The heat transfer characteristics were experimentally investigated in a wind channel with different types of cut baffles for heat transfer augmentation. The aim of using zigzag-cut baffles is to create 3D flow structure behind the baffles instead of transverse vortex flow leading to enhance heat transfer. In this study, 4 types of baffles were examined; conventional baffle (Rectangular cross section with no cut), baffle with rectangular zigzag-cut, baffle with triangle zigzag-cut at 45 degree and at 90 degree. All of the baffles have the same height at H = 15 mm and flow blocking area. In the experiment, the row of seven baffles was attached on the inner surface of wind channel. The effects of pitch spacing length were also investigated at baffle pitch distance P/H = 4, 6 and 8 (H: Height of baffle). The experiments were performed at constant Reynolds number (Re) of 20000. The heat transfer patterns via Thermochromic liquid crystal sheet were visualized and recorded with a digital camera. The recorded images were then analyzed with image processing technique to obtain the distribution of Nusselt number. The flow characteristics pass through the baffles were also numerically studied with CFD simulation for understanding the heat transfer characteristics. The friction losses were measured to evaluate the thermal performance for each baffle. It was found that the baffle with rectangular zigzag-cut gives the best thermal performance due to heat transfer augmentation in upstream and downstream side of baffle.

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In this work, flow and heat transfer in a channel having oval trench dimples were investigated numerically. 3-D channel flow with a cross-section of 300-mm width and 32-mm height were created using Computational Fluid Dynamic (CFD) with ANSYS, Fluent (V.15.0). Five oval trench dimples with 3-mm depth, 10.0-mm width and 45-mm length arranging with a single row and in-line configuration were located on the bottom surface of the channel. Reynolds number based on hydraulic diameter of the channel were fixed at Re=20,000 whereas a dimple inclined angle defined as the angle of dimple centreline to the mainstream was varied at 0, 15, 30 and 45 degrees. SST turbulent model was used to solve governing Equations. The result show that longitudinal vortex flow occurred at ?=15° to 45° which would be enhance heat transfer on the surface. When inclined angle became larger, the areas of Nusselt number and high total pressure coefficient took place at dimple edge in +Z direction. The peak of average spanwise Nusselt numbers took place for the case of ?=45°. Moreover, the area of high spanwise average Nusselt numbers (>100) for the case ?=30° was the largest.

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Abstract. Impinging jet is widely employed in thermal industrial applications due to having high heat transfer coefficient in impingement region. One method to increase heat transfer on an impingement surface is to increase turbulence intensity in jet flow. The mounting of an airinduced duct at nozzle outlet is a passive method to increase entrainment air resulting on increasing turbulence intensity. The aim of this research is to study flow and heat transfer characteristics of array of impinging jets mounting air-induced ducts. The investigation model was jets discharging from pipe nozzle having an inner diameter of d=17.2 mm and a length of 200 mm. Nozzle arrangement were inline configuration having 5 rows x 5 columns. A jet-to-jet distance (S) was S=6d, 8d and a jet-to-plate distance (H) was H=6d. The inner diameter (D) and the length (L) of the air-induced ducts were D=4d and L=4d, respectively. The Reynolds number was fixed at Re=20,000. In addition, the impinging jets without mounting the airinduced ducts were also investigated for benchmarking with the case of mounting the airinduced ducts. In the study, a thin foil technique was used to measure heat transfer on the impingement surface, and a computational fluid dynamic (CFD) using ANSYS, Fluent (V.15.0) was also adopted. The results showed that the effect of mounting air-induced duct can enhance entrainment air into the jet flow resulting on increasing of heat transfer of impinging jets on target surface, and the effects of mounting air-induced duct on increasing heat transfer in case of larger jet-to-jet distance (S/d=8) was more effective than that of smaller jet-to-jet distance (S/d=6).