Water (H2O), the most abundant substance on earth, is also a universal solvent. From rivers and lakes to seas and oceans, water is the main ingredient but its composition varies because of its solvent properties. As water falls through the air, it absorbs gases and picks up particulates such as dust and pollen. Then, as it trickles down through soil and rocks, it dissolves minerals along the way. As a result, water quality varies greatly both regionally and seasonally.
Water is also a highly effective heat transfer medium. Heat transfer is the process whereby thermal energy or heat moves from one body or substance to another, and from hot to cold. We’ve all noticed the large plumes rising from a hospital, hotel or a power plant.
Those are water vapors from cooling towers rejecting process heat into the atmosphere. When water is evaporated, only the gas phase or vapor is lost. Other ingredients, such as dissolved minerals and entrained particulates, stay behind in the liquid portion and, as evaporation continues, they become more concentrated. If not monitored and controlled, all those other ingredients in the water contribute to the formation of deposits, corrosion and microbial growth. In other words, to use water as a heat transfer medium, considerable maintenance and control is required. Let’s take a look at three key challenges when using water for heat transfer:
Deposits from water cause blockage and inhibit heat transfer. For example, calcium carbonate, a form of mineral deposit often referred to as scale, has thermal conductivity hundreds of times lower than copper, a metal frequently used in heat exchangers. It’s no wonder that even small amounts of scale can result in reduced heat transfer efficiency.
It does not stop there. Micro-organisms and algae thrive on these deposits and further contribute to the degradation of the heat transfer surfaces by aiding corrosion.
Corrosion is nature’s way of returning metals to their original state as ores. Heat exchange surfaces are often very thin in order to maximize the heat transfer process. However, this makes them even more vulnerable to degradation by corrosion. When it comes to equipment components, this natural process can lead to metal loss. Of particular concern are holes in thin equipment surfaces that can result in system failures.
If not properly maintained, cooling towers and the water they use can become a breeding ground for a wide variety of organisms. These organisms will form a slimy substance that promotes the corrosion process and reduces heat transfer efficiency. Additionally, Legionella, a pathogenic group of bacteria, thrives in warm waters such as the one found in cooling towers, and can be deadly.
To assure safety, maximize efficiency and the life of the equipment, proper maintenance and care is critical when using water as a heat transfer medium. Since not all water is equal, it is crucial to implement a customized treatment program to address each situation individually. Finding a reliable water expert with local experience can help ensure the wellbeing of your system for the long-term.