Evaporative cooling systems

Cooling systems using evaporative cooling towers are often called open systems because the systems are open to the atmosphere. The evaporative cooling towers can be classified in a number of ways. There are natural draft and mechanical draft towers. (Incidentally, dry cooling towers are also available in natural draft or mechanical draft designs.) 

Mechanical draft towers are always used for cooling systems requiring a low approach and typically have an L/G (liquid/gas) ratio within the range of 1 0.75 to 1 1. 

Hyperbolic towers also come in crossflow and counterflow configurations and can be recognized by their shape. Crossflow types have the fill outside 

2 NOTES ON SOME COMMON TYPES OF COOLING TOWERS 

As design plant heat loads increase, a point is reached when hyperbolic towers become a more economical choice compared to other designs. 

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Open steady-flow systems, which include almost all air conditioning processes, foUow this law. Examples include the energy flows in a cooling and dehurnidifying coil or an evaporative cooling system. 

The work required to drive the turbine eompressor is reduced by lowering the compressor inlet temperature thus increasing the output work of the turbine. Figure 2-35 is a schematic of the evaporative gas turbine and its effect on the Brayton cycle. The volumetric flow of most turbines is constant and therefore by increasing the mass flow, power increases in an inverse proportion to the temperature of the inlet air. The psychometric chart shown shows that the cooling is limited especially in high humid conditions. It is a very low cost option and can be installed very easily. This technique does not however increase the efficiency of the turbine. The turbine inlet temperature is lowered by about 18 °F (10 °C), if the outside temperature is around 90 °F (32 °C). The cost of an evaporative cooling system runs around 50/kw. 

The article features a two-stage evaporative cooling system with cooling tower and dry basin for freezing weather tower operation. Design conditions and visual problems are discussed together with cooling tower enclosure, structural and vibration considerations. 

This book is primarily concerned with the water treatment of evaporative cooling systems (see the schematic examples shown in Figures 1.1 and 1.2)... 

Evaporative cooling systems are used for the ultimate rejection of heat, but the actual transfer of heat from the manufacturing process is usually via a heat-exchanger (H/Ex). 

Planned inspection of evaporative cooling systems and air humidification systems (annual). 

FIGURE 10.3 Process outline for phosphoric acid production by sulfuric acid acidulation of phosphate rock. Fume control and slurry evaporative cooling systems are shown, together with a countercurrent filtration and washing system which serves to maximize product acid concentrations accessible without evaporation. (From Shreve and Brink [30 a] by permission, McGraw-Hill.)... 

If the relative humidity of the air needs to be further adjusted, a direct evaporative cooling system may be used (air temperature at this point is about 297 K). However, this option is not desirable if the process air is to be used in human-occupant environments. The process air can become saturated with moisture at this point and the final humidity of the air may not be controlled adequately. 

The presence of dissolved calcium and magnesimn compounds (termed hardness) leads to scale formation in boilers and fouling of evaporative cooling systems, and is the biggest canse of plant water problems. Other dissolved soUds may be considered as impurities, depending on their concentrations and the intended water use. 

EM-25 Install Evaporative Cooling Systems EM-26 Install Energy Efficient Chillers... 

Plant maintenance. Quality of air filtration system maintenance, frequency of compressor blade washing (deposition leads to higher surface blade rou mess, which in turn leads to faster rate of degradation), prevention of potential bearing seal oil leaks into air inlet stream, periodic water quality control in closed-loop evaporative cooling systems, etc., are all measures that can positively influence compressor fouling and their rate of fouling. 

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