| 1. |
- Berntsson, Fredrik
(författare)
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An Inverse Heat Conduction Problem and Improving Shielded Thermocouple Accuracy
- 2012
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Ingår i: Numerical Heat Transfer, Part A Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 61:10, s. 754-763
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Tidskriftsartikel (refereegranskat)abstract
- A shielded thermocouple is a measurement device used for monitoring the temperature in chemically, or mechanically, hostile environments. The sensitive parts of the thermocouple are protected by a shielding layer. In order to improve the accuracy of the measurement device, we study an inverse heat conduction problem where the temperature on the surface of the shielding layer is sought, given measured temperatures in the interior of the thermocouple. The procedure is well suited for real-time applications where newly collected data is continuously used to compute current estimates of the surface temperature. Mathematically we can formulate the problem as a Cauchy problem for the heat equation, in cylindrical coordinates, where data is given along the line r = r 1 and the solution is sought at r 1 < r ≤ r 2. The problem is ill-posed, in the sense that the solution (if it exists) does not depend continuously on the data. Thus, regularization techniques are needed. The ill–posedness of the problem is analyzed and a numerical method is proposed. Numerical experiments demonstrate that the proposed method works well.
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| 2. |
- Bovo, Mirko, 1979, et al.
(författare)
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On the Numerical Modeling of Impinging Jets Heat Transfer - A Practical Approach
- 2013
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Ingår i: Numerical Heat Transfer Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 64:4, s. 290-316
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Tidskriftsartikel (refereegranskat)abstract
- This article compares steady-state and transient simulations in predicting impinging jet heat transfer. The configurations tested are H/D=2 and 6, Re=10,000, 20,000, 23,000, and 30,000. The variables considered are: turbulence model (LES, k-E, k-, V2F), discretization schemes, mesh density and topology, inlet velocity profile, and turbulence. The V2F model performs best for the steady state simulations. The inlet velocity profile plays an important role. Mesh topology and distribution is also important. The turbulence created in the shear layer plays a stronger role than the inlet turbulence. The LES model reproduces the turbulent structures with a useful degree of accuracy.
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| 3. |
- Cao, Zhen, et al.
(författare)
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Numerical study on heat transfer enhancement for laminar flow in a tube with mesh conical frustum inserts
- 2017
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 72:1, s. 21-39
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Tidskriftsartikel (refereegranskat)abstract
- Enhanced heat transfer tubes (EHTT) with segmented mesh-conical frustums are considered. Tube diameter and frustum apex angle are fixed as 20 mm and 60o, respectively. The height ratio of frustum and sliced part are set as a golden ratio (1.618). Laminar thermal-hydraulic performance and effects of some parameters, e.g., bottom frustum diameter and pitch, are numerically simulated. The equal equivalent diameter and total flow area criteria are adopted to simplify 3D mesh pores to 2D ones. Flow and temperature fields show large velocities and gradients close to the wall and smaller velocities in the bulk region. This enhances heat transfer with a limited pressure drop. EHTTs obtain 1.4 - 3.3 times higher heat transfer than bare tubes and the performance evaluation criterion (PEC) varies from 1.3 to 1.8. Nusselt number (Nu) and friction factor (f) correlations are proposed. New insights into heat transfer enhancement and tube configuration are provided.
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| 4. |
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| 5. |
- Du, Kun, et al.
(författare)
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Effects of the layout of film holes near the vane leading edge on the endwall cooling and phantom cooling of the vane suction side surface
- 2017
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 71:9, s. 910-927
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Tidskriftsartikel (refereegranskat)abstract
- In the current research, effects of the layout of film holes near the first-stage vane leading edge on the endwall cooling and phantom cooling of the vane suction side surface were numerically studied. The computational results indicate that the case with a positive film-hole angle achieves a higher cooling effectiveness level on the endwall and vane suction side surface compared to the case with a corresponding negative film-hole angle. Furthermore, the location of the film hole has a significant influence on the cooling performance of the endwall and vane suction side surface. In addition, the case with a smaller distance from film holes to the vane stagnation also attains a slightly higher cooling effectiveness (phantom cooling effectiveness) on the vane suction side surface.
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| 6. |
- Du, Kun, et al.
(författare)
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Effects of the multicavity tip coolant injection on the blade tip and the over tip casing aerothermal performance in a high-pressure turbine cascade
- 2023
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 84:4, s. 340-354
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Tidskriftsartikel (refereegranskat)abstract
- In high performance gas turbine engines, the over tip leakage flow driven by the lateral pressure gradient is inevitably induced inside the blade tip gap in the high-pressure stage turbine due to the freestanding airfoil design methodology. To obtain an increasing level of thermal efficiency, the turbine inlet temperature is gradually increased in terms of the Brayton cycle. Hence, the blade tip and the over tip casing are subjected to high thermal load. In real turbine blade, cavity tips are widely used to decrease the over tip leakage flow and the thermal load on the blade tip and over tip casing. In the present study, the numerical simulations were conducted to investigate the effects of the multicavity coolant injection on the blade tip and the over tip casing aerothermal performance. Three-dimensional (3-D) Reynolds-averaged Navier–Stokes (RANS) equations and standard (Formula presented.) turbulence model were solved together in the simulations. The results indicate the ribs inside the tip cavity alter the distribution of film cooling efficiency by changing flow structure within the tip gap. Most of the coolant is limited in each little cavity owing to the blockage of ribs. Here, the swirling action of each cavity vortex results in the coolant providing a wider film cooling coverage. Therefore, the increase in film cooling effectiveness on the blade tip surface is more efficient than that of over-tip casing. The blade with four tip cavities film cooling (4CFC) obtains the largest area-averaged film cooling effectiveness, which is augmented by 14.3% in comparison with the case with a single tip cavity film cooling (1CFC).
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| 7. |
- Du, Kun, et al.
(författare)
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Influence of the pressure side injection slot on the cooling performance of endwall surface
- 2018
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 73:8, s. 517-534
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Tidskriftsartikel (refereegranskat)abstract
- In modern gas turbine engines, the first stage vane endwall endures high thermal load with the increase of the turbine inlet temperature and the uniformity of the temperature distribution at combustor outlet. Moreover, the endwall secondary flow forces the coolant flow toward the suction side, resulting in hot regions along the pressure side endwall. In the worst case, hot regions lead to thermal failure. In order to ensure that the gas turbine operates safely, advanced cooling techniques are urgently needed to be implemented to reduce the hot regions along the pressure side endwall. In the current research, the influences of the pressure side injection slot on the film cooling performance of the endwall surface were numerically investigated. The three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations combined with the shear stress transport (SST) (Formula presented.) turbulence model were solved to conduct the simulations. Cases with different injection slot configurations have been simulated. The results indicate that the hot region along the pressure side endwall is significantly reduced by introducing the pressure side injection slot. The coolant from the pressure side injection slot is assisted by the pressure side vertical flow toward the adjacent vane suction side. Therefore, the coolant coverage and the cooling effectiveness are increased. In this study, the expanded slot (ES) achieves a larger cooling effectiveness than the normal slot (NS) and convergent slot (CS) at a small blowing ratio M = 0.5. In contrast, the CS obtains a larger cooling effectiveness than the NS and ES at M = 1.0 and M = 1.5. In addition, the introduction of the pressure side injection slot has a small influence on the aerodynamic performance of the vane cascade.
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| 8. |
- Du, Wei, et al.
(författare)
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Heat transfer and flow structure in a rotating duct with detached pin fins
- 2019
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 75:4, s. 217-241
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Tidskriftsartikel (refereegranskat)abstract
- The realizable k - ε turbulence model was used to calculate flow and heat transfer characteristics in a rotating rectangular duct with detached pin fins in staggered arrangement. Transverse and longitudinal spacings of the pin fins were S 1 = 2.5 D and S 2 = 2.5 D, respectively. Reynolds number was 7,000 and Rotation number (Ro) varied from 0 to 1 while the clearance ranged from 0 to 0.5. Streamlines, vortex structure, wall shear stresses and Nusselt numbers were obtained. Flow phenomenon at the pin fin rear side and a leakage vortex near the pin fin tip were observed. High Nusselt numbers appeared on leading side. The leakage vortex imposed high energy losses in the mainflow. The flow and heat transfer characteristics were associated with Ro number and clearance. Middle values of Ro and clearance induced highest Nusselt numbers on leading side. However, high Ro and small clearance gave highest Nusselt numbers on trailing side.
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| 9. |
- Eriksson, John, 1973, et al.
(författare)
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Finite element analysis of coupled nonlinear heat and moisture transfer in wood
- 2006
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Ingår i: Numerical Heat Transfer, Part A Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 50:9, s. 851-864
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear model for analysing heat and moisture flow in wood during drying below the fiber saturation point is presented. The model used considers wood at a macro level without taking the various moisture transports mechanisms at the microscopic level into account. Based on the finite-element method, a coupled system of equations resulting from the adopted heat and moisture transfer equations is established and an iterative scheme is proposed. The numerical procedure is verified by a test example. In a two-dimensional analysis, the influence of the coupling on the combined heat and moisture transfer is studied for a board subjected to a typical kiln-drying condition. How well the results agree with those obtained by introducing a commonly applied simplification is discussed.
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| 10. |
- Etemad, Sassan, et al.
(författare)
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Numerical investigation of turbulent heat transfer in a rectangular-sectioned 90 degrees bend
- 2006
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Ingår i: Numerical Heat Transfer Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 49:4, s. 323-343
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Tidskriftsartikel (refereegranskat)abstract
- The flow and thermal fields in a rectangular-sectioned 90 degrees bend with a cross-section aspect ratio of 6 were investigated using four turbulence models. All models managed to reproduce the general flow and thermal patterns. Chen's high-Re k-epsilon model and Suga's cubic low-Re k-epsilon model performed well. The V2F k-epsilon model was found to be the least diffusive model and delivered good results. The RSM-GGDH model showed convergence difficulties and gave poor results. It was found that the boundary-layer thickness and the flow upstream of the bend are crucial for the character of the secondary flow, velocity profile, turbulence level, and heat transfer in the bend.
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