Enhancing performance of wet cooling towers (original) (raw)
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The performance of natural draft dry cooling towers under crosswind: CFD study
International Journal of Energy Research, 2004
The thermal performance of a natural draft dry cooling tower (NDDCT) under a crosswind has been investigated using a general-purpose CFD code. A three-dimensional study using the standard k–ε turbulence model to simulate airflow in and around an NDDCT has been conducted. A parametric study has been carried out to examine the effect of crosswind velocity profile and air dry-bulb temperature on the thermal performance of an NDDCT. Two approaches have been considered in this study to quantify the crosswind effect. Firstly, simulations have been conducted at the nominal conditions and crosswind effect has been represented by thermal effectiveness parameter. Secondly, the ejected heat from the NDDCT has been maintained at a constant value (285 MW) and the crosswind effect has been represented by the change in the cooling tower approach parameter. After quantifying the effect of the crosswind on the thermal performance, windbreak walls have been introduced as a means of reducing this effect. The results in this paper show the importance of considering the crosswind velocity profile. Moreover, the introduction of windbreak walls has indicated an improvement in reducing the thermal performance losses due to the crosswind. Copyright © 2004 John Wiley & Sons, Ltd.
2017
This article aims to study the thermal performances of four different natural draft cooling towers under crosswind condition. The windbreakers and the oblique exit plane have been simultaneously included in the structure of the new cooling tower. A finite volume method using SIMPLE algorithm was used to simulate the flow field around each cooling tower. The thermal performance of the new geometry has been compared with those of others for the generally investigated wind velocity profile for 10 m/s, and also two uniform wind velocities for 3 and 7 m/s. The cooling capacity of the cooling tower utilizing windbreakers and the oblique exit plane was predicted as 98.3% of the design value in the presence of generally studied wind velocity profile of 10 m/s, while that of the cooling tower utilizing windbreakers was predicted as 93.5%. Of course, the percentage of the thermal improvements of the different restoring strategies are sensitive to the profile of an approaching wind. The uniform wind velocity decreases the thermal efficiency of the cooling tower more than the distributed one, while the restoring strategies using windbreakers provide a higher percentage of thermal improvements in the presence of uniform wind velocity.
Simultaneous effects of water spray and crosswind on performance of natural draft dry cooling tower
Thermal Science, 2013
To investigate the effect of water spray and crosswind on the effectiveness of the natural draft dry cooling tower (NDDCT), a three-dimensional model has been developed. Efficiency of NDDCT is improved by water spray system at the cooling tower entrance for high ambient temperature condition with and without crosswind. The natural and forced heat convection flow inside and around the NDDCT is simulated numerically by solving the full Navier-Stokes equations in both air and water droplet phases. Comparison of the numerical results with one-dimensional analytical model and the experimental data illustrates a well-predicted heat transfer rate in the cooling tower. Applying water spray system on the cooling tower radiators enhances the cooling tower efficiency at both no wind and windy conditions. For all values of water spraying rate, NDDCTs operate most effectively at the crosswind velocity of 3m/s and as the wind speed continues to rise to more than 3 m/s up to 12 m/s, the tower effi...
Experimental Study Of Wind Effects On The Airflow Of Natural Draft Wet Cooling Towers
2010
Natural draft cooling towers may enhance the overall performance of a thermal or a nuclear power station by providing coolant water to the condenser at a reduced temperature. The cooling tower thermal performance and its air flow inside the tower are influenced by the prevailing cross winds which in turn are amplified or damped by the flowconditioning characteristics of surrounding structures, building and terrains in the relative proximity and orientation to the tower. These characteristics were investigated in the No-1 cooling tower at the Mount Piper Power Station near Sydney in Australia. The tower was instrumented using thermocouples and directional anemometers to measure air velocities and temperatures both inside and outside of the tower over three months period. The test results have indicated that surrounding structures and their relative orientations to the tower and wind directions affect on the air flow rate inside a tower and should be considered at the design stage..
Iranian Journal of Science and Technology, Transactions of Mechanical Engineering, 2018
The performance of natural draft dry cooling towers (NDDCTs) depends on the environmental conditions. Crosswind is known to have the most destructive effect, whereas the ambient temperature is marked as the next. A 3-D numerical model was developed to investigate the thermal performance of a single as well as three aligned units of NDDCTs under crosswind conditions. The computed results showed major discrepancies between computed velocity patterns and pressure fields around three aligned towers and those of the single tower due to windshield effect of neighboring cooling towers. The thermal performance losses for the single tower under crosswind showed higher values compared with those of towers in the aligned arrangement. The best thermal performance of three aligned NDDCTs was achieved when the crosswind was directed along the towers' connection line.
International Journal of Thermal Sciences, 2008
The experiment in terms of heat transfer performance of natural draft counter-flow wet cooling is done for cases with crosswind conditions. The variation of circulating-water temperature difference (T) and cooling coefficient of efficiency (η) with crosswind velocity, circulating water inlet temperature and flow rate, are shown under crosswind conditions, compared with cases without wind. According to experimental results, it is found that T and η are influenced by the crosswind , and T and η can decrease mostly by 6% and 5%, respectively. When the critical Fr l number is less than 0.174, T and η decrease with increasing crosswind velocity, however, when it is greater than 0.174, T and η increase with increasing crosswind velocity. In addition, based on the data regression analysis, the correlation between T , η and parameters, such as circulating-water inlet temperature and flow rate, is derived for cases with windless conditions. Furthermore, its correspondence is given out for cases with crosswind conditions.
Applied Thermal Engineering, 2018
• A cover to improve the NDDCT performance under crosswind conditions is presented. • The impact of crosswind on vortex formation inside NDDCT is explained. • The working mechanism of the cover and its effects are presented. • 4.5 m cover improves the tower heat load by 85-230% under crosswind conditions. A B S T R A C T This study proposes a tower inlet cover to improve the performance of the small natural draft dry cooling tower (NDDCT) under crosswind conditions. CFD analyses are performed on a small NDDCT with tower inlet covers of different lengths, and the CFD model is validated against experimental results. The air temperature, air pressure, air flow and heat flux fields are presented, and the thermal performance for each heat exchanger and the NDDCT are obtained using CFD simulations. The CFD simulation results show that the high-pressure zone around the tower side wall, formed by the crosswind, causes the decrease in air flow through the tower and the deterioration in tower performance with a crosswind. The tower inlet cover can improve the tower performance in crosswinds by increasing the air flow of the heat exchangers. Tower inlet covers with lengths of 1.5 m, 3 m and 4.5 m improve the tower heat load by 40-65%, 70-130% and 85-230%, respectively, when the crosswind increases from 4 m/s to 12 m/s.
Evaluation of thermal performance for natural and forced draft wet cooling tower
Journal of Mechanical Engineering and Sciences, 2019
This paper presents an experimental and numerical investigation of the thermal performance of natural draft wet cooling tower (NDWCT). The experimental investigation is carried out under natural draft condition and forced draft condition created by an axial fan. The operational parameters considered in this study are the thickness of the fill (10 and 20 cm), inlet water temperature (40, 45, and 50 °C) and inlet water volume flow rate (5.68, 7.75, and 9.46 L/min). The experimental results showed that the thermal performance is improved when the fans are used with the NDWCT. The temperature difference between inlet and outlet and effectiveness increase by 35% and 37.2%, respectively at fill thickness of 20 cm and water volume flow rate of 11.35 L/min. The temperature distribution of the air and the relative humidity were numerically simulated for both cases of natural and forced draft by employing the commercial CFD software ANSYS Fluent 15. The experimental and numerical results were validated with results from a previous work and showed a good agreement. The experimental results showed that the effectiveness increase by 22% and 30% for NDWCT and FDWCT respectively when in case of fill thickness 20 cm.
Experimental study on the effects of wind break walls on top of the natural dry draft cooling towers
Nomenclature avelocity ratio; C ppressure coefficient; Frfroude number; ggravity acceleration, m/s 2 ; hheight from bottom of the tower, m; Hcooling tower height, m; P θperimeter pressure at pharynx of the model tower, Pa; P ∞pressure of the air flow on the tower, Pa; Re-Reynolds number; V iaverage velocity in the pharynx of the model tower, m/s; V Wwind velocity above tower, m/s Greek symbols ρair flow density above tower, kg/m 3 ; ρ ∞air flow density inside tower, kg/m 3 ; ∆ρdifference between air density and average air density inside tower, kg/m 3 ; θperimeter angle around tower, deg; υkinematic viscosity, m 2 /s
CFD simulation of wet cooling towers
Applied Thermal Engineering, 2006
Heat and mass transfer inside a natural draft wet cooling tower (NDWCT) have been investigated numerically under different operating and crosswind conditions. The three-dimensional CFD model has utilized the standard k-e turbulence model as the turbulence closure. The current simulation has adopted both the Eulerian approach for the air phase and the Lagrangian approach for the water phase. The film nature of the water flow in the fill zone has been approximated by droplets flow with a given velocity. The required heat and mass transfer have been achieved by controlling the droplet velocity. At that specific droplet velocity, effects of the following operating parameters on the thermal performance of the NDWCT have been investigated: droplet diameter, inlet water temperature, number of nozzles, water flow rate and number of tracks per nozzle. As a result, the effect of crosswind velocity on the thermal performance has been found to be significant. Crosswinds with velocity magnitude higher than 7.5 m/s have enhanced the thermal performance of the NDWCT. (M. Behnia). 1 Tel.: +61 2 9036 9518; fax: +61 2 9036 9519; Mobile: +61 414 369 518. www.elsevier.com/locate/apthermeng Applied Thermal Engineering 26 (2006) 382-395