| 1. |
- Alhelfi, Ali Kadhim Hadi, et al.
(author)
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Assessing Learning in Higher Education
- 2012
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Reports (pop. science, debate, etc.)abstract
- Assessment is a key activity within the higher education system. From the student´s perspective, assessment shapes what is to be learned; from the perspective of the educator it gives clear inputs about the quality of learning. Thus, as defined by the term, ‘Constructive alignment’, by careful planning of the assessment strategy and wise selection of the assessment methods, the teaching-learning experience can be designed in an aligned manner towards the achievement of the learning outcomes. Although, defined in different ways, the basic purpose of assessment is to work as a feedback tool to both, students and teachers, to improve the student learning. In this work, we review and comment on theoretical aspects of assessment including its significance and characteristics. Moreover, some important considerations regarding the design of the assessment activities are presented, together with the description of some methods for assessing learning. With this work we would like to invite the reader to reevaluate the significance of assessment within the learning experience, and by this, hopefully the educator is “inspired” to improve the assessment activities in the classroom or another less conventional learning space.
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| 2. |
- Derakhhsandeh, Javad Farrokhi, et al.
(author)
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Thermo-fluids effects of a grooved circular cylinder in laminar flow regimes
- 2021
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In: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933. ; 124
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Journal article (peer-reviewed)abstract
- The force coefficients and heat transfer related to a circular cylinder with grooved surfaces are studied at Re ≤ 200. Three types of grooved surfaces are examined: square, triangle, and dimple. The grooves are arranged at θ = 0°, 30°, 45°, 60°, 90° from the forward stagnation point of the cylinder. It is shown that the existence of a groove controls the dynamic behavior of the vortices; as such lift and drag coefficients have been varied considerably, depending on the shape of the groove and θ. The coefficients appear very sensitive to triangle grooved surface, in particular, as θ varies to 45°. The results reveal that triangle grooved surface could produce minimum drag coefficient when θ varies to 45 for all examined Re; this is found much lower than that of the square and dimple grooved surfaces and even smooth cylinder. A significant enhancement of the Nu is attained in the wake of the triangle grooved cylinder surface with the angle of the location of 45 . At low Reynolds number (Re = 50), the Nu value of triangle grooved surface with θ = 0°is shown higher than that of other grooved surfaces, whereas this value is found to the lowest at high Reynolds number (Re = 200). 0 0
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| 3. |
- 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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| 4. |
- Ghorbani-Tari, Zahra
(author)
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Experimental Investigations of Heat Transfer in a Channel with Ribs and Obstacle
- 2014
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Doctoral thesis (other academic/artistic)abstract
- This thesis presents experimental investigations of local heat transfer in a rectangular channel (aspect ratio AR = 4) with continuous transverse ribs as well as an obstacle. Liquid crystal thermography (LCT) is employed to obtain the temperature fields in the heat transfer experiments. The liquid crystal applied here has a red start at 35°C and a bandwidth of 1°C. The work consists of (1) periodic ribs, (2) obstacle (3) integration of ribs with an obstacle. (1) The effect of (a) rib-pitch-to rib height ratio (p/e), and (b) rib height-to-channel hydraulic diameter ratio (e/Dh) on the local heat transfer in the first inter-rib regions (i.e., where thermal field is not yet periodically fully developed) are investigated. The Reynolds number, based on the channel hydraulic diameter, has the values 57000, 89000, and 127000. Concerning (a) with e/Dh = 0.078, the particular emphasis is on large p/e ratios, i.e., 10, 20 and 30, in the first inter-rib regions. It is conjectured that the main flow for all studied p/e ratios separates at the edge of the first rib and reattaches in the first inter-rib region at a distance of about 9-10e from the upstream rib edge, where a local maximum of the Nu number occurs. This distance is larger than that typically occurring in the periodically fully developed region. This may negatively affect the heat transfer in the entrance region if the p/e ratio is less than 10. Concerning (b), e/Dh = 0.039 and 0.078 have been selected for p/e = 10 and 20. The significant effect of the small blockage ratio on the local Nu number in the first inter-rib regions is found remarkable compared to the high blockage ratio. This effect is explained by the small thickness of the boundary layer in the developing region and it is conjectured that the core flow is strongly disturbed by the presence of the rib with high blockage ratio. (2) The end-wall heat transfer around a single obstacle is studied. The obstacle has a rectangular cross-section and blocks the whole height of the channel. The Reynolds number, based on the spanwise width of the obstacle, has the values 35600, 55600, and 79400. The appearance of a double peak of locally high heat transfer in the upstream junction indicates the existence of more than one vortex. As the Reynolds number increased, this double peak merged to a single peak. The Reynolds number effect is expected to affect the strength of the vortices demonstrated by higher local heat transfer from Reynolds number 35600 to 79400. The size of wake region with low heat transfer is shrinking by increasing the Reynolds numbers. (3) The aim is to control the heat transfer around an obstacle with the aid of a rib. The rib is positioned in (a) upstream region, and (b) downstream region of the obstacle. The Reynolds number varies between 35600 and 55600. In this study, the spacing between the rib and the obstacle is of primary importance. Concerning (a), the spacing S is normalized by the spanwise width of the obstacle and had values 1.25d and 0.625d. The effect of e/Dh is also of concern. The e/Dh varies between 0.039 and 0.078. It is found that the local heat transfer especially in the upstream region was strongly affected by the S/d and e/Dh. In the downstream region, the local heat transfer was more affected by the Reynolds number than S/d and e/Dh. Concerning (b) the spacing between the rib and the obstacle had the value 1.25d. It is shown that the local heat transfer in the upstream region of the obstacle remained unaffected by the presence of the rib for the considered rib heights and Reynolds numbers. In the downstream region of the obstacle, the heat transfer pattern was substantially modified by the presence of the rib for two considered rib height. In the upstream region of the rib, the small rib height presents higher local heat transfer than the large rib height for the considered Reynolds numbers. A larger region of high transfer in the downstream area of the rib reflects a stronger effect on the reattachment process caused by the large rib height.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- Ghorbani Tari, Zahra
(author)
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Flow boiling heat transfer characteristics of R245fa refrigerant in a plate heat exchanger
- 2020
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1599:1
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Conference paper (peer-reviewed)abstract
- Plate heat exchangers (PHEs) are used extensively in industrial applications and, owing to their compactness, and higher thermal efficiency, they are keys component of organic Rankine cycle (ORC) application. This study presents the experimental heat transfer characteristics during flow boiling of R245fa refrigerant with a commercial working fluid used in ORCs; inside brazed plate heat exchanger with chevron angle of 65 degree. The flow boiling heat transfer characteristics were measured with varying saturation temperatures, mass flux and heat flux, which range from 55.5 °C-61.8 °C, 15.5-17.4 kg m-2 s-1, and 6400-10120 W m-2, respectively. The experimental results showed that flow boiling heat transfer coefficient is dependent upon the heat flux and mass flux. The results showed that the heat transfer coefficient increases with the increase of heat flux, and then starts to decrease due to local dry out. However, at low mass flux, locally triggering dry out was more prominent than that high mass flux. The heat transfer coefficient showed to be sensitive to the change in the saturation temperature. Moreover, flow boiling heat transfer coefficient showed a linear relationship with mass flux of the refrigerant.
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| 9. |
- 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
-
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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| 10. |
- 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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