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Cooling Tower Performance For The Mechanical PE Examination

The professional engineer must be capable of correctly design and measurement and select a cooling tower to fit the HVAC and Refrigeration application. Cooling towers are characterized by two terms the method and the range. The vary of the cooling tower is the distinction between the getting into and exiting temperatures of the cooling tower water.


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The approach or approach to wet bulb is the temperature difference between the water out and the wet bulb temperature of the air.

Approach=T_(water,out)-T_(air in,WB)

The method is vital because it describes the extent of efficiency of the cooling tower. The smaller the method the higher the cooling tower is at offering cooling. The wet bulb temperature of the coming into air is the lowest the temperature of the exiting water can reach. If a cooling tower has a 0 diploma approach then the cooling tower is using all of the available heat alternate from the air to cool the water. Typical approaches are within the range of ~10 °F.

Approach also leads to a different essential term in determining the efficiency of cooling towers, known as effectiveness. Effectiveness is a time period used to describe how efficient the cooling tower is at cooling the water or how shut the precise temperature distinction between the water temperatures in and out is to the maximum temperature distinction. The utmost temperature distinction that a cooling tower can produce is the difference between the water temperature in and the air wet bulb temperature.

Effectiveness=Vary/(Vary+ Method)

The range is necessary because when used along side the water stream charge, the capability of the cooling tower may be discovered. The capability and the quantity of cooling provided by the cooling tower are discovered by multiplying the stream fee of the cooling water by the difference in temperature on the inlet and outlet of the cooling tower, using the following equation, Q = mc∆T and for a simplified equation to use throughout the take a look at, follow the derivation under.

Cooling Tower Water Loss and Make-up

In a cooling tower, water is misplaced as a result of multiple sources similar to evaporation, drift and blow-down. The first time period, evaporation, is calculated via the following equation, where the assumption is made that the whole heat loss is as a result of heat loss by way of evaporation.

The second water loss is because of drift. Drift is the quantity of water that is carried out by the airstream. Drift eliminators provided prior to the discharge are best described as a maze of baffles that the air must travel by earlier than exiting to environment. The drift eliminator trap the water droplets that get picked up by the exiting air and ship the droplets again to the fill materials. Typical water loss due to drift is lower than zero.2%.

The third main source of water loss is due to blow-down. Blow-down is required because as water is evaporated it leaves behind the total dissolved solids (TDS), which will increase the concentration of the TDS in the water. In order to bring the focus of the TDS again to regular situations in order that it could also be used safely with the tools, the high concentrated TDS water is drained recurrently and that is what’s referred to as blow-down. The water is then replaced with recent water and this is referred to as make-up water.

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