Heat exchangers have entered into almost every area of our lives. From auto engines to refrigerators, from water heaters to air conditioners, from smokestacks to brewery beer tanks, the efficiency and cost-effectiveness of heat exchangers have changed our world. As with all mechanical devices, however, heat exchangers are not foolproof. They are subject to wear and tear, collection of debris, or simple failure. When this happens, you can either fork out the cash for an entirely new system or seek repair. Following are six of the most common problems encountered with heat exchangers.
- Fouling. The most common cause of heat exchanger problems is fouling. Fouling is the word used to describe the buildup of material on the inside of an exchanger, typically inside a tube wall. When the materials and fluids build up over time, the efficiency of the exchanger is decreased. Worse, if not taken care of, heat transfer may be lessened, pressure drop can increase, and the exchanger may fail altogether.
Think of a fish tank left without cleaning for a month or more. The tank glass gets filthy, and, without cleaning, eventually the water becomes inhospitable. The same is true of your heat exchanger. While the most common cause of fish tank buildup is fish waste and bacteria, the most common causes of fouling include crystallization, decomposition, corrosion, and particle settlement.
The good news is that fouling is correctable and preventable in the future.
- Gasket failure. Different areas of many types of heat exchange units are separated by gaskets. These gaskets only work if an effective seal is created. When they do not seal properly, the heat exchangers lose efficiency and may fail altogether. Some common reasons gaskets fail include:
- Weakness. Sometimes a gasket is used that cannot handle the pressure it is placed under. Typically, this happens when a gasket that is not designed for use under certain circumstances is used anyway. Other times, the correct gasket is used for the pressure, but due to fouling or an issue with a pressure release valve, a pressure increase takes the system beyond the gasket’s capacity, and other times there is simply a structural problem with the gasket. The solution is simple: Replace the gasket.
- Improper positioning. Gaskets are loosened and taken off for routine maintenance and repair of heat exchangers. Sometimes, during reassembly, the gasket is not positioned properly. This is the most common cause of failures related to gaskets. Quite simply, a gasket cannot provide the proper seal if it is not in the correct position. When gaskets that fit into grooves (compressed joint gaskets) are used, the chances of improper positioning are greatly reduced.
- Erosion. A gasket may be worn down through use. After all, gaskets do not come with lifetime guarantees and are designed to be changed, not used forever. If a gasket is used beyond its recommended life, the inevitable erosion of the seating face may cause leaks which can lead to system inefficiency or failure.
- Hot air recirculation. In heat exchangers that use ambient air to cool tubes or bundles, the heated air that results from the air passing over the hotter surfaces must be released. If the air is allowed to recirculate around the tubes or bundles, the initial air temperature will rise, and the cooling effect will be reduced or minimized. Often the cause of this problem is a pressure issue at the inlet, since the main reason for hot air recirculation is an exit velocity that is less than the air approach velocity. High winds or crosswinds can affect the performance of heat exchangers for this very reason. In such circumstances, alternations, such as a screen or shield, may prevent the wind from causing such adverse effects.
- Improper Placement. In heat exchangers using ambient air as a cooling medium, it is important to keep the initial air input as cool as possible. If the heated air from the exhaust of one exchanger is drawn into the input of another, the second will have far less efficiency due to the initial warmer temperature of the air. In such circumstances, the position of the exchangers is the problem and not the exchangers themselves. If this poor placement is repeated several times, there will be an exceptional loss of efficiency due to hot air migration caused by the improperly placed heat exchangers.
- Debris. If there are things caught in the heat exchanger, it will not work right. Debris issues are typically found after installation or cleaning when things are left behind. There have been reports of trash, gloves, pencils, even wrenches left in the exchanger by mistake. Sometimes these will be caught by a strainer, but other times they will get stuck in the exchanger and cause an improper flow, lack of performance, or even a total system failure. The good news is that, once the debris is removed, the system is usually ready to run at peak performance.
- Installation mistakes. When you consider the number of heat exchangers that are installed each and every year, even at a 99 percent proper installation rate (which is likely a bit too high), there would be hundreds of exchangers with installation mistakes. If a system is piped wrong, a fluid which should be in one channel could be on the wrong side and vice versa. At times, this may only cause poor performance, but at other times the whole system may need to be completely cleaned out, and parts may need to be replaced. This would be especially true if a caustic or corrosive liquid were piped into a channel not designed for such a liquid.
Regardless of the type, size, or style of your heat exchanger, maintenance is the number one way to obtain optimal performance by keeping it running smoothly and efficiently. Since device downtime can have a significant impact on your bottom line, be sure that your maintenance is carried out by the best in the industry.