Calculation method for water loss in circulating water

The water loss in a cooling tower includes evaporative loss, wind-induced loss, and blowdown loss. 1. Evaporative water loss: (1) To initially determine the amount of water that needs to be replenished to the cooling tower, the following formula can be used: Qe = (0.001 + 0.00002θ)Δt. Alternatively, Qe = KΔt. Where: Qe – amount of water lost due to evaporation (m3/h); Δt – temperature difference between the inlet and outlet water of the cooling tower (°C); Q – volume of water circulating in the tower (m3/h); K – coefficient (1/°C). Values of K vary with temperature: Temperature (°C): -10, 0, 10, 20, 30, 40; K (1/°C): 0.0008, 0.001, 0.0012, 0.0014, 0.0015, 0.0016. (2) To determine the evaporative water loss more accurately, the following formula can be used: Qe = G(x1 – x2). Where: G – amount of dry air entering the cooling tower (Kg/h); x1, x2 – humidity levels of the air exiting and entering the tower, respectively (kg/kg). 2. Wind-induced water loss: In cooling towers equipped with dehumidifiers for mechanical ventilation, the wind-induced water loss is approximately (0.2%–0.3%) of Q. 3. Blowdown water loss: This depends on the requirements for the quality of circulating cooling water, the methods used for treating it, the quality of the water used for replenishment, and the degree of concentration of the circulating water. Overall, this amount is not very large.

In addition to the losses mentioned above, the losses due to pipe leaks should also be included.

How to calculate the make-up water volume for circulating water? The relationship between evaporation rate and circulating water volume is such that when the evaporation rate is 1% of the circulating water volume, the temperature difference between the inlet and outlet water of the circulating water is around 5.6°C; if a design value of 10°C is used, then the evaporation rate is approximately equal to the circulating water volume multiplied by 1.8%； Water to be added = concentration ratio / (concentration ratio – 1) × amount of water evaporated. The concentration ratio is usually set at 3, which means that the amount of water to be added is 1.5 times the amount of water that has evaporated. For the circulation tank, use a circulation water volume of 15 to 25 minutes; when the water volume is high, use the lower limit (to avoid making the tank too large), and when the volume is low, use the upper limit. The amount of water added to the circulation system should equal the sum of losses due to evaporation, wind effects, wastewater discharge, and leaks. 1. The methods for calculating evaporation loss water volume are divided into estimating the water volume and accurately calculating it. The estimated water volume is the product of the temperature difference between the inlet and outlet water of the circulating water and the volume of circulating water, multiplied by a coefficient (related to temperature) ； The exact amount of water is calculated as the difference between the humidity levels at the inlet and outlet of the tower, multiplied by the amount of dry air entering the cooling tower. 2. Water loss due to wind is difficult to calculate; generally, it is taken as 0.2%-0.3% of the cooling water volume in cases with a dehydrator, and ≥0.5% of the cooling water volume in cases without a dehydrator. 3. The amounts of waste discharge and leakage losses are related to the quality of the circulating cooling water and the methods used for its treatment, as well as the quality of the make-up water and the concentration ratio of the circulating water.

I learned it! Everyone is welcome to discuss more.