Local Heat/Mass Transfer Distributions Around Sharp 180 deg Turns in Two-Pass Smooth and Rib-Roughened Channels

Han, Je-Chin; Chandra, P. R.; Lau, S. C.

doi:10.1115/1.3250478

Cited by 144 publications

(31 citation statements)

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“…They found very large spanwise variation in mass (heat) transfer at the turn and upstream of the outlet pass. Han et al [16] studied the local mass/heat transfer distribution in two-pass square channels with smooth and 90°ribbed walls. It was found that the mass transfer in and after the turn was more than before the turn.…”

Section: List Of Symbolsmentioning

confidence: 99%

Flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular smooth channels

Siddique

El-Gabry

Shevchuk³

et al. 2011

Heat Mass Transfer

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Two-pass channels are used for internal cooling in a number of engineering systems e.g., gas turbines. Fluid travelling through the curved path, experiences pressure and centrifugal forces, that result in pressure driven secondary motion. This motion helps in moving the cold high momentum fluid from the channel core to the side walls and plays a significant role in the heat transfer in the channel bend and outlet pass. The present study investigates using Computational Fluid Dynamics (CFD), the flow structure, heat transfer enhancement and pressure drop in a smooth channel with varying aspect ratio channel at different divider-to-tip wall distances. Numerical simulations are performed in two-pass smooth channel with aspect ratio W in /H = 1:3 at inlet pass and W out /H = 1:1 at outlet pass for a variety of divider-to-tip wall distances. The results show that with a decrease in aspect ratio of inlet pass of the channel, pressure loss decreases. The divider-totip wall distance (W el ) not only influences the pressure drop, but also the heat transfer enhancement at the bend and outlet pass. With an increase in the divider-to-tip wall distance, the areas of enhanced heat transfer shifts from side walls of outlet pass towards the inlet pass. To compromise between heat transfer and pressure drop in the channel, W el /H = 0.88 is found to be optimum for the channel under study.

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Section: List Of Symbolsmentioning

confidence: 99%

Flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular smooth channels

Siddique

El-Gabry

Shevchuk³

et al. 2011

Heat Mass Transfer

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“…The effect of the bend on the heat transfer in smooth and ribbed stationary passages has been experimentally studied by Johnson and Launder. (1985), Metzger and Sahm (1986), Han et al (1988), Han and Zhang (1991), and Ekkad and Han (1995). The secondary flows and flow separation at the tip of the divider plate influence the heat transfer in the bend.…”

Section: Internal Cooling Of Turbine Bladesmentioning

confidence: 99%

PIV Investigation of the Flow Characteristics in an Internal Coolant Passage With Two Ducts Connected by a Sharp 180° Bend

Schabacker

Bölcs

Johnson

1998

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration

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A PIV study of the flow in a stationary model of a smooth two-pass internal coolant passage is presented, which focuses on the flow characteristics in the sharp 180º bend and downstream of the bend where the flow is redeveloping. Because PIV in its traditional conception only allows for the investigation of two-dimensional flow, a stereoscopic digital PIV system was assembled that measures all three velocity components simultaneously. The mean-velocity field and turbulence quantities of the flow are obtained from the PIV measurements. The model of the coolant passage consists of two square ducts, each having a length of 19 hydraulic diameters, which are connected by a sharp 180º bend with a rectangular outer wall. The measurements were obtained at one flow condition with a flow Reynolds number of 50,000. A strong secondary flow motion occurs in the bend of the smooth passage that consists of two counter rotating vortices, which impinge on the outer wall and influence the flow in the downstream leg. Both of the outer corners contain regions of recirculating flow. A separation bubble, about 1.5 hydraulic diameters long, occurs on the inner wall of the return pass. In the symmetry plane, the flow recovers from the bend effect within 10 hydraulic diameters.

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“…Park and Lau [2] studied the effect of sharp turning flows in a two-pass square channel and found very large spanwise variation in heat transfer at the turn and upstream of the outlet pass. Han et al [3] and Liou et al [4] showed that heat transfer enhances in a two-pass channel after the turn and this is due to the secondary flow generated by the centrifugal force at the turn. Many researchers [5][6][7][8][9] have studied the effect of channel aspect ratio on heat transfer characteristics.…”

Section: Introductionmentioning

confidence: 99%

Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge

Siddique

El-Gabry

Shevchuk³

et al. 2012

Journal of Turbomachinery

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High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. In particular, the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are twopass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer; therefore, for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at the trailing edge surface in-line with the ribs at the bottom surface, and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-e model, realizable k-e model, the RNG k-x model, low-Re k-x model, and SST k-x models are compared, whereas for ribbed channel, low-Re k-e model and SST k-x models are compared. The results show that the low-Re k-e model, which predicts the heat transfer in outlet pass of the smooth channels with difference of þ7%, underpredicts the heat transfer by À17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for the ribbed trailing edge only was found about 8% better than other configurations.

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Local Heat/Mass Transfer Distributions Around Sharp 180 deg Turns in Two-Pass Smooth and Rib-Roughened Channels

Cited by 144 publications

References 0 publications

Flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular smooth channels

Flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular smooth channels

PIV Investigation of the Flow Characteristics in an Internal Coolant Passage With Two Ducts Connected by a Sharp 180° Bend

Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge

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