Study on LCF Lifetime Prediction of Thermal Shock

2012 ◽  
Vol 152-154 ◽  
pp. 924-930
Author(s):  
Wei Mao Zhao ◽  
Wei Zheng Zhang ◽  
Zhao Ju Qin
Keyword(s):  
Heat Transfer ◽  
Thermal Shock ◽  
Energy Method ◽  
Heated Surface ◽  
Dissipated Energy ◽  
Stress Strain ◽  
Fixed Temperature ◽  
Cooling Temperature ◽  
Cooling Speed ◽  
Cyclic Heat

Gray cast iron specimen was heated to a fixed temperature with high frequency induction heating equipment, then was cooled to room temperature by spraying water to the heated surface. This process was repeated until a crack whose length exceeds 3mm appeared. Transient cyclic heat transfer and stress-strain FEA analysis was conducted to obtain specimen’s stress-strain state, then different LCF life prediction methods based on strain and energy were presented and contrasted, and results showed modified dissipated energy method with maximal hydrostatic pressure was more accurate than other methods. With the help of modified dissipated energy method, the relationship between thermal shock life, highest cooling temperature and cooling speed was studied, and the effect law of highest cooling temperature and cooling heat transfer coefficient on life was obtained.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

Numerical Simulation of Heat Transfer Mechanisms in Spray Cooling

2010 ◽  
Author(s):  
Eelco Gehring ◽  
Mario F. Trujillo
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Spray Cooling ◽  
Impingement Zone ◽  
Ongoing Work ◽  
Efficient Suppression ◽  
A Cell ◽  
Cooling Behavior ◽  
Free Surface Capturing ◽  
The Impact

A primary mechanism of heat transfer in spray cooling is the impingement of numerous droplets onto a heated surface. This mechanism is isolated in the present and ongoing work by numerically simulating the impact of a single train of FC-72 droplets employing an implicit free surface capturing methodology. The droplet frequency and velocity ranges from 2000–4000 Hz, and 0.5–2 m/s, respectively, with a fixed drop size of 239 μm. This gives a corresponding Weber and Reynolds range of 10–170 and 330–1300, respectively. Results show that the impingement zone is largely free of phase change effects due to the efficient suppression of the local temperature field well below the saturated value. Due in part to the relatively high value of the Prandtl number and the compression of the boundary layer from the impingement flow, a cell size on the order of 1 μm is necessary to adequately capture the heat transfer dynamics. It is shown that the cooling behavior increases in relation to increasing frequency and impact velocity, but is most sensitive to velocity. In fact, for sufficiently low velocities the calculations show that the momentum imparted on the film is insufficient to maintain a near stationary liquid crown. The consequence is a noticeable penalty on the cooling behavior.

Micro Fluidic Jets for Thermal Management of Electronics

Volume 4 ◽  
2004 ◽  
Author(s):  
Jivtesh Garg ◽  
Mehmet Arik ◽  
Stanton Weaver ◽  
Seyed Saddoughi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heated Surface ◽  
Turbulent Jets ◽  
Harmonic Signal ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Small Scale ◽  
Air Cooling ◽  
Infrared Thermal Imaging

Micro fluidics devices are conventionally used for boundary layer control in many aerospace applications. Synthetic Jets are intense small scale turbulent jets formed from entrainment and expulsion of the fluid in which they are embedded. The idea of using synthetic jets in confined electronic cooling applications started in late 1990s. These micro fluidic devices offer very efficient, high magnitude direct air-cooling on the heated surface. A proprietary synthetic jet designed in General Electric Company was able to provide a maximum air velocity of 90 m/s from a 1.2 mm hydraulic diameter rectangular orifice. An experimental study for determining the thermal performance of a meso scale synthetic jet was carried out. The synthetic jets are driven by a time harmonic signal. During the experiments, the operating frequency for jets was set between 3 and 4.5 kHz. The resonance frequency for a particular jet was determined through the effect on the exit velocity magnitude. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. A square heater with a surface area of 156 mm2 was used to mimic the hot component and extensive temperature maps were obtained. The parameters varied during the experiments were jet location, driving jet voltage, driving jet frequency and heater power. The output parameters were point wise temperatures (pixel size = 30 μm), and heat transfer enhancement over natural convection. A maximum of approximately 8 times enhancement over natural convection heat transfer was measured. The maximum coefficient of cooling performance obtained was approximately 6.6 due to the low power consumption of the synthetic jets.

An Experimental Study of High Rayleigh Number Mixed Convection in a Rectangular Enclosure With Restricted Inlet and Outlet Openings

1987 ◽  
Vol 109 (2) ◽  
pp. 446-453 ◽  
Author(s):  
L. Neiswanger ◽  
G. A. Johnson ◽  
V. P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Rayleigh Number ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Rectangular Enclosure

Measured local heat transfer data and the results of flow visualization studies are reported for cross-flow mixed convection in a rectangular enclosure with restricted inlet and outlet openings at high Rayleigh number. In this study, experiments using water as the test fluid were conducted in a small-scale test section with uniformly heated vertical side walls and an adiabatic top and bottom. As the flow rate through the enclosure increased, the enhancement of heat transfer, above that for natural convection alone, also increased. The variation of the local heat transfer coefficient over the heated surface was found to be strongly affected by the recirculation of portions of the forced flow within the enclosure. Mean heat transfer coefficients are also presented which were calculated by averaging the measured local values over the heated surface. A correlation for the mean heat transfer coefficient is also proposed which agrees very well with the experimentally determined values. A method of predicting the flow regime in this geometry for specified heating and flow conditions is also discussed.

scholarly journals A Parametrical Study on Convective Heat Transfer between High-Temperature Gas and Regenerative Cooling Panel

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1784
Author(s):  
Jiangyu Hu ◽  
Ning Wang ◽  
Jin Zhou ◽  
Yu Pan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
Thermal Protection ◽  
Flow Direction ◽  
Heated Surface ◽  
Heat Transfer Process ◽  
Cocurrent Flow ◽  
Regenerative Cooling ◽  
High Temperature Gas

Thermal protection is still one of the key challenges for successful scramjet operations. In this study, the three-dimensional coupled heat transfer between high-temperature gas and regenerative cooling panel with kerosene of supercritical pressure flowing in the cooling channels was numerically investigated to reveal the fundamental characteristics of regenerative cooling as well as its influencing factors. The SST k-ω turbulence model with low-Reynolds-number correction provided by the pressure-based solver of Fluent 19.2 is adopted for simulation. It was found that the heat flux of the gas heated surface is in the order of 106 W/m2, and it declines along the flow direction of gas due to the development of boundary layer. Compared with cocurrent flow, the temperature peak of the gas heated surface in counter flow is much higher. The temperature and heat flux of the gas heated surface both rises with the static pressure and total temperature of gas. The heat flux of the gas heated surface increases with the mass flow rate of kerosene, and it hardly changes with the pressure of kerosene. Results herein could help to understand the real heat transfer process of regenerative cooling and guide the design of thermal protection systems.

Thermo-mechanical analysis of a FGM plate subjected to thermal shock – A new numerical approach considering real time temperature dependent material properties

2021 ◽  
Vol 63 (4) ◽  
pp. 341-349
Author(s):  
Mete Onur Kaman ◽  
Nevin Celik ◽  
Resul Das
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Shock ◽  
Temperature Variation ◽  
Material Properties ◽  
Ambient Air ◽  
Transient Temperature ◽  
Heated Plate ◽  
The Heat Transfer Coefficient

Abstract In present the study, sudden cooling, in other words thermal shock, is applied to a plate that is originally a functionally graded material (FGM). The flat plate is assumed to have an edge crack on it. Hence a numerical couple-field analysis is performed on the plate. The FGM is a combination of Ni and Al2O3. The thermal and mechanical properties of the FGM are assumed to depend on temperature variation. The mixing percentages of the Ni and Al2O3 throughout the plate are considered to vary (i) linearly, (ii) quadratically and (iii) in half-order. In order to solve the problem, a new subroutine depending on temperature is written using APDL (ANSYS Parametric Design Language) codes. Three values of the heat transfer coefficient are applied to the initially heated plate. As a result, the transient temperature variation and stress intensity factor are presented to show the thermo-mechanical relation of the plate. The material properties changing with temperature results in more reliable temperature values. Increasing the heat transfer coefficient results in better cooling and in a lesser amount of time to reach ambient air temperature.

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