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Taking Heat Exchanger Design to the Next Level with High-Performance Geometry

Heat exchanger efficiency has long been held back by traditional modeling software and manufacturing processes not capable of producing advanced geometries. Read below to see how nTop Platform enables heat exchanger designs with optimized surface area and reduced weight as compared to their traditionally designed counterparts.

Ryan O'Hara
December 16, 2019

In our modern lives we are surrounded by devices that are intended to make our day to day experiences more productive and enjoyable. These devices can take many forms and are often composed of mechanical and electrical systems that require the regulation of temperature to perform their primary function. The technology associated with computers, televisions and smartphones enables our modern lifestyle. In these electronic devices, the heat associated with the processing of electricity must be mitigated for these devices to function. Mechanical systems associated with aircraft and automobile transportation also require the regulation and transfer of heat from the engines that power these systems.

Point being: Work creates heat and that heat must be transported away so that the modern devices we rely on are able to function. 

 

 Figure 1: Additively manufactured triply periodic minimal surface heatsinks for use in electronic applications.  Printed by Renishaw on an AM500Q

 

Types Of Heat Exchangers

There are many examples of heat exchangers that can be used to transport heat. These types are defined by the system requirement and the physical method in which they move heat away from critical areas. Conduction is the transfer of heat energy by direct contact, Convection is the movement of heat by actual motion of fluids and Radiation is the transfer of energy with the help of electromagnetic waves. For the purposes of this article, we will only consider heat exchangers that use conduction and convection.

 

Figure 2: There are three kinds of heat transfer: conduction, convection, and radiation

 

A heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device’s temperature at optimal levels.

 

Electronic Heat Dissipation – Conduction/Convection Heat Sink

Heat sinks are commonly found in electronic devices and their effectiveness is dominated by the surface area in contact with the cooling medium surrounding it. With today’s rising computational requirements designers are forced to maximize performance by maximizing the surface area of a heatsink in a given volume. This quickly becomes a geometry game and nTopology offers a competitive advantage to designers as we can leverage our advanced geometry kernel to provide complex surfaces with large amounts of surface area and very thin walls. 

Figure 3: nTopology can be used to enable design studies to identify the optimal geometry for an application.  In this example, a variety of TPMS structures: Gyroid, Schwarz-P, and Lidinoid structures with varying periodicity and thickness are demonstrated.

 

In this example, nTop Platform was used to define a volume that could be used to generatively design a heat sink that would maximize surface area while minimizing mass. This was implemented using an advanced geometry representation to mathematically and precisely control surfaces. In this case, Triply Periodic Minimal Surfaces (TPMS) were used, which have been shown to have an incredibly high strength to weight ratios for structural applications. When coupled with advanced manufacturing methods these structures offer unlimited possibilities that allow designers to create multifunctional structures with both high strength and heat dissipative properties.  

Gyroid = Sin(x)Cos(x)+Sin(y)Cos(z)+Sin(z)Cos(x)

For the purposes of this study, we chose to evaluate three classes of TPMS structures that are commonly referred to as Gyroids, Schwarz Primitives and Lidinoids. The key factor that makes these structures unique is that each of them is a linear combination of Sines and Cosines that combine to form a periodic waveform geometry in three-dimensional space. Just like a 2-D waveform, we can vary the amplitude and period of these equations to generatively design multitudes of design possibilities. By coupling these design inputs with a Design of Experiments (DOE) approach we can accurately evaluate the performance of these components.

A passive electronic heatsink is dominated by all three modes of heat transfer methods.  Heat must be conducted from the heat source (ie computer chip) to the base of the heatsink and is then dissipated from the heatsink via convection (70%) and radiation (30%).  To maximize the heat dissipation of a heat sink it is necessary to maximize the amount of ambient air that is in contact with the heatsink.

 

Figure 4: nTopology Platform workflow for passive heat sink design and evaluation

As heat is dissipated, convection will naturally induce the flow of air over the fins of the heatsink. The gyrating fins of a TPMS heatsink allow for enhanced boundary layer mixing that has the potential to provide a higher effective surface area than traditional heatsink designs. As part of this work, a simple numerical study was performed to identify the highest performing TPMS heat sink whose design inputs maximize surface area and minimize the mass of the resultant heat sink.  This experiment was enabled through the use of our computational geometry kernel coupled with advanced analytical methods that allow a designer to quickly make geometry changes and evaluate the performance outputs of the design inputs. From the image below it becomes quite clear which design meets has the highest surface area to mass from the designs that were explored.

 

Figure 5: Heatsink Performance chart identifying optimal heat sink design that maximizes surface area while minimizing mass.

 

Conclusion

This is part one of blog series taking you through the entire design and build of several heat exchangers. Our next blog in this series will go over the actual workflow used by our engineers to design and analyze a fuel cooled oil cooler. Stay tuned to learn more about how computational modeling can be used to maximize heat exchanger performance; it will surely be an epic journey! If you’d like to learn more click here to request a demo or trial. 

Written by
Dr. Ryan O’Hara is the Technical Director for Aerospace and Defense for nTopology. He brings 20 years of military service and experience as a Developmental Engineer to the nTopology team. Ryan has served all over the world leading engineers that have enabled incredible advanced material and engineering solutions through the use of composites and additive manufacturing. Most recently, he served as a Professor at the US Air Force Institute of Technology where he led over $5M in academic research programs while standing up one of the first metal additive manufacturing labs in the US Air Force.

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