Master of Science, Miami University, 2020, Mechanical and Manufacturing Engineering

In this study, air-side heat transfer enhancement via the introduction of hemispherical vortex generators (VGs) within a fin-and-tube heat exchanger was examined. A new technique for the deployment of hemispherical VGs utilizing the naturally-occurring condensation within the heat exchanger was employed. By using patterned surface wettability to collect condensate and encourage coalescence in predetermined locations, it was found that large frozen droplets can be formed in various configurations which can serve as VGs to enhance air-side heat transfer at airflow rates typical to domestic refrigeration (i.e. 1.0 to 2.0 m/s). These findings were then simulated numerically within ANSYS Fluent. Ten different configurations of VGs in channel flow were investigated using a fin spacing (5 FPI) typical to domestic refrigerator evaporators. Airflow of 1.0 to 2.0 m/s at 20°C was used for the flow through the channel where the walls and VGs were set to -9°C and the air-side heat transfer coefficient (h), pressure drop, and temperature changes were measured. Compared to a baseline configuration without VGs, h enhancements ranging from 14.0 – 75.9% were measured, with corresponding pressure drops ranging from 35.7 – 165.6%. The air-side temperature change within the test section ranged from 9.0 – 13.5°C between the inlet and outlet.

Committee: Andrew Sommers (Advisor); Ryan Clark (Committee Member); Edgar Caraballo (Committee Member); Carter Hamilton (Committee Member) Subjects: Mechanical Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering

This study investigates the effects of the micro-dimple texture on the friction and surface temperature performances of a ball-on-disk contact, operating under the speed and load ranges that cover typical gearing applications. Circular shaped micro-dimple arrays with different dimple center distances and dimple depths are implemented on the ball surface to quantify the impacts of these two parameters on the friction coefficient and the maximum ball surface temperature. In addition, the contacts of three surface texture combinations, namely micro-dimpled and polished ball surface versus polished disk surface, polished ball surface versus polished disk surface and ground ball surface versus ground disk surface, are compared to demonstrate any beneficial or detrimental effect of micro-dimples in heavily loaded high speed applications. This study adopts a thermal mixed EHL point contact model, whose capability and accuracy have been well demonstrated by comparing to the experimental measurements, to quantify the deterministic tribological behavior within the contact, allowing the exploration of the underlying mechanism that governs the role of micro-dimples in the elastohydrodynamic lubrication.

Committee: Sheng Li Ph.D. (Advisor); Ahsan Mian Ph.D. (Committee Member); Nikolai Priezjev Ph.D. (Committee Member) Subjects: Mechanical Engineering