Encyclopaedia Index


          

Click here for an example,
here for an input file and
here for the GROUND coding,

********************************************************* * * * TACT - THERMAL ANALYSIS OF COOLING TOWERS * * * *********************************************************

TACT is a computer program developed specifically for the simulation of natural-draught cooling towers. It is a derivative of the PHOENICS code, which bases its predictions on solving the fundamental equations of fluid flow.

Where is the need? ------------------ Cooling towers normally require a significant portion of the capital invested in any new plant, and therefore any reduction in number or size of towers can potentially lead to a large saving in initial cost. This can be achieved by testing the tower for various environmental scenarios in order to determine the most practicable and efficient design, so avoiding the traditional method of "over-design" to account for all eventualities.

Cooling-tower operators can benefit from optimal performance, by reducing running costs and by establishing the best control strategy.

Safety and environmental concerns can be alleviated by demonstrating all possible scenarios and situating towers to minimise environmental impact.

Why TACT? --------- TACT enables the user to represent the cooling tower fully in 3D, rigorously taking into account all features of its physical design, such as:-

1"""Internal and external tower geometry; 1"""Fill characteristics; 1"""Resistance of the fill zone, eliminator, sprinklers, struts & supports; 1"""Local wind patterns, in speed, direction, temperature & humidity; N?' Non-uniformities in fill & inlet water flow rates; 1"""Departure from conventional tower shapes.

TACT: Thermal Analysis of Cooling Towers

By fundamental representation of the physical processes of heat transfer and fluid flow which encompass the external environment as well as that inside the tower, TACT provides a complete prediction of both internal and external air conditions and interactions.

TACT Menu System ---------------- The TACT menu system has been developed to match practitioners requirements whilst consistently using plain English.

The menus are accessed by a branch-type structure and all defaulted values are set to describe a realistic tower size and condition which you can modify to your own requirements. Options can be chosen by mouse or keyboard, and a graphical capability enables the visualisation of the tower during set-up phase.

Flow Visualisation ------------------ To post-process results, TACT can use one or the other of the two stand-alone packages from the PHOENICS computational suite.

AUTOPLOT is the graph plotting package. This program enables you to trace profiles of wind pressure, velocity, temperature, water vapour concentration and all other results derived from TACT. It can also be used to plot results from multiple TACT runs, in order to display trends from parameric studies.

PHOTON is the visualisation package which enables you to view wind vectors and contours of properties in colour, thus enhancing the presentation of results for clear and concise interpretation.

(Picture: Tower performance as a function of wind speed, for various water distributions)

(Picture: Vapour contours plotted through the centre plane of a cooling tower)

(Picture: Wind vectors plotted on a horizontal lane at basin level)

TACT Menu Display

TACT: Thermal Analysis of Cooling Towers

TACT can be used to optimise the design of new cooling towers by way of parametric studies; and performance improvements of existing ones from changes in fill design or water distribution can be tested.

Results provided by TACT predictions can include performance related data such as:-

1"""Air temperature distribution and water vapour concentrations in and around the tower. 1"""Water temperatures within the tower. N?' Outlet water-temperature. N?' Evaporative water losses. N?' Air flowrate through the tower. N?' Thermal performance of the tower as a whole.

On the other hand...

Most contemporary models are too simplistic for reliable predictions of cooling tower performance, mainly due to their reliance on one- or two-dimensional representation of the geometry. Anything less than a three-dimensional model will not account correctly for local wind patterns that can have a profound effect on cooling rates. Before TACT there was no rigorous three-dimensional model.

Many existing models are based on expiricisms derived from measured data. These seldom hold true for other cooling towers of different size and capacity, or that operate in a different environment.

Main features of TACT --------------------- * Ease of use * TACT has a user-friendly menu which provides a straightforward and concise method for data input. * No specialist computer or mathematical knowledge is required.

Geometric Features ------------------ TACT provides a full three-dimensional representation of the cooling tower. The menu permits the user, who may be a designer or operator, to prescribe and modify details of the tower layout, such as location and characteristics of the air inlet, fill zone, eliminator, sprinklers, struts, supports and rain zone which can all be studied in detail.

* Mesh Generator

TACT works by solving balance equations for conservation of mass, momentum and energy across discrete, multiply linked, cell subdivisions which together form the entire calculation domain. The collective subdivisions which constitute the computational mesh conform to a non- orthogonal curvilinear coordinate system which is generated automatically by TACT.

* Turbulent Characteristics of the Flow

TACT uses an effective viscosity method for the representation of turbulence in the air, which influences air movement and energy transfer processes both inside and around the cooling tower.

* Buoyancy Effects

TACT includes buoyancy forces determined from differences in local air density, which in turn are accurately linked to air temperature and humidity.

* Prevailing Wind

TACT employs an atmospheric boundary-layer profile in order to represent the effect of the approaching wind on tower performance. This can be adjusted for different wind speeds, directions and ground effects.

On-line Help and Documentation ------------------------------ TACT comes complete with a comprehensive on-line help facility and carefully-prepared documentation which provide the user with clear instructions on how to apply the software and achieve a solution quickly and effectively.

Consultancy Service ------------------- CHAM offers a consultancy service. If users prefer, CHAM engineers will perform all the TACT calculations, supplying the results to the client, with advice as to how they should be interpreted.

The CHAM consultancy service can also perform CFD analyses of many other classes of equipment and processes of interest to engineers. CHAM engineers are all highly qualified professional engineers and scientists, experienced in many disciplines associated with the application of advanced Computational Fluid Dynamics to modelling of fluid-flow, heat transfer and chemical reaction for industry.

(Picture: Perspective view of a water vapour plume)

Availability of TACT -------------------- TACT is available for use on most computer software including PCs, workstations and super computers.

It can be purchased under annual or perpetual schemes. Licence fees depending on the computer type/power.