| 1. |
- Luo, Lei, et al.
(författare)
-
An experimental investigation on the thermal augmentation of internal endwall in a two-pass duct using an array of delta-winglet vortex generator pair
- 2022
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 182
-
Tidskriftsartikel (refereegranskat)abstract
- The present study experimentally demonstrates a novel design for an internal endwall in a two-pass duct heat exchanger. An array of delta-winglet vortex generator pairs with different aspect ratio, angle of attack, configuration are mounted on the internal endwall in a U duct. Liquid crystal thermalgraphy and static pressure measurements are utilized in this study to evaluate the heat transfer, thermal-hydraulic performance, and pressure drop penalty. The Reynolds number is varied from 10,000 to 20,000. A comparison between the current novel design and traditional enhanced heat transfer turbulators in the open literature is also included. The results show that the endwall heat transfer is enhanced greatly as the longitudinal vortex generator array is located on the endwall. The variation of the attack angle has great influence on the endwall heat transfer, The endwall fitted with turbulators with an aspect ratio (length/height) of 2 and attack angle of 45-deg provides the highest thermal-hydraulic performance with a relatively low pressure drop penalty as long lasting longitudinal vortices might be induced at this attack angle and the heat transfer is observed to be enhanced at the downstream part of the endwall. In addition, for the temperature uniformity on the endwall, the local heat transfer at the upstream part still has the potential to be further improved for all studied cases. The optimal thermalhydraulic performance is increased by more than 24% compared with that on the endwall in the smooth U duct. This novel design presents a rather high overall thermal performance compared with the traditional design in the open literature.
|
|
| 2. |
- Luo, Lei, et al.
(författare)
-
Computational investigation of curvature effects on jet impingement heat transfer at internally cooled turbine vane leading edge regions
- 2020
-
Ingår i: Heat Transfer Research. - 1064-2285. ; 51:4, s. 333-357
-
Tidskriftsartikel (refereegranskat)abstract
- This study is carried out by using numerical simulations to investigate the effect of target surface curvature and the nozzle-to-target surface distance on the flow structure and heat transfer characteristics in a pin-finned double-wall cooling structure. The flow is directly impinging on the target surface and is disturbed by the pin fins, and then released from the film holes after passing the double-wall chamber. The ratio between the radius of the concave outer surface and the chord length of the concave outer surface is varied from 0.500 to 1.300 and the ratio between nozzle-to-target surface distance and diameter of impingement hole is ranging from 0.5 to 2.0. The Reynolds number is between 10,000 and 50,000. Results of the flow structure in the chamber, heat transfer on the target surface, and friction factor of the pin-fi nned channel are included. It is found that an increase of the target surface curvature has signifi cant effects on the flow structure and thus the heat transfer on the target surface is augmented. The Taylor-Görtler vortices near the pin fins are also influenced by the target surface curvature. On the other hand, the nozzle-to-target surface distance influences the jet impingement and the vortices, which are generated by the curvature, remarkably. It is found that the area goodness factor and volume goodness factor are improved by the surface curvature.
|
|
| 3. |
- Luo, Lei, et al.
(författare)
-
Surface temperature reduction by using dimples/protrusions in a realistic turbine blade trailing edge
- 2018
-
Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 74:5, s. 1265-1283
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, numerical simulations have been conducted on the heat transfer effect of dimple/protrusion layouts of a pin-finned wedge duct. Conjugate heat transfer calculations are further performed to investigate the cooling effect of modified schemes with dimples and protrusions added. Comparisons are carried out with a turbine second stage guide vane employed as the prototype. The dimple/protrusion-pin fin arrangement is set as the optimum one obtained above, and dimple depth/protrusion height varies from 0.2 to 0.3 times the structure diameter. It is found that the side-by-side arrangement and protrusion structure is more beneficial for the wedge duct endwall heat transfer. Comparison with the prototype blade shows that the addition of both dimples and protrusions are helpful in enhancing the trailing edge cooling effect. The cooling effect is increased with an increase in dimple depth/protrusion height. The results also show that the modified blade with protrusions attached at 0.3 height saves 0.48 g/s cooling mass flow and reaches the most positive performance with a 17 K, 14 K average temperature reduction, 0.022, 0.018 cooling effect increasing for pressure, suction side, respectively.
|
|
| 4. |
- Meng, Weida, et al.
(författare)
-
Genotype-dependent epigenetic regulation of DLGAP2 in alcohol use and dependence
- 2021
-
Ingår i: Molecular Psychiatry. - : Springer Nature. - 1359-4184 .- 1476-5578. ; 26:8, s. 4367-4382
-
Tidskriftsartikel (refereegranskat)abstract
- Alcohol misuse is a major public health problem originating from genetic and environmental risk factors. Alterations in the brain epigenome may orchestrate changes in gene expression that lead to alcohol misuse and dependence. Through epigenome-wide association analysis of DNA methylation from human brain tissues, we identified a differentially methylated region, DMR-DLGAP2, associated with alcohol dependence. Methylation within DMR-DLGAP2 was found to be genotype-dependent, allele-specific and associated with reward processing in brain. Methylation at the DMR-DLGAP2 regulated expression of DLGAP2 in vitro, and Dlgap2-deficient mice showed reduced alcohol consumption compared with wild-type controls. These results suggest that DLGAP2 may be an interface for genetic and epigenetic factors controlling alcohol use and dependence.
|
|
| 5. |
- Qiu, Dandan, et al.
(författare)
-
Analysis of heat transfer and fluid flow of a slot jet impinging on a confined concave surface with various curvature and small jet to target spacing
- 2019
-
Ingår i: International Journal of Numerical Methods for Heat and Fluid Flow. - 0961-5539. ; 29:8, s. 2885-2910
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: This study aims to focus on the surface curvature, jet to target spacing and jet Reynolds number effects on the heat transfer and fluid flow characteristics of a slot jet impinging on a confined concave target surface at constant jet to target spacing. Design/methodology/approach: Numerical simulations are used in this research. Jet to target spacing, H/B is varying from 1.0 to 2.2, B is the slot width. The jet Reynolds number, Rej, varies from 8,000 to 40,000, and the surface curvature, R2/B, varies from 4 to 20. Results of the target surface heat transfer, flow parameters and fluid flow in the concave channel are performed. Findings: It is found that an obvious backflow occurs near the upper wall. Both the local and averaged Nusselt numbers considered in the defined region respond positively to the Rej. The surface curvature plays a positive role in increasing the averaged Nusselt number for smaller surface curvature (4-15) but affects little as the surface curvature is large enough (> 15). The thermal performance is larger for smaller surface curvature and changes little as the surface curvature is larger than 15. The jet to target spacing shows a negative effect in heat transfer enhancement and thermal performance. Originality/value: The surface curvature effects are conducted by verifying the concave surface with constant jet size. The flow characteristics are first obtained for the confined impingement cases. Then confined and unconfined slot jet impingements are compared. An ineffective point for surface curvature effects on heat transfer and thermal performance is obtained.
|
|
| 6. |
- Qiu, Dandan, et al.
(författare)
-
Effect of truncated pin-fins on flow and heat transfer characteristics with impinging jets on a concave surface
-
Ingår i: Numerical Heat Transfer; Part A: Applications. - 1040-7782.
-
Tidskriftsartikel (refereegranskat)abstract
- The double-wall cooling system containing jet impingement and full-length pin-in cooling structures shows good performance in heat transfer enhancement and uniformity, which has-been used in the blade cooling design. However, the pressure loss induced by the full-length pin-fin is relatively high. It is very meaningful to get a cooling type which can balance the heat transfer performance of double-wall cooling and flow resistance, especially for the blade leading edge. In this study, numerical simulations have been carried out to study the influences of truncated pin-fins height and arrangement on heat transfer increment and flow behavior of jets impinging onto a concave double wall channel with varying truncated pin-fins arranged, considering the heat transfer enhancement potential and relatively weaken pressure loss penalty of truncated/broken pin-fin. Jets impingement on a smooth-concave surface is regarded as Baseline. Streamlines in two-dimensional sections in the channel and limiting streamlines near the target wall conjugated with flow characteristics figures are applied to better understand the flow structures in the channel. The local and averaged heat transfer performance is analyzed based on the flow discussions. The overall parameters, i.e., thermal performance, friction factor and pumping power, are also obtained. The results show that the introduction of relatively high truncated pin-fins located on the upper wall presents higher heat transfer enhancement and lower pressure loss comparing with the full-length case and truncated pin-fins located on pressure loss comparing with the full-length case and truncated pin-fins located on target wall cases. The truncated pin-fins placed on the upper surface with relative height of 0.75 reaches the highest overall thermal performance and uniformity in this work.
|
|
| 7. |
- Qiu, Dandan, et al.
(författare)
-
On heat transfer and flow characteristics of jets impingement on a concave surface with varying pin-fin arrangements
- 2021
-
Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 170
-
Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations have been conducted to investigate the effects of pin-fin arrangement and jet Reynolds number on heat transfer enhancement and flow characteristics of a concave confined jet impingement cooled surface conjugated with pin-fins. The results without a pin-fin are used as a baseline. Vortices and different sections of streamlines in the channel are employed to understand the flow structures in this cooling system. Based on this, topology pictures are obtained with skin-friction lines to discuss the fluid flow near the target and pin-fin surface. The local and averaged heat transfer characteristics are analyzed using the flow characteristics. The overall parameters (friction factor, thermal performance, pumping power) are also obtained. The results show that the appearance of the pin-fin plays a positive role in heat transfer enhancement and uniformity. The case of a 35° pin-fin arrangement angle reaches the highest overall Nusselt number and heat transfer uniformity. The far away movement of the pin-fin is beneficial to decrease pumping power at a constant heat transfer. The thermal performance is highest for 55° pin-fin arrangement angle at a jet Reynolds number of 40,000 in this work.
|
|
| 8. |
- Qiu, Dandan, et al.
(författare)
-
On heat transfer and flow characteristics of jets impinging onto concave surface with varying bleeding arrangements
- 2021
-
Ingår i: International Journal of Numerical Methods for Heat and Fluid Flow. - 0961-5539. ; 31:12, s. 3642-3660
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this study is to investigate the effects of film holes’ arrangements and jet Reynolds number on flow structure and heat transfer characteristics of jet impingement conjugated with film cooling in a semicylinder double wall channel. Design/methodology/approach: Numerical simulations are used in this research. Streamlines on different sections, skin-friction lines, velocity, wall shear stress and turbulent kinetic energy contours near the concave target wall and vortices in the double channel are presented. Local Nusselt number contours and surface averaged Nusselt numbers are also obtained. Topology analysis is applied to further understand the fluid flow and is used in analyzing the heat transfer characteristics. Findings: It is found that the arrangement of side films positioned far from the center jets helps to enhance the flow disturbance and heat transfer behind the film holes. The heat transfer uniformity for the case of 55° films arrangement angle is most improved and the thermal performance is the highest in this study. Originality/value: The film holes’ arrangements effects on fluid flow and heat transfer in an impingement cooled concave channel are conducted. The flow structures in the channel and flow characteristics near target by topology pictures are first obtained for the confined film cooled impingement cases. The heat transfer distributions are analyzed with the flow characteristics. The highest heat transfer uniformity and thermal performance situation is obtained in present work.
|
|
| 9. |
- Zhao, Zhiqi, et al.
(författare)
-
Effect of divider wall-to-end wall distance on the vortical structures and heat transfer characteristics of two-pass channel using topological analysis
- 2022
-
Ingår i: International Journal of Numerical Methods for Heat and Fluid Flow. - 0961-5539. ; 32:1, s. 219-240
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: This study aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis and critical points principles of three-dimensional vortex flow. Design/methodology/approach: This aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis as well as critical points principles of three-dimensional vortex flow. Findings: The endwall heat transfer in the narrow spacing passage is significantly stronger than that in a wide spacing channel. As the gap clearance is kept at 0.87 times of the hydraulic diameter, the endwall heat transfer and thermal performance can be accordingly enhanced with low pressure drops, which is because a relatively strong concentrated impingement flow for the medium gap clearance helps to restrain the downstream fluid flow and enhance the shear effect of the secondary flow. Practical implications: The numerical results can be applied in designing sharp turn of serpentine channel in heat exchangers, heat sinks, piping system, solar receiver and gas turbine blades. Originality/value: The evolution mechanism of the vortices in the turning region under different gap clearance was analyzed, and thermal enhancement characteristics were predicted innovatively using topological analysis method.
|
|
| 10. |
- Zhao, Zhiqi, et al.
(författare)
-
Experimental evaluation of longitudinal and transverse vortex generators on the endwall of a serpentine passage
- 2022
-
Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 176
-
Tidskriftsartikel (refereegranskat)abstract
- A 180-deg turning channel can be seen in many heat exchange systems, and a strong three-dimensional flow phenomenon will occur at the turning point. In order to strengthen the heat transfer inside the turn and considering the lack of relevant enhanced endwall heat transfer approach, the present study innovatively demonstrates the measures of enhanced internal endwall heat transfer using arrays of delta-winglet and conical vortex generators. The studied parameters of the vortex generators include aspect ratio (AR), spacing, and angle of attack, etc. The experimental results indicate that the longitudinal vortex generators have more advantages in increasing the heat transfer than the transverse conical vortex generators in certain configurations with the same order of magnitude of the increased area. Besides, transverse conical vortex generators are more helpful to improve the endwall heat transfer uniformity than longitudinal vortex generators. The array of longitudinal vortex generators with 45-deg angle of attack, 0.02 m pitch, and 2 aspect ratio provides the highest thermal performance for all studied cases, indicating that the longitudinal delta-winglet vortex generators can induce near-wall flow turbulence as well as convective heat transfer of the endwall with a modest pressure loss penalty. For this optimally designed endwall, the Nusselt number is augmented by up to 35%. From the perspective of energy saving, the present studied vortex generators provide a superior thermal performance at identical pumping power, which can be useful in the future design of endwalls in sharp-turn channels.
|
|
