Research Papers

Evaporative Annular Flow in Micro/Minichannels: A Simple Heat Transfer Model

[+] Author and Article Information
Bengt Sundén

Department of Energy Sciences,
Lund University,
Box 118,
Lund SE-22100, Sweden
e-mail: bengt.sunden@energy.lth.se

Wei Li

Department of Energy Engineering,
Zhejiang University,
Hangzhou 310027, China

Vishwas V. Wadekar

AspenTech Ltd,
Reading RG2 6DT, UK

1Corresponding author.

Manuscript received October 27, 2012; final manuscript received December 12, 2012; published online June 24, 2013. Assoc. Editor: Hongbin Ma.

J. Thermal Sci. Eng. Appl 5(3), 031009 (Jun 24, 2013) (10 pages) Paper No: TSEA-12-1185; doi: 10.1115/1.4023310 History: Received October 27, 2012; Revised December 12, 2012

The present study collected and analyzed flow boiling data points which fall in the annular flow regime with an increasing heat transfer coefficient h - vapor quality x trend (h increases with increasing x) in small diameter channels (0.1 < dh < 3.1 mm) for halogenated refrigerants, CO2 and water. In this annular flow regime, heat transfer coefficient also depends on both heat flux and mass flux. It is proposed that the heat flux dependence comes mainly through its effect on interfacial waves and the fact that bubble growth and coalescence in isolated bubble flow and elongated bubble flow propagate oscillations downwards into the annular flow. In other words, heat flux affects the heat transfer coefficient in the annular flow regime by upstream effects or historical effects. A semi-empirical model for annular flow was developed by starting with pure thin film evaporation and then corrections were applied based on the Boiling number and the liquid Reynolds number. The resulting simple model can predict about 89.1% of the entire database within a ± 30% error band. Almost all data points can be predicted within a ± 50% error band. It is shown that the parametric trends are well captured by the new model. Besides, no noticeable macro-to-micro/miniscale transition was observed for the entire database of annular flow. Therefore, the new model can be applied to model annular flow covering from microchannels to relatively large channels.

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Fig. 1

A h-x trend of flow boiling in micro/mini-channels when x varies from 0 to 1

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Fig. 2

(a) hexp/hLF versus hydraulic diameter and (b) liquid film thickness versus hydraulic diameter

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Fig. 3

hexp/hLF versus Bl0.3Rel when local q < qONB

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Fig. 4

hexp/hLF versus Bl0.3Rel when local q > qONB

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Fig. 5

The ratio of the local experimental heat transfer coefficient to the heat transfer coefficient predicted by the new model against (a) Prl; (b) Rel; (c) bond number Bo; and (d) Bo*Rel0.5

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Fig. 6

Parametric-trend analysis of the new model: (a) Saitoh et al. [11] at Tsat = 10 °C; (b) Charnay et al. [12] at Psat = 3.3 bar; (c) Tibirica and Ribatski [14] at Tsat = 31 °C; (d) Consolini and Thome [15] at Tsat = 31 °C; (e) In and Jeong [16] at Psat = 9 bar; (f) Choi et al. [20] at Tsat = 10 °C; (g) Ducoulombier et al. [22] at Tsat = 0 °C; and (h) Tibirica et al. [23] Tsat = 31 °C.

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Fig. 7

The predictive ability of four existing correlations and the new model: (a) Gungor and Winterton [34]; (b) Li and Wu [7]; (c) Lazarek and Black [35]; (d) Bertsch et al. [36]; and (e) the new model.

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Fig. 8

Experimental Boiling number and CHF Boiling number predicted by the Katto correlation [37] and the Wojtan et al. correlation [38] against the reduced pressure

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Fig. 9

Experimental exit vapor quality and the dryout quality estimated from the Katto correlation [37] against the reduced pressure




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