Thermal effect on large-aspect-ratio Couette–Taylor system: numerical simulations

2015 ◽  
Vol 771 ◽  
pp. 57-78 ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang ◽  
Innocent Mutabazi
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Convective Cell ◽  
Base Flow ◽  
Large Aspect Ratio ◽  
Radial Temperature ◽  
Instability Modes ◽  
Momentum And Heat Transfer

We have performed numerical simulations of the flow in a large-aspect-ratio Couette–Taylor system with rotating inner cylinder and with a radial temperature gradient. The aspect ratio was chosen in such a way that the base state is in the conduction regime. Away from the endplates, the base flow is a superposition of an azimuthal flow induced by rotation and an axial flow (large convective cell) induced by the temperature gradient. For a fixed rotation rate of the inner cylinder in the subcritical laminar regime, the increase of the temperature difference imposed on the annulus destabilizes the convective cell to give rise to co-rotating vortices as primary instability modes and to counter-rotating vortices as secondary instability modes. The space–time properties of these vortices have been computed, together with the momentum and heat transfer coefficients. The temperature gradient enhances the momentum and heat transfer in the flow independently of its sign.

Effect of Rib Configuration and Lateral Ejection on a High Aspect Ratio Trailing Edge Channel

2013 ◽  
Author(s):  
Rui Kan ◽  
Li Yang ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Local Heat Transfer ◽  
Large Aspect Ratio ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Average Heat ◽  
Edge Channel ◽  
Heat Transfer Coefficients

Thermal issues of gas turbine blade trailing edge are complex and challenging, due to limited space for effective cooling. The trailing edge cavities are usually large aspect ratio ducts with lateral ejection. The objective of this study is to investigate the effects of different rib configurations and lateral ejection on heat transfer characteristics inside a trailing edge channel. The investigations were conducted on a large aspect ratio wedge-shaped channel with square ribs of e/Dh = 0.05, under Reynolds number 15,000. Twelve different configurations were tested: 1)three rib types, including a symmetry V-shaped rib configuration and two non-symmetry V-shaped rib configurations, of which the rib angles are 60 degrees, 2) two rib pitches, P/e = 10 and P/e = 5, 3) two flow directions, with an open tip outlet or with lateral ejection. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal experimental method. The configurations were also investigated numerically for the detailed flow field and for the validation of CFD codes. Results show that with lateral ejection, the heat transfer coefficients decrease from inlet to outlet. The heat transfer near the ejection holes is enhanced while heat transfer coefficients near the wall opposite to the exit holes decrease. The curvature of the streamlines creates a large separation area near the end of the channel and thus results in low local heat transfer coefficients. The P/e = 10 configurations have higher average heat transfer compared with P/e = 5 configurations. Average heat transfer coefficient is the highest with the center of the V-shaped rib placed at the middle of the channel, and is the lowest when the V-shaped rib center is located near the narrow part of the channel.

Increase in ovality of uranium tubes due to creep under external pressure

1968 ◽  
Vol 3 (3) ◽  
pp. 226-231
Author(s):  
W S Blackburn ◽  
J Percy
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Creep Rate ◽  
Temperature Gradient ◽  
Outer Surface ◽  
External Pressure ◽  
Radial Temperature Gradient ◽  
Radial Temperature ◽  
Principal Axes ◽  
Inner Surface

The increase in ellipticity of a concentric slightly elliptical tube is theoretically investigated for the case of external pressure and radial temperature gradient when the creep rate is proportional to the stress and the constant of proportionality varies slightly between the principal axes. The presence of a radial temperature gradient accelerates the increase in ovality due to initial ovality on the outer surface and that due to circumferential variation of strength (except after very small collapses) and decreases that due to initial inner ovality. Further allowance for circumferential variation in temperature, due to an insulated inner surface and to a uniform heat-transfer coefficient to a gas at constant temperature around the outer surface, reduces the increase in all cases.

Thermal Hydraulic Analysis of a Water Tank With Large Aspect Ratio

2014 ◽  
Author(s):  
Qi Min ◽  
Li Zhang ◽  
Hongtao Wang ◽  
Junpeng Zhai
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Aspect Ratio ◽  
Hot Water ◽  
Water Tank ◽  
Large Aspect Ratio ◽  
Strong Function ◽  
Uniform Temperature Field ◽  
Cooling Pipes ◽  
Thermal Hydraulic Analysis

A special-shaped water tank with large aspect ratio and limited volume for cooling was investigated using computational fluid dynamics. The influence of a separator on the heat transfer ability in the water tank is analyzed. When there is no separator, the arrangement of cooling pipes is very important to the heat transfer and temperature field in the water tank. The total heat flux of the pipe bundle and the temperature field will become bad if the pipe bundle is arranged not uniform in the water tank. Adding a separator can greatly enhance the integral natural convection of cold and hot water in the water tank and a uniform temperature field and regular velocity field could be got. The heat transfer ability for the structure with a separator is better than the structure without a separator, and is not sensible to the arrangement of the pipe bundle. The heat transfer ability also did not change when the position of separator and pipe bundle exchanged, and is not a strong function of the distance between separator and the pipe bundle or the wall of the water tank. Finally, the inclination of the water tank is discussed.

Numerical Simulations and Experimental Characterization of Heat Transfer From a Periodic Impingement of Droplets

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Mario F. Trujillo ◽  
Jorge Alvarado ◽  
Eelco Gehring ◽  
Guillermo S. Soriano
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Numerical Simulations ◽  
Droplet Impact ◽  
Numerical Comparison ◽  
Temperature Profiles ◽  
Conductive Heat ◽  
Radial Temperature ◽  
The Impact

In this combined experimental and simulation investigation, a stream of HFE-7100 droplets striking a prewetted surface under constant heat flux was studied. An implicit free surface capturing technique based on the Volume-of-Fluid (VOF) approach was employed to simulate this process numerically. Experimentally, an infrared thermography technique was used to measure the temperature distribution of the surface consisting of a 100 nm ITO layer on a ZnSe substrate. The heat flux was varied to investigate the heat transfer behavior of periodic droplet impingement at the solid–liquid interface. In both experiments and simulations, the morphology of the impact zone was characterized by a quasi-stationary liquid impact crater. Comparison of the radial temperature profiles on the impinging surface between the experiments and numerical simulations yielded reasonable agreement. Due to the strong radial flow emanating from successive droplet impacts, the temperature distribution inside the crater region was found to be significantly reduced from its saturated value. In effect, the heat transfer mode in this region was governed by single phase convective and conductive heat transfer, and was mostly affected by the HFE-7100 mass flow rates or the number of droplets. At higher heat fluxes, the minimum temperature, and its gradient with respect to the radial coordinate, increased considerably. Numerical comparison between average and instantaneous temperature profiles within the droplet impact region showed the effect of thermal mixing produced by the liquid crowns formed during successive droplet impact events.

The Effects of Blade 3D Designs in Different Orthogonal Coordinates on the Performance of Compressor Cascades

2014 ◽  
Vol 31 (4) ◽  
Author(s):  
Pengfei Xu ◽  
Xianjun Yu ◽  
Baojie Liu
Keyword(s):  
Aspect Ratio ◽  
Numerical Simulations ◽  
Cascade Model ◽  
Large Aspect Ratio ◽  
3D Design ◽  
Vector Decomposition ◽  
Simulation Results ◽  
Flow Effects ◽  
Superposition Effect ◽  
Orthogonal Coordinates

AbstractThe chordwise based Sweep-Dihedral Coordinates (SDC) and axial-tangential based Axial Sweep-Lean Coordinates (ASLC) are the two widely used coordinates systems for blade 3D design. In order to clarify the relationships between them, some numerical simulations were conducted in a simplified planar cascade model. The cascade model has a large aspect ratio of 3.0 and free-slip endwalls, which are used to minimize the endwall flow effects. The simulation results of totally 9 cases with different blade 3D design schemes, including sweep, dihedral, axial sweep and lean, were analyzed. Firstly, the effects of each type of blade 3D designs were summarized. And then, based on the rule of vector decomposition in an orthogonal coordinates, the effects of blade axial sweep and lean in ASLC were deduced from the effects of blade sweep and dihedral in SDC. It was found that forward/backward axial sweep is combined by positive/negative dihedral and forward/backward sweep, which have opposite trends of effects, resulting in a counterbalance phenomenon. Moreover, positive/negative lean is combined by positive/negative dihedral and forward/backward sweep, which have the same trends of effects, resulting in a superposition effect.

scholarly journals ASSESSMENT OF HEAT TRANSFER IN FUEL CHANNEL OF INDIAN PHWR UNDER POSTULATED LARGE BREAK LOSS OF COOLANT ACCIDENT: EXPERIMENTAL AND NUMERICAL STUDY

2021 ◽  
Vol 247 ◽  
pp. 11003
Author(s):  
Ketan Ajay ◽  
Ravi Kumar ◽  
Akhilesh Gupta
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Numerical Study ◽  
Safety Concern ◽  
Thermal Characteristics ◽  
Fission Products ◽  
Hydrogen Gas ◽  
Gas Generation ◽  
Radial Temperature ◽  
Fuel Bundle

The behaviour of the channel under postulated large break LOCA scenario had been a prime safety concern. The radiative heat transfer is predominant in a channel when the convective cooling environment is marred. The estimation of temperature distribution in the fuel pins at elevated temperature is essential from the point of view of hydrogen gas generation and release of fission products. In this paper, the thermal characteristics of a channel for Indian PHWR under critical break failure is studied using experimental and numerical techniques. The experiment is carried out on an Indian PHWR having a fuel bundle of 37-fuel elements. The temperature profiles for different parts of the simulated channel comprising of fuel pins, PT and CT are obtained under steady condition. The numerical analysis is also performed using ANSYS Fluent 19.0. From the study, it is found that there is a significant radial temperature gradient in the fuel bundle from the center ring to the outer ring. Also, no significant circumferential temperature gradient is observed in the fuel bundle, PT and CT.

scholarly journals On heat transfer of weakly compressible power-law flows

2017 ◽  
Vol 21 (6 Part B) ◽  
pp. 2709-2718
Author(s):  
Botong Li ◽  
Liangliang Zhu ◽  
Liancun Zheng ◽  
Wei Zhang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Power Law ◽  
Conductivity Model ◽  
Weakly Compressible ◽  
Power Law Fluids ◽  
Momentum And Heat Transfer ◽  
Thermal Conductivity Model ◽  
Dilatant Fluid

This paper completes a numerical research on steady momentum and heat transfer in power-law fluids in a channel. Weakly compressible laminar fluids are studied with no slip at the walls and uniform wall temperatures. The full governing equations are solved by continuous finite element method. Three thermal conductivity models are adopted in this paper, that is, constant thermal conductivity model, thermal conductivity varying as a function of temperature gradient, and a modified temperature-gradient-dependent thermal conductivity model. The results are compared with each other and the physical characteristics for values of parameters are also discussed in details. It is shown that the velocity curve from the solution becomes straight at higher power-law index. The effects of Reynolds numbers on the dilatant fluid and the pseudo-plastic look similar to each other and their trends can be easily predicted. Furthermore, for different models, the temperature curves also present pseudo-plastic and dilatant properties.

scholarly journals A computational modeling on transient heat and fluid flow through a curved duct of large aspect ratio with centrifugal instability

2021 ◽  
Vol 136 (4) ◽  
Author(s):  
Shamsun Naher Dolon ◽  
Mohammad Sanjeed Hasan ◽  
Giulio Lorenzini ◽  
Rabindra Nath Mondal
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Aspect Ratio ◽  
Computational Modeling ◽  
Flow Velocity ◽  
Numerical Technique ◽  
Large Aspect Ratio ◽  
Duct Flow ◽  
Curved Duct ◽  
Centrifugal Instability

AbstractDue to remarkable applications of the curved ducts in engineering fields, scientists have paid much attention to invent new characteristics of curved-duct flow in mechanical systems. In the ongoing study, a computational modeling of fluid flow and energy distribution through a curved rectangular duct of large aspect ratio is presented. Governing equations are enumerated by using a spectral-based numerical technique together with the function expansion and collocation method. The main purpose of the paper is to analyze the effect of centrifugal force in the flow transition as well as heat transfer in the fluid. The investigations are performed for the aspect ratio, Ar = 4; the curvature ratio, $$\delta = 0.5$$ δ = 0.5 ; the Grashof number, $${\text{Gr}} = 1000$$ Gr = 1000 ; and varying the Dean number, $$0 < {\text{Dn}} \le 1000.$$ 0 < Dn ≤ 1000 . It is found that various types of flow regimes including steady-state and irregular oscillations occur as Dn is increased. To well understand the characteristics of the flow phase spaces and power spectrum of the solutions are performed. Next, pattern variations of axial and secondary flow velocity with isotherms are illustrated for different Dn’s. It is revealed that the flow velocity and the isotherms are significantly influenced by the duct curvature and the aspect ratio. Convective heat transfer and temperature gradients are calculated which explores that the fluids are diversified due to centrifugal instability, and as a consequence the overall heat transfer is enhanced significantly in the curved duct.

Effect of Entrance Geometry and Rotation on Heat Transfer in a Narrow (AR = 1:4) Rectangular Internal Cooling Channel

2014 ◽  
Author(s):  
Krishnendu Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Flow Distribution ◽  
Leading Edge ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Cross Sectional ◽  
Density Ratios

This paper studies the effect of entrance geometries on the heat transfer and fluid flow in a narrow aspect ratio (AR = 1:4) rectangular internal cooling channel, representative of a leading edge of a gas turbine blade, under rotating condition. Numerical simulations are performed to understand the role of the rotation generated forces on the flow for different entrance geometries representative of those encountered in practice. Three different entrance geometries are tested: a S-shape entrance, a 90 degree bend entrance and a twisted entrance that changes its aspect ratio along its length. Numerical simulations are run at a constant Reynolds number (Re = 15000), for a range of rotation numbers (Ro = 0–0.2) and density ratios (DR = 0–0.4). Detailed heat transfer coefficient data at the leading and trailing walls are presented along with streamline profiles at different cross sectional planes that provide an insight into the flow field. It is seen that the entrance profile upstream of the actual test section is significantly different for the different entrance geometries, and has a significant impact on the rotation generated secondary flows. Non-uniformity in flow distribution at the exit of entrance geometry is small for the S-shape entrance while the non-uniformity is prominent at the exit of the changing AR entrance geometry. The entrance effect dies down as the flow progresses further downstream inside the cooling channel and the rotation effect becomes dominant.

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