Date of Award
2020
Document Type
Thesis
Degree Name
Master of Science in Engineering (MSE)
Department
Mechanical and Aerospace Engineering
Committee Chair
D. Keith Hollingsworth
Committee Member
Sarma L. Rani
Committee Member
Guangsheng Zhang
Subject(s)
Bubbles--Thermodynamics., Heat--Transmission--Mathematics.
Abstract
A numerical study of the effect of Prandtl number on the heat transfer in the wake of a highly confined bubble in a large-aspect-ratio minichannel was performed. The channel height was 1.25 mm, and the precursor liquid flow was laminar at channel Reynolds numbers of 169 and 338. The upper channel was modeled as an electrically heated metal foil, and the lower wall was adiabatic. The simulation was performed using ANSYS Fluent, with the volume-of-fluid method was used to determine the phase boundary. A Lagrangian reference frame translating at the average bubble velocity was used to simulate a channel of arbitrary length. The resulting numerical domain was 30 mm in the streamwise direction and 20 mm in the spanwise direction. This study adds a data set at Prandtl number of 6 to the results obtained by a previous study in which the numerical model was built, qualified, and executed for Prandtl numbers of 12 and 1. An investigation of the near-field of the bubble rear wake was performed using the expanded data set. A new Nusselt number correlation for the near-field heat transfer was proposed. A graphical examination of the velocity components and fluid temperature in the near-field region was performed to document evidence of dynamical structures near the bubble. The velocity components at specific locations supported the presence of dynamical structures which may operate to enhance the heat transfer rate. The material properties of the heated upper channel wall were altered to examine the effect of the thermal boundary condition imposed by the foil on the heat transfer in the bubble wake. Both the specific heat and thermal conductivity of the foil were reduced by a factor of three. The evolution of the wall-to-bulk temperature difference and the local wall heat flux were substantially changed. The resulting Nusselt number was largely unchanged at Prandtl number of 12, but was increased at Prandtl number of 6.
Recommended Citation
Amai, Joseah K., "The effect of Prandtl number on heat transfer in the wake of a highly confined bubble in a large-aspect-ratio minichannel" (2020). Theses. 334.
https://louis.uah.edu/uah-theses/334