Experimental study of surface-mounted obstacle effects on heat transfer enhancement using transient liquid crystal thermography

摘要

In the present work, local heat transfer enhancment on a plate with a single obstacle or single array of obstacles mounted on is explored by using transient liquid crystal thermograph technique. With emphasis on the short obstacles of the height no more than one hydraulic diameter (d), three cross-sectional shapes of obstacles, i.e. circular, square and diamond, with variations in number of obstacles, obstacle spacing, and free-stream Reynolds number are considered. The maximum number of the obstacles in tandem is 3; while the spacing between obstacles is d, 2d, or 4d. The free-stream Reynolds number ranges from 2100 to 4200. The experimental results reveal that, for a fixed obstacle configuration, an increase in Reynolds number alters vortical flow structure and, in turn, leads to an enhancement in heat transfer performance, especially in the near regions of stagnation point and wake behind obstacles. The size and strength of the horse-shoe vortex in front of the leading obstacles depend on the obstacle height as well as the free-stream Reynolds number. The present results of the short obstacles disclose that an intermediate height (0.5 d) of the protruding elements is more beneficial to the heat transfer enhancement. The obstacle of the circular shpae shows best performance among the three. The number of and the spacing between the obstacles in tandem array are also influential factors to the flow structure and, in turn, to the heat transfer enhancement on the base plate.