Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Controlling the area expansion of a backwards centrifugal fan blade passage using the principles of a diffuser and computational fluid dynamics(Montana State University - Bozeman, College of Engineering, 2021) Michalson, Adam Jeffrey; Chairperson, Graduate Committee: Erick JohnsonCentrifugal Fans are widespread in today's modern built environment. While a few variations of these fans exist, backward centrifugal fans are an efficient economical option capable of producing the pressure and airflow required for many modern building systems. Even though fans have become necessary piece of building engineering to facilitate occupant health and comfort, fan design almost exclusively relies on approximations to equations that have not changed since the 1950s and can consume, on average, 15% of a building's electrical consumption. Additionally, the approximations made support the ease and low cost of manufacturability. The traditional centrifugal fan design is made from stamped metal parts creating a fan blade sandwich with the blades held between an inlet shroud and a backplate. This rectangular blade passage is where the fluid flows through and picks up tangential acceleration. However, since the 1950s, nearly all advancements in fan design have been through incremental changes that are made by individual companies, and these resulting designs and performance data remain proprietary. This research revisits the foundations of centrifugal fan design with more modern tools and utilizes the concept of the diffuser to strictly control the expansion of the blade passage to improve centrifugal fan efficiency. Computational fluid dynamics was used to evaluate the performance of the new design against a traditionally manufactured fan. Combining the diffuser concept with an elliptical profile for the blade passage better controls the uniformity of the velocity field and pressure gradients through the passageway, while also reducing turbulence. Simulations of the new design against the traditional approach to fan design show an increase of nearly 10% in total efficiency.Item The design and testing of an axial condenser fan(Montana State University - Bozeman, College of Engineering, 2021) Kirk, David Michael; Chairperson, Graduate Committee: Kevin AmendeAxial or propeller fans are a subset of turbomachinery whose application is prevalent in everyday life. In the case of heating, ventilation, air conditioning, and refrigeration (HVAC&R), fans can be a large source of inefficient energy consumption due to their physical operating nature. With the global push for more efficient systems, components of HVAC&R equipment such as fans have become a focal point for researchers in academia and industry alike. Technological improvements in research equipment such as computational fluid dynamics (CFD) and additive manufacturing play a large role in achieving these improved efficiencies. The goal of this research is to improve the efficiency of an axial fan intended for cooling a micro-channel heat exchanger that is used in rooftop condenser units. A higher efficiency retrofit fan was iteratively designed using a commercial CFD software package, Star CCM+, which constitutes much of the research conducted in this project. The iterative models show that significant efficiency gains can be achieved through incremental alterations of classical fan blade geometry elements such as pitch, camber, skew, cross section loft path, chord length, thickness, etc. A physical model of the fan design thought to be the optimal choice for experimental analysis was 3D printed and tested using an AMCA Standard 210 setup. Upon analysis of the physical test results, several discrepancies between simulated and actual results were discovered, highlighting the importance of CFD model validation in the design process. Despite the efficiency gains and advancements in user-friendly packaged software, the simulation underpredicted the power demand and incorrectly depicted the fan's performance at critical operating points showing that improper usage of these experts' tools can inadvertently lead to developed solutions with significant error. While the designed fan achieves an improved peak static efficiency and volumetric flow rate of 53.9% and 4334 CFM respectively, it ultimately did not meet the operating parameters of the specific unit it was designed for and further improvements to the CFD model are needed.Item Characterization of airflow through an air handling unit using computational fluid dynamics(Montana State University - Bozeman, College of Engineering, 2015) Byl, Andrew Evan; Chairperson, Graduate Committee: Erick JohnsonHVAC equipment manufacturers spend a considerable amount of time and effort updating existing product lines in order to meet the ever-increasing demand for energy efficient systems. As a major part of HVAC systems, an air handling unit (AHU) controls the airflow through the system and regulates the indoor air quality. Plenum fans used in AHUs inherently produce a rotational airflow, which can create highly unstructured airflow as it enters a heat exchanger located downstream. This in turn leads to lower heat transfer rates and premature heat exchanger failure. As such, airflow uniformity is presently regarded as an important consideration in designing these systems. Through advancements in computer technologies within the last decade, computational fluid dynamics (CFD) has become an economical solution allowing HVAC equipment designers to numerically model prototypes and reduce the time required to optimize a given design and identify potential failure points. While CFD analysis also offers the ability to visualize and characterize the airflow through an AHU system, it has often been used to model individual components such as fans or heat exchangers without analyzing them as a single unit. This work presents the CFD models used to characterize the airflow within an AHU in order to aid in understanding the effects that flow uniformity has on heat exchanger performance. The airflow uniformity was analyzed over a range of volumetric flow rates, and experiments were used to validate the baseline simulations. Different baffle designs were then added into the validated simulations to observe their influence on both airflow uniformity and heat transfer performance. Results indicate that airflow uniformity is, by itself, an insufficient metric to predict heat transfer performance. Additionally, steady-state CFD analyses performed on simplified geometries are shown to provide a sufficient model to be used for further optimization, when the inlet conditions are well specified.