关键词: 受限横流通道, 方阵连续射流, 声激励器, 合成射流, 射流管延伸, 对流传热强化

Abstract: An experimental investigation is performed to the convective heat transfer in a confined crossflow channel with a specific dimension-less height of H/d=3, produced from a 2′2 square-array impinging jets with dimensionless pitches of X/d=Y/d=4. Particular focus is played on the heat transfer enhancement by using the passively extended jet pipes and the actively center-positioned synthetic jet in the continuous-jet square array, as well as their combination schemes. In the present study, square-array jet Reynolds number (Re)ranges from 3000~10000, and the synthetic jet acoustic actuator is driven at a fixed frequency of f=100Hz. Correspondingly, the synthetic jet velocity ratios (defined as the ratio of synthetic jet characteristic velocity to square-array jet ejecting velocity, RSJ-CJ)are varied from 2.0 (under Re=3000)to 0.6 (under Re=10000). From the jet pipe extension, the dimensionless normal distance between jet outlet and targeting wall is adjusted in a range of L/d=1~3. Within the scope of this study, the heat transfer enhancement roles are clearly illustrated. Under Re=3000, the synthetic jet integration demonstrates a significantly stronger heat transfer augment role than the jet pipe extension, taking on dominant heat transfer enhancement mechanism in the combination scheme. With respect to the base-line situation (no synthetic jet integration and no jet pipe extension), the area-averaged Nusselt number on a specified zone could be increased up to 200% when the crossflow velocity ratio (defined as the ratio of crossflow inlet velocity to square-array jet ejecting velocity, RCF-CJ)beyond 0.67. Whereas under Re=10000, the jet pipe extension plays dominant heat transfer enhancement mechanism on the otherwise. the area-averaged Nusselt number could be increased up to 100% at RCF-CJ=0.5 in relation to the baseline situation. Meanwhile, in the square array with the extended jet pipes, the role of synthetic jet integration is very faint. The most possibilities wherein the combination of synthetic jet integration and jet pipe extension could exhibit obviously its significance on heat transfer enhancement appear when both schemes display equivalent heat transfer augment roles. For instance, under Re=5000 and RCF-CJ=0.6~0.8, the combination scheme shows an obviously further improvement on heat transfer enhancement, in related to the single scheme either in active or passive.

Key words: Confined crossflow channel, Square-array continuous jets, Acoustic actuator, Synthetic jet, Extended jet pipe, Convective heat trans-fer enhancement