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Experimental study of frost formation on cold surfaces with various fin layouts
Author: Hu Shan | Print | Close | Text Size: A A A | 2017-11-28

Frost formation significantly increases the heat transfer resistance on heat exchangers and the flow resistance in the channels, so there is great interest in understanding the frost formation mechanism on a finned surface. Frost formation was experimentally investigated on several complex finned surfaces, including a single aligned fin, a single angled fin, a single row of aligned fins, a single column of angled fins and five columns of angled fins. The experimental conditions were 2 to 7 °C air temperatures, 80% air relative humidity, 0.3 to 1.1 m/s air velocities and 19 to 10 °C cold surface temperatures. The results show for all the investigated pieces, the frost weight per unit area in the fin region is greater than in the base region at a lower temperature, more frost was observed near the edges than in the middle of the fins, the fins angled with the airflow had more frost than the aligned fins and the multiple lines and columns of fins had the most frost on the frontal fins. A dimensionless empirical correlation for the frost weight in the fin area was developed with 85% of predictions within ±30% of the experimental data.

Conclusions

The frost growth on five types of enlarged louvered finned surfaces, a single aligned fin, a single angled fin, a single row of aligned fins, a single column of angled fins and five columns of angled fins, were experimentally investigated. An empirical correlation for the frost weight on fin surface was proposed. The conclusions can be drawn as follows:

(1) Based on the frost layer morphology observations, more frost is observed near the edges than in the middles of the fins. For angled fins, more frost grows on the windward side than on the leeward side. For a single column of angled fins, more frost develops on the fin in the first row than in the other fins. For five columns of angled fins, most frost forms on the fins in the first row, followed by in the last row, with more frost in the middle columns than in the side columns.

(2) The fin region accumulates more frost per unit area than the base region.

(3) The influence of the fin layout shows that the angled fins have more frost formation than the aligned ones, the frost weight per unit fin area decreases in order of the single angled fin, single aligned fin, single row of aligned fins, five columns of angled fins and single column of angled fins.

(4) The influence of fin orientation shows that more frost forms on horizontal fins than on vertical ones.

(5) The influence of entrance effect shows that more frost accumulated with a contraction inlet flow section than with a constant inlet flow section.

(6) The influence of the operating conditions shows that higher air velocities result in more frost formation, while the ratio of the frost weight to the total water vapor in the humid air flowing through the test section decreases with increasing velocity. Lower cold surface temperatures and higher inlet air temperatures also result in more frost formation.

(7) A dimensionless empirical correlation for the frost weight in the fin area as a function of the air and cold surface temperatures, air humidity ratio, Reynolds number, Fourier number, fin angle and fin thickness, was developed with 85% of its predictions falling within ±30% of the experimental data.

The results have been published on Applied Thermal Engineering 95 (2016) 95–105.

 
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