Wen-Lung Fu

Thermal Performance of Angled, V-Shaped, and W-Shaped Rib Turbulators in Rotating Rectangular Cooling Channels (AR=4:1)

An experimental study was performed to measure the heat transfer distributions and frictional losses in rotating ribbed channels with an aspect ratio of 4:1. Angled, discrete angled, V-shaped, and discrete V-shaped ribs were investigated, as well as the newly proposed W-shaped and discrete W-shaped ribs. In all cases, the ribs are placed on both the leading and trailing surfaces of the channel, and they are oriented 45 deg to the mainstream flow. The rib height-to-hydraulic diameter ratio (e/D) is 0.078, and the rib pitch-to-height ratio (P/e) is 10. The channel orientation with respect to the direction of rotation is 135 deg. The range of flow parameters includes Reynolds number (Re =10,000-40,000), rotation number (Ro=0.0-0.15), and inlet coolant-to-wall density ratio (Δρ/ρ=0.12). Both heat transfer and pressure measurements were taken, so the overall performance of each rib configuration could be evaluated. It was determined that the W-shaped and discrete W-shaped ribs had the superior heat transfer performance in both nonrotating and rotating channels. However, these two configurations also incurred the greatest frictional losses while the discrete V-shaped and discrete angled ribs resulted in the lowest pressure drop. Based on the heat transfer enhancement and the pressure drop penalty, the discrete V-shaped ribs and the discrete W-shaped ribs exhibit the best overall thermal performance in both rotating and nonrotating channels. These configurations are followed closely by the W-shaped ribs. The angled rib configuration resulted in the worst performance of the six configurations of the present study.

Rotational Buoyancy Effects on Heat Transfer in Five Different Aspect-Ratio Rectangular Channels With Smooth Walls and 45Degree Ribbed Walls

This paper experimentally studies the effects of the buoyancy force and channel aspect ratio (W:H) on heat transfer in two-pass rotating rectangular channels with smooth walls and 45 deg ribbed walls. The channel aspect ratios include 4:1, 2:1, 1:1, 1:2, and 1:4. Four Reynolds numbers are studied: 5000, 10,000, 25,000, and 40,000. The rotation speed is fixed at 550 rpm for all tests, and for each channel, two channel orientations are studied: 90 deg and 45 or 135 deg, with respect to the plane of rotation. The maximum inlet coolant-to-wall density ratio (Δρ/ρ) inlet is maintained around 0.12. Rib turbulators are placed on the leading and trailing walls of the channels at an angle of 45 deg to the flow direction. The ribs have a 1.59 by 1.59 mm square cross section, and the rib pitch-to-height ratio (P/e) is 10 for all tests. Under the fixed rotation speed (550 rpm) and fixed inlet coolant-to-wall density ratio (0.12), the local buoyancy parameter is varied with different Reynolds numbers, local rotating radius, local coolant-to-wall density ratio, and channel hydraulic diameter. The effects of the local buoyancy parameter and channel aspect ratio on the regional Nusselt number ratio are presented. The results show that increasing the local buoyancy parameter increases the Nusselt number ratio on the trailing surface and decreases the Nusselt number ratio on the leading surface in the first pass for all channels. However, the trend of the Nusselt number ratio in the second pass is more complicated due to the strong effect of the 180 deg turn. Results are also presented for this critical turn region of the two-pass channels. In addition to these regions, the channel averaged heat transfer, friction factor, and thermal performance are determined for each channel. With the channels having comparable Nusselt number ratios, the 1:4 channel has the superior thermal performance because it incurs the least pressure penalty.

Influence of Entrance Geometry on Heat Transfer in Rotating Rectangular Cooling Channels (AR=4:1) With Angled Ribs

The effect of entrance geometry on the heat transfer in rotating, narrow rectangular cooling channels is investigated in this study. Both smooth channels and channels with angled ribs are considered with three different entrance conditions: fully developed, sudden contraction, and partial sudden contraction. The rectangular channel has as aspect ratio of 4:1, and it is oriented at 135° with respect to the plane of rotation. In the test section with angled ribs, the ribs are angled at 45° to the mainstream flow. The rib height-to-hydraulic diameter ratio (e/D h ) is 0.078, and the rib pitch-to-height ratio (P/e) is 10. The range of flow parameters includes Reynolds number (Re=5000-40,000), rotation number (Ro=0.0-0.302), and inlet coolant-to-wall density ratio (Δρ/ρ=0.12)

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:2 and AR=1:4) With 45 Deg Angled Rib Turbulators

This paper reports the heat transfer coefficients in two-pass rotating rectangular channels (AR=1:2 and AR=1:4) with rib roughened walls. Rib turbulators are placed on the leading and trailing walls of the two-pass channel at an angle of 45 deg to the flow direction. Four Reynolds numbers are considered from 5000 to 40 000. The rotation numbers vary from 0.0 to 0.3. The ribs have a 1.59 by 1.59 mm square cross section. The rib height-to-hydraulic diameter ratios (e/D h ) are 0.094 and 0.078 for AR=1:2 and AR=1:4, respectively. The rib pitch-to-height ratio (P/e) is 10 for both cases, and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115. For each channel, two channel orientations are studied, 90 deg and 45 deg with respect to the plane of rotation. The results show that the rotation effect increased the heat transfer on trailing wall in the first pass, but reduced the heat transfer on the leading wall. For AR=1:4, the minimum heat transfer coefficient was 25% of the stationary value. However, the rotation effect reduced the heat transfer difference between the leading and trailing walls in the second pass.

Rib Spacing Effect on Heat Transfer in Rotating Two-Pass Ribbed Channel (AR 1:2)

Rib turbulators are commonly used to enhance the heat transfer within internal cooling passages of advanced gas turbine blades. Many factors affect the thermal performance of a cooling channel with ribs. This study experimentally investigates the effect of rib spacing on the heat transfer enhancement, pressure penalty, and thus the overall thermal performance in both rotating and nonrotating rectangular, cooling channels. In the 1:2 rectangular channels, 45 deg angled ribs are placed on the leading and trailing surfaces. The pitch of the ribs varies, so rib pitch-to-height (P/e) ratios of 10, 7.5, 5, and 3 are considered. Square ribs with a 1.59 mm x 1.59 mm cross section are used for all rib spacing, so the height-to-hydraulic diameter (e/D h ) ratio remains constant at 0.094. With a constant rotational speed of 550 rpm and the Reynolds number ranging from 5000 to 40,000, the rotation number in turn varies from 0.2 to 0.02. Because the skewed turbulators induce secondary flow along the length of the rib, the very close rib spacing of P/e = 3 has the best thermal performance in both rotating and nonrotating channels. This close spacing yields the greatest heat transfer enhancement, whereas the P/e = 5 spacing has the greatest pressure penalty. In addition, the effect of rotation is more pronounced in the channel with the rib spacing of 3. As more ribs are added, the channel is approaching a smooth channel, and the strength of the rotation induced vortices increases.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:2 and AR=1:4) With Smooth Walls

The experiments are conducted at four Reynolds numbers: 5000, 10,000, 25,000, and 40,000. The rotation numbers vary from 0.0 to 0.21 and 0.0 to 0.3 for AR=1:2 and AR=1:4, respectively. For each channel, two channel orientations are studied, 90° and 45° with respect to the plane of rotation

Buoyancy Effects on Heat Transfer in Five Different Aspect-Ratio Rectangular Channels With Smooth Walls and 45-Degree Ribbed Walls

This paper experimentally studies the effects of the buoyancy force and channel aspect ratio on heat transfer in two-pass rotating rectangular channels with smooth walls and 45° ribbed walls. The channel aspect ratios include 4:1, 2:1, 1:1, 1:2 and 1:4. Four Reynolds numbers are studied: 5000, 10000, 25000 and 40000. The rotation speed is fixed at 550 rpm for all tests, and for each channel, two channel orientations are studied: 90° and 45° or 135°, with respect to the plane of rotation. Rib turbulators are placed on the leading and trailing walls of the channels at an angle of 45° to the flow direction. The ribs have a 1.59 by 1.59 mm square cross section, and the rib pitch-to-height ratio (P/e) is 10 for all tests. The effects of the local buoyancy parameter and channel aspect ratio on the regional Nusselt number ratio are presented. The results show that increasing the local buoyancy parameter increases the Nusselt number ratio on the trailing surface and decreases the Nusselt number ratio on the leading surface in the first pass for all channels. However, the trend of the Nusselt number ratio in the second pass is more complicated due to the strong effect of the 180° turn. Results are also presented for this critical turn region of the two-pass channels. In addition to these regions, the channel averaged heat transfer, friction factor, and thermal performance are determined for each channel. With the channels having comparable Nusselt number ratios, the 1:4 channel has the superior thermal performance because it incurs the least pressure penalty.Copyright

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=2:1) with Discrete Ribs

This paper reports the heat transfer coefficients and friction factors in a two-pass rotating rectangular channel with ribs, applicable to an internally cooled turbine blade. The channel aspect ratio is 2:1. Five different turbulators are studied: 45-deg angled ribs, V-shaped ribs, discrete 45-deg angled ribs, discrete V-shaped ribs, and crossed V-shaped ribs. The ribs are placed on the leading and trailing surfaces. The Reynolds number ranges from 5000 to 40,000. The corresponding rotation numbers vary from 0.206 to 0.026 for a fixed rotation speed of 550 rpm. The rib-height-to-hydraulic-diameter ratio (elD) is 0.094, the rib-pitch-to-height ratio (Pie) is 10, and the inlet-coolant-to-wall-density ratio (Ap/p) is maintained around 0.115. For each case, two channel orientations with respect to the plane of rotation are studied, 90 and 135 deg. The results show that the V-shaped ribs and discrete V-shaped ribs have higher heat transfer enhancement than the 45-deg angled ribs and discrete 45-deg angled ribs for both rotating and nonrotating cases. The pressure measurements show the 45-deg angled ribs incurred the highest frictional losses. Based on the present study, the discrete V-shaped ribs have the best overall thermal performance in both rotating and nonrotating channels.

Rib Spacing Effect on Heat Transfer and Pressure Loss in a Rotating Two-Pass Rectangular Channel (AR=1:2) With 45-Degree Angled Ribs

Rib turbulators are commonly used to enhance the heat transfer within internal cooling passages of advanced gas turbine blades. Many factors affect the thermal performance of a cooling channel with ribs. This study experimentally investigates the effect of rib spacing on the heat transfer enhancement, pressure penalty, and thus the overall thermal performance in both rotating and non-rotating rectangular, cooling channels. In the 1:2 rectangular channels, 45° angled ribs are placed on the leading and trailing surfaces. The pitch of the ribs varies, so rib pitch-to-height (P/e) ratios of 10, 7.5, 5, and 3 are considered. Square ribs with a 1.59 mm × 1.59 mm cross-section are used for all spacings, so the height-to-hydraulic diameter (e/Dh ) ratio remains constant at 0.094. With a constant rotational speed of 550 rpm and the Reynolds number ranging from 5000 to 40000, the rotation number in turn varies from 0.2 to 0.02. Because the skewed turbulators induce secondary flow along the length of the rib, the very close rib spacing of P/e = 3, has the best thermal performance in both rotating and non-rotating channels. This close spacing yields the greatest heat transfer enhancement, while the P/e = 5 spacing has the greatest pressure penalty. In addition, the effect of rotation is more pronounced in the channel with the rib spacing of 3. As more ribs are added, the channel is approaching a smooth channel, and the strength of the rotation induced vortices increases.Copyright

Thermal Performance of Angled, V-Shaped, and W-Shaped Rib Turbulators in Rotating Rectangular Cooling Channels (AR = 4:1)

An experimental study was performed to measure the heat transfer distributions and frictional losses in rotating ribbed channels with an aspect ratio of 4:1. Angled, discrete angled, V-shaped, and discrete V-shaped ribs were investigated, as well as the newly proposed W-shaped and discrete W-shaped ribs. In all cases, the ribs are placed on both the leading and trailing surfaces of the channel, and they are oriented 45° to the mainstream flow. The rib height-to-hydraulic diameter ratio (e/D) is 0.078, and the rib pitch-to-height ratio (P/e) is 10. The channel orientation with respect to the direction of rotation is 135°. The range of flow parameters includes Reynolds number (Re = 10000–40000), rotation number (Ro = 0.0–0.15), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). Both heat transfer and pressure measurements were taken, so the overall performance of each rib configuration could be evaluated. It was determined that the W-shaped and discrete W-shaped ribs had the superior heat transfer performance in both non-rotating and rotating channels. However, these two configurations also incurred the greatest frictional losses while the discrete V-shaped and discrete angled ribs resulted in the lowest pressure drop. Based on the heat transfer enhancement and the pressure drop penalty, the discrete V-shaped ribs and the discrete W-shaped ribs exhibit the best overall thermal performance in both rotating and non-rotating channels. These configurations are followed closely by the W-shaped ribs. The angled rib configuration resulted in the worst performance of the six configurations of the present study.Copyright