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SPECIAL SECTION ON CFD METHODS

A Numerical Model for the Mist Dynamics and Heat Transfer at Various Ambient Pressures

[+] Author and Article Information
Roy J. Issa

Department of Mathematics, Physical Sciences and Engineering, Mechanical Engineering Division, West Texas A&M University, Canyon, TXrissa@mail.wtamu.edu

S. C. Yao

Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PAsy0d@andrew.cmu.edu

J. Fluids Eng 127(4), 631-639 (Apr 09, 2005) (9 pages) doi:10.1115/1.1976743 History: Received August 23, 2004; Revised April 09, 2005

A numerical model is developed to simulate the dynamics of the droplet-wall interaction and heat transfer mechanisms at sub-atmospheric to elevated ambient pressures, and for surface temperatures ranging from nucleate to film boiling. This is the first time a general model is developed to study these phenomena over a wide range of ambient pressures. The model provides insight to the optimal flow conditions, and droplet size distribution for best heat transfer enhancement. Simulations are provided for single stream droplet impactions, and for full conical sprays using nozzles that dispense a spectrum of non-uniform droplets. The model simulation was compared against available test data for single stream of droplets at non-atmospheric conditions, and the simulation compared favorably well with the test data.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Droplet coefficient of restitution as function of Wen at about Leidenfrost temperature (1 atm) (15)

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Figure 2

Water droplet maximum spread versus wall temperature (Adapted from Chandra and Avedisian (20))

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Figure 3

Basic mechanisms for spray heat transfer (22)

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Figure 4

Droplet contact heat transfer effectiveness in the transition to film boiling region (at 1 atm) (15)

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Figure 5

Effect of pressure on water enthalpy of vaporization and specific heat constant

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Figure 6

Variation in the Leidenfrost temperature with ambient pressure

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Figure 7

Minimum heat flux as function of ambient pressure

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Figure 8

Variation in the temperature at the critical heat flux with ambient pressure

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Figure 9

Critical heat flux as function of ambient pressure

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Figure 10

Comparison in droplet contact heat transfer effectiveness between 1 and 0.1 atm ambient pressures

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Figure 11

Comparison in droplet contact heat transfer effectiveness between 1 and 50 atm ambient pressures

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Figure 12

Model boundary conditions (shown here for the case of full spray injection)

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Figure 13

Droplet-wall interaction using multiple streams of droplets at 0.5 atm ambient pressure

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Figure 14

Droplet-wall interaction using multiple streams of droplets at 1 atm ambient pressure

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Figure 15

Droplet-wall interaction using multiple streams of droplets at 5 atm ambient pressure

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Figure 16

Comparison between the total heat flux at various ambient pressures

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Figure 17

Total heat flux and droplet contact heat transfer effectiveness at 2kg∕m2s for various ambient pressures

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Figure 18

Droplet sub-cooling versus ambient pressure

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Figure 19

Mist spray pattern at 0.5 atm ambient pressure (Avg.d=19.2μm by volume)

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Figure 20

Mist spray pattern at 1 atm ambient pressure (Avg.d=19.2μm by volume)

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Figure 21

Mist spray pattern at 10 atm ambient pressure (Avg.d=19.2μm by volume)

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Figure 22

Droplet count distribution based on the experiment by Sozbir and Yao (2)

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Figure 23

Mist spray heat transfer coefficient profile versus ambient pressure using the same droplet size spectrum

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Figure 24

Mist spray heat transfer coefficient versus ambient pressure using different droplet size spectrum

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Figure 25

Mist spray pattern at 0.5 atm ambient pressure (Avg.d=7.6μm by volume)

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Figure 26

Mist spray pattern at 10 atm ambient pressure (Avg.d=60μm by volume)

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