Counter Flow Wet Cooling Tower Research Articles

Optimal design of forced-draft counter-flow evaporative-cooling towers through single and multi-objective optimizations using oppositional chaotic artificial hummingbird algorithm

In this study, single-objective (SOP) and multi-objective (MOP) design optimization problems have been solved for mechanical forced-draft counter-flow wet-cooling towers using an enhanced-search variant of a recently proposed swarm-intelligence based metaheuristic, artificial hummingbird algorithm (AHA). Incorporating the oppositional rule to ensure a faster convergence by avoiding unnecessary search of the space, and with chaos-embedded sequences to obtain more diversifying search-population towards more accuracy in the obtained solutions, the proposed oppositional chaotic artificial hummingbird algorithm (OCAHA) has been implemented for effective design optimizations of cooling towers. In SOP, six number cases of literature have been algorithmically experimented for minimizing the total annual cost TAC as the single-objective function with mass flow rate of cooling air and cross-sectional area of tower fill as the two decision variables and with fourteen number of design inequality constraints based on the process temperatures and enthalpies. Merkel’s method has been used for deriving the tower geometrical dimensions from empirical correlations of overall mass transfer-coefficient and loss-coefficient for the specified type of tower fill-packing. In MOP, range, tower characteristic ratio, effectiveness are the three objective functions, which have been maximized simultaneously with minimizing the water evaporation rate as the fourth objective for the problem. Mass flow rates of cooling air and circulating water are the two decision variables with the required input parameters of recent literature have been considered for multi-objective problem. The obtained designs through SOP and MOP have been analyzed with the competing designs, and a superior performance of OCAHA in both the optimizations have been validated.

HEAT TRANSFER AND PSYCHOMETRIC ANALYSIS OF A COUNTER-FLOW WET COOLING TOWER

Heat exchange takes place between two fluids (such as water and air or water and steam) in a cooling tower. A cooling tower (CT) is a critical element of the condenser unit. It plays a major role in enhancing the effectiveness and efficiency of the condenser. The CT has a variety of application and is widely used in petroleum refineries, chemical plants, steam power plants, nuclear power plants, processing plants, textile industries, etc. The impact of environment on the performance of CT plays a major role as it varies with temperature and humidity of the ambient condition. In the present work, a counter-flow wet cooling tower (CFWCT) operation under humid circumstances has been compared both experimentally and numerically. The performance analysis of the CT is carried out for such parameters as evaporation loss and energy loss from water to air. The temperature ratio (TR) and the effectiveness (ε) of CT are analyzed with the variation of the water flow rate (<i>m</i><sub>ω</sub>), air flow rate (<i>m</i><sub>a</sub>), water temperature (<i>T</i><sub>ω</sub>), and air temperature (<i>T</i><sub>a</sub>). The cooling tower temperature profile is determined by numerical analysis through ANSYS Fluent along the fluid flow path. The numerical analysis of CFWCT is validated with the experimental results. The present work will contribute to the literature of the design and performance analysis of cooling tower.

The Effect of Air Parameters on the Evaporation Loss in a Natural Draft Counter-Flow Wet Cooling Tower

The measures to reduce the impact of evaporation loss in a natural draft counter-flow wet cooling tower (NDWCT) have important implications for water conservation and emissions reduction. A mathematical model of evaporation loss in the NDWCT was established by using a modified Merkel method. The NDWCTs in the 300 MW and 600 MW power plant were taken as the research objects. Comparing experimental values with calculated values, the relative error was less than 3%. Then, the effect of air parameters on evaporation loss of NDWCT was analyzed. The results showed that, with the increase of dry bulb temperature, the evaporation heat dissipation and the evaporation loss decreased, while the rate of evaporation loss caused by unit temperature difference increased. The ambient temperature increased by 1 °C and the evaporation loss was reduced by nearly 26.65 t/h. When the relative air humidity increased, the evaporation heat dissipation and evaporation loss decreased, and the rate of evaporation loss caused by unit temperature difference decreased. When relative air humidity increased by 1%, the outlet water temperature rose by about 0.08 °C, and the evaporation loss decreased by about 5.63 t/h.

Performance Enhancement of Induced Draft Counter Flow Wet Cooling Tower with Different Types of Modified Shaped Fill Assembly

This paper presents an experimental analysis of heat transfer using different shaped fills in a counter flow induced draft cooling tower. The main objective is to determine and compare the characteristics of the cooling tower using newly shaped (splash and film) fills and the regular used fills. The newly shaped fills are inverted U-shape cross-sectional splash fill and film fill with ripple plates. The obtained results show that the performance is affected by the type and arrangement of the fills. The modified splash fill has increased the wetted surface area of fill within the same volume compared to regular fills. The film fill with ripple plates has been used such that water from the distribution device ran down on both surfaces of each ripple plate. By the arrangement of ripple plates, cooling loss by premature dropping off of water has been avoided. Performance factors like range, approach, effectiveness, cooling capacity, evaporation loss, percent loss are calculated from collected data for newly shaped fills, and regular shaped fills. It is observed that range, effectiveness, and cooling capacity increases with both newly shaped fills. When ripple plated film fill is used; range, effectiveness, and cooling capacity is found highest among the different shape of fills used in this study. At the same time evaporation loss and percent loss are found lowest for inverted-U shaped splash fill.

Effect of Thermal Load on Evaporation Loss of Natural Draft Counter-Flow Wet Cooling Towers

Abstract Based on the Merkel method, a mathematical model for calculating the evaporation loss of natural draft counterflow wet cooling towers (NDWCTs) was established. Taking the NDWCTs of the representative 300 MW and 600 MW power plants as the experimental objects, the calculated values obtained by the mathematical method were in good agreement with field experiment. Then, the effect of thermal load on evaporation loss of NDWCT was analyzed. The results showed that with the thermal load of NDWCT increasing, the evaporation loss increased, while the rate of evaporation loss caused by per unit change in temperature decreased. When the thermal load is the same, the evaporation loss was basically equal no matter by changing the mass flowrate or the inlet water temperature.

Hybrid Artificial Cooperative Search - Crow Search Algorithm for Optimization of a Counter Flow Wet Cooling Tower

In this paper, an improved version of Artificial Cooperative Search (ACS) algorithm is applied on a counter flow wet-cooling tower design problem. The Merkel’s method is used to determine the characteristic dimensions of cooling tower, along with empirical correlations for the loss and overall mass transfer coefficients in the packing region of the tower. Basic perturbation schemes of the Crow Search Algorithm, a recent developed metaheuristic algorithm inspired by the food searching behaviors intelligent crows, are incorporated into ACS to enhance the convergence speed and increase the solution diversity of the algorithm. In order to assess the solution performance of the proposed method, fourteen widely known optimization test function have been solved and corresponding convergence histories has been depicted. .Then the improved ACS algorithm (IACS) is applied on six different examples of counter flow wet-cooling tower optimization problem. The results obtained by applying the proposed algorithm are compared with the results of some other algorithms in the literature. Optimization results show that IACS is an effective algorithm with rapid convergence performance for the optimization of counter flow wet-cooling towers.

Parallel hybrid model for mechanical draft counter flow wet-cooling tower

A parallel hybrid model for mechanical draft counter flow wet-cooling tower is proposed in this paper. The model consists of mechanistic model based on Merkel’s theory and Least Squares Support Vector Machine (LSSVM) model which is used to remedy the decline of prediction accuracy brought about by the theoretical assumptions in the mechanistic model. Moreover, in consideration of the variation of outlet water temperature caused by the changes of operating conditions in the cooling tower, the Gaussian Mixture Model (GMM) is applied to assess the performance of the parallel hybrid model and the model is updated according to the assessment results. The simulation results show that the proposed parallel hybrid model has better prediction accuracy compared with the mechanistic model and the hybrid model without updating, which lays an important foundation for energy-saving optimization of the mechanical draft counter flow wet-cooling tower.

Performance analysis of a counter flow wet cooling tower and selection of optimum operative condition by MCDM-TOPSIS method

This work aimed at presenting a new technique for optimization of a counter flow wet cooling tower (CFWCT). First, the thermal performance characteristics and exergy analysis for a CFWCT were presented. The mathematical model consists of a set of three ODEs explaining the mass and energy conservation equations for air and water flows. In such case, the performance effect of CFWCT was clearly analyzed by changing water and air temperatures as well as the evaporation and convection heat transfer potentials through the height of the fill using the POPPE method. Next, the optimum operative conditions for a specific working CFWCT was determined by using the results of the elementary step, by considering some parameters controlled by user (inlet water temperature, inlet mass flow rate, air velocity, and cycle of concentration), and by using TOPSIS method. The results indicated the improvement in the CFWCT performance with a decision-making process.

Modeling and simulation of counterflow wet-cooling towers and the accurate calculation and correlation of mass transfer coefficients for thermal performance prediction

This work provides a detailed mathematical derivation of a steady-state one-dimensional continuous differential air-water contactor (CDAWC) model that describes the material and energy balances in a counterflow wet-cooling tower. The model consists of four ordinary differential equations that describe the changes (along the packed height) of the liquid water temperature, dry-bulb temperature of moist air, liquid water mass flowrate, and moist-air humidity mass ratio. The model is formulated for the cases of unsaturated and supersaturated air, and the model equations are compared to those of previous works. It is shown that the equations of some previous models are approximately equivalent to the equations of the CDAWC model. However, the formulation of the CDAWC model is simpler and the resulting equations have a more general form. A simulation method is proposed to determine accurate values of the volumetric mass transfer coefficient by matching the experimental thermal performance of counterflow wet-cooling towers.

Innovative correlation for calculating thermal performance of counterflow wet-cooling tower

This paper presents an innovative correlation associating the effectiveness (ε) of the cooling tower with its number of transfer unit (NTU) and vice versa. The new correlations can be used simply to predict the performance of wet counterflow cooling tower. Those correlations are based on solving heat and mass-transfer equation “enthalpy potential method” coupling with energy equations simultaneously. The validity of the correlations was checked by experimental data reported in the available literature. The results obtained from those new correlations showed a very good agreement with deviation less than 10% with those obtained from the literature for a temperature difference between the inlet water temperature and inlet air wet-bulb temperature (Twi−Wbti) equal to or less than 10 K. The main advantages of those correlations are: (1) its simplicity to be implemented through simple calculations of input parameters; (2) it provides helpful guidelines for optimization of cooling tower performance during its operation coupling with the thermal system at which the tower is connected.

Concept of CFD model of natural draft wet-cooling tower flow

The article deals with the development of CFD model of natural draft wet-cooling tower flow. The physical phenomena taking place within a natural draft wet cooling tower are described by the system of conservation law equations along with additional equations. The heat and mass transfer in the counterflow wet-cooling tower fill are described by model [1] which is based on the system of ordinary differential equations. Utilization of model [1] of the fill allows us to apply commonly measured fill characteristics as shown by [2].The boundary value problem resulting from the fill model is solved separately. The system of conservation law equations is interlinked with the system of ordinary differential equations describing the phenomena occurring in the counterflow wet-cooling tower fill via heat and mass sources and via boundary conditions. The concept of numerical solution is presented for the quasi one dimensional model of natural draft wet-cooling tower flow. The simulation results are shown.

Optimization of mechanical draft counter flow wet-cooling towers using a rigorous model

In this paper, an optimal design algorithm for mechanical draft counter flow wet-cooling towers based on the rigorous Poppe model and mixed-integer nonlinear programming (MINLP) is presented. Unlike the widely used Merkel method, the Poppe model takes into consideration the effects of the water loss by evaporation and the nonunity of the Lewis factor. As a result, the Poppe model is able to predict the performance of wet-cooling towers very accurately compared to the Merkel method. The optimization problem is formulated as an MINLP model by considering all the mass and energy balances, equations for physical properties, and empirical correlations for the loss and overall mass transfer coefficients in the packing region of the tower, in addition to feasibility constraints. The objective function to be minimized is the total annual cost, which includes capital and operating costs. The mathematical programming problem is solved with the GAMS software. Six case studies are used to show the application of the proposed algorithm. The case studies demonstrate that there can be large differences between the optimal designs based on the Poppe method and the Merkel method.

Optimization of mechanical draft counter flow wet-cooling tower using artificial bee colony algorithm

This study explores the use of artificial bee colony (ABC) algorithm for design optimization of mechanical draft counter flow wet-cooling tower. Minimizing the total annual cost for specific heat duty requirement is considered as objective function. Three design variables such as water to air mass ratio, mass velocity of water and mass velocity of air are considered for optimization. Evaluations of the cooling tower geometry and performances are based on an adaptive version of Merkel’s method. Temperature and enthalpy constraints are included in the optimization procedure. Six examples are presented to demonstrate the effectiveness and accuracy of the proposed algorithm. The results of optimization using ABC are validated by comparing with those obtained by using GAMS optimization package. The effect of variation of ABC parameters on the convergence and optimum value of the objective function has also been presented.

Exergy transfer and parametric study of counter flow wet cooling towers

Abstract A thermodynamic analysis of the counter flow wet cooling tower (CWCT) is performed in this paper. Both energy and exergy formulations are developed and validated for the system. Four types of exergy transfer processes occurring inside the CWCT are investigated schematically. A parametric study is conducted under various operating conditions in order to investigate the effects of thermal efficiency and water-to-air ratio on the exergy performance of the CWCT. Unlike past studies, the transiting exergy contained in the inlet and outlet water is not considered. It is found that the exergy efficiency is always less than 25%. The exergy parameters including evaporation water loss, exergy efficiency, exergy input, internal and external exergy losses are very sensitive to the thermal efficiency when it is very close to 1.0 at lower water-to-air ratios.

MINLP optimization of mechanical draft counter flow wet-cooling towers

In this paper, the problem of the optimal design of mechanical draft counter flow cooling towers that meets a set of specified constraints is formulated as a mixed-integer nonlinear programming (MINLP) problem. The Merkel's method is used to specify the characteristic dimensions of cooling towers, together with empirical correlations for the loss and overall mass transfer coefficients in the packing region of the tower. Water-to-air mass ratio, water mass flow rate, water inlet and outlet temperatures, operational temperature approach, type of packing, type of draft, height and area of the tower packing, total pressure drop of air flow, power consumption of the fan, and water consumption provide the set of optimization variables. The MINLP problem is formulated so as to minimize the total annual cost of the cooling tower. The performance of the proposed procedure is shown with the solution of six examples.

Solution of heat and mass transfer in counterflow wet-cooling tower fills

Model of heat and mass transfer in wet cooling tower fills is presented. The model consist of a set of four 1D ODEs describing the mass and energy conservation and kinetics with boundary conditions prescribed on opposite sides of the computational domain. Shooting technique with self adaptive Runge–Kutta step control is applied to solve the resulting model equations. The developed model is designed to be included in a large scale CFD calculations of a natural draft cooling tower where the fill is treated as a porous medium with prescribed distributions of mass and heat sources. Thus, the technique yields the spatial distributions of all flow parameters, specifically the heat and mass sources. Such distributions are not directly available in standard techniques such as Merkel, Poppe and e-NTU models of the fill where the temperature of the water is used as an independent variable. The method is validated against benchmark data available in the literature.

Numerical simulation of counter-flow wet-cooling towers

Cooling towers are used to cool a warm water stream through evaporation of part of the water into an air stream. A cooling tower consists of three zones; namely spray, packing and rain zones. In cooling towers, a significant portion of the total heat rejected may occur in the spray and rain zones. These zones are modeled and solved numerically using a computer code. The developed models of these zones are validated against experimental data. For the case study under consideration, the error in calculation of the tower volume is 1.5% when the spray and rain zones are neglected. This error is reduced to 1.1% and 0.25% as the spray and rain zones are incorporated in the model, respectively. Furthermore, the effect of the Lewis factor on the performance prediction of wet-cooling towers is investigated using Bosnjakovic equation.

Drop size distribution below different wet-cooling tower fills

Drop size distribution is measured photographically below three different counter-flow wet-cooling tower fills (cross-fluted film, trickle and fibre cement) and a number of splash grid configurations installed below a trickle fill. The air and water flow rates are varied to investigate their influence on drop size. The data for each test case is presented as a cumulative mass distribution curve, Sauter mean diameter, Rosin–Rammler distribution curve and Rosin–Rammler function. The main objectives are to describe the implemented experimental apparatus and measurement techniques and to determine the drop size distribution beneath different fills and ultimately the drop size reduction capability of grids installed below the fill. An important conclusion is that the Rosin–Rammler distribution curve generally does not fit the measured data adequately and thus should be avoided.

A critical investigation into the heat and mass transfer analysis of counterflow wet-cooling towers

This study gives a detailed derivation of the heat and mass transfer equations of evaporative cooling in wet-cooling towers. The governing equations of the rigorous Poppe method of analysis are derived from first principles. The method of Poppe is well suited for the analysis of hybrid cooling towers as the state of the outlet air is accurately predicted. The governing equations of the Merkel method of analysis are subsequently derived after some simplifying assumptions are made. The equations of the effectiveness-NTU method applied to wet-cooling towers are also presented. The governing equations of the Poppe method are extended to give a more detailed representation of the Merkel number. The differences in the heat and mass transfer analyses and solution techniques of the Merkel and Poppe methods are described with the aid of enthalpy diagrams and psychrometric charts. The psychrometric chart is extended to accommodate air in the supersaturated state.

Inlet Losses in Counterflow Wet-Cooling Towers

The inlet loss coefficients for dry, isotropically packed, circular and rectangular counterflow cooling towers are determined experimentally and empirical correlations are formulated to fit this data. Computational fluid dynamics is used to investigate the dependence of the inlet loss coefficient on the rain zone characteristics. The rain zone generally dampens the inlet loss, but the coupling is indirect and involves a large number of dependent variables. The numerical model is validated by means of experimental data for dry towers and it is found that the degree of accuracy achieved for circular towers exceeds that for rectangular towers. Consequently, the correlation derived to predict this occurrence for circular towers can be applied more confidently than its rectangular counterpart.