A New Two-Dimensional CFD Model to Predict the Performance of Natural Draught Wet-Cooling Towers Packed With Trickle or Splash Fills

2010 ◽  
Author(s):  
Hanno C. R. Reuter ◽  
Detlev G. Kro¨ger
Keyword(s):  
Cooling Tower ◽  
Air Flow ◽  
Linear Interpolation ◽  
Atmospheric Temperature ◽  
Performance Characteristics ◽  
Cooling Towers ◽  
Cfd Model ◽  
Flow Angle ◽  
Cfd Models ◽  
Air Inlet

In the design of a modern natural draught wet-cooling tower, structural and performance characteristics must be considered. Air flow distortions and resistances must be minimised to achieve optimal cooling which requires that the cooling towers must be modelled two-dimensionally and ultimately three-dimensionally to be optimized. It is found that CFD models in literature are limited to counterflow cooling towers packed with film fills which are porous in one direction only and generally have a high pressure drop, as well as purely crossflow cooling towers packed with splash fill, which simplifies the analysis considerably. Many counterflow cooling towers are however packed with trickle and splash fills which have anisotropic flow resistances, which means the fills are porous in all flow directions and thus air flow can be oblique through the fill, particularly near the cooling tower air inlet. This provides a challenge since available fill test facilities and subsequently fill performance characteristics are limited to purely counter- and crossflow configuration. This paper presents a CFD model to predict the performance of natural draught wet-cooling tower with any type of fill configuration, which can be used to investigate the effects of different atmospheric temperature distributions, air inlet and outlet geometries, air inlet heights, variations in radial water loading and fill depth, fill configurations, rain zone drop size distributions, and spray zone performance characteristics on cooling tower performance for optimization purposes. Furthermore the effects of damage or removal of fill in annular sections and boiler flue gas discharge in the centre of the tower can be investigated. The fill performance characteristics for oblique air flow are determined by linear interpolation between counter- and crossflow fill characteristics in terms of the air flow angle. The CFD results are validated by means of corresponding one-dimensional computational model data.

Computational Models for Predicting Cooling Tower Fill Performance in Cross-Counterflow Configuration

2010 ◽  
Author(s):  
Hanno C. R. Reuter ◽  
Detlev G. Kro¨ger
Keyword(s):  
Computational Models ◽  
Cooling Tower ◽  
Air Flow ◽  
Three Dimensional ◽  
Cooling Water ◽  
Transfer Characteristic ◽  
Linear Interpolation ◽  
Water Evaporation ◽  
Cooling Towers ◽  
Flow Angle

In cooling towers packed with trickle or splash fills, which have almost isotropic or anisotropic flow resistance, the air flow through the fill is oblique or in cross-counterflow to the water flow, particularly at the cooling tower inlet when the fill loss coefficient is small or when the fill hangs down into the air inlet region. This results that the fill Merkel number or transfer characteristic for cross-counter flow is between that of purely counter- and crossflow fills. When using CFD to model natural draught wet-cooling tower performance for isotropic fill resistance, two- or three-dimensional models are therefore required to determine fill performance. In this paper, the governing fundamental partial differential equations are derived in cylindrical and Cartesian co-ordinates to determine the cooling water temperature, water evaporation rate, air temperature and air humidity ratio in two-dimensional cross-counterflow fills for both saturated and supersaturated air. To solve these equations, a relation is proposed to determine Merkel numbers for oblique air flows by linear interpolation and extrapolation of purely cross- and counterflow Merkel numbers in terms of the air flow angle. This model is compared to analytical Merkel numbers obtained for different air flow angles using a single drop trajectory model. A linear upwind computational model and an Eulerian FLUENT® model are developed to evaluate fill performance characteristics from test data and to model fill performance in cooling towers respectively. The results of these two models are compared and verified with a FLUENT® Euler-Lagrange model.

Computational Models for Predicting Cooling Tower Fill Performance in Cross-Counterflow Configuration

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
H. C. R. Reuter ◽  
D. G. Kröger
Keyword(s):  
Computational Models ◽  
Cooling Tower ◽  
Air Flow ◽  
Three Dimensional ◽  
Cooling Water ◽  
Transfer Characteristic ◽  
Linear Interpolation ◽  
Water Evaporation ◽  
Cooling Towers ◽  
Flow Angle

In cooling towers packed with trickle or splash fills, which have anisotropic flow resistance, the air flow through the fill is oblique or in cross-counterflow to the water flow, particularly at the cooling tower inlet when the fill loss coefficient is small or when the fill hangs down into the air inlet region. This results in that the fill Merkel number or transfer characteristic for cross-counter flow is between that of purely counter- and crossflow fills. When using CFD to model natural draught wet-cooling tower performance for isotropic fill resistance, two- or three-dimensional models are therefore required to determine fill performance. In this paper, the governing fundamental partial differential equations are derived in cylindrical and Cartesian coordinates to determine the cooling water temperature, water evaporation rate, air temperature, and air humidity ratio in two-dimensional cross-counterflow fills for both saturated and supersaturated air. To solve these equations, a relation is proposed to determine Merkel numbers for oblique air flows by linear interpolation and extrapolation of purely cross- and counterflow Merkel numbers in terms of the air flow angle. This model is compared to analytical Merkel numbers obtained for different air flow angles using a single drop trajectory model. A linear upwind computational model and an Eulerian FLUENT® model are developed to evaluate fill performance characteristics from test data and to model fill performance in cooling towers, respectively. The results of these two models are compared and verified with a FLUENT Euler–Lagrange model, showing minor deviations.

Computational Fluid Dynamics Analysis of Cooling Tower Inlets

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
H. C. R. Reuter ◽  
D. G. Kröger
Keyword(s):  
Cooling Tower ◽  
Flow Patterns ◽  
Full Scale ◽  
Loss Coefficient ◽  
Cooling Towers ◽  
Cfd Model ◽  
Shell Wall ◽  
Natural Draft ◽  
Flow Losses ◽  
Loss Coefficients

Cooling tower inlet losses are the flow losses or viscous dissipation of mechanical energy affected directly by the cooling tower inlet design, which according to the counterflow natural draft wet-cooling tower performance analysis example given in Kröger (Kröger, 2004, Air-Cooled Heat Exchangers and Cooling Towers: Thermal-Flow Performance Evaluation, Pennwell Corp., Tulsa, OK), can be more than 20% of the total cooling tower flow losses. Flow separation at the lower edge of the shell results in a vena contracta with a distorted inlet velocity distribution that causes a reduction in effective fill or heat exchanger flow area. In this paper, a two-dimensional (axi-symmetric) computational fluid dynamic (CFD) model is developed using the commercial CFD code ANSYS FLUENT, to simulate the flow patterns, loss coefficients and effective flow diameter of circular natural draft cooling tower inlets under windless conditions. The CFD results are compared with axial velocity profile data, tower inlet loss coefficients and effective diameters determined experimentally by Terblanche (Terblanche, 1993, “Inlaatverliese by Koeltorings,” M. Sc. Eng. thesis, Stellenbosch University, Stellenbosch, South Africa) on a cylindrical scale sector model as well as applicable empirical relations found in Kröger, determined using the same experimental apparatus as Terblanche. The validated CFD model is used to investigate the effects of Reynolds number, shell-wall thickness, shell wall inclination angle, fill loss coefficient, fill type, inlet diameter to inlet height ratio and inlet geometry on the flow patterns, inlet loss coefficient and effective diameter of full-scale cooling towers. Ultimately, simple correlations are proposed for determining the cooling tower inlet loss coefficient and inlet effective flow diameter ratio of full-scale cooling towers excluding the effect of rain zones and the structural supports around the cooling tower entrance.

scholarly journals Numerical Simulation of the Performance Characteristics of the Hybrid Closed Circuit Cooling Tower

2008 ◽  
Vol 13 (1) ◽  
pp. 89-101 ◽  
Author(s):  
M. M. A. Sarker ◽  
E. Kim ◽  
G. C. Moon ◽  
J. I. Yoon
Keyword(s):  
Pressure Drop ◽  
Experimental Measurement ◽  
Cooling Tower ◽  
Cfd Simulation ◽  
Air Flow ◽  
Flow Distribution ◽  
Cooling Capacity ◽  
Performance Characteristics ◽  
Closed Circuit ◽  
Flow Rates

The performance characteristics of the Hybrid Closed Circuit Cooling Tower (HCCCT) have been investigated applying computational fluid dynamics (CFD). Widely reported CFD techniques are applied to simulate the air-water two phase flow inside the HCCCT. The pressure drop and the cooling capacity were investigated from several perspectives. Three different transverse pitches were tested and found that a pitch of 45 mm had lower pressure drop. The CFD simulation indicated that when air is supplied from the side wall of the HCCCT, the pressure drop can be over predicted and the cooling capacity can be under predicted mainly due to the non-uniform air flow distribution across the coil bank. The cooling capacity in wet mode have been calculated with respect to wet-bulb temperature (WBT) and cooling water to air mass flow rates for different spray water volume flow rates and the results were compared to the experimental measurement and found to conform well for the air supply from the bottom end. The differences of the cooling capacity and pressure drop in between the CFD simulation and experimental measurement in hybrid mode were less than 5 % and 7 % respectively for the uniform air flow distribution.

scholarly journals Energy resource efficient designs of small-sized devices for recycled water cooling

2020 ◽  
Vol 12 (6) ◽  
pp. 339-348
Author(s):  
K.E. Bondar ◽  
N.S. Shulaev ◽  
S.P. Ivanov ◽  
S.V. Laponov
Keyword(s):  
Mass Transfer ◽  
Power Law ◽  
Cooling Tower ◽  
Air Flow ◽  
Vertical Component ◽  
Energy Resource ◽  
Laboratory Research ◽  
Cooling Towers ◽  
Water Cooling ◽  
Recycled Water

Introduction. To use natural sources in rational way, plantsof continuous cooling of closed systems of recycling water supply are used. The paper presents designs of small-sized devices for recycling water cooling which are energy resource effective due to twisted motion of air flow, moving countercurrent to the cooled water. Heat and mass transfer is a nanotechnological process that occurs at the intermolecular level. Methods and materials. Countercurrent mini cooling towers are widely used in all industries,but there are some disadvantages, the main of which is the insufficient interaction time of the moving phases. Screw motion of air flow is created by the tangential supply of cooling air in the bottom part of cylindrical small-sized cooling tower. The rate of rotary motion decreases as air flow moves up in cooling towers, and vertical parameter of the rate – increases. Such scheme of the air flow motionmakes it possible to decrease average vertical parameter of the rate and to increase phases contact time. Laboratory research. To determine the technological and hydroaerothermal characteristics, as well as to estimate the efficiency of cooling recycled water, and to carry out mass-heat exchange at the intermolecular stagean experimental facility of small-sized cooling tower with twisted air flow has been developed. Conclusions. In accordance with the exponential law it is shown that the rotational component decreases at increasing height, and in accordance with the power law the vertical component increases component with the exponent ~1,79. It is determined that moisture content x and air temperature tv in the volume of the height of the sprinkler varies according to a power law, in particular for a screw cooling tower proportionally x ~ h0,83, t в ~ h1,25. It was determined that the coefficients of mass transfer βxv and heat transfer αv of a mini cooling tower with twisted air flow at the intermolecular level with equal irrigation densities are 20% higher than the coefficients of a mini cooling tower with counter-current flow. Also it has been determined experimentally a dependence of aerodynamics resistance coefficient of the twisted irrigator of the cooling tower on criterium Refor air flow, and it was determined that it decreases like Re–K2 as the exponent K2 varies in the range 0.114÷0.193 depending on the irrigation density

Cooling Tower Performance Evaluation: Merkel, Poppe, and e-NTU Methods of Analysis

2005 ◽  
Vol 127 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Johannes C. Kloppers ◽  
Detlev G. Kro¨ger
Keyword(s):  
Performance Evaluation ◽  
Analytical Approach ◽  
Cooling Tower ◽  
Performance Characteristics ◽  
Cooling Towers ◽  
Ambient Conditions ◽  
Natural Draft ◽  
Ambient Humidity ◽  
Fill Material ◽  
Methods Of Analysis

The heat rejected and water evaporated in mechanical and natural draft cooling towers are critically evaluated by employing the Merkel, Poppe, and e–number-of-transfer-units e-NTU methods of analysis, respectively, at different operating and ambient conditions. The importance of using a particular method of analysis when evaluating the performance characteristics of a certain fill material and subsequently employing the same analytical approach to predict cooling tower performance is stressed. The effect of ambient humidity and temperature on the performance of cooling towers employing the Merkel, e-NTU, and Poppe methods of analysis are evaluated.

Case study: Theoretical calculation model and variable condition analysis research on the water-splashing noise for natural draft wet cooling towers

2020 ◽  
Vol 68 (2) ◽  
pp. 137-145
Author(s):  
Yang Zhouo ◽  
Ming Gao ◽  
Suoying He ◽  
Yuetao Shi ◽  
Fengzhong Sun
Keyword(s):  
Theoretical Model ◽  
Sound Pressure Level ◽  
Water Droplet ◽  
Water Distribution ◽  
Sound Pressure ◽  
Cooling Tower ◽  
Distribution Patterns ◽  
Calculation Model ◽  
Pressure Level ◽  
Cooling Towers

Based on the basic theory of water droplets impact noise, the generation mechanism and calculation model of the water-splashing noise for natural draft wet cooling towers were established in this study, and then by means of the custom software, the water-splashing noise was studied under different water droplet diameters and water-spraying densities as well as partition water distribution patterns conditions. Comparedwith the water-splashing noise of the field test, the average difference of the theoretical and the measured value is 0.82 dB, which validates the accuracy of the established theoretical model. The results based on theoretical model showed that, when the water droplet diameters are smaller in cooling tower, the attenuation of total sound pressure level of the water-splashing noise is greater. From 0 m to 8 m away from the cooling tower, the sound pressure level of the watersplashing noise of 3 mm and 6 mm water droplets decreases by 8.20 dB and 4.36 dB, respectively. Additionally, when the water-spraying density becomes twice of the designed value, the sound pressure level of water-splashing noise all increases by 3.01 dB for the cooling towers of 300 MW, 600 MW and 1000 MW units. Finally, under the partition water distribution patterns, the change of the sound pressure level is small. For the R s/2 and Rs/3 partition radius (Rs is the radius of water-spraying area), when the water-spraying density ratio between the outer and inner zone increases from 1 to 3, the sound pressure level of water-splashing noise increases by 0.7 dB and 0.3 dB, respectively.

scholarly journals Geometrical Optimization of a Venturi-Type Microbubble Generator Using CFD Simulation and Experimental Measurements

Designs ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 4
Author(s):  
Dillon Alexander Wilson ◽  
Kul Pun ◽  
Poo Balan Ganesan ◽  
Faik Hamad
Keyword(s):  
Water Flow ◽  
Flow Rate ◽  
Cfd Simulation ◽  
Air Flow ◽  
Bubble Diameter ◽  
Diameter Ratio ◽  
Experimental Measurements ◽  
Cfd Model ◽  
Flow Rates ◽  
Throat Diameter

Microbubble generators are of considerable importance to a range of scientific fields from use in aquaculture and engineering to medical applications. This is due to the fact the amount of sea life in the water is proportional to the amount of oxygen in it. In this paper, experimental measurements and computational Fluid Dynamics (CFD) simulation are performed for three water flow rates and three with three different air flow rates. The experimental data presented in the paper are used to validate the CFD model. Then, the CFD model is used to study the effect of diverging angle and throat length/throat diameter ratio on the size of the microbubble produced by the Venturi-type microbubble generator. The experimental results showed that increasing water flow rate and reducing the air flow rate produces smaller microbubbles. The prediction from the CFD results indicated that throat length/throat diameter ratio and diffuser divergent angle have a small effect on bubble diameter distribution and average bubble diameter for the range of the throat water velocities used in this study.

scholarly journals Cooling tower plume abatement and plume modeling: a review

2021 ◽  
Author(s):  
Shuo Li ◽  
M. R. Flynn
Keyword(s):  
Public Health ◽  
Solar Energy ◽  
Cooling Tower ◽  
Plume Rise ◽  
Cooling Towers ◽  
Moist Air ◽  
Novel Technologies ◽  
Plume Modeling ◽  
Dry Cooling Tower ◽  
Dry Cooling

AbstractVisible plumes above wet cooling towers are of great concern due to the associated aesthetic and environmental impacts. The parallel path wet/dry cooling tower is one of the most commonly used approaches for plume abatement, however, the associated capital cost is usually high due to the addition of the dry coils. Recently, passive technologies, which make use of free solar energy or the latent heat of the hot, moist air rising through the cooling tower fill, have been proposed to minimize or abate the visible plume and/or conserve water. In this review, we contrast established versus novel technologies and give a perspective on the relative merits and demerits of each. Of course, no assessment of the severity of a visible plume can be made without first understanding its atmospheric trajectory. To this end, numerous attempts, being either theoretical or numerical or experimental, have been proposed to predict plume behavior in atmospheres that are either uniform versus density-stratified or still versus windy (whether highly-turbulent or not). Problems of particular interests are plume rise/deflection, condensation and drift deposition, the latter consideration being a concern of public health due to the possible transport and spread of Legionella bacteria.

Predicting cooling tower plume dispersion

1997 ◽  
Vol 211 (4) ◽  
pp. 291-297 ◽  
Author(s):  
B E A Fisher
Keyword(s):  
Cooling Tower ◽  
Industrial Process ◽  
Local Environment ◽  
Meteorological Conditions ◽  
Performance Criteria ◽  
Plume Dispersion ◽  
Cooling Towers ◽  
Atmospheric Conditions ◽  
Operating Characteristics

An assessment of the effects of visible cooling tower plumes on the local environment can be a necessary part of any proposal for a new large industrial process. Predictions of the dispersion of plumes from cooling towers are based on methods developed for chimney emissions. However, the kinds of criteria used to judge the acceptability of cooling tower plumes are different from those used for stack plumes. The frequency of long elevated plumes and the frequency of ground fogging are the two main issues. It is shown that events associated with significant plume visibility are dependent both on the operating characteristics of the tower and on the occurrence of certain meteorological conditions. The dependence on atmospheric conditions is shown to be fairly complex and simple performance criteria based on the exit conditions from the tower are not sufficient for assessments.

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