| 1. |
- Ghorbani-Tari, Zahra, et al.
(author)
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Characteristics of heat transfer around an obstacle controlled by the presence of ribs
- 2016
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In: Heat Transfer Research. - 1064-2285. ; 47:10, s. 893-906
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Journal article (peer-reviewed)abstract
- Using liquid crystal thermography, experimental studies were carried out to investigate the local heat transfer of an obstacle integrated with a rib. The rib was positioned in the upstream region of the obstacle to disturb the boundary layer of the approaching flow by precipitating the flow separation and reatt achment. The spacing between the rib and the obstacle is of primary importance. The spacing S, which is normalized by the spanwise width of the obstacle, is equal to 1.25d and 0.625d. The effect of the rib height-To-hydraulic diameter ratio e/Dh is also of concern in this study. The e/Dh is between 0.039 or 0.078. The Reynolds number based on the spanwise width of the obstacle ranges between 35,600 and 55,600. It was found that the local heat transfer especially in the upstream region was strongly affected by e/Dh and S/d. In the downstream region, the local heat transfer was more affected by the Reynolds number than the rib height and the spacing.
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| 2. |
- Ghorbani-Tari, Zahra, et al.
(author)
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Experimental Study of Convection Heat Transfer in the Entrance Region of a Rectangular Duct with Transverse Ribs
- 2012
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In: Proceedings of the ASME Summer Heat Transfer Conference, 2012, Vol 1. ; , s. 769-777
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Conference paper (peer-reviewed)abstract
- The paper presents an experimental study on heat transfer coefficients in a straight rectangular channel containing continuous transverse ribs. The ribs were located on one side of the channel which is heated with a uniform heat flux. Three values of the rib pitch-to-height ratio (10, 20 and 30) were considered, with the Reynolds number, based on the channel hydraulic diameter, ranging from 57,000 to 127,000. The studied geometry is relevant for hot internal structures in aircraft engines. The steady state, liquid crystal thermography technique was used to obtain detailed heat transfer coefficients in the inter-rib surface regions. The main purpose of this study was to investigate the heat transfer behavior between the first repeated ribs, i.e., in the regions where the flow and thermal fields are not yet periodically fully developed.
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| 3. |
- Ghorbani-Tari, Zahra, et al.
(author)
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Experimental Study of Heat Transfer Characteristics of a Bluff Body Interacting With a Rib by Using Liquid Crystal Thermography
- 2014
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In: Proceedings of the ASME 2013 International Mechanical Engineering Congress and Exposition Volume 8B: Heat Transfer and Thermal Engineering. - 9780791856352 ; 8B, s. 08-060
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Conference paper (peer-reviewed)abstract
- In the present study, the effects of a single rib on the local heat transfer around a bluff body are examined by using the steady state liquid crystal technique. By varying the spacing between the bluff body and the rib, the interaction between the rib and the bluff body can be controlled. The bluff body is oriented vertically towards the flow direction and spans the whole height of the channel. The bluff body has a rectangular cross-section (height b = 80 mm, width 40 mm) while the rib has a square cross-section (rib height e= 10 mm, rib width 10 mm). The rib is placed in the upstream region of the bluff body either by a spacing L = 100 and 50 mm to yield nondimensional spacing to rib height ratios L/e = 10 and 5 respectively. Here, the re-attachment length (x(R)) for a single rib is about 7.5e. The values of the Reynolds number based on the channel hydraulic diameter (D-h) are 55,000 and 89,000. The experimental results revealed that the presence of the rib at L/e = 10 has a more pronounced effect on the enhancement of the heat transfer upstream region of the bluff body. The effect of different L/e on the local Nu number distribution in the wake of the bluff body is small.
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| 4. |
- Ghorbani-Tari, Zahra, et al.
(author)
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Experimental study of heat transfer control around an obstacle by using a rib
- 2016
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In: Heat Transfer Research. - 1064-2285. ; 47:8, s. 781-795
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Journal article (peer-reviewed)abstract
- This paper investigates the effect of the presence of a rib on the end-wall heat transfer of an obstacle by liquid crystal thermography. An obstacle with a rectangular cross section is placed in a rectangular channel and blocks the entire height of it (AR = 4). A rib with a square cross section is placed at two positions, i.e., in the upstream and downstream areas of the obstacle, respectively. An important parameter in dealing with the control of heat transfer around an obstacle using a rib is the spacing between them. The spacing S, normalized by the spanwise width of the obstacle, has the values 1.25 and 0.625. The effect of the rib height, normalized by the channel hydraulic diameter, e/Dh, is also investigated by considering two values of it, i.e., 0.078 and 0.039, respectively. The results show that the local heat transfer especially in the upstream region of the obstacle is substantially modified by the upstream rib, e/Dh and S/d. The local heat transfer in the downstream region is more affected by the rib height, e/Dh. The local heat transfer in the upstream area of the obstacle is found nearly unaffected by the downstream rib regardless of the rib height e/Dh and S/d. It is found that the local heat transfer in the downstream area of the obstacle is modified differently and it is strongly affected by the rib height e/Dh and S/d. The heat transfer pattern due to the flow reattachment in the downstream area is significantly modified by the rib height e/Dh. The area influenced by the enhancement is found to be more affected by S/d. A larger enhancement area reflected a stronger impact associated with the heat transfer mechanism for e/Dh = 0.078.
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| 5. |
- Ghorbani-Tari, Zahra, et al.
(author)
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Heat Transfer Control Around an Obstacle by Using Ribs in the Downstream Region
- 2014
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In: Journal of Thermal Science and Engineering Apllications. - : ASME International. - 1948-5093 .- 1948-5085. ; 6:4
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Journal article (peer-reviewed)abstract
- This paper investigates the effect of the presence of a rib on the local heat transfer around an obstacle using liquid crystal technique. An obstacle with a rectangular cross section is placed in a channel and attached to the end-wall. A rib is positioned in the downstream region of the obstacle. The spacing S between the rib and the obstacle is normalized by the spanwise width of the obstacle and the value is 1.25d. The effects of the rib height e/D-h and Reynolds number are investigated. The e/D-h has the values 0.039 and 0.078. The Reynolds number varies between 35,600 and 55,600. It is shown that the local heat transfer in the upstream region of the obstacle remained unaffected by the presence of the rib. The feature of local heat transfer in the downstream area of the obstacle was substantially modified by the presence of the rib.
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| 6. |
- Li, Shian, et al.
(author)
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AN EXPERIMENTAL AND NUMERICAL STUDY OF FLOW AND HEAT TRANSFER IN RIBBED CHANNELS WITH LARGE RIB PITCH-TO-HEIGHT RATIOS
- 2013
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In: Journal of Enhanced Heat Transfer. - 1563-5074. ; 20:4, s. 305-319
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Journal article (peer-reviewed)abstract
- This paper presents an experimental and numerical study of flow and heat transfer char teristics in rectangular cross-section ribbed channels with continuous transverse ribs with large pitch-to-height ratios. Five ribs are regularly placed on the bottom wall of the channels with varied rib pitch-to-height ratios ranging from 10 to 30. The channel inlet Reynolds number ranges from 57,000 to 127,000 based on the channel hydraulic diameter. The studied geometry is relevant for hot internal structures in aircraft engines. In this study, the steady state, liquid crystal thermography (LCT) technique is used to obtain detailed heat transfer coefficients in the inter-rib surface regions. Then a computational fluid dynamics (CFD) technique based on the solution of the Reynolds-averaged Navier-Stokes (RANS) equations is employed to study flow and heat transfer characteristics in ribbed channels. The realizable k - epsilon turbulence model is used as the turbulence closure. The numerical results show a good agreement with the experimental data. An important purpose of this study is to investigate the flow and heat transfer behavior between the first repeated ribs, i.e., in the regions where the flow and thermal fields are not yet periodically fully developed.
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| 7. |
- Wang, Lei, et al.
(author)
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ENDWALL HEAT TRANSFER AT THE TURN SECTION IN A TWO-PASS SQUARE CHANNEL WITH AND WITHOUT RIBS
- 2013
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In: Journal of Enhanced Heat Transfer. - 1563-5074. ; 20:4, s. 321-332
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Journal article (peer-reviewed)abstract
- The endwall heat transfer characteristics at the turn section in a two-pass square channel have been examined experimentally using a liquid crystal thermal imaging technique. The effects of periodic ribs on the endwall heat transfer are also discussed. Results indicate that the heat transfer at the turn section in the absence of ribs is dominated by the flow impingement. Close to the impingement region, the Nusselt number is scaled by Re-0.56; further downstream, the scaling factor changes to Re-0.62. The heat transfer distribution on the endwall is not monotonic and a local minimum region is observed. It is believed that the local minimum region is associated with the transition between two regimes with distinct turbulence levels. In the presence of ribs, the heat transfer patterns are significantly altered. Due to the increased turbulence levels induced by the protrusion of ribs, the local minimum Nu region cannot be detected. In addition, thermal performance is evaluated based on the constant flow rate and pumping power criteria. It is found that the highest heat transfer enhancement factor is obtained at a rib pitch ratio of 12.
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