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Design Considerations with Vipertex®
Vipertex® enhanced surfaces, either in a tube or flat rolled configuration, can be used in a variety of applications. These engineered surfaces are rolled into coils of metal, promoting repeatability, volume production and cost efficiency.
Vipertex® makes it possible to incorporate enhanced surfaces into heat exchanger designs with greater flexibility and scalability, helping you optimize a solution for your project.
Whether you are retrofitting an existing installation or building new, let us help you determine the economic value of using Vipertex®.
Operating Conditions
Heat exchangers using Vipertex® tubes and/or flat goods can be substantially more efficient than those produced with conventional materials. Various operating conditions need to be considered so that the appropriateness of Vipertex® can be determined and optional strategies can be considered before making final design decisions. An example of an optional strategy is the fact that the Vipertex® heat transfer efficiency curve is not linear. In the case of the Vipertex® 1EHT, the same heat transfer can be achieved at a much lower flow rate, which can inform optimization decisions about pumping power, size of the overall unit, footage and diameter of tubing required, etc.
HTRI® members can take advantage of a calculation tool that plugs into HTRI® Xchanger Suite software to help them optimize installations using Vipertex® tubing.
Pressure Applications
Vipertex® tubes can be applied to exchangers operating at various pressure levels. Different alloy systems, wall thicknesses and processing specifications contribute to the achievement of various pressure ratings.
Burst and collapse tests of welded Vipertex® tubes confirm higher ratings than their smooth, welded tube counterparts. It is apparent that the enhanced surface pattern serves to create a stronger, more rigid tube.
Flow Rate
Vipertex® optimal performances produce a more than 500% improvement at Reynolds numbers at 1000. At other flow rates, performance enhancement values of 90-100% are seen. It is very interesting to note that there is an opportunity to reduce flow rate in your design to take advantage of this high-efficiency at the lower rate to reduce pumping power. For instance, you may be able to provide less pumping power to accomplish the same result.
The intersection of lines A and B shows the maximum heat transfer for the Vipertex® enhanced 1EHT tube. In order to obtain the same amount of heat transfer at the point of maximum heat transfer in the 1EHT tube (shown by the intersection of lines A and C), it would require roughly twenty times the flow in a smooth tube. At higher flow rates, there is a 90-100% increase in heat transfer.
Two Phase Applications
Vipertex® tubes work extraordinarily well in single phase processes, but also enhance two phase applications. Vipertex® is available in various surface texture options that may, based on other operating conditions, be more appropriate for particular functions, such as evaporators or condensers.
Fouling
Vipertex® enhanced surfaces have heat transfer anti-fouling characteristics for many conditions. Studies have been performed in crude, and once through water. Results show the design of the Vipertex® surface produces a wall shear that cleans the tube surface, allowing less debris to form on the surface. For many applications involving fouling, Vipertex® designs produce more heat transfer and less fouling than other tubes (smooth and other enhanced tubes). In a recent crude oil fouling evaluation, it was shown that a heat duty increase (when compared to other tubes) of up to 19% was achieved when using Vipertex® tubes. Additionally results have shown that in order to achieve the same heat duties, a flow rate reduction of up to 30% could be utilized.
It is important to consider what substances come in contact with the enhanced surfaces in your heat exchanger. As the leader in metal surface engineering, Rigidized® Metals has other surface designs like hydrophobic stainless steel and titanium finishes that may further enhance the anti-fouling performance of Vipertex® tubes in certain applications.
Charging Substance
Since Vipertex® tubes are produced in a variety of alloy systems, optimization is possible to accommodate a wide variety of charging substances. It is important to consider what substances come in contact with the enhanced surfaces in your heat exchanger. This is helpful in determining a suitable alloy, as well as a suitable enhanced heat transfer pattern.
The increased thermal efficiency of a Vipertex® installation can reduce the amount of charging substance required, which provides the following benefits:
- Less cost to charge
- Less environmental liability in the case of a spill
- Less cost in maintaining a supply of substances that decay through use
- Reduced space required
Temperature Range
Vipertex® enhanced surfaces can be produced in a number of alloy systems that can be optimized for operating temperatures ranging from high temperature to cryogenic, allowing the use of Vipertex® products in a wide variety of conditions.
Solving Space Constraints
The highly efficient heat transfer, made possible by Vipertex® enhanced surfaces, allows for more compact heat exchanger designs where space is constrained, such as a retrofit scenario or transportation applications like automotive, aircraft or marine.
Vipertex® can make the following possible:
- Less tubing
- Less charging fluid
- Smaller overall footprint of the installation
- Tightly-wound enhanced coil sections – it is possible to have tight geometry with Vipertex® tube arrays. It is often necessary to allow larger return radii in the case of finned tubes.
A recent analysis was performed to evaluate the performance of a Liquid/Liquid Horizontal TEMA BEM heat exchanger that required 1003 smooth wall, 5/8 in OD Titanium tubes in a 32 inch shell. Ratings using the HTRI®’s Xchanger Suite software yielded an overdesign of 11.99%. Producing the same duty and utilizing 532 Vipertex® 1EHT tubes with a 21 inch shell yielded an overdesign of 10.75. This solution produced the same duty while providing a substantial saving in both material and space.
Fabricability
Vipertex® tubes and sheets are produced by a rolling process, which promotes surface condition repeatability, supporting steady-state conditions as these materials are fabricated and installed. These surfaces are readily fabricated.
Joinery Methods
Vipertex® enhanced surfaces are produced in a variety of alloy systems, which individually lend themselves to processes such as welding, brazing, soldering, etc. While we will not go into detail about the merits of each of these hot processes in various metals, be assured that Vipertex® patterns are embossed into the parent metal and conform to your expectations regarding the alloy from which a particular Vipertex® product is made.
Vipertex® tubes are produced from pre-textured strip and will have enhanced pattern from end to end. In our experience, most heat exchanger operations are able to overcome ends with these surface patterns with procedures conducted in-house. For cases where this is not readily solved in the customer’s shop, we are able to condition the ends to remove the textured pattern for ready introduction to the customer’s operation at added cost.
Vipertex® tubes are produced from pre-textured strip and will have enhanced pattern from end to end. In our experience, most heat exchanger operations are able to overcome ends with these surface patterns with procedures conducted in-house. For cases where this is not readily solved in the customer’s shop, we are able to condition the ends to remove the textured pattern for ready introduction to the customer’s operation at added cost. Below is a video demonstration on how this process is done.
Fabrication Benefits
- Tightly-wound enhanced coil sections – it is possible to have tight geometry with Vipertex® tube arrays. It is often necessary to allow larger return radii in the case of finned tubes.
- Tubes & flat-rolled shipable in coil form – enhanced tubes can be produced in large coils, adding flexibility for downstream applications and installations. Likewise, flat goods are also produced in coil, optimizing Vipertex® for efficient stamping operations that produce a large number of parts.
- More homogeneous properties are present since Vipertex® tubes are annealed after the surface pattern is imparted.
- Scalability – our ability to produce large quantities of enhanced surface material rapidly gives Vipertex® an advantage in high-volume manufactured parts, as well as large scale projects, that can challenge capacity to produce enhanced surfaces in the conventional manner.
- Vipertex® tubes bend more gracefully, exhibiting less wrinkling than smooth tubes. This is a result of the complex surface pattern, allowing metal to flow in more directions during the bending process. The bent sections of Vipertex® tubes are stronger and present less restriction of the fluid flow within the tube. This presents an opportunity, in some cases, to reduce wall thickness and design a tighter bend radii.