Your cooling system needs a new heat exchanger. You’ve done your homework and selected the best equipment for the job, and the system’s performance claims look great. But no matter how good everything looks on paper, the equipment will not operate as designed if the proper installation, operating and maintenance procedures are not followed.
1. Install the Equipment ProperlyAs soon as you receive the exchanger, inspect it carefully for shipping damage, especially to the connections. If damage is present, especially if it is extensive, notify the carrier immediately. Also check the heat exchanger against the final drawings and spec sheets to make sure everything is as expected.
Before piping up, inspect all of the openings in the heat exchanger for foreign material. Remove all of the plugs and shipping covers immediately prior to installing the exchanger. Clean the exchanger thoroughly to remove all preservation materials, if any were used, unless the manufacturer specifies that the material is soluble in the system fluid.
For single-phase fluids, the heat exchanger can be mounted in any orientation that is convenient and should be piped in a counter-current, parallel-flow arrangement. For two-phase fluids, the heat exchanger should be mounted vertically and piped as shown in figure 1. The connections might be on either the front or back of the exchanger. Be sure to provide air-vent valves for the heat exchanger so that it can be purged to prevent or relieve vapor or gas binding.
Install the proper relief valves and temperature alarms to ensure that the heat exchanger is not subject to conditions beyond its intended design. To prevent damage to the brazing alloy, do not weld or braze brackets or attachments directly to the body of the heat exchanger.
To minimize distortion of the connection and prevent damage to the braze alloy, braze with a minimum 45 percent silver solder at a maximum 1,200°F (649°C) for soldering-type connections, and use tungsten inert gas (TIG) or metal inert gas (MIG) welding for welded-type connections. To avoid overheating and damaging the exchanger components, place a wet cloth or rag around the base of the connection, use a nitrogen purge to avoid internal oxidation, and braze or weld with the exchanger in the vertical position.
When tightening the connections, be careful not to use too much force. The nozzle connections on most brazed plate heat exchangers are designed for normal torque force and can be damaged if they are over-tightened. For threaded connections, use pipe sealant materials that are compatible with the system fluids. Finally, be sure to observe all connection load limits indicated by the equipment supplier.
2. Operate the Equipment Within Its Designed ParametersBefore starting the heat exchanger, make sure that the entire system is clean to prevent the passages from being plugged with debris. If the fluid quality is poor (contains excessive dirt, debris or other contaminants), use settling tanks or strainers with a strainer size of 20 to 24 mesh in the pipelines leading to the heat exchanger. Start operating the system gradually, following the suggested startup and shutdown procedures for most applications shown in table 1. When in doubt, consult the heat exchanger supplier for specific instructions. Do not operate the heat exchanger under pressure or temperature conditions that exceed the specified design limits, which typically are shown on the nameplate attached to the heat exchanger. Also, be sure to drain all fluids when shutting down the equipment to avoid possible freezing and corrosion problems.
3. Follow All Recommended Maintenance ProceduresA buildup of sludge or scale on the heat exchanger plates can reduce the equipment’s effectiveness. Heat exchangers that are subject to fouling should be cleaned at regularly scheduled intervals, depending on the specific conditions. A marked increase in the pressure drop or a sudden reduction in the system’s performance usually indicates that cleaning is necessary. As mentioned previously, the use of a strainer is recommended if the fluid quality is poor. If the fluids are relatively clean, fouling should be minimal and a periodic cleaning should be adequate.
Some suggested methods for cleaning either side of the heat exchanger include the following:
- Backflush with a high-pressure stream of hot water to remove loose deposits.
- Circulate a hot wash oil or a light distillate through the system to remove sludge or similar soft deposits.
- Use a 5 percent solution of phosphoric or oxalic acid to remove more stubborn deposits. For optimum results, the solution should be in a backflush-type flow pattern. Rinse the heat exchanger with clean, fresh water after using these chemicals. To avoid damaging sensitive components, do not chemically clean the refrigerant circuit.
By following the correct installation, operating and maintenance procedures, you can help ensure that your heat exchangers will operate efficiently over a long service life.
This article was submitted by ITT Standard, Cheektowaga, N.Y., a manufacturer of heat transfer equipment for process cooling and other industrial applications. For more information, call (800) 447-7700, e-mail firstname.lastname@example.org or visit www.ittstandard.com.