Counter Flow Cooling Tower

A: The process water is discharged downwards from a network of sprinklers at the top of the tower. The water droplets fall through a multi-layer lattice structure called the fill, being cooled by heat and mass transfer with the upward moving air stream.

A: Generally speaking, If you have a long approach (difference between wet bulb and cold water temperatures) the counter flow is most efficient. Less total pump head and fan power. At closer approach temperatures and especially with low design wet bulb the cross flow can be more efficient.

A: COUNTER FLOW TOWERS + The coldest water comes in contact with the driest air maximizing tower performance. + Smaller foot print of the tower + Smaller tower height due to compact infill. + More efficient air/water contact due to droplet distribution. - Noise production due to spraying and falling water.

A: Recirculation Rate Formula:
Recirculation Rate=Exit Flow Rate/Makeup Water Flow Rate.
Blowdown Rate=[(Cycles of Concentration−1) / Cycles of Concentration]×100%
Corrosion Rate (mpy)=Weight Loss (g) / [Area (in2)×Exposure Time (hours)×87,600]
TR=Actual Range / Ideal Range.

A: Counter flow cooling towers are widely used in industrial processes to eject heat. As cooling tower water is cycled and evaporated, total dissolved solids (TDS) and scaling ions concentrate. This accumulation results in the need to periodically 'blow down' the cooling tower water and replace it with freshwater.

A: A general rule of thumb is 3 gpm of recirculating flow per ton of cooling at 10°F delta-T. Evaporation is estimated at 1.8 gallons/hour per ton of cooling. Follow-up calculations to estimate make-up volume, cycles of concentration, and blowdown volume can be found in this article on water use in cooling towers.

A: The circulating water is aerated each time it passes over the cooling tower. This reduces the carbon dioxide concentration in the water to the equilibrium value for the atmospheric conditions, causing the pH to rise. The rapid increase in pH across the tower can lead to calcium carbonate scaling on the tower fill.

A: For anyone familiar with chiller sizing, 2.4 GPM/ton will give you a 10F delta-T across the evaporator. For cooling tower sizing, the rule of thumb is 3.0 GPM/ton for a 10F delta-T across the tower. You may also be aware that although a cooling ton is 12,000 BTUH, a heat rejection ton is 15,000 BTUH.

A: The system capacity varies with design temperature as limited by process conditions. The usual cooling range is between 25 and 30°F. The inlet temperature of water to cooling equipment is established by ambient conditions, generally in the range 75–86°F, and the outlet temperature is in the range 104–114°F.

A: By following some simple operating guidelines, cooling towers can and have been successfully operated in very cold climates (-15°C / 5°F) as shown in the photograph at right.

A: A nominal counter flow cooling tower ton is defined as the capability to cool 3 GPM (0.19 lps) of water from a 95ºF (35.0ºC) entering water temperature to an 85ºF (29.4ºC) leaving water temperature at a 78ºF (25.6ºC) entering wet-bulb temperature.

A: The air becomes saturated as it passes through the tower in the water which increases the relative humidity of the air. The evaporation process allows water to be cooled to temperatures that are below the ambient temperature and which approaches the wet bulb temperature.

A: Cooling range is the difference in temperature between the hot water entering the tower and the cold water leaving the tower. Cycles of concentration compares dissolved solids in makeup water with solids concentrated through evaporation in the circulating water.

A: In general, counter flow cooling towers' life expectancy ranges between 15 – 20 years with proper water treatment and proper maintenance. After years and years of relentless operation, counter flow cooling towers require more than regular service or components replacement to maintain their original performance.

A: Cooling towers are designed to create effective heat transfer by connecting air and water in an efficient and expedient manner. Anywhere from 75–95 percent of the heat from the process, equipment, or buildings is removed through evaporation and only 5–25 percent is removed via convection.

A: Cooling tower approach is the difference in temperature of the water entering the basin (cold) and the wet bulb temperature. For the purpose of tower design, a tower with a smaller approach (small delta between basin water temperature and wet bulb temperature) is considered superior.

A: Discharge and inlets should be unimpeded by obstacles to airflow. Locations should be avoided where carryover and mist will be a problem. Also, like most mechanical equipment, cooling towers are a source of noise and should not be located where noise will be a problem.

A: Crossflow towers will serve better for maintenance access, variable flow, and cold weather operation. Counterflow towers may serve better in tight spaces under 750 tons, or in spaces where lower operating weight is required.

A: Counterflow cooling towers turn the air from horizontal to vertical flow beneath the fill media. While this gives good access to the cold water basin, the rest of the tower is more compact with lower overall height.

A: In the industrial setup, the system rejects heat from machinery, heated process material among other sources. Specifically, industrial cooling towers are common in food processing plants, petroleum refineries, natural gas plants and petrochemical plants.