A Method to Achieve Robust Aerodynamics and Enhancement of Updraft in Natural Draft Dry Cooling Towers

Abstract

A method to stabilize the draft through natural cooling towers is introduced. Natural draught dry cooling towers are widely used in arid regions of the world for the power industry especially those employing nuclear reactors. Their presence has become iconic of the process industry for their dominance of the landscape. These towers control the overall efficiency of power plants, and with the ongoing energy crisis it is desirable to raise efficiency by stabilising the draught through the tower. Energy comsumption is a substantial part of the overall cost of plant operation, and therefore even with a conservative 5 per cent improvement is feasible. It has been noted by some researchers like Baer, Ernst and Wurz (1980) that cooling towers do experience unstable flow with breezes. This phenomenon can be explained by Jo¨rg and Scorer (1967) to occur even in a still ambience with cold air inflow down into the tower shell from exit. Jo¨rg and Scorer (1967) developed a correlation to predict cold inflow to a glass tube for various fluids in a laboratory. By using their formula, it is found that under typical exit bulk velocities, of 3–5 m/s or below, cold air is liable to ‘sink’ into the shell, even in a quiescent surrounding. Indeed this phenomenon was demonstrated in the laboratory using a duct of size 457 × 457 mm2 of a heat exchanger by employing a smoke generator to detect that cold air did flow into the duct rather than the hot air filling the entire cross sectional area of the duct exit. A device was applied by Chu (1986) to prevent this cold air from sinking into the duct and enhance the stability and quantity of the updraft. In this paper, for the first time data obtained from a 700 × 700 mm2 cross-sectional flow area model air-cooled heat exchanger are presented that proves the air flow rate enhancement due to this device. It is hoped that more tests can be conducted to optimize the design for application in boiler chimneys and natural draught dry cooling towers.