Heat exchange passages (or cooling passages) are commonly used to transfer heat away from heat generating areas of a device to prevent the generation of heat from affecting the performance of the device. The passages are typically filled with a gas or liquid that flows through the passages providing a conduit for the heat. Some devices require close tolerance cooling passages that are a challenge to manufacture. Such devices include metallic structures exposed to high heat flux such as ramjet/scram jet combustors. In these types of combustors, the passages need to be small and close together. An example of a passage diameter is 0.090 inches with a distance between the passages of 0.060 to 0.120 inches.
One method of providing passages with such small diameters in close proximity is by machining grooves into one part and then attaching a face sheet to the part covering the grooves. A method machining grooves is with the use of water jets. A typical method of attachment of the face sheet is by welding or brazing the face sheet to the part with the machined grooves. This technique has its limitations however. For example, when the combustor is cylindrical in shape having a relatively small diameter it can be difficult to form the grooves in the part as well as attach the face sheet to the part. Moreover it is difficult to make select shapes of passages such as circular passages with a face sheet. Another method used to achieve circular passages is by machining semi-circular grooves in two parts and then mating the parts together. However, this technique requires twice the machining since the semi-circular grooves have to be formed in both parts. In addition, the length of passages and the proximity of the passages may make conventional drilling with a bit difficult if not impossible. For example, the passages in ramjet/scram jet combustors can be 16 inches or longer. This length makes the use of a conventional drill bit difficult because it is hard to keep the drill bit from penetrating a surface of the interior chamber or from drifting into another cooling passage.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a technique to make cooling passages of small diameters and long in depth in an effective and efficient manner and for an improved cooling structure.