Figure 1. Tube-side water is the most common design for process cooling applications. The cooling water passes through the tubes while the process fluid passes in the shell.

Part one of this series discussed the types of cooling water systems (i.e., cooling towers, closed and once-through) and the types of problems found on water-contacted surfaces (i.e., deposits, corrosion and biological). A thorough knowledge of the cooling water equipment and the cooling system operation is required prior to determining or selecting a water treatment program.

Selecting and implementing a water treatment program does not initially require knowledge of the water quality. Yet this is often what is done. Instead, the first step is to identify the various components that the cooling water will contact that require protection from deposits and deterioration. Whether it is a cooling tower system, closed cooling system, or once-through cooling water system, a thorough knowledge is necessary of its design and materials of construction.

I identified this need as "know your system." What are you trying to protect? Don't just say, "the entire system" -- be specific. Is it the tubing in the heat exchangers? Is it the piping? Is it a jacketed vessel? Is it the cooling tower? Is it a compressor? Is it all of these or several? Prioritize them from most important to protect to least important.

So, what do you need to know about this equipment? Actually, you need to know all about that equipment: its design, materials of construction, and operation. So, the next step is to identify each component within the cooling system that is contacted by the cooling water, then record this information.

Let's discuss that equipment. The need-to-know details about cooling water equipment are design and materials of construction. Design refers mainly to the cooling-water-contacted equipment and how water flows through that equipment. Several types of heat transfer equipment are:

• Water through the heat exchanger tubes -- process on the shell.

• Water on the shell -- process through the tubes.

• Water in jackets.

Enlarge this picture Figure 2. Shell-side water designs are uncommon, primarily because they are hard to protect even with good water treatment. In this design, the process fluid flows through the tubes and the cooling water flows through the shell.

Figure 1 shows cooling water through the tubes of a heat exchanger or condenser. This is referred to as "tube-side water." It is the most common in many industries and is very desirable. Cooling water that passes through or inside the tubes is the easiest to treat and protect due to acceptable water velocities.

Figure 2 shows cooling water on the shell-side or outside of the tubes in a heat exchanger. This is referred to as "shell-side water." It is uncommon except in certain industries such as chemical and petroleum plants. It is the hardest equipment design to protect even with very good water treatment. Though a number of design variations are utilized, the major difficulty with "shell-side water" is poor, even stagnant, water flow. It is almost impossible to protect even with outstanding water treatment.

In the next issue, I will continue this discussion by looking at heat transfer equipment.