| Summary: | 碩士 === 國立勤益科技大學 === 冷凍空調系 === 100 === The single and double row curved fin-and-tube heat exchangers with continuous staggered X-type slit fin and continuous and staggered flat plate fin two row heat exchangers are studied numerically. The row number (1 or 2), fin pitch and the heat exchanger curvature(R) are varied to see the variations of heat transfer rate and air flow rate. The performances of curved heat exchangers are compared with the straight one at the same pressure drop to show the curvature effect on the fin-and-tube heat exchangers.
The results show that in the both curvatures of R=100mm and 60mm, the heat transfer rates of curved heat exchangers are smaller than the straight one under 5%, and the air flow rates of the curved heat exchangers are smaller than the straight one under 8% in the single row case, the higher the air velocity the smaller the difference.
The curvature has greater effect on the heat transfer and air flow rate in the double row than the single row heat exchanger. For the curvatures of R=150 mm, 100 mm, and 60 mm with the same pressure drop with the straight heat exchanger, the heat transfer rate of the curved heat exchanger is at least 10% less than the straight one, the air flow rate is at least 12% less than the straight one. The heat transfer and air flow rate in the double row heat exchanger are influenced more obviously than in the single row by the heat exchanger curvature.
In the curved double row continuous and staggered flat plate fin-and-tube heat exchanger, the staggered type has higher heat transfer rate than the continuous one, and the smaller the curvature the smaller the effect. But the air flow rate is smaller in the staggered type than in the continuous type, and the higher bent curvature the higher air flows rate. The staggered type heat exchangers have higher Colburn j factor and friction factor f than the continuous one, and the smaller the curvature the higher the factors. This result could provide some information in the design of fin and tube heat exchanger with curved parts.
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