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Research Papers: Two-Phase Flow and Heat Transfer

Accelerated Cryogenic Cooling Caused by the Temporary Frost Layer Enhancer

[+] Author and Article Information
Gedalya Mazor, Alon Alfi, Andrei Rabin, Elad Yehud

Department of Mechanical Engineering,
SCE—Shamoon College of Engineering,
Beer-Sheva 84100, Israel

Izhak Ladizhensky, Eli Korin

Department of Chemical Engineering,
Ben-Gurion University of the Negev,
Beer-Sheva 84105, Israel

Dmitry Nemirovsky

Department of Physics,
SCE—Shamoon College of Engineering,
Beer-Sheva 84100, Israel
e-mail: demitryn@sce.ac.il

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received November 21, 2015; final manuscript received September 26, 2016; published online November 8, 2016. Assoc. Editor: Ali Khounsary.

J. Heat Transfer 139(2), 022901 (Nov 08, 2016) (7 pages) Paper No: HT-15-1744; doi: 10.1115/1.4034899 History: Received November 21, 2015; Revised September 26, 2016

The possibility of using a frost layer, created on the surface of a sample that undergoes cryogenic treatment, as a heat transfer enhancer was recently studied. This layer grows on the preliminary cooled sample surface as a result of its contact with moist air flow prior to its immersion into liquid nitrogen. A significant increase in the outflow heat flux (up to 12.8 times), or, alternatively, a cooling time shortening, in comparison with the bare sample was found. A detailed description of the frost layer development along with the influence of the thickness of the layer on the efficiency of the cooling process, as well as environmental parameters that affect the thickness itself is presented in the paper.

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Figures

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Fig. 1

Heat flux density and surface temperature of the bare (uncoated) sample as a function of time [1]

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Fig. 2

Three stages of cryogenic treatment: (I) preliminary cooling of the sample inside the Dewar prior to the frost layer growth. (II) Frost layer growth in the flow of moist air. (III) Completion of the treatment inside the liquid nitrogen. The data were acquired for the initial surface temperature of 28.5 °C and the frost growth period of 3 min. The sample was exposed to the moisture in the air (VA = 0.5 ms−1, RH = 85%) after cooling, until TS = −20 °C.

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Fig. 3

The experimental system

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Fig. 4

Threadlike crystallites grown on the sample surface during the beginning of the frost layer formation stage (7× magnification). An average crystallite height is 0.04 mm and the average surface density is 1400 mm−2. The measurement took place at TS = −300 °C, VA = 1 ms−1, TA = 25.5 °C, RH = 60%, texp = 30 s.

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Fig. 5

Sample surface temperature change, ΔT, as a function of the frost layer growth time for different TS. The measurements were made at RH = 45%, VA = 0.5 ms−1, TA = 25 °C.

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Fig. 6

Highest thickness of the frost layer, δmax, as a functionof layer growth time, texp, for VA = 1 ms−1, RH = 60%, TA = 22.8 °C, and TS = −300 °C

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Fig. 7

(a) Highest layer thickness reaching time, tδmax, as function of the initial surface temperature, TS, for different air velocities (RH = 60%, TA = 25 °C). (b) Frost layer thickness, δ, as a function of initial surface temperature at t = 90 s, TA = 24 °C, RH = 60%, and VA = 1 ms−1. (c) Frost layer thickness, δ, as a function of moist air velocity at texp = 90 s, TA = 24 °C, RH = 60%, and TS = −30 °C. (d) Frost layer thickness, d, as a function of air humidity at TA = 24 °C, TS = −30 °C, VA = 1 ms−1 at three different frost creation times, 60, 90, and 120 s.

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Fig. 8

(a) Sample surface temperature as a function of time for different frost layer creation times and different δmax for RH = 72%, VA = 1.0 ms−1, TS = −30 °C, and TA = 23 °C. (b) Sample surface temperature as a function of time for different initial surface temperatures TS, for RH = 72%, VA = 1.0 ms−1, texp = 120 s, and TA = 23 °C.

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Fig. 9

Heat flux density as a function of temperature excess for: (a) uncoated copper ball of 30 mm diameter (quenching in liquid nitrogen), (b) frost covered copper ball of 30 mm diameter (quenching in liquid nitrogen, ε = 12.8), and (c) water quenched copper ball of 25.4 mm diameter [25]

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Fig. 10

Heat flows (denoted by black arrows) from the sample surface are transferred to the surrounded liquid by different channels: (A) film boiling near the sample surface, (B) transition and nucleate boiling along the fin, and (C) natural convection on the top of the fin

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Fig. 11

Efficiency of heat transfer as a function of frost layer thickness for different experimental conditions. The line shows only the trend in the data.

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