The warm water from the condensers needs to be cooled to the lowest practical temperature before being re-used. The cooling process is carried out in cooling towers or spray ponds after which the water is pumped back to the condensers. In cooling towers or spray ponds the exchange of heat between the warm water and ambient air is by,
The efficiency of the system is mainly dependent on the relative humidity of the air. The efficiency should be between 50% and 70%, 60% being a satisfactory average, and the efficiency can be calculated from
η = (Th - Tc) / (Th-Twb)
An approach temperature of between 8°C and 10°C is possible. Approach temperature is defined as
Tapp = Tc - Twb
Two criteria are involved namely
This has virtually no influence on the cooling of the water. An average depth of 1 metre should be adequate provided there is sufficient water to fill the flumes, seal wells and flood the injection and export pump suctions at the starting up of the plant. There is no advantage in exceeding a depth of 1 metre, since the increase in the mass of water in the circuit has only a negligible influence on the cooling. The surface area only is important.
The area of the pond is important on account of the necessity of arranging the nozzles so that the curtains of water formed by them do not overlap or interfere with each other, and so that air may circulate between the sprays. The area of the pond is deduced from the quantity of water which it can treat per hour per unit area of the pond. Tromp suggests 120 lb/ft2/h (585 kg/m2/h), Webre and Robinson 150 lb/ft2/h (732 kg/m2/h). Other figures given are (lb/ft2/h)
Among French manufacturing firms, Fives Lille bases its calculations on 164 lb/ft2/h (800 kg/m2/h). We consider that the best value to adopt is: 750 kg/m2/h
Do an online sizing calculation for a spraypond
The main design features are that nozzles should:
This is calculated from
q = C·S √(2gH)
Nozzles are mounted on pipes called laterals at right angles to the main pump delivery line. Laterals decrease in size towards the end.
These are best grouped in a star pattern with the following dimensions given as guidelines:
then ab = q/750, in which q = output/nozzle, in kg/h