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TECHNICAL BRIEFS

Frost-Air Interface Characterization Under Natural Convection

[+] Author and Article Information
Y. L. Hao1

Department of Mechanical and Materials Engineering,  Florida International University, Miami, FL 33174

J. Iragorry

Department of Mechanical and Materials Engineering,  Florida International University, Miami, FL 33174

Y.-X. Tao

Department of Mechanical and Materials Engineering,  Florida International University, Miami, FL 33174taoy@fiu.edu

1

Present address: Southeast University, Nanjing, 210096, People’s Republic of China.

J. Heat Transfer 127(10), 1174-1180 (Apr 05, 2005) (7 pages) doi:10.1115/1.2033901 History: Received March 16, 2004; Revised April 05, 2005

Surface frosting from atmospheric humidity under natural convection is encountered in conventional refrigeration systems, cryogenic surgery, and cryogenic stress relief of die casting metal forming applications. To advance the predictability of frost initiation and formation processes, this study reports a microscopic analysis of frost growth on a flat surface during the onset period of freezing when subcooled droplets are formed and changed to the ice phase. The onset of freezing is quantified by the mean droplet size and ice particle fractions at a critical time (when water droplet freezing point is reached) with the aid of a video microscope. An early-stage frost formation model with effective parameters is demonstrated to provide the important information for the transition to the steady-growth model. The model results are compared with the measured air-frost surface temperatures at different cooling and ambient boundary conditions, using holographic interferometry. The comparison between the model prediction and experimental results demonstrates the sensitivity of effective parameters in simulating the frost thickness and air-frost interface temperature.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematics of (a) the model for the initial conditions for the solidification and tip-growth (STG) period, (b) the microscopic video system characterizing microdroplets/particles and the test section, and (c) the holographic interferometry system

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Figure 2

(a) Critical time and (b) temperature under different conditions, and (c) droplet diameter and site-length scale for nucleation sites and ice fraction at the critical time

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Figure 3

Typical holographic image: dry surface—(a) holographic interferometry fringes and (b) temperature profile in the thermal boundary layer. Ta=23°C, RHa=61%, Tw=−18°C, t=60min

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Figure 4

(a) Variation of temperature difference between air-frost interface and cold surface with time, (b) variation of thickness of frost layer with time, and (c) comparison of the simulation and experiment results of the temperature difference between ambient and air-frost interface: dry surface, ⟨Ta⟩=23.2°C, ⟨RHa⟩=56%, ⟨Tw⟩=−32.8°C

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Figure 5

Time variations of (a) air-frost interface temperature, (b) frost layer thickness, (c) temperature difference between air-frost interface and cold plate surface, (d) temperature difference between the ambient and air-frost interface, (e) heat flux through frost layer, and (f) bulk effective thermal conductivity of frost for two different cold plate temperatures: ⟨Ta⟩=23°C, ⟨RHa⟩=61%

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Figure 6

(a) Time variations of convection coefficient for the two different cold plate temperatures: ⟨Ta⟩=23°C, ⟨RHa⟩=61%, (b) correlation of Nusselt number and Rayleigh number

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