Application of the Transient Heat Transfer Measurement Technique in a Low Aspect Ratio Pin Fin Cooling Channel

2015 ◽  
Author(s):  
Meriam Axtmann ◽  
Jens von Wolfersdorf ◽  
Georg Meyer
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Aspect Ratio ◽  
Measurement Technique ◽  
Thermal Inertia ◽  
Reference Temperature ◽  
Bulk Temperature ◽  
Cooling Channel ◽  
Pin Fin ◽  
The Impact

This study investigates on heat transfer enhancement in pin fin cooling channels. Experiments are conducted in a staggered pin fin array consisting of 15 rows. Heat transfer measurements are conducted in the pin fin cooling channel using the transient liquid crystal technique. The reference temperature is approximated by the fluid bulk temperature, acquired by thermocouples at specific positions. Thermal inertia of the used thermocouples is considered. One other problem that occurs while using relatively long thermocouples in short aspect ratio ducts is the heat conduction along the wires, the so called stem effect. This can lead to erroneous temperature measurements. The impact of the thermocouple immersion length on the temperature measurement is investigated. A detailed assessment of the space and time-wise varying temperature distribution is conducted for the appropriate reference temperature. This paper gives an overview about the experimental setup and the used transient measurement technique. Results are represented in terms of temperature distribution, heat transfer distribution and averaged Nusselt number at the endwall.

Application of the Transient Heat Transfer Measurement Technique in a Low Aspect Ratio Pin Fin Cooling Channel

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Meriam Axtmann ◽  
Jens von Wolfersdorf ◽  
Georg Meyer
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Aspect Ratio ◽  
Measurement Technique ◽  
Thermal Inertia ◽  
Reference Temperature ◽  
Bulk Temperature ◽  
Cooling Channel ◽  
Pin Fin ◽  
The Impact

This study investigates on heat transfer enhancement in pin fin cooling channels. Experiments are conducted in a staggered pin fin array consisting of 15 rows. Heat transfer measurements are conducted in the pin fin cooling channel using the transient liquid crystal technique. The reference temperature is approximated by the fluid bulk temperature, acquired by thermocouples at specific positions. Thermal inertia of the used thermocouples is considered. One other problem that occurs while using relatively long thermocouples in short aspect ratio ducts is the heat conduction along the wires, the so-called stem effect. This can lead to erroneous temperature measurements. The impact of the thermocouple immersion length on the temperature measurement is investigated. A detailed assessment of the space and timewise varying temperature distribution is conducted for the appropriate reference temperature. This paper gives an overview about the experimental setup and the used transient measurement technique. Results are represented in terms of temperature distribution, heat transfer distribution, and averaged Nusselt number at the endwall.

scholarly journals Efficiency Improvement of Miniaturized Heat Exchangers

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 25
Author(s):  
Iris Gerken ◽  
Thomas Wetzel ◽  
Jürgen J. Brandner
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Assessment Method ◽  
Flow Path ◽  
Transfer Enhancement ◽  
Pressure Losses ◽  
Pin Fin ◽  
Additional Pressure ◽  
The Impact

Micro heat exchangers have been revealed to be efficient devices for improved heat transfer due to short heat transfer distances and increased surface-to-volume ratios. Further augmentation of the heat transfer behaviour within microstructured devices can be achieved with heat transfer enhancement techniques, and more precisely for this study, with passive enhancement techniques. Pin fin geometries influence the flow path and, therefore, were chosen as the option for further improvement of the heat transfer performance. The augmentation of heat transfer with micro heat exchangers was performed with the consideration of an improved heat transfer behaviour, and with additional pressure losses due to the change of flow path (pin fin geometries). To capture the impact of the heat transfer, as well as the impact of additional pressure losses, an assessment method should be considered. The overall exergy loss method can be applied to micro heat exchangers, and serves as a simple assessment for characterization. Experimental investigations with micro heat exchanger structures were performed to evaluate the assessment method and its importance. The heat transfer enhancement was experimentally investigated with microstructured pin fin geometries to understand the impact on pressure loss behaviour with air.

scholarly journals Optimization Design of Lattice Structures in Internal Cooling Channel with Variable Aspect Ratio of Gas Turbine Blade

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3954
Author(s):  
Liang Xu ◽  
Qicheng Ruan ◽  
Qingyun Shen ◽  
Lei Xi ◽  
Jianmin Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Optimization Model ◽  
Lattice Structure ◽  
Turbine Blades ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Cooling Channels ◽  
Mechanical Performances ◽  
Type Lattice

Traditional cooling structures in gas turbines greatly improve the high temperature resistance of turbine blades; however, few cooling structures concern both heat transfer and mechanical performances. A lattice structure (LS) can solve this issue because of its advantages of being lightweight and having high porosity and strength. Although the topology of LS is complex, it can be manufactured with metal 3D printing technology in the future. In this study, an integral optimization model concerning both heat transfer and mechanical performances was presented to design the LS cooling channel with a variable aspect ratio in gas turbine blades. Firstly, some internal cooling channels with the thin walls were built up and a simple raw of five LS cores was taken as an insert or a turbulator in these cooling channels. Secondly, relations between geometric variables (height (H), diameter (D) and inclination angle(ω)) and objectives/functions of this research, including the first-order natural frequency (freq1), equivalent elastic modulus (E), relative density (ρ¯) and Nusselt number (Nu), were established for a pyramid-type lattice structure (PLS) and Kagome-type lattice structure (KLS). Finally, the ISIGHT platform was introduced to construct the frame of the integral optimization model. Two selected optimization problems (Op-I and Op-II) were solved based on the third-order response model with an accuracy of more than 0.97, and optimization results were analyzed. The results showed that the change of Nu and freq1 had the highest overall sensitivity Op-I and Op-II, respectively, and the change of D and H had the highest single sensitivity for Nu and freq1, respectively. Compared to the initial LS, the LS of Op-I increased Nu and E by 24.1% and 29.8%, respectively, and decreased ρ¯ by 71%; the LS of Op-II increased Nu and E by 30.8% and 45.2%, respectively, and slightly increased ρ¯; the LS of both Op-I and Op-II decreased freq1 by 27.9% and 19.3%, respectively. These results suggested that the heat transfer, load bearing and lightweight performances of the LS were greatly improved by the optimization model (except for the lightweight performance for the optimal LS of Op-II, which became slightly worse), while it failed to improve vibration performance of the optimal LS.

scholarly journals Heat Transfer From Low Aspect Ratio Pin Fins

2007 ◽  
Author(s):  
Michael E. Lyall ◽  
Alan A. Thrift ◽  
Atul Kohli ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Gas Turbines ◽  
Channel Height ◽  
Internal Cooling ◽  
Number Range ◽  
Pin Fin ◽  
Heat Transfer Augmentation ◽  
Low Aspect Ratio ◽  
Pin Fins

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Heat transfer augmentation in internal flows is commonly achieved through the use of pin fins, which increase both surface area and turbulence. The present research is focused on internal cooling of turbine airfoils using a single row of circular pin fins that is oriented perpendicular to the flow. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. A number of spanwise spacings were investigated for a Reynolds number range between 5000 to 30,000. Both pressure drop and spatially-resolved heat transfer measurements were taken. The heat transfer measurements were made on the endwall of the pin fin array using infrared thermography and on the pin surface using discrete thermocouples. The results show that the heat transfer augmentation relative to open channel flow is the highest for smallest spanwise spacings and lowest Reynolds numbers. The results also indicate that the pin fin heat transfer is higher than the endwall heat transfer.

Heat Transfer in a Rotating, Two-Pass, Variable Aspect Ratio Cooling Channel With Profiled V-Shaped Ribs

2020 ◽  
Author(s):  
I-Lun Chen ◽  
Izzet Sahin ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Channel Modeling ◽  
Cooling Channel ◽  
Transfer Enhancement ◽  
Rotation Numbers ◽  
First Pass ◽  
Rib Turbulators

Abstract The thermal performance of two V-type rib configurations is measured in a rotating, two-pass cooling channel. Modeling modern, high pressure, turbine blades, the cross-section of the cooling channel varies from the first pass to the second pass. The coolant travels radially outward in the rectangular first pass with an aspect ratio of 4:1. Near the tip region, the coolant turns 180°, and travels radially inward in a 2:1 rectangular channel. The serpentine passage is positioned such that both the first and second passes are oriented 90° to the direction of rotation. The leading and trailing surfaces of both the first and second pass of the channel are roughened with V-type rib turbulators. The thermal performance of two V-type configurations is measured in this two-pass channel. The first V-shaped configuration is similar to a traditional V-shaped turbulator with a narrow gap at the apex of the V. The configuration is modified by off-setting one leg of the V to create a staggered discrete, V-shaped configuration. The ribs are oriented 45° relative to the streamwise coolant direction. In both passes, the rib spacing is P/e = 10 and the rib height – to – channel height is e/H = 0.16. The heat transfer enhancement and frictional losses are measured for both rib configurations with varying Reynolds and rotation numbers. The Reynolds number varies from 10,000 to 45,000 in the AR = 4:1 first pass; this corresponds to 16,000 to 73,500 in the AR = 2:1 second pass. Considering the effect of rotation, the rotational speed of the channel varies from 0–400 rpm with maximum rotation numbers of 0.39 and 0.16 in the first and second passes, respectively. The heat transfer enhancement on both the leading and trailing surfaces of the first pass of the 45° V-shaped channel is slightly reduced with rotation. In the second pass, the heat transfer increases on the leading surface while it decreases on the trailing surface. The 45° staggered, discrete V-shaped ribs provide increased heat transfer and thermal performance compared to the traditional V-shaped and standard, 45° angled rib turbulators.

Heat Transfer Characteristics of a Flow Passage With Long Pin Fins and Improving Heat Transfer Coefficient by Adding Turbulence Promoters on a Endwall

2001 ◽  
Author(s):  
K. Takeishi ◽  
T. Nakae ◽  
K. Watanabe ◽  
M. Hirayama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
High Heat ◽  
Atmospheric Conditions ◽  
Pin Fin ◽  
High Heat Transfer ◽  
Turbine Vanes ◽  
Pin Fins

Pin fins are normally used for cooling the trailing edge region of a turbine, where their aspect ratio (height H/diameter D) is characteristically low. In small turbine vanes and blades, however, pin fins may also be located in the middle region of the airfoil. In this case, the aspect ratio can be quite large, usually obtaining values greater than 4. Heat transfer tests, which are conducted under atmospheric conditions for the cooling design of turbine vanes and blades, may overestimate the heat transfer coefficient of the pin-finned flow channel for such long pin fins. The fin efficiency of a long pin fin is almost unity in a low heat transfer situation as it would be encountered under atmospheric conditions, but can be considerably lower under high heat transfer conditions and for pin fins made of low thermal conductivity material. A series of tests with corresponding heat transfer models has been conducted in order to clarify the heat transfer characteristics of the long pin-finned flow channel. It is assumed that heat transfer coefficients can be predicted by the linear combination of two heat transfer equations, which were separately developed for the pin fin surface and for tubes in crossflow. To confirm the suggested combined equations, experiments have been carried out, in which the aspect ratio and the thermal conductivity of the pin were the test parameters. To maintain a high heat transfer coefficient for a long pin fin under high-pressure conditions, the heat transfer was augmented by adding a turbulence promoter on the pin-finned endwall surface. A corresponding equation that describes this situation has been developed. The predicted and measured values showed good agreement. In this paper, a comprehensive study on the heat transfer of a long pin-fin array will be presented.

scholarly journals Effects of a Rotating Cone on the Mixed Convection in a Double Lid-Driven 3D Porous Trapezoidal Nanofluid Filled Cavity under the Impact of Magnetic Field

Nanomaterials ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 449 ◽  
Author(s):  
Ali J. Chamkha ◽  
Fatih Selimefendigil ◽  
Hakan F. Oztop
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Mixed Convection ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Rotational Velocity ◽  
Rotating Cone ◽  
The Impact

Effects of a rotating cone in 3D mixed convection of CNT-water nanofluid in a double lid-driven porous trapezoidal cavity is numerically studied considering magnetic field effects. The numerical simulations are performed by using the finite element method. Impacts of Richardson number (between 0.05 and 50), angular rotational velocity of the cone (between −300 and 300), Hartmann number (between 0 and 50), Darcy number (between 10 − 4 and 5 × 10 − 2 ), aspect ratio of the cone (between 0.25 and 2.5), horizontal location of the cone (between 0.35 H and 0.65 H) and solid particle volume fraction (between 0 and 0.004) on the convective heat transfer performance was studied. It was observed that the average Nusselt number rises with higher Richardson numbers for stationary cone while the effect is reverse for when the cone is rotating in clockwise direction at the highest supped. Higher discrepancies between the average Nusselt number is obtained for 2D cylinder and 3D cylinder configuration which is 28.5% at the highest rotational speed. Even though there are very slight variations between the average Nu values for 3D cylinder and 3D cone case, there are significant variations in the local variation of the average Nusselt number. Higher enhancements in the average Nusselt number are achieved with CNT particles even though the magnetic field reduced the convection and the value is 84.3% at the highest strength of magnetic field. Increasing the permeability resulted in higher local and average heat transfer rates for the 3D porous cavity. In this study, the aspect ratio of the cone was found to be an excellent tool for heat transfer enhancement while 95% enhancements in the average Nusselt number were obtained. The horizontal location of the cone was found to have slight effects on the Nusselt number variations.

Effect of Wall Conduction on Combined Free and Forced Laminar Convection in Horizontal Rectangular Channels

1987 ◽  
Vol 109 (4) ◽  
pp. 936-942 ◽  
Author(s):  
G. J. Hwang ◽  
F. C. Chou
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Temperature Distribution ◽  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Numerical Study ◽  
Fully Developed Flow ◽  
Rectangular Channels ◽  
Laminar Convection

This paper presents a numerical study of the effect of peripheral wall conduction on combined free and forced laminar convection in hydrodynamically and thermally fully developed flow in horizontal rectangular channels with uniform heat input axially, In addition to the Prandtl number, the Grashof number Gr+, and the aspect ratio γ, a parameter Kp indicating the significance of wall conduction plays an important role in heat transfer. A finite-difference method utilizing a power-law scheme is employed to solve the system of governing partial differential equations coupled with the equation for wall conduction. The numerical solution covers the parameters: Pr = 7.2 and 0.73, γ = 0.5, 1, and 2, Kp = 10−4–104, and Gr+ = 0–1.37×105. The flow patterns and isotherms, the wall temperature distribution, the friction factor, and the Nusselt number are presented. The results show a significant effect of the conduction parameter Kp.

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