Effect of thermal conductivity of solid wall on combustion efficiency of a micro-combustor with cavities

2015 ◽  
Vol 96 ◽  
pp. 605-612 ◽  
Author(s):  
Jianlong Wan ◽  
Aiwu Fan ◽  
Hong Yao ◽  
Wei Liu
Keyword(s):  
Thermal Conductivity ◽  
Solid Wall ◽  
Combustion Efficiency ◽  
Micro Combustor

scholarly journals Effect of Channel Diameter on the Combustion and Thermal Behavior of a Hydrogen/Air Premixed Flame in a Swirl Micro-Combustor

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3821 ◽  
Author(s):  
Xiao Yang ◽  
Zhihong He ◽  
Lei Zhao ◽  
Shikui Dong ◽  
Heping Tan
Keyword(s):  
Thermal Conductivity ◽  
Thermal Behavior ◽  
Thermal Performance ◽  
Wall Temperature ◽  
Outer Wall ◽  
Combustion Efficiency ◽  
Premixed Flame ◽  
Channel Diameter ◽  
Recirculation Zones ◽  
Micro Combustor

Improving the flame stability and thermal behavior of the micro-combustor (MC) are major challenges in microscale combustion. In this paper, the micro combustions of an H2/air premixed flame in a swirl MC with various channel diameters (Din = 2, 3, 4 mm) were analyzed based on an established three-dimensional numerical model. The effects of hydrogen mass flow rate, thermal conductivity of walls, and the preferential transport of species were investigated. The results indicated that the flame type was characterized by the presence of two recirculation zones. The flame was anchored by the recirculation zones, and the anchoring location of the flame root was the starting position of the recirculation zones. The recirculation zones had a larger distribution of local equivalence ratio, especially in the proximity of the flame root, indicating the formation of a radical pool. The combustion efficiency increased with an increasing Din due to the longer residence time of the reactants. Furthermore, the MC with Din = 2 mm obtained the highest outer wall temperature distribution. However, the MC with Din = 4 mm had a better uniformity of outer wall temperature and large emitter efficiency due to the larger radiation surface. An increase in thermal conductivity boosts the thermal performance of combustion efficiency, emitter efficiency, and wall temperature uniformity. But there is a critical point of thermal conductivity that can increase the thermal performance. The above results can offer us significant guidance for designing MC with high thermal performance.

A numerical study on the blow-off limit of premixed hydrogen/air flames in a cylindrical micro-combustor

2020 ◽  
pp. 095441002097144
Author(s):  
Saeed Naeemi ◽  
Seyed Abdolmehdi Hashemi
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Flow Velocity ◽  
Equivalence Ratio ◽  
Numerical Study ◽  
Flame Stability ◽  
Convection Coefficient ◽  
Inlet Flow ◽  
Micro Combustor ◽  
Emissivity Coefficient

In the current work, a numerical study on combustion of premixed H2–air in a micro-cylindrical combustor was carried out and the critical velocity of inlet flow that causes the blow-off was obtained. Furthermore, the effects the equivalence ratio, wall thickness, geometry of combustor and thermal properties of walls on the critical blow-off velocity were studied. The numerical results showed that, increasing the equivalence ratio results in higher critical blow-off velocity. A micro combustor with thicker wall had better flame stability. As the combustor dimeter is decreased the blow-off occur in lower inlet flow velocity. Higher thermal conductivity of walls increases the critical blow-off velocity. In addition, with varying heat convection coefficient (h) and emissivity coefficient [Formula: see text] of the walls from 1 to 60 W/m2.K and 0.2 to 0.8 respectively, the critical blow-off velocity is reduced and shows the importance of wall thermal properties in the design and operation of micro-combustors.

Improved Construction of Multilayer Vessels to Apply the ASME Code Section VIII, Division 2

1975 ◽  
Vol 97 (1) ◽  
pp. 14-21
Author(s):  
T. Yamauchi
Keyword(s):  
Thermal Conductivity ◽  
Stress Analysis ◽  
Test Piece ◽  
Solid Wall ◽  
Nondestructive Inspection ◽  
Construction Method ◽  
Asme Code ◽  
Welding Part ◽  
Section Viii ◽  
Division 2

It has been made possible to design the multilayered vessel by employing stress analysis according to ASME Section VIII, Division 2, using the construction method of reinforcing the flexual rigidity at the discontinuous part, and assuring the shell thermal conductivity to some fraction of the solid wall shell. Nondestructive inspection for the welding part has been tested to improve the construction method by the test piece.

Numerical investigation of natural convection in two enclosures separated by anisotropic solid wall

2014 ◽  
Vol 24 (8) ◽  
pp. 1928-1953 ◽  
Author(s):  
Amgad Salama ◽  
Mohamed El Amin ◽  
Shuyu Sun
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Solid Wall ◽  
Control Volume ◽  
Flow Patterns ◽  
Temperature Fields ◽  
Conductivity Anisotropy ◽  
Content Type ◽  
Wide Range ◽  
Heat And Fluid Flow

Purpose – The problem of natural convection in two cavities separated by an anisotropic central solid wall is considered numerically. When the thermal conductivity of the central wall is anisotropic, heat flux and temperature gradient vectors are no longer coincidence. This apparently has interesting influences on the heat and fluid flow patterns in this system. The paper aims to discuss these issues. Design/methodology/approach – In this work, several flow patterns have been investigated covering a wide range of Rayleigh number up to 108. Several thermal conductivity anisotropy scenarios of the central wall have been investigated including 0, 30, 60, 120 and 150° principal anisotropy directions. The governing equations have been solved using control volume approach. Findings – Probably the most intriguing is that, for some anisotropy scenarios it is found that the temperature at the same elevation at the side of the central wall which is closer to the colder wall is higher than that at the side closer to the hot wall. Apparently this defies intuition which suggests the reverse to have happened. However, this behavior may be explained in light of the effect of anisotropy. Furthermore, the patterns of streamlines and temperature fields in the two enclosures also changes as a consequence of the change of the central wall temperatures for the different anisotropy scenarios. Originality/value – This work discusses a very interesting topic related to heat energy exchange among two compartments when the separating wall is anisotropic. In some anisotropy scenarios, this leads to more uniform distribution of Nusselt number than the case when the wall is isotropic. Interesting patterns of natural convection is investigated.

Tool Wear Characteristics of Cylindrical Cutting of Nickel-Based Super Alloy

2016 ◽  
Vol 1136 ◽  
pp. 168-172
Author(s):  
Shinji Yamada ◽  
Yukio Maeda ◽  
Tatsuo Motoyoshi ◽  
Hideaki Tanaka ◽  
Kazuya Kato ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Tool Wear ◽  
Inconel 718 ◽  
Chemical Properties ◽  
Combustion Efficiency ◽  
Aircraft Industry ◽  
Jet Engines ◽  
Jet Engine ◽  
Super Alloy ◽  
And Chemical Properties

Recently, high-combustion-efficiency jet engines have become essential in the aircraft industry. High burning temperatures are necessary to maximize the combustion efficiency of jet engines. Inconel 718, which has excellent mechanical and chemical properties, has been selected for use in many jet engine parts. However, it is difficult to cut because of its low thermal conductivity. Consequently, wet cutting is typically used to reduce the heat generated in cutting Inconel 718. In this study, we conducted experiments to examine the relationships between the cutting characteristics and tool fracture in wet cutting.

scholarly journals Homogeneous and Heterogeneous Combustion in Hydrogen-Fueled Catalytic Microreactors

2016 ◽  
Vol 66 ◽  
pp. 133-142
Author(s):  
Jun Jie Chen ◽  
Bao Fang Liu
Keyword(s):  
Thermal Conductivity ◽  
Solid Wall ◽  
Heterogeneous Reaction ◽  
Radiation Heat Transfer ◽  
Heat Losses ◽  
Surface Radiation ◽  
Flame Stability ◽  
Heterogeneous Chemical Reaction ◽  
Inlet Velocity ◽  
Homogeneous Combustion

The hetero-/homogeneous combustion and interaction of hydrogen-fueled catalytic microreactors were investigated numerically. A two-dimensional CFD (computational fluid dynamics) model was developed, using elementary homogeneous and heterogeneous chemical reaction schemes, surface radiation heat transfer, heat conduction in the solid wall, and external heat losses. Computations were carried out to study the effects of the wall thermal conductivity, equivalence ratio, microreactor dimension, and inlet velocity on combustion characteristics, flame stability, and hetero-/homogeneous interaction. Despite the micro-scale, large transverse gradients in species mass fractions and temperature exist in the fluid and large axial gradients in temperature may exist in the walls. Wall thermal conductivity is crucial in determining the flame stability, as the walls transfer heat upstream for ignition of the cold incoming reactants but at the same time are responsible for heat losses. Combustible mixtures with compositions away from the stoichiometric point decrease the homogeneous chemistry contribution and the operating temperature. The microreactor dimension and inlet velocity have a strong effect on homogeneous flame stability. Smaller microreactors result in extinction because of the inhibition of homogeneous combustion induced by heterogeneous reaction; larger microreactors result in blowout due to the reduction of the heterogeneous contribution. Hetero-/homogeneous interaction maps were constructed in terms of microreactor dimension and inlet velocity.

Effects of Slitting Size and Inlet Operating Conditions on Hydrogen Combustion Characteristics in a Micro-Combustor With a Controllable Vortex Slotted Bluff Body

2019 ◽  
Vol 142 (4) ◽  
Author(s):  
Yunfei Yan ◽  
Kaiming Shen ◽  
Yu Cui ◽  
Ziqiang He ◽  
Li Zhang ◽  
...  
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Bluff Body ◽  
Combustion Efficiency ◽  
Combustion Characteristics ◽  
Operating Conditions ◽  
Flow Ratio ◽  
Gas Flow Rate ◽  
Slit Size ◽  
Micro Combustor

Abstract Effects of controllable vortex slotted bluff body parameters (position of a bluff body, slit size, and controllable flow ratio) on the combustion characteristics of hydrogen/air in a micro-combustor with a bluff body were investigated numerically. The results illustrated that the combustion efficiency of hydrogen decreases with increasing distance (L1) between the front edge of the bluff body and the combustor inlet. The combustion characteristics of the micro-combustor are optimum when L1 is 0 mm. The blow-off limit of the combustor reaches a maximum (564 cm3/s) when the slit width (d) is 20% of the bluff body width. The blow-off limit first increases and then decreases when the equivalence ratio (φ) increases and reaches a maximum (732 cm3/s) when φ is 1.0, and the controllable flow ratio is 0.2. The combustion efficiency of hydrogen is gradually increased with the increase in the controllable flow ratio. When φ is less than 1.0, the optimal controllable flow ratio gradually decreases with the increase in the premixed gas flow rate, and the optimal controllable flow ratio basically remains at 0.6 when the premixed gas flow rate is less than 360 cm3/s.

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