Murat Dinc

Date of Graduation

2015

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Donald D Gray

Committee Co-Chair

Leslie Hopkinson

Committee Member

Wade W Huebsch

Committee Member

John M Kuhlman

Committee Member

Lian-Shin Lin

Abstract

Spray cooling is a key technology in the thermal management of the next generation electronic, aircraft and spacecraft systems. There have been relatively fewer computational studies of spray cooling because simulating all the detailed physics and dynamics of a spray consisting of millions of drops per second is computationally very expensive.;In this study, computational approaches have been used to analyze single drops and sprays for spray cooling applications. The commercially available Computational Fluid Dynamics (CFD) code ANSYS Fluent (versions 14, 14.5, 15) has been used to perform single drop and spray simulations on two desktop workstations and the High Performance Computing (HPC) cluster at West Virginia University (WVU).;Single drop impingement on wet surfaces has been studied using the 2D axisymmetric Volume of Fluid (VOF) model in ANSYS Fluent 14 and 14.5. The free surface shape and hydrodynamics of single drops after they impact on wet surfaces have been validated with the experiments performed by members of the WVU Spray Cooling team in the Mechanical and Aerospace Engineering Department (MAE) at WVU. Initial film thickness, initial drop diameter, initial drop shape and gravity effects have been investigated for water at room temperature. It has been concluded that gravity has significant effects on the drop and film dynamics while drop shape does not have any significant effects.;The 2D axisymmetric Discrete Phase Model (DPM) with the wall film submodel in ANSYS Fluent 14 has been used to perform simulations of spray impact on flat surfaces. The effects of the nozzle-to-surface distance, spray half angle, spray coolant, spray mass flow rate and gravity on spray variables (e.g. average drop diameters, drop velocities, etc.) have been analyzed for a full cone spray based on the Spraying System 1/8 G nozzle operating at 40 psi which has been used in the spray experiments performed by members of the WVU Spray Cooling team.;Full cone 40 psi water spray cooling simulations with phase change have been performed in 3D coordinates using the DPM, Eulerian Wall Film (EWF) and the Species Transport Model (STM) in ANSYS Fluent 15. The free surface shape and hydrodynamics of the film have been analyzed. The film thickness results have been compared with experiments. The effects of the surface temperature, spray temperature and air temperature on the film characteristics (e.g. film thickness, film velocity magnitude) and heat transfer (e.g. surface heat flux) have been studied. It has been concluded that air temperature does not have a significant effect on the film characteristics and heat transfer whereas spray temperature has significant effects. Increasing the spray temperature 50 K (from 300 K to 350 K) causes a 62% decrease in the surface heat flux.;Full cone 40 psi water spray cooling simulations have been also performed in 2D axisymmetric coordinates using the Eulerian Multiphase (EM) model in ANSYS Fluent. The computed average surface heat flux value was 8% different compared to the 3D DPM-EWF-STM model. However, there has been a large discrepancy in the film characteristics between these two models and also between the EM model and experiments. In conclusion, the 3D DPM-EWF-STM model is the preferred method in order to analyze spray cooling at the present time.

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