Numerical Investigation of Convective Heat Transfer to Supercritical Pressure Hydrogen in a Straight Tube

2018 ◽  
Vol 4 (3) ◽  
Author(s):  
Yu Ji ◽  
Jun Sun ◽  
Lei Shi
Keyword(s):  
Heat Transfer ◽  
Velocity Profile ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Supercritical Pressure ◽  
Bulk Temperature ◽  
High Heat Flux ◽  
Straight Tube ◽  
Heat Transfer Deterioration ◽  
Pressure Hydrogen

Hydrogen is adopted as coolant for regenerative cooling nozzle and reactor core in nuclear thermal propulsion (NTP), which is a promising technology for human space exploration in the near future due to its large thrust and high specific impulse. During the cooling process, the hydrogen alters its state from subcritical to supercritical, accompanying with great variations of fluid properties and heat transfer characteristics. This paper is intended to study heat transfer processes of supercritical pressure hydrogen under extremely high heat flux by using numerical approach. To begin with, the models explaining the variation of density, specific heat capacity, viscosity, and thermal conductivity are introduced. Later on, the convective heat transfer to supercritical pressure hydrogen in a straight tube is investigated numerically by employing a computational model, which is simplified from experiments performed by Hendricks et al. During the simulation, the standard k–ε model combining the enhanced wall treatment is used to formulate the turbulent viscosity, and the results validates the approach through successful prediction of wall temperature profile and bulk temperature variation. Besides, the heat transfer deterioration which may occur in the heat transport of supercritical fluids is also observed. According to the results, it is deduced that the flow acceleration to a flat velocity profile in the near wall region due to properties variation of hydrogen contributes to the suppression of turbulence and the heat transfer deterioration, while the “M-shaped” velocity profile is more often correlated to the starting of a recovery phase of turbulence production and heat transfer.

Numerical Investigation of Convective Heat Transfer to Supercritical Hydrogen in a Straight Tube

2017 ◽  
Author(s):  
Yu Ji ◽  
Lei Shi ◽  
Jun Sun
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Specific Impulse ◽  
Local Heat Transfer ◽  
Heat Transfer Process ◽  
Subcritical State ◽  
High Heat Flux ◽  
Straight Tube ◽  
Heat Transfer Deterioration

Hydrogen is adopted as coolant for regenerative cooling nozzle and reactor reflector in nuclear thermal propulsion (NTP), which may be a promising technology for human space exploration in the near future due to its large thrust and high specific impulse. During the cooling processes, the hydrogen experiences the transition from subcritical state to supercritical state, which influences the heat transfer severely. This paper is intended to study the characteristic of convective heat transfer to supercritical hydrogen in a straight tube under high heat flux through numerical simulation, which is a common phenomenon in NTP operation. The thermophysical properties and transport properties including the equation of state, specific heat capacity, viscosity and thermal conductivity of hydrogen are evaluated firstly by compared with the data from National Institute of Standards and Technology (NIST). Then, the flow and heat transfer process is investigated using Reynolds Averaged Naiver-Stokes (RANS) model, and the approach is validated by the successfully predicted behavior called local heat transfer deterioration. Moreover, the mechanism of heat transfer deterioration is analyzed briefly according to the detailed information of flow field. This work herein contributes to the further NTP design and research.

Assessment of Turbulence Models Against Supercritical Hydrogen Flows in a Straight Tube

2018 ◽  
Author(s):  
Zhipeng Wang ◽  
Yu Ji ◽  
Jun Sun ◽  
Lei Shi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Turbulence Models ◽  
High Heat ◽  
High Heat Flux ◽  
Straight Tube ◽  
Velocity Magnitude ◽  
Rsm Model

Convective heat transfer to supercritical hydrogen under high heat flux is a complex phenomenon in nuclear thermal propulsion (NTP), which has been regarded as a promising technology for human space exploration in the following decades. In this paper, concentration is mainly focused on exploring convective heat transfer to supercritical hydrogen in a strongly heated straight tube numerically based on several turbulence models. Differences between the standard k-ε model and the sst k-ω model in terms of the simulation results like the wall temperature profile, the bulk parameters, the velocity magnitude distributions and the turbulence kinetic energy profile are discussed in the first part. And the approach is validated through comparisons with experimental data. In the second part, the effects of heat flux is under investigation, combined with four turbulence models where the RSM model and the V2F model are newly included. Generally, this work will contribute to the design and analysis of nuclear thermal propulsion system.

Conditions for Equivalency of Countercurrent Vessel Heat Transfer Formulations

1999 ◽  
Vol 121 (5) ◽  
pp. 514-520 ◽  
Author(s):  
R. B. Roemer
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Temperature Difference ◽  
Bulk Temperature ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Heat Transfer Coefficients ◽  
The Difference ◽  
Convective Heat Transfer Coefficients

Previous models of countercurrent blood vessel heat transfer have used one of two, different, equally valid but previously unreconciled formulations, based either on: (1) the difference between the arterial and venous vessels’ average wall temperatures, or (2) the difference between those vessels’ blood bulk fluid temperatures. This paper shows that these two formulations are only equivalent when the four, previously undefined, “convective heat transfer coefficients” that are used in the bulk temperature difference formulation (two coefficients each for the artery and vein) have very specific, problem-dependent relationships to the standard convective heat transfer coefficients. (The average wall temperature formulation uses those standard coefficients correctly.) The correct values of these bulk temperature difference formulation “convective heat transfer coefficients” are shown to be either: (1) specific functions of (a) the tissue conduction resistances, (b) the standard convective heat transfer coefficients, and (c) the independently specified bulk arterial, bulk venous and tissue temperatures, or (2) arbitrary, user defined values. Thus, they are generally not equivalent to the standard convective heat transfer coefficients that are regularly used, and must change values depending on the blood and tissue temperatures. This dependence can significantly limit the convenience and usefulness of the bulk temperature difference formulations.

Experimental Investigation of Convective Heat Transfer of Supercritical Pressure Hydrocarbon Fuel in a Horizontal Section of a Rotating U-Duct

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Zelong Lu ◽  
Yinhai Zhu ◽  
Yuxuan Guo ◽  
Peixue Jiang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Rotational Speed ◽  
Convective Heat Transfer Coefficient ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Horizontal Section ◽  
Static Conditions

Abstract The experimental and numerical investigations of the heat transfer of supercritical pressure n-decane flowing through a pipe at various rotational speeds, mass flow rates, heat fluxes, and pressures, are presented. This pipe is 2 mm in diameter, 200 mm in length, with a radius of 0.328 m, and is parallel to the rotating axis. The wall temperature was measured at four positions around the periphery of the pipe at each of the five selected cross section along the pipe's length. Maximum convective heat transfer was observed at the outer edge of the horizontal section, while its corresponding minimum was observed at the inner edge. The heat transfers at the two sides of the channel were observed to be similar. The density and pressure differences between the outer and inner edges increased at increasing rotating speeds. However, the temperature difference between the outer and inner edges decreased with increased rotational speed mainly because of the increase of secondary flows in the section. The section's average convective heat transfer coefficient increased with an increase in the rotational speed, and its value at 1000 rpm was approximately twice than that at static conditions. The phenomenon of oscillation was observed near the exit of the horizontal section, and was caused by the flow and considerable property changes near the pseudo critical temperature. A computational fluid dynamics (CFD) model was developed using the real gas thermal properties and was coupled with the heat transferred owing to fuel flow. The predicted fuel and wall temperatures were in good agreement with the experimental data. A new local Nusselt number correlation of the heat transfer of n-decane in a rotating horizontal section was proposed.

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