Leave it to a topology optimization program to make the most marvelously efficient heat exchangers.
Bradley Rothenberg, a wunderkind in computational design and leader of nTop, has seized upon heat exchangers as a perfect use case for his company’s software – and he may be right. At least in part. Other types of designs can benefit from the optimization of irregular geometry, of course. Still, as a business, he is wise to take advantage of a clear and impending need in heat exchanger design.
nTop is particularly well suited for designing heat exchangers due to its ability to handle complex geometries and optimize them for performance. Traditional CAD tools, according to Rothenberg, are limited to regular shapes, those that are repeatable, composed of primitive shapes and neatly arranged in an array of pins and fins, the guts of a heat exchanger. They can make vast amounts of these, hundreds of thousands of pins and fins, all neatly arranged, to transfer heat from one fluid to another while minimizing pressure drops. SolidWorks, for example, can create this type of geometry ad infinitum. But is it optimal for heat exchange?
Fluid and heat transfer experts say not
Turbulent is Good for Heat Exchange
Fluid flow through paths around regular geometry can become laminar, which is less than turbulent flow. Turbulent flow is better than laminar flow for heat exchangers because it enhances the rate of heat transfer. In turbulent flow, fluid particles move in chaotic, irregular patterns, which increases mixing across the fluid layers. This disrupts the formation of a thermal boundary layer near the surface of the heat exchanger, allowing heat to be transferred more efficiently from the hot surface to the cooler fluid or vice versa. In contrast, laminar flow has smooth, orderly layers of fluid, resulting in slower mixing and less efficient heat transfer. Therefore, turbulent flow helps achieve a higher heat transfer coefficient, making it more desirable for heat exchangers.
Creating Irregular Geometry with CAD Programs. Good Luck with That.
In this niche of heat exchanger design, NTop stands alone. The lot of topology optimization programs are sold on their ability to perfect every type of design but fail to perfect any. Watch a topology optimization program on a bridge or a bike, for example, is a laughable and futile exercise supreme. That optimization may have been nearly achieved by. However, for irregular geometry, computational design is the best hope for optimization.
Why? The ultimate heat exchanger depends on irregular geometry, something CAD programs are woefully inadequate at.
How Does It Work?
NToP addresses these challenges by allowing engineers to capture the essential parameters of a design, such as the number of tubes, their arrangement, and other features, within a parametric model. The software’s use of implicit modeling (more on that later) means that once these relationships are defined, changes can be made rapidly. For example, if an engineer wants to explore the performance of a heat exchanger with 10,000 tubes versus 20,000, they can change a parameter, and the model will update instantly. This eliminates the need to manually redraw the geometry with each iteration manually, dramatically speeding up the design process.
How to Tell? Simulation.
One of the critical advantages of NToP is its integration with simulation tools, which allows for real-time evaluation of each design's performance. In the case of heat exchangers, engineers can run simulations to measure how effectively the design transfers heat between fluids and whether the pressure drop across the system is within acceptable limits. With each change in the design, these simulations can be rerun, providing immediate feedback. This tight coupling between design and analysis ensures that engineers can make informed decisions quickly and optimize their heat exchanger designs far more efficiently than they could with traditional tools.
Moreover, Rothenberg highlights the flexibility of NToP’s parametric models. Instead of creating a single version of a design, NToP allows engineers to capture all possible variations of a heat exchanger in one model. This makes it possible to conduct extensive design studies to find the optimal solution based on performance criteria such as heat transfer efficiency and pressure drop.
Making Changes
The parametric nature of NToP means that even highly complex designs, such as those involving thousands of tubes weaving through each other, can be managed with relative ease. The software’s ability to automatically adjust and update designs based on new inputs makes it particularly valuable for industries that require high-performance heat exchangers, such as aerospace and energy.
Finally, Rothenberg points out that NToP’s core technology, which is based on signed distance fields, allows it to store very complex models in a highly compact form. A traditional CAD model of a heat exchanger might take up gigabytes of storage, whereas the same model in NToP could be just a few megabytes. This not only makes the software faster and more efficient but also enables engineers to handle larger, more complex models without the performance issues they would encounter with traditional tools.
Why Can’t I Use CAD Again?
Everyday design tools (CAD or computer-aided design) are not particularly useful for creating the most efficient heat exchangers because they focus on regular geometric design rather than performance optimization. CAD tools excel in defining the physical structure and layout of components but need to be coupled with fluid dynamics and heat transfer simulation, both of which are crucial for heat exchanger efficiency.
Heat exchanger design requires an understanding of how fluids interact with surfaces under different flow conditions, such as turbulence, and how these interactions affect heat transfer rates. This involves solving complex equations related to thermodynamics, fluid mechanics, and material properties areas where plain old design tools could be more helpful.
While CAD can model the physical shape of a heat exchanger, it needs to account for the intricacies of flow patterns, pressure drops, and heat transfer coefficients that determine its performance. For optimal efficiency, engineers often rely on simulation tools like computational fluid dynamics (CFD) to analyze and optimize fluid flow and heat transfer. These tools can predict how changes in geometry or operating conditions will impact performance, something CAD is not built to do.
Moreover, designing efficient heat exchangers often involves multi-objective optimization—balancing factors like cost, weight, and thermal performance—an area that CAD, once again, is not built to do. Therefore, advanced tools like nTop with built-in simulation and optimization algorithms are more suitable for achieving the best design outcomes.
How to Manufacture the Irregular Shapes in an Optimized Heat Exchanger
Conventional subtractive manufacturing tools, like CAM (computer-aided manufacturing) and CNC (computer numerical control), may not be suitable for producing optimum heat exchangers because they are limited in their ability to create complex geometries that are often required for maximum efficiency. Subtractive manufacturing involves removing material from a solid block, which restricts the shapes that can be produced to relatively simple and accessible forms, such as straight channels or smooth curves.
The most efficient heat exchangers often require intricate designs that maximize surface area and promote turbulence, such as complex, intertwined channels or porous structures that optimize fluid flow and heat transfer. These designs may include geometries that are difficult, if not impossible, to achieve with traditional subtractive techniques due to the limitations of tooling and machining accessibility. Even with a 5-axis CNC machine that can cut to millimeter accuracy, it may not be able to reach internal geometry.
Additionally, subtractive manufacturing methods tend to generate material waste and may involve costly processes to produce parts with high precision. This contrasts with additive manufacturing techniques, like 3D printing, which can build complex, optimized designs layer by layer with minimal waste and greater flexibility. The additive processes allow for the creation of more organic, non-linear forms that are ideal for enhancing thermal performance.
Enter 3D Printing
3D printing, or additive manufacturing, is well suited for producing optimized heat exchangers due to its ability to create complex geometries that traditional subtractive methods, like CAM and CNC, cannot easily achieve. With 3D printing, intricate and highly efficient designs can be fabricated layer by layer, allowing for the production of structures with enhanced surface area, optimized flow paths, and minimal material waste.
One of the key advantages of 3D printing for heat exchangers is its capacity to fabricate internal channels and lattice structures that promote turbulence, enhancing heat transfer. In a heat exchanger, efficient heat transfer often requires complex geometries like twisted or braided channels, thin walls, and irregular surfaces, which help to disrupt laminar flow and improve the mixing of fluids. These designs can be nearly impossible to achieve with traditional subtractive techniques, but 3D printing allows for the direct creation of such features without the need for assembly or post-processing.
Moreover, 3D printing enables rapid prototyping and iteration, which allows engineers to test and refine heat exchanger designs for maximum efficiency quickly. This flexibility, combined with the ability to create intricate, performance-boosting geometries, makes 3D printing a superior choice for manufacturing optimized heat exchangers.
What is Implicit Modeling?
nTop’s implicit modeling is a design approach that uses mathematical equations, rather than traditional boundary representations, to define complex geometries. This method is particularly powerful in creating optimized, high-performance structures, such as those needed in industries like aerospace, automotive, and medical devices. Implicit modeling represents geometry as continuous, smooth functions, which allow for seamless transitions between different design features and intricate, organic shapes that would be difficult to achieve with conventional CAD tools.
One of the key advantages of implicit modeling is its scalability in handling complex geometries, such as lattices, porous structures, and topology-optimized designs. Unlike traditional solid or surface modeling in CAD, which relies on discrete edges and faces, implicit modeling can represent highly detailed and intricate designs without becoming overly complicated or heavy in terms of data. This makes it ideal for tasks like designing heat exchangers, where maximizing surface area and optimizing flow paths are essential for performance.
Another benefit of implicit modeling is that it can be easily modified by changing parameters within the equations, allowing for rapid design iterations. This flexibility makes nTop’s implicit modeling particularly useful for advanced manufacturing techniques, such as 3D printing, where complex, optimized geometries can be efficiently realized.
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