Core and frame material specifications can add significantly to the cost of a heat exchanger. The core, which may consist of tubes, fin, and/or sheet metal, can be manufactured using a variety of metals. The metals most commonly used in heat exchangers are copper, aluminum, and stainless steel. The cost of these metals has risen significantly over the past several years, making their percent of the total heat exchanger cost even greater. Since stainless steel is more expensive than copper or aluminum, it makes sense to opt for copper or aluminum unless your application requires stainless steel. Heat exchangers may also be manufactured using nickel, cupronickel, hastelloy®, inconel®, titanium, or other metals. However, these metals are not used as frequently due to their higher costs.
Usually the core's materials are specified to ensure that fluid path metals are compatible with the coolant selected for the application. For example, stainless steel might be specified for use with deionized water, whereas cupronickel might be specified for use with saltwater. Heat exchanger core material may also be selected based on weight. Aluminum and titanium are preferential for military and aerospace applications since these metals are less dense.
Core costs can also vary based on the type of heat exchanger selected. Cost variations are due to the different amounts of materials required to make the specific heat exchanger as well as the amount of factory time required to manufacture the part. The least expensive type of heat exchanger to manufacture is a copper tube-fin heat exchanger. Stainless steel tube-fin heat exchangers are more expensive than copper because stainless steel is more expensive by weight, it requires more time to punch, and it must be welded. Like tube-fin heat exchangers, vacuum-brazed flat tube oil cooler heat exchangers are relatively easy to produce. Conversely, the most expensive type of heat exchanger to produce is a vacuum-brazed plate-fin heat exchanger.
Other heat exchanger specifications that can add cost are the materials and processes used to attach the heat exchanger's frame to the core. Pop rivets are the least expensive option, followed by screws and then welding. Screws will provide a bit more strength than pop rivets. Flat tube heat exchanger frames are generally attached with rivets or welding. With welding, the result is an even stronger and more reliable part that is better able to handle shock and vibration. Welding is also preferable when space and weight are concerns, such as with plate-fin heat exchangers that are used in weight sensitive applications (e.g. airborne applications). Welding eliminates the need to use rivets, which can add weight. In addition, rivets may require a larger heat exchanger frame than welding does since the rivets need a wide section of metal to pass through and effectively hold the heat exchanger frame and core together. Due to additional factory time involved in the welding process, however, welding is more expensive than the other two methods.