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Research Papers

Numerical Simulation of Saturated Flow Boiling Heat Transfer of Ammonia/Water Mixture in Bubble Pumps for Absorption–Diffusion Refrigerators

[+] Author and Article Information
Soo W. Jo

e-mail: soowjo@gmail.com

W. E. Lear

Department of Mechanical and
Aerospace Engineering,
University of Florida,
MAE-A Building: 231 MAE-A Building,
P.O. Box 116250,
Gainesville, FL 32611-6250

1Corresponding author.

2Present address: Samsungtechwin R&D Center, Power Systems Division, 701 Sampyeong-dong, Bundang-gu, Seongnam, Gyeonggi-do 463-400, Republic of Korea.

Manuscript received April 11, 2013; final manuscript received July 21, 2013; published online October 21, 2013. Assoc. Editor: Zahid Ayub.

J. Thermal Sci. Eng. Appl 6(1), 011007 (Oct 21, 2013) (9 pages) Paper No: TSEA-13-1067; doi: 10.1115/1.4025091 History: Received April 11, 2013; Revised July 21, 2013

This paper addresses a multidimensional numerical simulation of the saturated flow boiling heat transfer in bubble pumps of absorption–diffusion refrigeration cycles. The bubble pump with a shape of vertical tube is subjected to a uniform heat flux from the tube outer wall surface along the entire pump length. As the bubble pump wall is heated, a nonazeotropic mixture of saturated strong ammonia/water entering into the bubble pump transforms to ammonia vapor and diluted ammonia/water mixture. The weaker ammonia/water mixture is lifted by the buoyant force created by the ammonia vapor. The present multidimensional numerical simulation was performed using the two-fluid model with the equilibrium phase change model and the standard k-ε turbulence model. The numerical model designed for the present simulation was validated through a comparative study referring to available experimental data. The present numerical model was compared with the one-dimensional model to assess its applicability for numerical simulation of the saturated flow boiling heat transfer in bubble pumps. As a result, it is seen that the present numerical model predicts the performance of ammonia/water bubble pumps more realistically than the one-dimensional model. In addition, the effects of the bubble pump's geometrical dimension and heat input on the pump performance were investigated using the present numerical approach.

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References

Figures

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Fig. 1

Schematic of an absorption–diffusion refrigerator with a bubble pump

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Fig. 2

Schematic of the simplified simulation model

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Fig. 3

Isometric mesh views of pumps A and D

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Fig. 4

Comparison of void fraction between the original mesh and the finer mesh

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Fig. 5

Comparison of vapor and liquid velocities between the original and finer meshes

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Fig. 6

Discretized solution domain with a fine grid in the near-wall region

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Fig. 7

Comparison between the predicted and measured void fraction profiles

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Fig. 8

Comparison between the predicted and measured liquid temperature profiles at 0.82 m height

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Fig. 9

Liquid and vapor velocity contours in pump D (Enlarged in the radial direction, the right side of each drawing is the pump wall)

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Fig. 10

Liquid and vapor velocity vectors in pump D subjected to qw =  25 kW/m2 (The right side of each drawing is the pump wall)

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Fig. 11

Void fractions in pump D (Enlarged in the radial direction, the right side of each drawing is the pump wall)

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Fig. 12

Comparisons of void fraction in the pump A between the present model and the 1D model [11]

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Fig. 13

Comparisons of void fraction in the pump D between the present model and the 1D model [11]

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Fig. 14

Void fraction profiles for pump D

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Fig. 15

Comparison of pumping ratio at the pump outlet between the present model and the 1D model [11]

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Fig. 16

Slip ratio for pump A

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Fig. 17

Slip ratio for pump D

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