scholarly journals Heat Transfer Considerations on the Spontaneous Triggering of Vapor Explosions—A Review

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 55
Author(s):  
Arne Simons ◽  
Inge Bellemans ◽  
Tijl Crivits ◽  
Kim Verbeken
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Point Of View ◽  
Vapor Film ◽  
Vapor Explosion ◽  
Main Interest ◽  
Safety Risks ◽  
Fundamental Research ◽  
Vapor Explosions ◽  
Transient Models

Vapor explosions have been investigated both theoretically and experimentally for several decades, focusing either on the vapor film, or on mechanical aspects. Where the main interest for industry lies in the safety risks of such an event, fundamental research is focusing on all partial processes that occur during a vapor explosion. In this paper, vapor explosions are discussed from a heat transfer point of view. Generally accepted knowledge of heat transfer between hot surfaces and liquids is compared to early investigations regarding the origin of vapor explosions. Both steady state and transient models are discussed. The review of available literature suggests that vapor explosions trigger spontaneously by the collapse of the boiling film. Better understanding of the fundamental aspects of vapor explosions might give rise to future ideas on how to avoid them.

Destabilization of Film Boiling Due to Arrival of a Pressure Shock—Part I: Experimental

1981 ◽  
Vol 103 (3) ◽  
pp. 459-464 ◽  
Author(s):  
A. Inoue ◽  
S. G. Bankoff
Keyword(s):  
Heat Transfer ◽  
Horizontal Tube ◽  
Nucleate Boiling ◽  
Transient Heat Transfer ◽  
Film Boiling ◽  
Vapor Film ◽  
Pressure Shock ◽  
Transfer Rates ◽  
Vapor Explosions ◽  
Film Collapse

Transient heat transfer from an electrically-heated 3 mm o.d. horizontal tube, initially in subcooled film boiling, was measured immediately after passage of a shock wave of 1–5 × 105 N/m2 over-pressure. The fluids tested were Freon-113 and 95 percent ethanol-5 percent water at initially 0.5–2 × 105 N/m2 at 22–24° C. Transient heat transfer rates, averaged over 0.5–1 ms after vapor film collapse, ranged up to 20 times the steady-state value. The maximum transient flux occurred at supercritical contact temperatures, with frequently a minimum in the range of contact temperatures between the homogeneous nucleation and the critical temperature. Photography at 5000 frames/s showed apparently complete vapor film collapse within one or two frames, followed by re-establishment of film boiling in ∼1 ms, and eventually nucleate boiling in ∼100 ms. The surface temperature which gave the highest peak transient flux shifted appreciably with increasing shock pressure, which indicates some compressibility even after “contact” was made. Implications for vapor explosions are discussed.

An Investigation of the Effect of interrupted fin arrangements on the Thermal Performance of a Heat Sink under a Free Convection Condition

2019 ◽  
Vol 7 (1) ◽  
pp. 43-53
Author(s):  
Abbas Jassem Jubear ◽  
Ali Hameed Abd
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Performance ◽  
Heat Sink ◽  
Numerical Study ◽  
Ansys Fluent ◽  
Fluent Software ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The heat sink with vertically rectangular interrupted fins was investigated numerically in a natural convection field, with steady-state heat transfer. A numerical study has been conducted using ANSYS Fluent software (R16.1) in order to develop a 3-D numerical model.  The dimensions of the fins are (305 mm length, 100 mm width, 17 mm height, and 9.5 mm space between fins. The number of fins used on the surface is eight. In this study, the heat input was used as follows: 20, 40, 60, 80, 100, and 120 watts. This study focused on interrupted rectangular fins with a different arrangement and angle of the fins. Results show that the addition of interruption in fins in various arrangements will improve the thermal performance of the heat sink, and through the results, a better interruption rate as an equation can be obtained.

scholarly journals Prediction of Liner Metal Temperature of an Aeroengine Combustor with Multi-Physics Scale-Resolving CFD

Entropy ◽  
2021 ◽  
Vol 23 (7) ◽  
pp. 901
Author(s):  
Davide Bertini ◽  
Lorenzo Mazzei ◽  
Antonio Andreini
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Turbulence Models ◽  
Metal Temperature ◽  
Lean Burn ◽  
Turbulence Scale ◽  
Ansys Fluent ◽  
Multi Scale ◽  
Assessment Tests ◽  
Rans Turbulence Models

Computational Fluid Dynamics is a fundamental tool to simulate the flow field and the multi-physics nature of the phenomena involved in gas turbine combustors, supporting their design since the very preliminary phases. Standard steady state RANS turbulence models provide a reasonable prediction, despite some well-known limitations in reproducing the turbulent mixing in highly unsteady flows. Their affordable cost is ideal in the preliminary design steps, whereas, in the detailed phase of the design process, turbulence scale-resolving methods (such as LES or similar approaches) can be preferred to significantly improve the accuracy. Despite that, in dealing with multi-physics and multi-scale problems, as for Conjugate Heat Transfer (CHT) in presence of radiation, transient approaches are not always affordable and appropriate numerical treatments are necessary to properly account for the huge range of characteristics scales in space and time that occur when turbulence is resolved and heat conduction is simulated contextually. The present work describes an innovative methodology to perform CHT simulations accounting for multi-physics and multi-scale problems. Such methodology, named U-THERM3D, is applied for the metal temperature prediction of an annular aeroengine lean burn combustor. The theoretical formulations of the tool are described, together with its numerical implementation in the commercial CFD code ANSYS Fluent. The proposed approach is based on a time de-synchronization of the involved time dependent physics permitting to significantly speed up the calculation with respect to fully coupled strategy, preserving at the same time the effect of unsteady heat transfer on the final time averaged predicted metal temperature. The results of some preliminary assessment tests of its consistency and accuracy are reported before showing its exploitation on the real combustor. The results are compared against steady-state calculations and experimental data obtained by full annular tests at real scale conditions. The work confirms the importance of high-fidelity CFD approaches for the aerothermal prediction of liner metal temperature.

scholarly journals Computational Performance of Disparate Lattice Boltzmann Scenarios under Unsteady Thermal Convection Flow and Heat Transfer Simulation

Computation ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 65
Author(s):  
Aditya Dewanto Hartono ◽  
Kyuro Sasaki ◽  
Yuichi Sugai ◽  
Ronald Nguele
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Lattice Boltzmann ◽  
Numerical Results ◽  
Convection And Heat Transfer ◽  
Steady State Condition ◽  
Physical Systems ◽  
Flow And Heat Transfer ◽  
Computational Performance

The present work highlights the capacity of disparate lattice Boltzmann strategies in simulating natural convection and heat transfer phenomena during the unsteady period of the flow. Within the framework of Bhatnagar-Gross-Krook collision operator, diverse lattice Boltzmann schemes emerged from two different embodiments of discrete Boltzmann expression and three distinct forcing models. Subsequently, computational performance of disparate lattice Boltzmann strategies was tested upon two different thermo-hydrodynamics configurations, namely the natural convection in a differentially-heated cavity and the Rayleigh-Bènard convection. For the purposes of exhibition and validation, the steady-state conditions of both physical systems were compared with the established numerical results from the classical computational techniques. Excellent agreements were observed for both thermo-hydrodynamics cases. Numerical results of both physical systems demonstrate the existence of considerable discrepancy in the computational characteristics of different lattice Boltzmann strategies during the unsteady period of the simulation. The corresponding disparity diminished gradually as the simulation proceeded towards a steady-state condition, where the computational profiles became almost equivalent. Variation in the discrete lattice Boltzmann expressions was identified as the primary factor that engenders the prevailed heterogeneity in the computational behaviour. Meanwhile, the contribution of distinct forcing models to the emergence of such diversity was found to be inconsequential. The findings of the present study contribute to the ventures to alleviate contemporary issues regarding proper selection of lattice Boltzmann schemes in modelling fluid flow and heat transfer phenomena.

scholarly journals Multifunctional Cantilevers as Working Elements in Solid-State Cooling Devices

Actuators ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 58
Author(s):  
Andraž Bradeško ◽  
Lovro Fulanović ◽  
Marko Vrabelj ◽  
Aleksander Matavž ◽  
Mojca Otoničar ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Ethylene Glycol ◽  
Contact Resistance ◽  
High Efficiency ◽  
Thermal Contact ◽  
Point Of View ◽  
Practical Implementation ◽  
Cooling Devices ◽  
Cascade Structure ◽  
Lead Magnesium

Despite the challenges of practical implementation, electrocaloric (EC) cooling remains a promising technology because of its good scalability and high efficiency. Here, we investigate the feasibility of an EC cooling device that couples the EC and electromechanical (EM) responses of a highly functionally, efficient, lead magnesium niobate ceramic material. We fabricated multifunctional cantilevers from this material and characterized their electrical, EM and EC properties. Two active cantilevers were stacked in a cascade structure, forming a proof-of-concept device, which was then analyzed in detail. The cooling effect was lower than the EC effect of the material itself, mainly due to the poor solid-to-solid heat transfer. However, we show that the use of ethylene glycol in the thermal contact area can significantly reduce the contact resistance, thereby improving the heat transfer. Although this solution is most likely impractical from the design point of view, the results clearly show that in this and similar cooling devices, a non-destructive, surface-modification method, with the same effectiveness as that of ethylene glycol, will have to be developed to reduce the thermal contact resistance. We hope this study will motivate the further development of multifunctional cooling devices.

Resistance to Outflow of Cerebrospinal Fluid Determined by Bolus Injection Technique and Constant Rate Steady State Infusion in Humans

Neurosurgery ◽  
1985 ◽  
Vol 16 (3) ◽  
pp. 336-340 ◽  
Author(s):  
Michael Kosteljanetz
Keyword(s):  
Cerebrospinal Fluid ◽  
Steady State ◽  
Bolus Injection ◽  
Point Of View ◽  
Injection Technique ◽  
Communicating Hydrocephalus ◽  
Constant Rate ◽  
High Degree ◽  
Infusion Technique

Abstract Two methods for the determination of resistance to the outflow of cerebrospinal fluid, the bolus injection technique and the constant rate steady state infusion technique, were compared. Thirty-two patients with a variety of intracranial diseases (usually communicating hydrocephalus) were studied. There was a high degree of correlation between the resistance values obtained with the two methods, but values based on the bolus injection technique were systematically and statistically significantly lower than those obtained with the constant rate infusion test. From a practical point of view. both methods were found to be applicable in a clinical setting.

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