Heat Transfer by Radiation and Other Transport Mechanisms : 3 rd Report, the Entrance Region of a Flow between Parallel Flat Plates with Simultaneous Radiation and Convection

This study investigated the thermal transport behaviors of branched carbon nanotubes (CNTs) with cross and T-junctions through non-equilibrium molecular dynamics (NEMD) simulations. A hot region was created at the end of one branch, whereas cold regions were created at the ends of all other branches. The effects on thermal flow due to branch length, topological defects at junctions, and temperature were studied. The NEMD simulations at room temperature indicated that heat transfer tended to move sideways rather than straight in branched CNTs with cross-junctions, despite all branches being identical in chirality and length. However, straight heat transfer was preferred in branched CNTs with T-junctions, irrespective of the atomic configuration of the junction. As branches became longer, the heat current inside approached the values obtained through conventional prediction based on diffusive thermal transport. Moreover, directional thermal transport behaviors became prominent at a low temperature (50 K), which implied that ballistic phonon transport contributed greatly to directional thermal transport. Finally, the collective atomic velocity cross-correlation spectra between branches were used to analyze phonon transport mechanisms for different junctions. Our findings deeply elucidate the thermal transport mechanisms of branched CNTs, which aid in thermal management applications.

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A Numerical Study Of Mixed Convective Heat Transfer From Narrow Side-Up Two-Sided Isothermal Flat Plates

10.32393/csme.2021.157 ◽

2021 ◽

Author(s):

Mohamed Elkhmri ◽

Patrick H Oosthuizen

Keyword(s):

Heat Transfer ◽

Convective Heat Transfer ◽

Convective Heat ◽

Numerical Study ◽

Flat Plates ◽

Narrow Side

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Experimental Study of Multiple Air Jets Impinging a Moving Flat Plate

Volume 11: Heat Transfer and Thermal Engineering ◽

10.1115/imece2020-23996 ◽

2020 ◽

Author(s):

Flavia Barbosa ◽

Senhorinha Teixeira ◽

Carlos Costa ◽

Filipe Marques ◽

José Carlos Teixeira

Keyword(s):

Heat Transfer ◽

Flat Plate ◽

Jet Impingement ◽

Plate Motion ◽

Test Facility ◽

Flat Plates ◽

Target Plate ◽

Wall Jets ◽

Air Jets ◽

Flow Interactions

Abstract The motion of the target plate is important in some industrial applications which apply multiple jet impingement, such as reflow soldering, drying and food processing. Multiple jet impingement is widely used due to its ability to generate high heat transfer rates over large and complex areas. This convective process is characterized by several flow interactions essentially due to adjacent jets mixing prior the impingement, wall jets collision after the impingement, as well as crossflow interactions induced by the motion of the wall jets that flow through the exits of the domain. These interactions lead to strong flow recirculation, pressure gradients and boundary layer development. However, the complexity of the flow interactions is increased with the surface motion in confined space, due to the generation of strong shear regions. These interactions can induce problems and product defects due to complicated thermal behavior and non-uniform heating or cooling, being important to fully understand the process in order to reduce time and costs. This work addresses the experimental analysis of multiple air jets impinging on a moving flat plate. The experiments are conducted on a purpose-built test facility which has been commissioned, using a 2D-PIV system. Through this technique, the flow structure and velocity profiles will be analyzed in detail. The effects of the impinging plate motion on the resulting global and local velocity profile is compared with a static flat plate. The multiple jet configuration consists on air flowing through 14 circular nozzles, at a Reynolds number of 690 and 1,380. The experiments are conducted for a nozzle-to-plate distance of 8 and a jet-to-jet spacing of 2. The target plate motion remains constant throughout the experiments and equal to 0.03 m/s. The results are compared for both stationary and moving flat plates cases and express the increased complexity of the flow due to strong interaction between jets and the target surface, which affects the heat transfer performance. The results obtained experimentally are important to clearly define this complex flow and these data can be used in future works for numerical model validation.

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