical Draft Cooling Towers

In recent years,water collecting systems,with the associated advantages of energy saving and noise reduction,have become the foundation for the development of a scheme to optimize the structure of cooling towers.To explore the feasibility of this approach for mechanical draft cooling towers,a small-scale experimental device has been built to study the resistance and splash performances of three U-type water collecting devices(WCDs)for different water flow rates and wind speeds.The experimental results show that within the considered ranges of wind speed and water flow rate,the pressure drop of the different WCDs can vary significantly.The resistance and local splash performances can also be remarkably different.Some recommendations about the most suitable system are provided.Moreover,a regression analysis of the experimental data is conducted,and the resulting fitting formulas for resistance and splash performance of WCD are reported.

Spray Effect on the Thermal Performances of a Dry Cooling Tower

Pre-cooling the inlet air of a dry cooling tower by means of a spray can improve the tower performance during periods of high temperature.To study the spray effect on the thermal performance of natural draft dry cooling towers(NDDCTs),in this study 3-D numerical simulations of such a process have been conducted using Fluent 16.2(a two-way coupled Eulerian-Lagrangian approach).The considered NDDCT is 120 m high and only half system is simulated due to its structural symmetry.Three different spray strategies have been investigated at a typical crosswind speed of 4 m/s,which is the most frequent wind speed.The results have shown that:(1)The three implemented spray strategies can improve the thermal performance of the studied NDDCT with a vary-ing degree of success.In one case,the heat rejection rate can be increased by 35.2%,and the tower outlet water temperature can be decreased by 2.1℃ when compared with the no spray case;(2)To improve the thermal per-formance of the NDDCT using a small amount of water,the design of the spray pre-cooling system must include more nozzles on the windward and fewer or even no nozzles on the leeward sides of the NDDCT.

Wind-induced responses of super-large cooling towers

Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.

NUMERICAL INVESTIGATION OF THE ADVERSE EFFECT OF WIND ON THE HEAT TRANSFER PERFORMANCE OF TWO NATURAL DRAFT COOLING TOWERS IN TANDEM ARRANGEMENT

This article reports the findings on the adverse effect of the crosswind on the performance of natural draft cooling towers through numerical computation with the k-epsilon eddy-viscosity turbulence model. It is observed here that the cause of the adverse effect of the crosswind on the cooling towers call be attributed to the around flow effect which destroys the radial inflow into the cooling towers when the wind is absent. Hence, a significant deterioration in the heat transfer from the heat exchangers at lateral sides occurs.

Collapse Simulation and Response Assessment of a Large Cooling Tower Subjected to Strong Earthquake Ground Motions

Large cooling towers in thermal power plants and nuclear power plants are likely to suffer from strong earthquakes during service periods.The resulting destructions of the cooling towers would endanger the power plants and threaten the security of the related areas.It is important to use effective means to evaluate the safety status of the cooling towers and guide further precautions as well as retrofitting efforts.This paper is therefore focused on an elaborate numerical investigation to the earthquake-induced collapses of a large cooling tower structure.A complete numerical work for simulation of material failure,component fracture,structural buckling and system collapse is presented by integrating the stochastic damage constitutive model of concrete,refined structural element models,and some other key techniques.Numerical results indicate that the damage behavior and collapse mode of the cooling tower are affected notably by the randomness specification of ground motions.The collapse mechanisms of the cooling tower are studied from the energy absorption and dissipation points of view.An effective energy-based criterion is introduced to identify the collapse of the cooling tower under ground motion excitations.While distinct collapse modes are observed,the collapse criterion can predict well the damage and failure of the cooling tower.The proposed methodology is vital to better understanding the disastrous mechanisms and potential failure paths in optimal design of the cooling towers to ensure safety.

A reversibly used cooling tower with adaptive neuro-fuzzy inference system

An adaptive neuro-fuzzy inference system(ANFIS) for predicting the performance of a reversibly used cooling tower(RUCT) under cross flow conditions as part of a heat pump system for a heating mode in winter was demonstrated.Extensive field experimental work was carried out in order to gather enough data for training and prediction.The statistical methods,such as the correlation coefficient,absolute fraction of variance and root mean square error,were given to compare the predicted and actual values for model validation.The simulation results predicted with the ANFIS can be used to simulate the performance of a reversibly used cooling tower quite accurately.Therefore,the ANFIS approach can reliably be used for forecasting the performance of RUCT.

Case Study of Wind-Induced Vibration of a Cooling Tower Under Typhoon Environment

As high-rise cooling towers are constantly emerging,wind effects on this kind of wind-sensitive structures have attracted more and more attention,especially in typhoon prone areas.Terrain Type B turbulent flow fields under the normal wind and typhoon are simulated by active wind tunnel technology,and rigid-pressure-measurement model and aero-elastic-vibration-measurement model of a large cooling tower are built.The stagnation point,peak suction point,separation point and leeward point of the throat position shell are selected to analyze pressure coefficient,probability distribution,peak factor,power spectral density and dynamic amplification factor under normal wind and typhoon.It is clarified that there exists a significant non-Gaussian characteristic under typhoon condition,which also exists in structural response level.Resonance response ratio of the total response is higher during typhoon condition.The maximum value of dynamic amplification coefficient under typhoon field is up to 1.18 times over that under normal wind.The findings of this study are expected to be of interest and practical use to professional and researchers involved in the wind-resistant designs of super-large cooling towers in typhoon prone regions.

Wind?Induced Interference Effect Between Newly?Built Cooling Tower and Existing Cooling Tower

Disturbance effect is one of the important factors for wind damage to large cooling towers.Existing studies on the wind-induced interference of cooling tower groups are aimed at the same size and the lack of wind-induced interference effects between cooling towers of different sizes.With the background of the additional cooling tower project at Shandong Luxi Power Plant in China,the rigid body pressure wind tunnel test is carried out to obtain 194 conditions for the three combinations of the existing four-tower combination(small size),the new two-tower combination(large size)and the six-tower combination surface wind pressure distribution.Numerical simulation of the surrounding flow field of the cooling tower group with the most unfavorable interference condition of the six-tower combination is conducted using the computational fluid dynamics(CFD)method.Based on this,the characteristics of the average and pulsating wind pressure distribution of the cooling tower surface under the six-tower combination are mainly studied,and the load interference coefficients of the large-sized cooling tower and the small-sized cooling tower under the three tower group combinations are compared.The velocity flow field and vorticity changes around the cooling tower group at unfavorable wind angles are analyzed,and the wind-induced interference mechanism between cooling tower groups of different sizes is mainly refined.Research shows that the interference effect between such cooling tower groups of different sizes is much larger than that of cooling tower groups of the same size,which is specifically manifested as the enhancement effect of small-sized cooling towers and the shielding effect of large-sized cooling towers.The interference coefficient of large-sized cooling tower groups increases by 28%,and the interference coefficient of small-sized cooling tower groups decreases by 6.4%.The airflow acceleration caused by the pinch effect between small-sized cooling tower groups has an adverse effect on large-sized cooling towers and can significantly increase the magnitude of local wind load.The shielding effect of large-sized cooling towers can reduce the overall wind load of small-sized cooling towers.The research conclusions can provide the basis of wind load value design for wind resistance design of such large cooling tower addition projects.

Updating empirical results of wind loads on cooling towers for turbulence intensity effects

Variations of wind effects on large cooling towers observed at different turbulence intensities for our previous full-scale measurements might be caused by the inherent uncertainties in our physical experiments.Accordingly,the one-way analysis of variance(ANOVA)technique is employed for analyzing the data measured on the prototype Pengcheng cooling tower.Because ANOVA indicates that the variations of full-scale wind effects are basically the effects of turbulence intensity,the empirical results of wind loads on cooling towers obtained by generalizing physical experimental data without considering the turbulence intensity effects are updated using model test results obtained in multiple flow fields.The empirical fluctuating wind pressure distribution is updated based on the fact that the fluctuating wind pressure coefficient linearly increases with the increase in the turbulence intensity,and the empirical formulae of the spectra and the coherences is updated based on conservative assumptions.Comparisons of the empirical results and full-scale measurement data suggest that the original empirical results are either too conservative or unsafe for use.However,economic efficiency and conservativeness will be balanced if the updated empirical results are employed for the wind engineering design.

BUCKLING OF COOLING TOWER SHELLS WITH RING-STIFFENERS

With the stability analysis of hyperbolic cooling tower shells with ring-stiffeners. our paper proposes the linear pre-buckling consistent theory. The numerical result shows that this linear analysis method is very effective and practical in engineering, for its precision of compulation is up to the level of the nonlinear analysis when it is used for the study of critical loads of the hyperbolic cooling tower which is mainly governed by wind pressure and for the study of the effect of some oilier factors concerned in design on the buckling of shells. Based on that, we have obtained a scries of conclusions whicii will greatly benefits the engineering design when discussing the effect on the critical windloading of the shell which is caused by the following factors such as the position of rings, the number of rings and the dead weight.

Thermodynamic Analysis of Double Effect Absorption System along with Boiler and Cooling Tower

Many researchers have studied single and double effect absorption cycles based on first and second lows of thermodynamics But so far the relation of different parameters inside these cycles to the second law of thermodynamics in boiler and cooling tower has not been investigated. In this paper, a system comprised of a series flow double effect water-Lithium bromide absorption chiller, a boiler and a cooling tower is studied based on the first and second laws of thermodynamics, and also exergy analysis is investigated. For this purpose, mass and energy conservation laws governing the system are written, and coefficient of performance of the system, exergy destruction （loss） of each component and exergy efficiency have been calculated.

Bacterial Colonization and Occurrence of Legionella in Cooling Towers of Southern General Company for Fertilizer Production in Basrah City

Sixty six water samples were collected from inlets, inside and outlets of cooling towers （22 samples each, once a week）. Samples were screened for bacterial colonization with special focus on Legionella. Percentage occurrence of predominant bacteria present in water samples collected from inlets included： Klebsiella （95.45%）, Enterobacter （90.9%）, Pseudomonas （86.36%）, Escherichia coli （81.81%）, and Legionella （72.72%）. While those predominant in water inside cooling towers were： Pseudomonas （100%）, Staphylococci （81.81%）, Legionella （81.81%） and Bacillus （72.72%）. Incidence of Legionella recovered from inside and outlets of cooling towers sites was similar. Four species of Legionella were identified in water samples collected from inlets, inside and outlets of cooling towers, in the following consecutive frequencies L. pneumophila （72.72%, 81.81% and 81.81%）, L. jordans （18.18%, 36.36% and 27.27%）, L. dumffii （9.09%, 22.72% and 22.72%） and L. oekidegenes （4.54%, 13.63% and 18.18%）. The increased percentage occurrence of Legionella in water collected from inlets and inside cooling towers, as well as those of Pseudomonas and Staphylococci suggest that Legionella is also a hardy organism, being potentially survive as free organism despite water disinfection.

NONLINEAR BUCKLING ANALYSIS OF HYPERBOLIC COOLING TOWER SHELL WITH RING-STIFFENERS

This paper is concerned with a numerical solution of hyperbolic cooling tower shell, a class of full nonlinear problems in solid mechanics of considerable interest in engineering applications. In this analysis, the post-buckling analysis of cooling tower shell with discrete fixed support and under the action of wind loads and dead load is studied. The influences of ring-stiffener on instability load are also discussed. In addition, a new solution procedure for nonlinear problems which is the combination of load increment iteration with modified R-C are-length method is suggested. Finally, some conclusions having important significance for practice engineering are given.

A New Water Saving Device of Swirling Flow for Cooling Towers

This paper is concerned with water saving for water-loop cooling tower system in power plants. A newly developed water saving device of swirling flow is presented. The key point is that the new water saving device makes the steam swirl up along the device wall rather than engender laminar flow in a corrugated plate. The corrugated plate device can save approximately 10 percent of the total lost water. In contrast to the scale model of corrugated plate water saving device, experimental analyses have demonstrated that the new water saving device of swirling flow is more efficient, with a capacity of saving more than 20 percent of water.

THREE-DIMENSIONAL REGULARITIES OF DISTRIBUTION OF AIR-INLET CHARACTERISTIC VELOCITY IN NATURAL-DRAFT WET COOLING TOWER

A model for heat and mass transfer in a natural-draft wet cooling tower was established. Numerical simulation with the κ-ε turbulent model was conducted. Distribution rules of air inlet aerodynamic field were studied. Field experiments were done in a cooling tower in power plant, and the test data was compared with the related results. The definition of characteristic air velocity was proposed and its influencing factors, such as the cross-wind velocity and circumferential angle, were quantitatively studied. It can be used to evaluate the performance of cooling tower and to calculate the ventilation quantity and resistance of air inlet. It is also a theoretical basis for cooling tower design and performance optimization.

NUMERICAL SIMULATION OF FLOW FIELDS IN A NATURAL DRAFT WET-COOLING TOWER

The flow field in the hyperbolic natural draft wet-cooling tower, which has great effects on the economy and security of power plant, was studied through numerical simulation. The mathematical model was established and analyzed in order to optimize the cooling-tower and to evaluate its efficiency. Various working conditions were considered and compared with each other, such as the circulating water flux, air temperature and tower resistance. It is concluded that when the cooling-tower runs without wind, there is a vacuum region inside the tower and the pressure rises with the increase of the tower height. Meanwhile, the inner flow field is axisymmetrical. The air velocity achieves its climax at the axis. It is also found that the effect of circulating water temperature is equivalent to that of the water flux.

A decoupled method to identify affecting mechanism of crosswind on performance of a natural draft dry cooling tower

The natural draft dry cooling tower(NDDCT)has been increasingly used for cooling in power generation in arid area.As crosswind affects the performance of a NDDCT in a complicated way,and the basic affecting mechanism is unclear,attempts have been made to improve the performance of a NDDCT based on limited experiences.This paper introduces a decoupled method to study the complicated crosswind effects on the inlet and outlet of a NDDCT separately by computational fluid dynamics(CFD)modeling and hot state experiments.Accordingly,the basic affecting mechanism of crosswind on the NDDCT performance is identified.Crosswind changes the inlet flow field of a NDDCT and induces mainstream vortices inside the tower,so as to degrade the ventilation.Besides,low crosswind deflects the upward plume at the outlet to further degrade the ventilation,while high crosswind induces the low pressure area at the outlet to reduce the ventilation degradation.

Evaporative Cooling Applied in Thermal Power Plants:A Review of the State-ofthe-Art and Typical Case Studies

A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-cooled systems,gas turbine inlet cooling,wet cooling towers,and hybrid cooling towers with a crosswind effect.Some effort is provided to describe the advantages related to direct evaporative cooling when it is applied in thermal power plants and illustrate the research gaps,which have not been filled yet.In particular,typical case studies are intentionally used to compare the cooling performances when direct evaporative cooling is implemented in different types of cooling towers,including the natural draft wet cooling tower(NDWCT)and the pre-cooled natural draft dry cooling tower(NDDCT).It is shown that the NDWCT provides the best cooling performance in terms of power station cooling,followed by the pre-cooled NDDCT,and the NDDCT;moreover,the evaporative pre-cooling is able to enhance the cooling performance of NDDCT.Besides,on a yearly basis,better NDDCT cooling performances can be obtained by means of a spray-based pre-cooling approach with respect to wet media pre-cooling.Therefore,the use of nozzle spray is suggested for improvement in the performance of indirect/direct air-cooling systems with controlled water consumption.

A Novel Approach for Energy and Water Conservation by Using Silver-Carbon Quantum Dots Hybrid Nanofluids in Wet Cooling Towers Systems

This study presents the use of Silver-Carbon Quantum Dots(Ag-CQD)hybrid nanofluids,prepared by a facile wet chemical method,for heat transfer enhancement of wet cooling towers systems.The samples were characterized using different analyses,including FT-IR,XRD and TEM.After synthesizing the CQD,it was hybridized with silver nanoparticles and dispersed in water,using ultrasonic probe.The viscosity and density of the prepared nanofluid were investigated as a function of temperature and nanoparticles concentration,which demonstrated that there were no noticeable changes at lower particles concentration.Then,thermal conductivity and convective heat transfer coefficient were measured to evaluate the heat transfer enhancement of the nanofluid.At 45℃ and 0.5 wt%,the most significant thermal conductivity improvement compared to the base fluid was 24%;and 28%enhancement of the heat transfer coefficient was obtained at Reynolds number of 15529.The nanofluid performance was evaluated in a wet cooling tower for investigating the efficiency and water consumption rate.The results indicated that the efficiency of the cooling tower,by applying Ag-CQD nanofluid,enhanced from 23.72%to 28.23%;consequently,the amount of the consumed water decreased from 80.76 mL·min^(−1)to 69.67 mL·min^(−1).The results proved that the prepared nanofluid is a successful and promising candidate to enhance heat transfer.

A Novel Approach for Energy Efficiency Prediction of Various Natural Draft Wet Cooling Towers Using ANN

Cooling tower is crucial equipment in the cool-end system of power plant and the natural draft counter-flow wet cooling tower(NDWCT)gets wide application.The artificial neural network(ANN)technique is becoming an effective method for the thermal performance investigation of cooling towers.However,the neural network research on the energy efficiency performance of NDWCTs is not sufficient.In this paper,a novel approach was proposed to predict energy efficiency of various NDWCTs by using Back Propagation(BP)neural network:Firstly,based on 638 sets of field test data within 36 diverse NDWCTs in power plant,a three-layer BP neural network model with structure of 8-14-2 was developed.Then the cooling number and evaporation loss of water of different NDWCTs were predicted adopting the BP model.The results show that the established BP neural network has preferable prediction accuracy for the heat and mass transfer performance of NDWCT with various scales.The predicted cooling number and evaporative loss proportion of the testing cooling towers are in good agreement with experimental values with the mean relative error in the range of 2.11%–4.45%and 1.04%–4.52%,respectively.Furthermore,the energy efficiency of different NDWCTs can also be predicted by the proposed BP model with consideration of evaporation loss of water in cooling tower.At last,a novel method for energy efficiency prediction of various NDWCTs using the developed ANN model was proposed.The energy efficiency index(EEI)of different NDWCTs can be achieved readily without measuring the temperature as well as velocity of the outlet air.