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3rd Thermal and Fluids Engineering Conference (TFEC)

ISSN: 2379-1748

MODELING OF FROST GROWTH ON SURFACES WITH VARYING CONTACT ANGLE

Ellyn Harges
Auburn University, Auburn, AL 36830, USA

Lorenzo Cremaschi
Auburn University, Department of Mechanical Engineering, Auburn, AL 36830, USA

DOI: 10.1615/TFEC2018.efm.020908
pages 811-822


KEY WORDS: frost modeling, crystal growth, surface contact angle

Abstract

Frost decreases the heat transfer performance of outdoor evaporators during winter months by increasing thermal resistance and decreasing airflow passage through the fins. Several experimental and theoretical studies focused on understanding the major factors affecting frost growth and methods for limiting frost. A method of inhibiting frost growth is to coat the surfaces with hydrophilic, hydrophobic, or biphilic coatings. Researchers modeled frost growth for these coating types; however, most of the existing models depend on empirical correlations specific to the contact angle.

This paper presents a physics-based model for frost growth on a flat plate that accounts for varying surface contact angle. The contact angle primarily affects the very beginning of frost growth, and this model captures well the actual mechanisms of early frost growth. The model consists of three parts: droplet growth, crystal growth, and full growth phases. The droplet growth phase, often neglected in previous frosting models, is directly affected by contact angle so was observed to be key in the present work. The crystal growth phase is less directly affected by contact angle, though the contact angle was observed to play a role when determining how crystals grow from droplets with different sizes and shapes. Finally, the full growth phase is not affected by contact angle; the only variables dependent on it are initial frost density and thickness. This model was extensively validated against frost data with varying contact angle both from the literature as well as from a new data set presented in a companion paper.

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