Like the low-fin tube, the medium-height finned tube is a single monolithic tube, made of a single material, but the fin is slightly taller, with a height of 3 mm or 1/3 inch. Of course, higher fin height provides greater surface area and greater heat transfer capacity.
Medium and high finned tubes are mainly made of copper alloy. We extrude the fins out of the wall of the tube to form a slightly larger diameter than the parent tube. Because copper provides high heat transfer in water applications, mid-height finned tubes are primarily used in the refrigeration, heating, and cooling industries. These tubes are commonly used in heaters, water heaters, process coolers, and heat exchangers. They are also used in oil heating and cooling applications.
The advantage of medium to high finned tubes is their flexible support in bending applications. We use a set of proprietary molds during the machining process, which form a special profile to extrude the heat sink from the tube. This results in a corrugated inner ridged surface that allows a small bending radius to be achieved — the potential for bending configurations is unlimited.
Not only can the outside diameter be controlled and slightly larger than the mother tube diameter, but the fin pitch is very suitable for bending – usually 11 fins per inch. After annealing during the manufacturing process, the tube can be bent.
Advantages of integral fin tube
Unlike the already applied finned tube, in which the fin is added as a separate material to the tube, the integrated tube extracts the fin from the tube itself. The finned tube is made of one material so there is no gap problem – the fin is always in contact with the tube because the fin and tube are one piece of material.
Without the risk of gaps, the all-in-one tube produces better heat transfer — although it is not as customizable as applied finned tubes, nor does it take advantage of the heating/cooling properties of various materials.
You do face certain limitations in terms of fin height and fin per inch. But find a homogeneous solution within those limits, and you’ll usually get a better product.
To bend or not to bend? Should the tubes be annealed or finished?
When planning a medium-high finned tube, the first factor you need to determine is whether the tube will be used for bending applications.
For straight applications, a fine finned tube can be purchased to be detached from the machine in a hardening state. However, if the pipe is to be bent, it needs to be bent through a heat treatment process called annealing, which is the process of placing the pipe in a controlled atmosphere furnace. We then bring the tubes back to room temperature in a specified time sequence that follows specifications such as baking recipes.
After annealing, the tube can be bent, coiled or made into any desired shape. Typical shapes include:
The flat spiral
Tapered flat screw
Determine the grain size of medium and high finned tube
In addition to deciding whether to use the medium-height finned tube for bending or straight tube applications, we also need to determine the grain size of the tube. We determine the grain size of the tube by examining the grain size of the tube microscopically. This is a factor that customers and suppliers need to agree on.
However, ASME codes tend to be a bit vague when it comes to grain sizes – there is a general range, but for bending applications we need to be more specific. One way to determine the ideal grain size is to construct a sample tube and try it out. We can mimic your end use on request, for example by winding the tube around a 5 “diameter die or making other appropriate measurements. We can bend the tube to the size you want and then send the sample to you for inspection.
Once we and the customer have determined which grain size is most suitable, we will begin full production of your order.
Custom fin tube
The truth is, many customers have been surprised by the power transfer capabilities of curved copper finned tubes. Some companies keep buying a product that is the worst fit for their app because they don’t know their options.
So when we ask, “Do you want the tube to be finned or annealed?” — This is a great opportunity to illustrate Murphy’s manufacturing prowess.
We do all our own finned tube manufacturing and machining in our in-house custom machining shop. Through decades of experimentation and innovative systems, we have developed a proprietary method for bending medium-height finned tubes.
We’ll make them cheaper than what you can get overseas.
If you have interest, please contact us!