Blowdown in a cooling tower

ANS:B - increases the scale forming tendencies of water.

When water is heated or evaporated, dissolved minerals and salts become more concentrated. If the concentration of these minerals and salts exceeds their solubility limits, they can precipitate out of solution and form solid deposits on surfaces. This process is known as scaling. Blowdown in a cooling tower helps control the concentration of dissolved minerals and salts in the circulating water. If blowdown is insufficient and the concentration of these substances becomes too high, it can actually increase the likelihood of scaling. Here's how:

1. Increased Concentration: When water evaporates in a cooling tower, the concentration of dissolved minerals and salts in the remaining water increases. Without adequate blowdown to remove some of this concentrated water, the overall concentration of these substances in the cooling tower's water loop rises.
2. Exceeding Solubility Limits: As the concentration of minerals and salts increases, it can exceed their solubility limits in the water. When this happens, these substances can no longer remain dissolved and begin to precipitate out as solid deposits.
3. Scale Formation: The precipitated minerals and salts adhere to surfaces within the cooling system, such as heat exchanger tubes, piping, and cooling tower fill material. Over time, these deposits accumulate and form scale. Scale deposits reduce heat transfer efficiency, restrict flow, increase energy consumption, and promote corrosion.

Therefore, insufficient blowdown that leads to higher concentrations of dissolved minerals and salts in the cooling tower's water can indeed increase the scale-forming tendencies of the water, making it more prone to scaling issues. Proper blowdown practices help mitigate this risk by maintaining the concentration of dissolved solids within acceptable limits and preventing scale formation.