Modeling of Premixed Combustion in a Double-Layered Radiant Porous Burner

2001 ◽  
Author(s):  
L. Younis ◽  
A. A. Mohamad ◽  
I. Wierzba
Keyword(s):  
Thermal Conductivity ◽  
Solid Phase ◽  
Combustion Process ◽  
Radiant Energy ◽  
Flame Stabilization ◽  
High Thermal Conductivity ◽  
Energy Output ◽  
High Porosity ◽  
Porous Burner ◽  
Low Porosity

Abstract Porous radiant burners are widely used in industry to provide a uniform source of heat flux with reduced emissions. Such burners have provided high rates of heat transfer by radiation while preventing flame flashback. The work to be presented relates to the modeling of the combustion process in a double-layered flat porous burner. The burner employs a low porosity layer on the upstream side and high porosity layer on the downstream side of the homogenous fuel-air mixture flow. The nonequilibrium model is adopted. The energy equations for the gas and solid media are solved numerically with a one step reaction (Arrhenius type) energy release rate for the gas-phase. The solid phase is considered to be non-reactive. The thermophysical properties of the gas and solid phases are assumed to be functions of temperature. The effects of thermal conductivity and thickness of the layers on the flame stabilization within the porous medium and radiant energy output are investigated and discussed. The high thermal conductivity layer diffuses heat and thus has significant effects on the flame location and flame temperature. However, the high thermal conductivity of the layer also contributes to a decrease in the radiant energy. It was found that generally the flame stabilizes at the interface between the two layers. When the thermal conductivity of the upstream low porosity layer was too low (e.g. 0.1 W/m.K), the flame was stabilized within the low porosity layer.

Mechanical Properties of Microscale Graphitic Carbon Foam Ligaments and Nodes

2009 ◽  
Author(s):  
S. Ganguli ◽  
A. K. Roy ◽  
R. Wheeler
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Thermal Protection ◽  
Solid Phase ◽  
Coefficient Of Thermal Expansion ◽  
Carbon Foam ◽  
High Thermal Conductivity ◽  
Uniform Size ◽  
Open Cell ◽  
Carbon Foams

Carbon foam is recognized as having the greatest potential to replacement for metal fins in thermal management systems such as heat exchangers, space radiators, and thermal protection systems [1–5]. Carbon foam refers to a broad class of materials that include reticulated glassy, carbon and graphitic foams that are generally open-cell or mostly open-cell. They can be tailored to have low or high thermal conductivity with a low coefficient of thermal expansion and density. These foams have high modulus but low compression and tensile strength. Among the carbon foams, the graphitic foam offers superior thermal management properties such as high thermal conductivity. Graphitic foams are made of a network of spheroidal shell segments. Each cell has thin, stretched ligaments in the walls that are joined at the nodes or junctions. The parallel arrangement of graphene planes in the ligaments confers highly anisotropic properties to the walls of the graphitic foams. The graphene planes tend to be oriented with the plane of the ligaments but become disrupted at the junctions (nodes) of the walls. Since conduction is highest along parallel graphene planes, the thermal conductivity is highest in the plane of the ligaments or struts, and much lower in the direction transverse to the plane of these ligaments. In a previous study [6] extensive mechanical and thermal property characterization of carbon foams from Kopper Inc. (L1) and POCO Graphite, Inc. (P1) were reported. These foams were graphitic ones that are expected to have high thermal conductivity. Figure 1 shows sections of light microscopy images of the three foams of four foams. The most important thing to notice is that the images were not at the same magnification. The large cells in the GrafTech foam have an average diameter of only ∼100 μm but have a bimodal distribution cells with many small closed-cells few micrometers in diameter. Changes in density in the GrafTech foam was accompanied by a change in the large cells’ diameter — larger diameter giving greater porosity and lower density without changing the smaller cells’ sizes that filled the solid phase between the larger bubbles. The POCO foam has a fairly uniform size cell distribution of a few hundred micrometers. The Koppers’ foams show larger cells yet with the left (“L” precursor) having a uniform size while the right-hand (“D” precursor) is a less uniform and lower porosity.

Laser Melting of High Thermal Conductivity Steel (HTCS) Surface

2017 ◽  
Vol 890 ◽  
pp. 380-383 ◽  
Author(s):  
Norhafzan Bariman ◽  
Syarifah Nur Aqida ◽  
Fazliana Fauzun
Keyword(s):  
Thermal Conductivity ◽  
Surface Roughness ◽  
Pulse Repetition Frequency ◽  
Average Power ◽  
High Thermal Conductivity ◽  
Composition Analysis ◽  
High Porosity ◽  
Laser Melting ◽  
Metallographic Study ◽  
Modified Layer

This paper presents a laser melting of high thermal conductivity steel (HTCS) dies for surface properties modification due to die failures during operations. Sample were cut from as-received die without any defect or crack. Melting process was conducted using Nd:YAG laser system with pulse mode at 50 W average power. The laser beam was defocused to a spot size of 1 mm on the sample surface. Parameters controlled in this study were peak power of 800 and 1200 W, and pulse repetition frequency of 80 and 90 Hz. Metallographic study and chemical composition analysis were conducted using Hitachi TM3030Plus scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDXS). Surface roughness was measured using Mitutoyo SURFTEST SJ-410 stylus profilometer. Hardness properties of the modified layer were characterized by Wilson Hardness tester at 100 N force. The metallographic study showed high porosity at partially melted zone (PMZ) area. From overall findings, laser processing parameter affected hardness properties and surface roughness of modified layer. Where the surface roughness value obtained is between 1.49 and 3.15 μm, while the hardness value is between 550.9 and 610.9 HV0.1. These findings are significant to parameters selection for hot stamping die surface repair and prolong its service.

Preparation of 1D C/C Composites with High Thermal Conductivity

2013 ◽  
Vol 28 (12) ◽  
pp. 1338-1344 ◽  
Author(s):  
Jian-Feng LIN ◽  
Guan-Ming YUAN ◽  
Xuan-Ke LI ◽  
Zhi-Jun DONG ◽  
Jiang ZHANG ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Thermal Conductivity

High thermal conductivity carbon fiber reinforced polymer based on a carbon fiber from pitch and dispersed-filled ENPB matrix

2018 ◽  
pp. 130-137
Author(s):  
E. A. Nikolaeva ◽  
A. N. Timofeev ◽  
K. V. Mikhaylovskiy
Keyword(s):  
Thermal Conductivity ◽  
Carbon Fiber ◽  
High Thermal Conductivity ◽  
Fiber Reinforced Polymer ◽  
Carbon Fiber Reinforced Polymer ◽  
Carbon Powder ◽  
Fiber Reinforced ◽  
Thermophysical Characteristics ◽  
Reinforced Polymer ◽  
Carbon Fiber Reinforced

This article describes the results of the development of a high thermal conductivity carbon fiber reinforced polymer based on carbon fiber from pitch and an ENPB matrix modified with a carbon powder of high thermal conductivity. Data of the technological scheme of production and the results of determining the physicomechanical and thermophysical characteristics of carbon fiber reinforced polymer are presented. 

Strain tuned high thermal conductivity in boron phosphide at nanometer length scales – a first-principles study

2020 ◽  
Vol 22 (36) ◽  
pp. 20914-20921 ◽  
Author(s):  
Rajmohan Muthaiah ◽  
Jivtesh Garg
Keyword(s):  
Thermal Conductivity ◽  
First Principles ◽  
High Thermal Conductivity ◽  
Biaxial Strain ◽  
Length Scales ◽  
First Principles Study ◽  
Boron Phosphide

We report novel pathways to significantly enhance the thermal conductivity at nanometer length scales in boron phosphide through biaxial strain.

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