HEAT TRANSFER ENHANCEMENT OF UNIFORMLY/LINEARLY HEATED SIDE WALL IN A SQUARE ENCLOSURE UTILIZING ALUMINA-WATER NANOFLUID

To evaluate the application of the impingement cooling in a trapezoidal duct, particularly the influence on internal cooling of the cross flow and swirl flow. Experimental and numerical studies have been performed. The experiment focuses on the heat transfer characteristics in the duct, when the numerical simulation focuses on the flow characteristics. Four Reynolds numbers (10000, 20000, 30000 and 40000), six cross flow mass flow ratios (0, 0.1, 0.2, 0.3, 0.4 and 0.5) and two impingement angle (35° and 45°) are considered in both the experiment and the numerical simulation. The temperature on the target wall and the exit side wall is measured by the thermocouples, when the realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. The results show that only part of the jets contribute in the heat transfer enhancement on the target wall, the other jets improve a large anticlockwise vortex occupied the upper part of the duct and drive strong swirl flow. The heat transfer on the exit side wall is enhanced by the swirl flow. The cross flow is induced in the duct by the outflow of the end exit hole. It deflects the jets and abates the impingement cooling on the target wall in the downstream region but has no evidently effect on the heat transfer on the exit side wall. Higher impingement angle helps to augment the impingement cooling on the target wall and improves the resistance ability of the jets against the effect of the cross flow. The heat transfer enhancement ability on the target wall and exit side wall in the present duct is compared to that of a smooth duct. The Nusselt number of the former is about 3 times higher than that of the latter. It indicates that the impingement and swirl play equally important roles in the heat transfer enhancement in the present duct. Empirical dimensionless correlations based on the present experiment data are presented in the paper.

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Numerical Investigation of Secondary Flow Vortex Core Structure in the Two-Pass Rectangular Channel With 45° Ribs

Volume 5A: Heat Transfer ◽

10.1115/gt2015-42782 ◽

2015 ◽

Cited By ~ 4

Author(s):

Jiangnan Zhu ◽

Tieyu Gao ◽

Jun Li ◽

Guojun Li ◽

Jianying Gong

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Secondary Flow ◽

Gas Turbine ◽

Vortex Core ◽

Side Wall ◽

Main Flow ◽

Transfer Enhancement ◽

Cooling Channels ◽

Flow Vortex

The secondary flow which is generated by the angled rib is one of the key factors of heat transfer enhancement in gas turbine blade cooling channels. However, the current studies are all based on the velocity vector and streamline, which limit the research on the detailed micro-structure of secondary flow. In order to make further targeted optimization on the flow and heat transfer in the cooling channels of gas turbine blade, it is necessary to firstly investigate the generation, interaction, dissipation and the influence on heat transfer of secondary flow with the help of new topological method. This paper reports the numerical study of the secondary flow and the effect of secondary flow on heat transfer enhancement in rectangular two-pass channel with 45° ribs. Based on the vortex core technology, the structure of secondary flow can be clearly shown and studied. The results showed that the main flow secondary flow is thrown to the outer side wall after the corner due to the centrifugal force. Then it is weakened in the second pass and a new main flow secondary flow is generated at the same time near the opposite side wall in the second pass. The Nusselt number distribution has also been compared with the secondary flow vortex core distribution. The results shows that the heat transfer strength is weakened in the second pass due to the interaction between the old main flow secondary flow and the new one. These two secondary flows are in opposite rotation direction, which reduces the disturbance and mass transfer strength in the channel.

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Heat Transfer Enhancement of a Backward-Facing Step Flow in a Duct by Static and Dynamic Devices

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 1 ◽

10.1115/ht2007-32660 ◽

2007 ◽

Cited By ~ 1

Author(s):

Kyoji Inaoka ◽

Kouji Kawakami ◽

Yoshi Nishii ◽

Mamoru Senda

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Large Scale ◽

Fluid Motion ◽

Side Wall ◽

Transfer Enhancement ◽

Backward Facing Step ◽

Electromagnetic Actuators ◽

Flow Recirculation ◽

Flow Modification

Flow modification downstream of a backward-facing step has been tried in order to achieve heat transfer enhancement by introducing two kinds of devices, a triangle prism rib and electromagnetic actuators, on the step edge. The triangle rib attached to the side-wall corner makes the downward flow inclined and generates a circulation-like fluid motion behind it. Because both flows work effective in reducing the flow re-circulation caused behind the step, large heat transfer recovery is obtained near the side-wall. This advantage of the triangle rib remains effective when the flap actuations are imposed. Thus, the large-scale unsteady vortex intensively reduces the flow recirculation, the triangle rib with flap actuations attains the largest heat transfer recovery behind the step.

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