This month’s article provides an overview of types of finned tubes (extended surface tubes) you may come across and the applications they are suitable for. In our previous article, we focused on problems such as corrosion, erosion, and thermal fatigue in tubes of Shell & Tube heat exchangers.
As a general rule, a flanged tube heat exchanger uses air to cool or heat fluids such as air, water, oil, or gas, or to recover heat from waste sources. Oil & gas, power generation, marine, and HVAC&R can all take advantage of these heat exchangers.Heat exchangers with flanged tubes are often used in situations where air is the preferred cooling or heating medium, especially when water is scarce or of low quality. FinnedTube heat exchangers exchange heat between a thermally efficient fluid, such as a liquid that has some viscosity, and a fluid with no viscosity, such as air or gas with little density. To enhance the surface of the tube on the air side, fins or other elements, such as looped wires, are added to increase its surface area and improve its thermal performance.Fins can be either attached to the tube surface by pressure or molded into the tube surface. Fins can be either high or low in height.
Finned tubes can be manufactured in various designs and incorporate a combination of varying materials for both the tubes and fins according to the intended use and the environment in which they will operate. We will examine only the most common types and combinations of tubes and fins in this article.
Profile of Fintech
The performance of a finned tube heat exchanger is influenced greatly by the fin profile. Each fin must be tightly connected to the tube surface in order to ensure maximum thermal conductivity.A fin pitch that is tighter and larger will provide more thermal conductivity. Performance may be adversely affected due to an increase in pressure drop. Effective and optimal thermal performance and equipment performance require a balance between the two opposing functions.
Technology provided by Elfin
‘Elfin’ finned tubes provide long-term and reliable cooling for hydro power generator coolers, including those used by Snowy Hydro, Hydro Tasmania, and Origin Energy.Elfin computer-generated technology mechanically forces each fin strip over the tube’s outside, resulting in a tight, thermally efficient fit. In addition to ensuring excellent adhesion of the fin to the tube, this process protects the essential inner tube wall.The walls of bulleted tubes are forced outward into the fins by passing a bullet through the tubes to enlarge them and form a bond with the fins.
Figure 1 illustrates the situation. Four of the fins have been precision punched to ensure that the fin pitch spacing between fins is exactly right. The computerized punching process can adjust tube pitch to 0.01mm tolerance to match the exacting computer calculations. Elfin finned tubes come in blocks that are specifically sized to fit the heat exchanger’s duty requirements and dimensions.
Normally, bullets require tubes that are sufficiently thin and ductile to allow for expansion, however, Elfin technology allows tubes with any wall thickness and material to be used, and ensures the inner surface of the tubes is not compromised, as well as the strength of both the tubes and the fins.