A comprehensive approach to cooling tower design (original) (raw)
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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
Numerical simulation of counter-flow wet-cooling towers
International Journal of Refrigeration-revue Internationale Du Froid, 2009
Heat transfer Comparison Experiment a b s t r a c t 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.
Thermal performance analysis of a closed wet cooling tower
Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 2007
A detailed model was developed and employed to examine the thermal performance of a closed wet cooling tower. The model is capable of predicting the variation of air thermodynamic properties, sprayed and serpentine water temperature as well as heat transfer rates exchanged between air and falling water stream inside the indirect wet cooling tower. The reliability of simulations was tested against experimental data obtained from the literature. A parametric study was conducted to evaluate the thermal behaviour of the indirect cooling tower under various air mass flowrates, serpentine water mass flowrates and inlet temperatures. The results of the theoretical investigation revealed an increase in cooling capacity and percentage loss of sprayed water due to evaporation, with increasing air mass flowrate. On the other hand, the increase of serpentine water mass flowrate resulted in slight increase in the overall temperature reduction of serpentine water. The effect of variable serpentine water inlet temperature on thermal performance of the indirect wet cooling tower was insignificant compared to other cases. Thermal performance analysis of a closed wet cooling tower Proc. IMechE Vol. 221 Part E: J. Process Mechanical Engineering JPME119 © IMechE 2007 Thermal performance analysis of a closed wet cooling tower JPME119
Thermodynamic study of wet cooling tower performance
International Journal of Energy Research, 2006
An analytical model was developed to describe thermodynamically the water evaporation process inside a counter-flow wet cooling tower, where the air stream is in direct contact with the falling water, based on the implementation of the energy and mass balance between air and water stream describing thus, the rate of change of air temperature, humidity ratio, water temperature and evaporated water mass along tower height. The reliability of model predictions was ensured by comparisons made with pertinent experimental data, which were obtained from the literature. The paper elaborated the effect of atmospheric conditions, water mass flow rate and water inlet temperature on the variation of the thermodynamic properties of moist air inside the cooling tower and on its thermal performance characteristics. The analysis of the theoretical results revealed that the thermal performance of the cooling tower is sensitive to the degree of saturation of inlet air. Hence, the cooling capacity of the cooling tower increases with decreasing inlet air wet bulb temperature whereas the overall water temperature fall is curtailed with increasing water to air mass ratio. The change of inlet water temperature does not affect seriously the thermal behaviour of the cooling tower.
Performance characteristics of counter flow wet cooling towers
Energy Conversion and Management, 2003
Cooling towers are one of the biggest heat and mass transfer devices that are in widespread use. In this paper, we use a detailed model of counter flow wet cooling towers in investigating the performance characteristics. The validity of the model is checked by experimental data reported in the literature. The thermal performance of the cooling towers is clearly explained in terms of varying air and water temperatures, as well as the driving potential for convection and evaporation heat transfer, along the height of the tower. The relative contribution of each mode of heat transfer rate to the total heat transfer rate in the cooling tower is established. It is demonstrated with an example problem that the predominant mode of heat transfer is evaporation. For example, evaporation contributes about 62.5% of the total rate of heat transfer at the bottom of the tower and almost 90% at the top of the tower. The variation of air and water temperatures along the height of the tower (process line) is explained on psychometric charts.
Application of CFD to closed-wet cooling towers
Computational¯uid dynamics (CFD) is applied to predicting the performance of closed-wet cooling towers (CWCTs) for chilled ceilings according to the cooling capacity and pressure loss. The prediction involves the two-phase¯ow of gas and water droplets. The predicted thermal performance is compared with experimental measurement for a large industrial CWCT and a small prototype cooling tower. CFD is then applied to the design of a new cooling tower for ®eld testing. The accuracy of CFD modelling of the pressure loss for¯uid¯ow over the heat exchanger is assessed for a range of¯ow velocities applied in CWCTs. The predicted pressure loss for single-phase¯ow of air over the heat exchanger is in good agreement with the empirical equation for tube bundles. CFD can be used to assess the eect of¯ow interference on the¯uid distribution and pressure loss of single-and multi-phase¯ow over the heat exchanger. 7
Studies and Experimentation on Cooling Towers: A Review
2015
Cooling tower is one of the important utility in chemical industries. Normally they are used to dissipate heat from heat sources to heat sink. The cooling of hot effluent and process water is required from reuse and environmental point of view. Induced, forced and natural draft cooling towers are used according to the requirements in industries. Natural draft cooling towers use atmospheric air. In forced draft cooling air is forced into the tower using blower. In induced draft cooling towers, air is sucked from other end. The water cooling happens because of humidification of air. The heat lost by water is heat gained by air. Water recirculation is also important aspect in the cooling towers. The effectiveness of cooling tower depends on flow rates of air and water and water temperature. Minimization of heat loss is one of the important aspect of studies carried out by various investigators. The interfacial area between air and water is also crucial factor in cooling towers. Three types of packings used in cooling towers are film, splash and film-grid packings. Also it was observed that drift is one of the important losses in cooling towers. Various shapes of cooling towers are tried by various investigators to study effectiveness. Hyperbolic shape was advantageous due to higher area at bottom. It provides aerodynamics, strength, and stability. The present review is aimed at summarizing studies and research on cooling tower for increasing efficiency and power savings to make it more economical and efficient.
Applied Thermal Engineering, 2013
Cooling towers are evaporative heat transfer devices in which atmospheric air cools warm water, with direct contact between the water and the air by evaporating part of the water. The principle of operation of cooling towers requires spraying or distributing water over a heat transfer surface (packing) across or through which a stream of air is passing. As a result, water droplets are incorporated in the air stream and, depending on the velocity of the air, will be taken away from the unit. This is known as drift. Although cooling tower drift is objectionable for several reasons, the most hazardous problem concerning human health is the emission of chemicals or microorganisms into the atmosphere. Undoubtedly, regarding microorganisms, the most well-known pathogens are the multiple species of bacteria collectively known as legionella. The binomial water distribution system-drift eliminator is identified to be that mainly responsible for cooling tower drift. While water distribution systems affect the mechanics of setting up the drops, drift eliminators work by changing the direction of the airflow and separating droplets from the airstream through inertial impact. The drift eliminator's performance can be quantified mainly by two factors: droplet collection efficiency and the pressure drop across the eliminator. In contrast, water distribution systems are characterized by the pressure drop across itself and the achieved size of the particle spread. Alongside drift, the binomial water distribution system-drift eliminator affects the cooling tower performance. From the reviewed bibliography, some studies assessing the effect of the drift eliminator on cooling tower performance have been found. Nevertheless, no studies regarding the influence of the water distribution system on the cooling tower's performance have been detected. In this sense, this paper studies the thermal performance of a forced draft counter-flow wet cooling tower fitted with two water distribution systems (the pressure water distribution system (PWDS) and gravity water distribution system (GWDS)) for six drift eliminators for a wide range of air and water mass flow rates. The data registered in the experimental setup were employed to obtain correlations of the tower characteristic, which defines the cooling tower's thermal performance. The outlet water temperature predicted by these correlations was compared with the experimentally registered values, obtaining a maximum averaged difference of ±0.95%.
Analysis of mechanical draft wet cooling towers
1991
The objective of the paper is to present a review on the analysis of mechanical-draft wet cooling towers. Starting with the basic fundamentals of a cooling tower, an attempt is made here to present an analysis of the important computational models available. The physical situation within a cooling tower is very complex (films and droplets of water in air are in a constantly changing configuration). There is no mathematical model which is capable of simulating every detail of simultaneous heat and mass transfer process occurring within the tower. Consequently, simplifying assumptions must be made for the analysis. A comprehensive list of assumptions is provided which are used for the different models. Eight computational models are analyzed here, namely (a) ESC code, (b) FACTS, (c) VERAZD, (d) STAR, (e) Sutherland's Model, (f) Model by Fujita and Tezuka, (g) Webb's Model, (h) Model by Jaber and Webb. Each model makes use of somewhat different set of assumptions. So, the resul...