The Wall Heat Transfer Phenomenon of Premixed CH4/Air Catalytic Combustion in a Pt Coated Microtube

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Jing-yu Ran ◽  
Sheng Wu ◽  
Lin Yang ◽  
Li Zhang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Loss ◽  
Catalytic Combustion ◽  
External Surface ◽  
Convective Heat Transfer Coefficient ◽  
Chemical Mechanism ◽  
Solid Structure ◽  
Transfer Phenomenon ◽  
Heat Transfer Phenomenon

In this paper, a 2D model with detailed heterogeneous chemical mechanism has been employed to investigate the heat transfer phenomenon of premixed CH4/air catalytic combustion in a Pt coated microtube. Especially, the thermal processes such as coupled heat transfer between the internal surface of the microtube and the gas phase, thermal conduction along the solid structure, convection and radiation between the external surface and the environment are comprised in the simulation. The results show that the thermal conductivity of different solid wall materials dramatically affects the uniformity of temperature distribution of the catalytic surface. To maintain stable combustion in the microtube, the thermal conductivity should exceed 0.49 W/m/K at least and conductive walls (FeCr alloy and corundum ceramic) are more appropriate to manufacture microcombustors. The extremely small Biot number at the external surface indicates that convective heat transfer coefficient and emissivity to the environment are the key factors determining the heat loss of the microtube. The amount of heat loss influences the reaction rate and residence time of the mixtures in the microtube, which would affect the conversion of CH4. An increase of the wall thickness improves the heat transfer along the solid structure, also increases the total heat loss.

scholarly journals Wall-to-Bed Heat Transfer at Minimum Gas-Solid Fluidization

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Huili Zhang ◽  
Jan Degrève ◽  
Jan Baeyens ◽  
Raf Dewil
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Fluidized Bed ◽  
Convective Heat Transfer Coefficient ◽  
Bubble Flow ◽  
Heat Transfer Characteristics ◽  
Renewal Models ◽  
Heat Transfer Phenomenon ◽  
Cooling Jacket

The heat transfer from a fluidized bed to the cooling jacket of the vessel has been studied for various powders at minimum fluidization conditions, by both convection and conduction approaches. These heat transfer characteristics are important as the point of transition between packed and fluidized bed operations and are needed in designing heat transfer operations where bubble-flow is not permitted. The effective thermal conductivity of the emulsion moreover determines the contact resistance at the heating or cooling surface, as used in packet renewal models to predict the wall-to-bed heat transfer. In expressing the overall heat transfer phenomenon as a convective heat transfer coefficient, it was found that the results could be fitted by Numf,j=0.01Ar0.42.

Numerical Study to Analyze the Effects of Hot/Cold Aisle Configurations on Heat Transfer Phenomenon in a Data Center

2013 ◽  
Author(s):  
Kamran Nazir ◽  
Naveed Durrani ◽  
Imran Akhtar ◽  
M. Saif Ullah Khalid
Keyword(s):  
Heat Transfer ◽  
Data Center ◽  
Data Centers ◽  
Cooling System ◽  
Numerical Study ◽  
High Energy ◽  
Research Area ◽  
Transfer Phenomenon ◽  
Heat Transfer Phenomenon ◽  
Active Research

Due to high energy demands of data centers and the energy crisis throughout the world, efficient heat transfer in a data center is an active research area. Until now major emphasis lies upon study of air flow rate and temperature profiles for different rack configurations and tile layouts. In current work, we consider different hot aisle (HA) and cold aisle (CA) configurations to study heat transfer phenomenon inside a data center. In raised floor data centers when rows of racks are parallel to each other, in a conventional cooling system, there are equal number of hot and cold aisles for odd number of rows of racks. For even number of rows of racks, whatever configuration of hot/cold aisles is adopted, number of cold aisles is either one greater or one less than number of hot aisles i.e. two cases are possible case A: n(CA) = n(HA) + 1 and case B: n(CA) = n(HA) − 1 where n(CA), n(HA) denotes number of cold and hot aisles respectively. We perform numerical simulations for two (case1) and four (case 2) racks data center. The assumption of constant pressure below plenum reduces the problem domain to above plenum area only. In order to see which configuration provides higher heat transfer across servers, we measure heat transfer across servers on the basis of temperature differences across racks, and in order to validate them, we find mass flow rates on rack outlet. On the basis of results obtained, we conclude that for even numbered rows of rack data center, using more cold aisles than hot aisles provide higher heat transfer across servers. These results provide guidance on the design and layout of a data center.

scholarly journals Heat Transfer Modelling and Simulation of a 120 mm Smoothbore Gun Barrel During Interior Ballistics

2022 ◽  
Vol 72 (1) ◽  
pp. 30-39
Author(s):  
Cigdem Susantez ◽  
Aldelio Bueno Caldeira
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Numerical Model ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Gas Temperature ◽  
Interior Ballistics ◽  
Heat Transfer Phenomenon

Understanding the heat transfer phenomenon during interior ballistics and consequently presenting a realistic model is very important to predict the temperature distribution inside the cannon barrel, which influences the gun wear and the cook-off. The objective of this work is to present a new detailed numerical model for the prediction of thermal behaviour of a cannon barrel by combining PRODAS interior ballistics simulation with COMSOL simulation. In this study, a numerical model has been proposed for the heating behaviour of a 120 mm smoothbore cannon barrel, taking into account the combustion equation of the JA-2 propellant. Temperature dependent thermophysical properties of product gases were used for the calculation of the convective heat transfer coefficient inside the barrel. Projectile position, velocity of the projectile, gas temperature inside the barrel, volume behind the projectile and mass fraction during interior ballistics have been obtained by PRODAS software and used in the numerical model performed by COMSOL multiphysics finite element modelling and simulation software. Temperature simulations show that maximum wall temperature inside the cannon barrel is observed after 3 ms from fire, when maximum value of the convective heat transfer coefficient inside the barrel is observed. The results reveal that the convective heat transfer coefficient of burned gases inside the gun has major effect than the burned gas temperature on the heat transfer phenomenon.

Numerical Analysis of Convection Heat Transfer for Subsea Xmas Tree Assembly

2012 ◽  
Author(s):  
Kuang Ding ◽  
Hongwu Zhu ◽  
Jinya Zhang ◽  
Xuan Luo ◽  
Junyao Zhu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Loss ◽  
Convective Heat ◽  
Structural Reliability ◽  
Sea Water ◽  
Convective Heat Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Water Velocity ◽  
Convection Heat

This study aims to investigate the convection heat transfer of a horizontal subsea Xmas tree assembly at a high spatial resolution. Such study is important for increasing the structural reliability design and flow assurance level of subsea Xmas tree. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) is adopted to evaluate the forced convective heat transfer of the subsea Xmas tree assembly. The temperature, the convection heat loss and the convective heat transfer coefficient (CHTC) at the surfaces of the subsea Xmas tree assembly are numerically obtained with low-Reynolds number modeling (LRNM). The numerical results show that the outer surface temperatures of the subsea tree are close to that of the ambient cold sea water with the exception of the pipeline. The components along the internal production tubes are typical “hot spots,” which have high CHTHs and cause a great deal of heat loss. Under the designed water depth, the effects of installation orientation and sea water velocity on convective heat transfer are investigated. The overall average CHTCs and the local CHTC distribution of the subsea Xmas tree assembly are depended on the installation orientation. Meanwhile, with the increase of the sea water velocity, the growth rates of the CHTCs for individual components show great difference. Ultimately, for selected installation orientation, the CHTC-sea water velocity correlation is derived by using a power-law CHTC-Uin correlation.

Investigations on Transient Natural Convection in Boron Nitride-Mineral Oil Nanofluid Systems

2012 ◽  
Author(s):  
Shijo Thomas ◽  
C. B. Sobhan ◽  
Jaime Taha-Tijerina ◽  
T. N. Narayanan ◽  
P. M. Ajayan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Boron Nitride ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Mineral Oil

Nanofluids are suspensions or colloids produced by dispersing nanoparticles in base fluids like water, oil or organic fluids, so as to improve their thermo-physical properties. Investigations reported in recent times have shown that the addition of nanoparticles significantly influence the thermophysical properties, such as the thermal conductivity, viscosity, specific heat and density of base fluids. The convective heat transfer coefficient also has shown anomalous variations, compared to those encountered in the base fluids. By careful selection of the parameters such as the concentration and the particle size, it has been possible to produce nanofluids with various properties engineered depending on the requirement. A mineral oil–boron nitride nanofluid system, where an increased thermal conductivity and a reduced electrical conductivity has been observed, is investigated in the present work to evaluate its heat transfer performance under natural convection. The modified mineral oil is produced by chemically dispersing boron nitride nanoparticles utilizing a one step method to obtain a stable suspension. The mineral oil based nanofluid is investigated under transient free convection heat transfer, by observing the temperature-time response of a lumped parameter system. The experimental study is used to estimate the time-dependent convective heat transfer coefficient. Comparisons are made with the base fluid, so that the enhancement in the heat transfer coefficient under natural convection situation can be estimated.

Numerical Study on the Surface Convective Heat Transfer of Mass Concrete Structure

2015 ◽  
Vol 723 ◽  
pp. 992-995
Author(s):  
Biao Li ◽  
Fu Guo Tong ◽  
Chang Liu ◽  
Nian Nian Xi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Flow Velocity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Convective Heat Transfer Coefficient ◽  
Concrete Surface ◽  
Mass Concrete ◽  
Air Flow Velocity

The surface convective heat transfer of mass concrete is an important element of concrete structure temperature effect analysis. Based on coupled Thermal Fluid governing differential equation and finite element method, the paper calculated and analyzed the dependence of the concrete surface convective heat transfer on the air flow velocity and the concrete thermal conductivity coefficient. Results show that the surface convective heat transfer coefficient of concrete is a quadratic polynomial function of the air flow velocity, but influenced much less by the air flow velocity when temperature gradient is dominating in heat transfer. The concrete surface convective heat transfer coefficient increases linearly with the thermal conductivity of concrete increases.

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