Conversion Correction for Evaluating Net Heat Flux into a Liquid Hydrogen Container

A novel turbine film-cooling hole shape has been conceived and designed at NASA Glenn Research Center. This “antivortex” design is unique in that it requires only easily machinable round holes, unlike shaped film-cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film-cooling holes. This vorticity typically entrains hot freestream gas and is associated with jet separation from the turbine blade surface. The antivortex film-cooling hole concept has been modeled computationally for a single row of 30 deg angled holes on a flat surface using the 3D Navier–Stokes solver GLENN-HT. A blowing ratio of 1.0 and density ratios of 1.05 and 2.0 are studied. Both film effectiveness and heat transfer coefficient values are computed and compared to standard round hole cases for the same blowing rates. A net heat flux reduction is also determined using both the film effectiveness and heat transfer coefficient values to ascertain the overall effectiveness of the concept. An improvement in film effectiveness of about 0.2 and in net heat flux reduction of about 0.2 is demonstrated for the antivortex concept compared to the standard round hole for both blowing ratios. Detailed flow visualization shows that as expected, the design counteracts the detrimental vorticity of the round hole flow, allowing it to remain attached to the surface.

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Influence of Film Cooling Hole Angles and Geometries on Aerodynamic Loss and Net Heat Flux Reduction

Volume 5: Heat Transfer, Parts A and B ◽

10.1115/gt2011-45721 ◽

2011 ◽

Cited By ~ 1

Author(s):

Chia Hui Lim ◽

Graham Pullan ◽

Peter Ireland

Keyword(s):

Heat Flux ◽

Film Cooling ◽

Turbine Blades ◽

Three Dimensional ◽

Design Parameters ◽

Aerodynamic Loss ◽

Design Engineers ◽

Net Heat Flux ◽

Cooling Hole ◽

Shaped Hole

Turbine design engineers have to ensure that film cooling can provide sufficient protection to turbine blades from the hot mainstream gas, while keeping the losses low. Film cooling hole design parameters include inclination angle (α), compound angle (β), hole inlet geometry and hole exit geometry. The influence of these parameters on aerodynamic loss and net heat flux reduction is investigated, with loss being the primary focus. Low-speed flat plate experiments have been conducted at momentum flux ratios of IR = 0.16, 0.64 and 1.44. The film cooling aerodynamic mixing loss, generated by the mixing of mainstream and coolant, can be quantified using a three-dimensional analytical model that has been previously reported by the authors. The model suggests that for the same flow conditions, the aerodynamic mixing loss is the same for holes with different α and β but with the same angle between the mainstream and coolant flow directions (angle κ). This relationship is assessed through experiments by testing two sets of cylindrical holes with different α and β: one set with κ = 35°, another set with κ = 60°. The data confirm the stated relationship between α, β, κ and the aerodynamic mixing loss. The results show that the designer should minimise κ to obtain the lowest loss, but maximise β to achieve the best heat transfer performance. A suggestion on improving the loss model is also given. Five different hole geometries (α = 35.0°, β = 0°) were also tested: cylindrical hole, trenched hole, fan-shaped hole, D-Fan and SD-Fan. The D-Fan and the SD-Fan have similar hole exits to the fan-shaped hole but their hole inlets are laterally expanded. The external mixing loss and the loss generated inside the hole are compared. It was found that the D-Fan and the SD-Fan have the lowest loss. This is attributed to their laterally expanded hole inlets, which lead to significant reduction in the loss generated inside the holes. As a result, the loss of these geometries is ≈ 50% of the loss of the fan-shaped hole at IR = 0.64 and 1.44.

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Solution of the Radiative Integral Transfer Equations in Rectangular Absorbing, Emitting, and Anisotropically Scattering Homogeneous Medium

Journal of Heat Transfer ◽

10.1115/1.1578503 ◽

2004 ◽

Vol 126 (1) ◽

pp. 137-140 ◽

Cited By ~ 6

Author(s):

Zekeriya Altac¸ ◽

Mesut Tekkalmaz

Keyword(s):

Heat Flux ◽

Incident Energy ◽

Homogeneous Medium ◽

Diffuse Radiation ◽

Bottom Wall ◽

Tabular Form ◽

Benchmark Problem ◽

Net Heat Flux ◽

Transfer Equations

Radiative integral transfer equations for a rectangular absorbing, non-emitting, and linearly anisotropically scattering homogeneous medium are solved numerically for the incident energy and the net heat flux components using the method of “singularity subtraction.” A benchmark problem is chosen as a rectangular homogeneous cold participating medium which is subject to externally uniform diffuse radiation on the bottom wall. The solutions for the incident energy and net heat flux components for selected points for a square domain are provided in tabular form for benchmarking purposes.

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Molecular Dynamics Simulation of Heat Conduction in Si Thin Films Induced by Ultrafast Laser Heating

Volume 2: Heat Transfer Enhancement for Practical Applications; Fire and Combustion; Multi-Phase Systems; Heat Transfer in Electronic Equipment; Low Temperature Heat Transfer; Computational Heat Transfer ◽

10.1115/ht2012-58229 ◽

2012 ◽

Author(s):

Yu Zou ◽

Xiulan Huai ◽

Fang Xin ◽

Zhixiong Guo

Keyword(s):

Molecular Dynamics ◽

Heat Flux ◽

Heat Conduction ◽

Temperature Distribution ◽

Laser Heating ◽

Ultrafast Laser ◽

Average Stress ◽

Dynamics Simulation ◽

Net Heat Flux ◽

Si Films

Molecular dynamics simulations are carried out to study the thermal and mechanical phenomena of ultra-high heat flux conduction induced by ultrafast laser heating in thin Si films. Nanoscale Si films with various depths in heat flux direction are treated as a semi-infinite model for the study of ultrafast heat conduction. A distribution of internal heat source is applied to simulate the absorption of the laser energy in films and the induced temperature distribution. Stress distribution and the evolution of the displacement are calculated. Thermal waves are observed from the development of temperature distribution in the heat flux direction, though the average temperature of the simulated Si films increases monotonically. The average stress shows periodic oscillations. The time development of strain has the same trend as the average stress, and the net heat flux shows the same trend as the stress at different depths of the Si films in the direction of heat flux. This reveals a close relationship between stress and net heat flux in the Si films in the process of ultrafast laser heating.

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Two-Phase Pipe Quenching Correlations for Liquid Nitrogen and Liquid Hydrogen

Journal of Heat Transfer ◽

10.1115/1.4041830 ◽

2019 ◽

Vol 141 (4) ◽

Cited By ~ 5

Author(s):

S. R. Darr ◽

J. W. Hartwig ◽

J. Dong ◽

H. Wang ◽

A. K. Majumdar ◽

...

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Liquid Nitrogen ◽

Critical Heat Flux ◽

Flow Boiling ◽

Nucleate Boiling ◽

Liquid Hydrogen ◽

Two Phase ◽

Cryogenic Flow ◽

Two Phase Heat Transfer

Recently, two-phase cryogenic flow boiling data in liquid nitrogen (LN2) and liquid hydrogen (LH2) were compared to the most popular two-phase correlations, as well as correlations used in two of the most widely used commercially available thermal/fluid design codes in Hartwig et al. (2016, “Assessment of Existing Two Phase Heat Transfer Coefficient and Critical Heat Flux on Cryogenic Flow Boiling Quenching Experiments,” Int. J. Heat Mass Transfer, 93, pp. 441–463). Results uncovered that the correlations performed poorly, with predictions significantly higher than the data. Disparity is primarily due to the fact that most two-phase correlations are based on room temperature fluids, and for the heating configuration, not the quenching configuration. The penalty for such poor predictive tools is higher margin, safety factor, and cost. Before control algorithms for cryogenic transfer systems can be implemented, it is first required to develop a set of low-error, fundamental two-phase heat transfer correlations that match available cryogenic data. This paper presents the background for developing a new set of quenching/chilldown correlations for cryogenic pipe flow on thin, shorter lines, including the results of an exhaustive literature review of 61 sources. New correlations are presented which are based on the consolidated database of 79,915 quenching points for a 1.27 cm diameter line, covering a wide range of inlet subcooling, mass flux, pressure, equilibrium quality, flow direction, and even gravity level. Functional forms are presented for LN2 and LH2 chilldown correlations, including film, transition, and nucleate boiling, critical heat flux, and the Leidenfrost point.

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