Advancing Heat Exchangers: A Look at STBE’s Best Paper of the Year
From eSociety, August 2018
Four researchers associated with the University of Maryland’s Center for Environmental Energy Engineering won the best paper award for Science and Technology for the Built Environment for 2017.
Daniel Bacellar, Ph.D.; Vikrant Aute, Ph.D., Member ASHRAE; Zhiwei Huang, Ph.D; and Reinhard Radermacher, Ph.D., Fellow/Life Member ASHRAE and editor of STBE, won for their paper, “Design Optimization and Validation of High Performance Heat Exchangers using Approximation Assisted Optimization and Additive Manufacturing.”
In 2017, STBE published 107 manuscripts. Of those articles, this paper was deemed the best by a panel of judges from the STBE editorial board, the ASHRAE publications office and STBE publisher, Taylor & Francis. 2017-2018 ASHRAE President Bjarne Olsen, Ph.D., presented the award during the ASHRAE Annual Conference in Houston in June.
Aute, one of the paper’s researchers who also serves on ASHRAE’s Conferences and Expositions Committee, discusses the significance of the paper’s research and why he thinks it was named best paper of the year.
1. What is the significance of this research?
Heat exchangers are a key component in HVAC&R systems, and each of these systems has at least two heat exchangers.
Specifically, air-to-refrigerant heat exchangers are required in all HVAC&R devices that cool or heat air, either for space conditioning or for refrigeration. These heat exchangers have a direct impact on the energy consumption of these systems.
This current research shows novel heat exchanger designs that are at least 20% lighter, 20% smaller and 20% more efficient compared to current state of the art.
Furthermore, these heat exchangers also have reduced volume resulting in reduced refrigerant use, thereby curbing GHG emissions.
2. Why is it important to explore this topic now?
The topic of novel heat exchangers and heat transfer surfaces has always been important, since they are a fundamental component in all energy transfer and conversion systems.
Our Center (the Center for Environmental Energy Engineering at University of Maryland) has been pursuing the next generation heat exchangers research for more than a decade now.
In the context of this research, the recent developments in computing technologies and additive manufacturing made it possible to actually build and test a novel heat exchanger design,which was not possible five or ten years ago.
3. What lessons, facts and/or guidance can an engineer working in the field take away from this research?
Small hydraulic diameter flow channels are the future of air-to-refrigerant heat exchangers. In addition, the conventional round or rectangular shapes are not insufficient to achieve next-gen performance and we need to explore shape-optimized tubes.
With these small flow channels and design optimization:
A. A significant benefit in compactness (heat transfer area per unit external volume) and material utilization (heat transfer area per unit material volume) is achieved, compared to traditional heat exchanger geometries.
B. There is potential to have all primary heat transfer area and thereby eliminate fins, resulting in significant material savings.
C. The impact of material thermal resistance on the performance of these heat exchangers is greatly reduced, which opens up possibilities to use other materials such as plastics, which are lightweight and potentially cheaper.
4. How can this research further the industry's knowledge on this topic?
One of the main findings of this research is that the industry really needs to explore shape-optimized-small-hydraulic-diameter flow channels for air-to-refrigerant heat exchangers if we want to achieve next level of performance.
More concretely, new equations for evaluating air-side heat transfer and pressure drop have been developed. Engineers/researchers can use these equations to design heat exchangers based on the novel geometries invented in this research.
Since the publication of this research, our team has been investigating low cost manufacturing techniques to facilitate mass production of these novel heat exchangers.
5. Were there any surprises or unforeseen challenges for you when preparing this research?
Our biggest challenges were related to manufacturing of prototypes. We went through numerous trials and even with the best expertise in the industry, some of the optimal heat exchanger designs could not be prototyped using conventional manufacturing techniques. The most promising designs were pushing the boundaries of additive manufacturing.
Another challenge, though not unforeseen, in pursuing such research is the computational effort required in optimizing the novel designs. Some of the creative solutions developed by the team allow us to “invent” new heat exchangers in a matter of weeks instead of months or years.
6. Why do you think this paper was named best paper?
The paper highlights the complete and systematic workflow from the conceptualization stage all the way to prototype fabrication and testing of a newly invented heat exchanger. The research presented in this paper shows promising novel heat exchangers that present a significant performance improvement for air-to-refrigerant heat exchangers in more than two decades.
7. What differentiates this research from other research on this topic?
The research presented here uses mathematically rigorous optimization techniques to systematically “invent” new air-to-refrigerant heat exchangers for a given application. Through laboratory testing of a prototype, we show that the approach actually works and has the potential to change the way heat exchangers are designed in the future. This opens up the possibility of custom designing heat exchangers for each system, there by optimizing the system, instead of using the same geometry across the board.
Having said this, we have lot more to do in order to mass produce these novel heat exchangers and bring them to the market.
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