Simulation of the UQ Gatton natural draft dry cooling tower

Natural draft dry cooling tower (NDDCT) is an effective cooling technology which can be utilized in most of geothermal and concentrated solar thermal (CST) power plants. The experimental studies of the full scale cooling tower, especially the small size NDDCTs, are still not extensive. To fill this gap, Queensland Geothermal Energy Centre of Excellence (QGECE) at The University of Queensland has built a 20m high NDDCT. In this paper, the 1D analytical model and the 3D CFD model of this cooling tower were developed and its cooling performance was investigated at different ambient temperatures, hot water temperatures and velocities of cross wind. The result shows that the small size NDDCT is suitable for 2~3MW CST power plants. The cooling performance decreases with the increase in the ambient temperature and the decrease in the hot water temperature. In terms of the cross wind, the heat rejection ratio decreases with the increase of the cross wind velocity when cross wind velocity is low. However, when velocities of the cross wind become large enough, the heat dumped at the bottom of the tower can compensate some loss caused by cross wind. The results found in the present paper give reference for planed future experiments

Influence of ambient conditions and water flow on the performance of pre-cooled natural draft dry cooling towers

A simplified heat and mass transfer model in cellulose medium was developed to predict the air outlet temperature and humidity after evaporative cooling. The model was used to simulate the operation of pre-cooled Natural Draft Dry Cooling Towers (NDDCTs) by a validated MATLAB code. The effects of supplied water flow rate to the media, ambient temperature and humidity on the performance of pre-cooled NDDCTs were investigated. It was found that the effect of the selected water flow rates on tower performance is negligible. Both ambient temperature and humidity affect the tower performance

Modeling and characteristics analysis of hybrid cooling-tower-solar-chimney system

The hybrid cooling-tower-solar-chimney system (HCTSC), combining solar chimney with natural draft dry cooling tower, generates electricity and dissipates waste heat for the coupled geothermal power plant simultaneously. Based on a developed 3-D model, performance comparisons between the HCTSC system, solar chimney and natural draft dry cooling tower were performed in terms of power output of turbine and heat dissipation capacity. Results show that compared to the traditional solar chimney with similar geometric dimensions, HCTSC system can achieve over 20 times increase in the power output of turbine. However, this huge jump in power output is at the expense of heat dissipation capacity, which may lead to the malfunction of the coupled thermal power plant. By increasing the heat transfer area of the heat exchanger, the HCTSC system can manage to recover its heat dissipation capacity

A Review of the Flow-Induced Noise Study for Centrifugal Pumps

Flow-induced noise is a significant concern for the design and operation of centrifugal pumps. The negative impacts of flow-induced noise on operating stability, human health and the environment have been shown in many cases. This paper presents a comprehensive review of the flow-induced noise study for centrifugal pumps to synthesize the current study status. First, the generation mechanism and propagation route of flow-induced noise are discussed. Then, three kinds of study methodologies, including the theoretical study of hydrodynamic noise, numerical simulation and experimental measurement study, are summarized. Subsequently, the application of the three study methodologies to the analysis of the distribution characteristics of flow-induced noise is analyzed from aspects of the noise source identification and comparison, the frequency response analysis, the directivity characteristics of sound field and the noise changing characteristics under various operating conditions. After that, the analysis of the noise optimization design of centrifugal pumps is summarized. Finally, based on previous study results, this paper puts forward the unsolved problems and implications for future study. In conclusion, the information collected in this review paper could guide further study of the flow-induced noise of centrifugal pumps

A new method for preparing hydrophilic-activated carbon through ester hydrolysis in an alkaline environment

Hydrophilic-activated carbon was prepared by ester hydrolysis reactions, and was characterized by surface area analysis, Fourier transform infrared spectroscopy, scanning electron microscopy energy dispersive X-ray spectroscopy, and X-ray diffraction. Hydrophilic groups that were introduced on activated carbon surface through ethyl acetate hydrolysis in an alkaline environment were more efficient than those introduced with sodium acetate. During adsorption, the hydrophilic groups on modified activated carbon surface bound with water molecules through H-bonding and increased the adsorption capacity of water vapor. The adsorption isotherms of water vapor were well fitted by the Do model. Water molecules generated larger water clusters around the functional groups at 303 and 313 K. In addition, water desorption from the samples was analyzed by thermogravimetry. Water molecules that were hydrogen-bonded to functional groups exhibited higher thermal stability than those adsorbed in the micropore of activated carbon Besides, the process of sodium acetate formation on the surface of modified activated carbon was discussed

A review of wetted media with potential application in the pre-cooling of natural draft dry cooling towers

There is no dearth of published data concerning direct evaporative cooling, especially concerning the wetted media used in this technique. In spite of the data abundance, the lack of a comprehensive review of wetted media with potential use for inlet air pre-cooling of Natural Draft Dry Cooling Towers (NDDCTs) triggered the motivation of this paper. This paper reviews the wetted media with potentiality in the pre-cooling application of NDDCTs in terms of wetted medium types, mathematical models, performance studies and empirical relations. A method to compare wetted media in terms of the balance between cooling potential and pressure drop is proposed and validated. This method should be useful for comparative evaluation of wetted medium types or at least to differentiate between good and bad medium types. The medium cost, the service life, the type of process to be cooled, environmental conditions, water quality, space availability, locations and economic requirements are essential considerations, and some significant trade-offs have to be made during medium selection. A framework for medium selection is presented and the advantages and disadvantages of different medium types are summarized to provide a starting point for such selection. The empirical correlations appeared in the literature are synthesized to better correlate and compare the test data of wetted media and subsequently to provide prerequisite information for performance prediction. Controversies concerning wetted medium studies are discussed, and finally the gaps related to wetted medium studies are articulated

Pre-cooling with Munters media to improve the performance of Natural Draft Dry Cooling Towers

This paper presents a simulation study on pre-cooling of inlet air using Munters media to enhance the performance of a Natural Draft Dry Cooling Tower (NDDCT) on hot and dry days. The ambient humidity was kept constant at 30% while the ambient temperature ranged from 10° to 50 °C during simulation. Three Munters media (CELdek7060, CELdek7090 and CELdek5090), each with three thicknesses, were employed to pre-cool the tower inlet air. Results show that NDDCT can benefit from pre-cooling with wetted media when the ambient air is hot and dry. The trade-off between the air pressure drop across the media and the benefit of evaporative pre-cooling of the inlet air was also examined. It was found that there is a critical ambient temperature below which pre-cooling application does not benefit NDDCT performance. The value of this critical temperature is a function of the tower design and the selection of wetted media. Amongst the studied media, only the pre-cooling with 0.10 m and 0.15 m CELdek7060 is to be useful in the studied case. The dependence of heat rejection improvement of the proposed tower on medium thickness is weak. Besides, thicker medium does not necessarily bring more benefit

Experimental study on the effects of a tri-blade-like windbreak wall on small size natural draft dry cooling towers

Cooling efficiency of heat exchangers in conventional large natural draft dry cooling towers (NDDCTs) is often affected by crosswind. In the authors’ previous work, it was proved that the crosswind influence is more significant on short NDDCTs (height< 30 m) with horizontal heat exchangers than on large towers at a same wind speed, and a new triblade-like windbreak was proposed and analysed through CFD method only. The numerical models have not been validated by testing data yet. Therefore, an experiment on a 1:12.5 scaled NDDCT equipped with a novel round heat exchanger model was carried out and is presented in this paper. The study obtained the real measurements on the air temperatures and velocities as well as the heat rejection rates in the scaled cooling tower model with and without the windbreak wall. The influences of three wind attack angles (0°, 30°, and 60°) with respect to the windbreak wall were investigated. The angle was found sensitive to the overall heat transfer performance of the cooling tower. The study found that the cooling performance is improved most if the tri-blade-like windbreaks placed in the attack angle of 0°.The experiment results agreed with the predictions of the two 3D CFD models, the 15 mtall prototype and the 1.2 m-tall tower model, so that verified the validity of the previous CFD modelling