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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

FRACTAL HEAT TRANSFER MODEL FOR POOL BOILING ON MICRO-PIN-FINNED SURFACES IN MICROGRAVITY

Baojin Qi
School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an 710049, China; Xi'an Jiaotong University Suzhou Institute, Shuzhou 215123, China

Ya Wang
School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an 710049, China

Jinjia Wei
School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, P.R. China; Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong Uniersity, Xi'an, 710049, P.R.China

Yonghai Zhang
State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, P.R. China; School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an 710049, China

Ting Yu
School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an 710049, China

DOI: 10.1615/IHTC16.bae.022274
pages 1085-1095


KEY WORDS: Boiling and evaporation, Heat transfer enhancement, fractal method

Abstract

Scientifically and accurately predicting the distribution of the bubble sizes on the heating surface is a key step to improve the calculation accuracy of the boiling heat transfer model. In the present study, a new nucleate boiling heat transfer model was developed on the basis of random fractal function of the bubble sizes distribution. Compared to the previous correlations, the present model considered the bubble sizes distribution, fractal dimension dƒ, the effective area ratio P, and maximum and minimum bubble radii. Theoretical results show that the fractal dimensiondƒ tended to increase with the increase of the effective area ratio P, and the fractal dimension was remarkable influenced by the small value of ratio P. The fractal dimension dƒ and the values of bubble generations τ both decreased rapidly with the increase of the ratio of radii between any two neighboring generations γ firstly, and then gradually approached a constant. Moreover, the experimental data and photograph of boiling heat transfer on micro-pin-finned are compared with the new fractal heat transfer model. The results indicated that the image of bubble distribution obtained from the random fractal model is very similar to the experimental photograph statistically and the heat transfer is in good agreement with the experimental data when the superheat ΔT is higher than 5 °C, and the error is less than 20%.

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