Abstract
Under cold ambient conditions, the freezing risk of air-cooled heat exchangers, especially the frontal finned tube bundles, has been a critical concern in power plants. Based on the freezing conditions of the cooling deltas under windy conditions, the flow and heat transfer characteristics of natural draft dry cooling system (NDDCS) with 30%, 40% and 50% increased water flow rates are investigated in this work, and the outlet circulating water temperatures of the easily freezing cooling deltas and sectors are obtained. The results show that the deltas in the middle front and rear sectors become free from freezing at all wind speeds when the circulating water flow rate is increased. For the frontal sector with increased water flow rate, the outlet water temperatures of deltas increase conspicuously at 4 m/s and 8 m/s, while as the wind speed rises to 16 m/s, these deltas still face serious freezing risks due to the huge heat rejection to ambient air. Therefore, freezing prevention of air-cooled NDDCS heat exchangers can be achieved by increasing the water flow rates at small wind speeds, while as the wind speed becomes high, the water flow redistribution is suggested for the frontal and middle sectors due to their big performance difference.
Highlights
With almost no additional consumption of water resource, natural draft dry cooling system (NDDCS) (Natural Draft Dry CoolingSystem) has been widely employed by power generating units in arid regions [1]
The freezing risks are most likely to occur in the cooling deltas of the frontal, middle front as case so as to study the potential for avoiding freezing issues by increasing the water flow rate
The freezing risks are most likely to occur in the cooling deltas of the frontal, middle front as well flow directly through the first two deltas in frontal sector with the big pressure gradient, while it as leeward sectors due toofhigh heat from these sectors
Summary
With almost no additional consumption of water resource, NDDCS The pre-heating/peak cooler installation was proposed for NDDCS [8] These studies imply that the freezing risk of NDDCS is deeply related to the crosswinds and circulating water, which cause the heat transfer variations among all sectors. In such a case, it can be seen the outlet water temperatures of sectors will vary from each other. Lu et al [10] explored the wind effects by experiment with a 1:12.5 scaled cooling towermiddle equipped electric heater theeffects horizontal heat exchanger based on cooling a 15 m-tall ones.
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