Author: James Tancabel
Date: Friday, November 4th, 2022 at 1:00pm
Location: Martin Hall, Room EGR-4164B
Committee Members:
Professor Reinhard Radermacher, Chair/Advisor
Professor James Baeder, Dean’s Representative
Associate Professor Johan Larsson
Professor Jungho Kim,
Professor Jelena Srebric
Research Professor Vikrant Aute
Title of Paper: “MULTI-PHYSICS MODELING OF THERMAL-HYDRAULIC AND MECHANICAL PERFORMANCE, AIRFLOW MALDISTRIBUTION, AND DEHUMIDIFCATION FOR HIGH PERFORMANCE, REDUCED CHARGE AIR-TO-REFRIGERANT HEAT EXCHANGERS WITH SHAPE-OPTIMIZED TUBES”
Abstract:
Air-to-fluid Heat eXchangers (HX) are fundamental components of many systems we encounter in our daily lives, from Heating, Ventilation, Air-Conditioning and Refrigeration (HVAC&R) systems to electronics cooling, automotive, power plants, and aviation applications. The importance of HXs is evident in the level of investment devoted to HX innovation in recent years. While current state-of-the-art HXs have adequately addressed past challenges, ever-increasing energy demands and increasingly stringent global energy standards require novel tools and methodologies which can quickly and efficiently develop the next generation of high-performance HXs.
In recent years, advancements in computational tools and advanced manufacturing technologies have enabled engineers to consider small characteristic diameter HX tubes with novel shapes and topologies which were not feasible even a decade ago. These small diameter, shape-optimized tubes have been shown to perform the same job as existing HXs while offering significant and desirable improvements in performance metrics such as envelope volume, face area, weight, and refrigerant charge. However, the structural integrity of shape-optimized tubes was often guaranteed by utilizing conservative tube thicknesses to ensure equipment safety, prevent refrigerant leakages, and satisfy product qualification requirements, resulting in increased material consumption and manufacturer costs while reducing the likelihood of industry acceptance for the new technology.
Additionally, the actual HX operating conditions are often different from design conditions, resulting in significant performance degradations. For example, novel HX design is typically assumes uniform normal airflow on the HX face area even though HXs in HVAC&R applications rarely experience such flows, and compact HXs have been shown to experience water bridging under dehumidification conditions, which greatly impacts HX performance.
This research sheds light on the next generation of air-to-refrigerant HXs and aims to address several practical challenges to HX commercialization such as novelty, manufacturing, and operational challenges through the use of comprehensive multi-physics and multi-scale modeling. The novelty of this research is summarized as follows:
i. A new, comprehensive and experimentally validated air-to-refrigerant HX optimization framework with simultaneous thermal-hydraulic performance and mechanical strength considerations for novel, non-round, shape- and topology-optimized tubes capable of optimizing single and two-phase HX designs for any refrigerant choice and performance requirement with significant engineering time savings compared to conventional design practices. The framework was exercised for a wide range of applications, resulting in HXs which achieved greater than 20% improved performance, 20% reductions in size, and 25% reductions in refrigerant charge.
ii. Development of a fundamental understanding of performance degradation for HXs with shape- and topology-optimized tubes under typical HX installation configurations in practical applications such as inclined and A-type configurations. New modeling capabilities were integrated into existing HX modeling tools to accurately predict the airflow maldistribution profiles for HXs with shape- and topology-optimized tubes without the need for computationally-expensive CFD simulations.
iii. Development of a framework to model and understand the impact of moist air dehumidification on the performance of highly compact HX tube bundles which utilize generalized, non-round tubes. Correlations for Lewis number were developed to understand whether traditional HX dehumidification modeling assumptions remained valid for new HXs with generalized, non-round tube bundles. Such an understanding is critical to accurately and efficiently modeling HX performance under dehumidifying (i.e., wet-coil) conditions.