Effect of front air attack angles on heat transfer coefficient of the cross‐flow of four flat tube

Heat transfer coefficients are studied experimentally for airflow over a four‐flat‐tube configuration with different inlet attack angles. The range of Re numbers was from 1668 to 3782. The heat fluxes are 13.2, 38.5, and 99.8 W/m2. In this paper, 45 samples of a flat tube with inlet airflow angles (30°, 45°, and 90°) are set up to investigate its thermal performance. The design of experimental approach was used to conduct the heat transfer parametric study by designing 45 experiments, analyzing the empirical model, and optimizing heat transfer. The response was modeled using a general factorial design model based on experimental data. From analysis of variance (ANOVA), we obtained significant coefficients by performing the 5% test of level of significance. The results indicated that both the Nu and Re numbers increase for all heat flux cases and these decrease with increasing the air attack. Also shown are that the Colburn j‐factor decreases with increase of air velocity. It was found that the ANOVA results are appropriate to the collected experimental data, as the R2 and R2‐adjusted statistics are found to be 92.61% and 90.97%, respectively, for Nu number. In a similar manner, for Colburn j‐factor, the R2 and R2‐adjusted statistic are 96.97% and 96.29%, respectively.