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International Review of Mechanical Engineering - Special Issue February 2010 - Papers

Transient Heat Conduction in Solids Irradiated by a Moving Heat Source with Combined Donut and Gaussian Distributions
Numerical Model for Back Treatment of Multilayer Thin Films by a Moving Laser Source
Some Analytical Solutions of Steady-State Heat Conduction Problems in Non-Homogeneous Solid Bodies
Combustion and Heat Transfer in Furnaces and Combustion Chambers
Heat Transfer in Open Microchannels at Constant Heat Flux
A Comparative Study of Different Roughness Geometries Proposed for Solar Air Heater Ducts
Application of Multi Objective Genetic Algorithm to Optimize Heat Transfer Enhancement from a Flat Plate
Cooling Parameters and Heat Quantity of the Metal During Continuous Casting of Blooms
Steady Heat Transfer Boundary Layer Solutions Of Polar Fluid
Verification and Experimental Validation of Flatness-Based Control for Distributed Heating Systems
The Influence of Different Turbulence Models on the Predictions for Turbulent Non-Premixed Flames
Analytic Methods for the Calculation of the Heat Transfer Coefficient

International Review of Mechanical Engineering - Papers

Transient Heat Conduction in Solids Irradiated by a Moving Heat Source with Combined Donut and Gaussian Distributions
by Oronzio Manca, Alina A. Minea, Sergio Nardini, Salvatore Tamburrino

Vol. 4. n. 2, pp. 123-127

Abstract - In this paper a three dimensional conductive field in a semi-infinite solid with finite thickness and width heated by a moving laser source is numerically studied. In the numerical model convective heat losses through the surface are taking into account. Thermal properties are considered temperature dependent and the materials are considered isotropic. The considered laser source is a linear combination of Gaussian and donut distribution and it moves with a constant velocity along motion direction. The simulation model is solved by means of the COMSOL Multiphysics code.
Results in terms of temperature profiles as a function of time are given for Peclet equal to 0.1, 0.5 and 1.0 and several Biot number values. Three heat source distributions are examined Gaussian, donut and a donut-Gaussian. It is observed that different behaviours are detected between the Gaussian and donut distributions whereas the combined donut-Gaussian and Gaussian distributions present similar qualitative.

Keywords: Transient Heat Conduction, Laser Source, Manufacturing, Moving Sources.

Numerical Model for Back Treatment of Multilayer Thin Films by a Moving Laser Source
by Nicola Bianco, Oronzio Manca, Alina A. Minea, Vincenzo Naso, Daniele Ricci

Vol. 4. n. 2, pp. 128-133

Abstract - A two-dimensional non stationary analysis of the conjugate optical-thermal fields induced in a multilayer thin film structure on a glass substrate by a moving Gaussian laser source is carried out numerically in order to study laser back treatment processes. The work-piece is considered semi-infinite along the motion direction and different thicknesses of the thin film are considered. Thermal and optical non-linearities are induced during transient heating, since the response of weakly absorbing thin films depends on temperature. The heat source impinges on the back surface of the glass substrate. The optical field is assumed to be locally one-dimensional and Maxwell equations are solved in order to evaluate the energy absorption in the thin films; the thermal field is assumed to be two-dimensional. COMSOL Multiphysics 3.4 code was employed to solve the conjugate thermal and electromagnetic problem Transient temperature profiles and temperature fields for different Peclet numbers and amorphous silicon thicknesses are presented.

Keywords: Combined Heat Conduction and Radiation, Laser Source, Moving Sources, Thin Films, Manufacturing.

Some Analytical Solutions of Steady-State Heat Conduction Problems in Non-Homogeneous Solid Bodies
by István Ecsedi, Attila Baksa

Vol. 4. n. 2, pp. 134-141

Abstract - The steady-state heat conduction problems in non-homogeneous solid body is treated by an analytical method. The temperature distribution for non-homogeneous body is derived from the solution of the steady-state heat conduction problem of a homogeneous body which has the same geometry as the considered non-homogeneous body. The thermal conductivity of the non-homogeneous solid body is a given function of the temperature field of a homogeneous body having the same geometry as the non-homogeneous one. Five examples illustrate the developed method. The present paper is a contribution to the existing exact benchmark solutions for steady-state heat conduction problems in non-homogeneous isotropic solid bodies. The heat conductivity is a smooth function of spatial coordinates, the considered solid bodies are made of functionally graded materials.

Keywords: Functionally Graded, Heat Conduction, Non-Homogeneous, Steady-State.

Combustion and Heat Transfer in Furnaces and Combustion Chambers
by Essam E. Khalil

Vol. 4. n. 2, pp. 142-149

Abstract - Efficient fossil energy utilization in power generation together with low pollution in conventional thermal power plants is of growing interest internationally. Efficient energy use is favorable for better productivity product quality, costs, and quality of human life but the energy use adversely impacts our environment. The present paper briefly summaries the basic combustion modeling techniques for furnace flames under steady and time dependent configurations. The ability of numerical computations to predict the boiler furnace thermal behavior is an ultimate goal. The heat transfer to furnace walls through thermal radiation is reviewed briefly to demonstrate the present capabilities.

Keywords: CFD, Combustion Modelling, Heat Transfer in Furnaces.

Heat Transfer in Open Microchannels at Constant Heat Flux
by J. A. Esfahani, M. Malek-Jafarian

Vol. 4. n. 2, pp. 150-158

Abstract - The present work studies heat transfer of the gas fluid in open microchannels at constant wall heat flux boundary conditions. The proposed model assumes the fluid is a continuum, but employs a slip boundary condition on the channel wall. Using appropriate similarity variables, the fundamental equations of the boundary layer are transformed to ordinary differential equations containing a Prandtl number. These ordinary differential equations are solved numerically using a fifth order Runge-Kutta and shooting method. Consequently, the velocity profiles, the temperature profiles, the wall shear stress and the local Nusselt number exhibit a dependence on the slip coefficient. The results illustrate that the thermal creep term has a very small effect on the solution. It is shown that laminar boundary layer of gas fluid with slip flow tends to increase near wall fluid axial velocity and temperature jump on the wall as the flow becomes more rarefied. It will be seen that heat transfer in open microchannels is affected with temperature jump more than slip velocity under constant wall heat flux boundary condition.

Keywords: Thermal Creep, Open Microchannel, Slip Flow, Wall Shear Stress, Nusselt Number.

A Comparative Study of Different Roughness Geometries Proposed for Solar Air Heater Ducts
by Rajendra Karwa, Anil Sharma, Nitin Karwa

Vol. 4. n. 2, pp. 159-166

Abstract - In the present work, a comparative study of different roughness geometries proposed for high aspect ratio rectangular ducts with asymmetric heating has been carried out to suggest the preferred type of roughness for the solar air heater ducts because the thermal boundary conditions of these studies confirm to that of solar air heaters. The enhancement in the Nusselt number and friction factor for the roughness geometries over the smooth duct has been found to be 1.04–5.38 and 1.42–7.66 times, respectively, which is a strong function of the geometry of the roughness and flow Reynolds number. A thermo-hydraulic performance analysis, based on equal pumping power for the smooth and roughened ducts, shows that in the lower Reynolds number range (up to a Reynolds number of about 7000) corresponding to low flow rates per unit area of absorber plate, the v-down continuous and discrete roughness geometries are better than all other roughness types, while in the higher Reynolds number range (Re = 7000-20000) the expanded metal wire mesh is better in performance.
Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

Keywords: Solar Air Heater, Roughened Duct, Thermo-Hydraulic Performance.

Application of Multi Objective Genetic Algorithm to Optimize Heat Transfer Enhancement from a Flat Plate
by Mohsen Kahrom , Seyed Mohammad Javadi , Payam Haghparast

Vol. 4. n. 2, pp. 167-175

Abstract - A quad inserted to a turbulent boundary layer of a flat plate and effect on average heat transfer and friction coefficient is studied. To optimize the effect, the edge sizes and distance of the quad from the flat plate is changed to achieve the best enhancement in heat transfer and better reduction in skin friction. For optimization, the genetic algorithm is employed and Pareto curves followed. Flow equations together with SST k-ω turbulence model proved to give reliable solution and stability over 1600 cases under consideration. Governing equations are developed employing TEACH-t algorithm. Based on Pareto front curve, results show that, with no exception over the whole computations, as the heat transfer coefficient rises, skin friction decreases. Three dimensional Pareto curve constructed and results show that, by increasing obstacle cross sectional area, heat transfer coefficient increases as skin friction decreases. The rate of heat transfer enhancement is more sensitive to changes of small geometry modification than for large ones. Since experimental validation for too many cases is impracticable, random comparison between some numerical results and experiments is made, numerical results are in good agreement with experiments.
Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

Keywords: Genetic algorithm, Pareto front, Heat Transfer Enhancement, Reynolds Analogy.

Cooling Parameters and Heat Quantity of the Metal During Continuous Casting of Blooms
by Emil G. Mihailov, Venko I. Petkov

Vol. 4. n. 2, pp. 176-184

Abstract - The effective realization of the hot charging requires planning and control of operations, beginning with steel making and ending with rolling, to ensure a high quality of the metal. The quality of continuously cast steel is determined largely by the conditions existing during cooling and solidification. An extended mathematical model for solidification based on the finite differences analysis of heat transfer and solidification kinetics has been used for the calculation of cooling parameters, temperature redistribution, shell thickness, deformation and stresses. The analysis include the determination of boundary conditions describing the heat flux, cooling parameters at the metal surface, correction of areas, which are covered by the cooling jets and heat quantity of metal during continuous casting of steel.
Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

Keywords: Continuous Cast, Mathematical Modeling, Cooling Parameters.

Steady Heat Transfer Boundary Layer Solutions Of Polar Fluid
by M Ferdows, Motaleb Hossain, S. Sivasankaran, Masahiro Ota

Vol. 4. n. 2, pp. 185-187

Abstract - Polar fluid behavior on steady flow through a vertical infinite plate with the boundary layer has studied numerically. This study is mainly based on the similarity approach. Non-similarity equations of the corresponding continuity, momentum and angular momentum equations are derived by employing the usual non-similarity technique. With the help of the graphs, the effects of Dimensionless material property (∆) and Dimensionless spin gradient viscosity parameter ( λ) on the velocity, angular velocity within the boundary layer are separately presented.
Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

Keywords: Polar Fluid, Momentum Boundary, Angular Momentum Boundary, Numerical Simulation, Similarity Solution.

Verification and Experimental Validation of Flatness-Based Control for Distributed Heating Systems
by Andreas Rauh, Georgy V. Kostin, Harald Aschemann, Vasily V. Saurin, Velko Naumov

Vol. 4. n. 2, pp. 188-200

Abstract - In this paper, we consider boundary control problems for a distributed heating system. The dynamical model of the heating system under consideration is given by a parabolic partial differential equation. This type of mathematical model is also a common description for other distributed parameter systems involving heat and mass transfer. After derivation of a suitable, general-purpose solution procedure for the design of flatness-based open-loop as well as closed-loop boundary control strategies, we present experimental results, which highlight the applicability in a real-world experiment. An alternative solution to the control problem is derived based on the method of integrodifferential relations. The quality of the flatness-based approximation is verified by comparison of the results of both design procedures. For the experimental validation, a test setup at the University of Rostock is used. It consists of a metallic rod equipped with a finite number of Peltier elements which are used as distributed control inputs allowing for active cooling and heating. To compensate unmodeled disturbances, closed-loop output feedback control strategies are extended by state and disturbance observers.

Keywords: Flatness-Based Control, Distributed Parameter Systems, Integrodifferential Relations, Heat Transfer Equation, State and Disturbance Estimation.

The Influence of Different Turbulence Models on the Predictions for Turbulent Non-Premixed Flames
by C. Pfeiler, H. Raupenstrauch

Vol. 4. n. 2, pp. 201-207

Abstract - Especially for the steel and refractory industry, combustion of gaseous fuels via non-premixed burners is used for many technical applications. Accurate turbulent flow and temperature fields are of major importance in order to predict details on the concentration fields. In this regard a detailed study of different turbulence models is performed. The performances of the standard k-, the realizable k- the standard k-ω and the Reynolds Stress turbulence model (RSM) are compared. Detailed chemistry is included with the GRI-Mech 3.0 mechanism in combination with the laminar flamelet combustion model. The combustion systems selected for this comparison are piloted non-premixed methane flames surrounded by co-flowing air. The simulation results are compared with experimental data from literature. The predicted turbulence and temperature field show some differences to the experimental data. A modification of a single empirical model constant for the turbulence helped to get better results for both flame configurations.

Keywords: Burner, Combustion, Flamelet, Non-Premixed, Turbulence.

Analytic Methods for the Calculation of the Heat Transfer Coefficient
by M. Merklein, M. Wieland, T. Stoehr, J. Lechler, M.Gruener

Vol. 4. n. 2, pp. 208-215

Abstract - In the product development cycle numerical simulations are commonly used for the process layout. In case of hot stamping the process layout gets quite complex because material’s thermal and mechanical properties have to be taken into account. Hot stamping can be explained as forming and quenching in one process step and therefore the knowledge of thermal properties is indispensable to fulfill the opposing requirements of a good heat flux with respect to a good energy balance of the tool. A description of this energy exchange between the hot blank and the tool is given by the heat transfer coefficient. The determination of the heat flux under process relevant conditions for hot stamping is influenced by several variables. Within the scope of this work, these different variables are compared using two analytical methods to calculate the heat transfer coefficient based on the same measurement data. Furthermore the advantage of these analytical methods and the possibility of improvement is shown up. At least a validation of the calculated heat transfer coefficients by simulation is presented.

Keywords: Heat Transfer Coefficient, Hot Stamping.