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heat-transfer
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Study of Mechanism of Formation of Metal Oxide Nanoparticles in Supercritical Water Medium
, M.Sc. Thesis Sharif University of Technology ; Outokesh, Mohammad (Supervisor) ; Ahmadi, Javad (Co-Advisor)
Abstract
One of the most convenient methods for the synthesis of metal oxide nanoparticles, inorganic ceramic materials and catalysts is supercritical hydrothermal method. In its pure form or mixed metal oxide nanoparticles have potential applications are wide. An important aspect of functional metal oxides of uranium dioxide as the selective catalyst for the conversion of methane to methanol and chlorinated organic matter decomposition is used. The main issue that led to the definition of this project was that nanoparticles synthesized with supercritical hydrothermal conditions influenced by change in the temperature. Temperature also affects the particle size and the conversion efficiency. This...
, M.Sc. Thesis Sharif University of Technology ; Dolati, Abolghasem (Supervisor)
Abstract
In recent years, different of nanoparticles as oil additives has been investigated in many studies . These research show that nanoparticles are deposited on the surface friction and improve tribology properties of base oil and also significant reduction of wear and friction caused by the nanoparticles. Compared with metal and metal oxide nanoparticles , carbon nanotubes (CNT) due to the high thermal conductivity and high aspect ratio , is an excellent candidate as the nanoparticle is dispersed . For preparing useful oil it is essential to stabilize nanoparticles in fluid that will not settle over long time . Oils containing nanoparticles by increasing the heat transfer coefficient...
Experimental Investigation on Forced Convection Heat Transfer of Ferrofluids under an Alternating Magnetic Field
, M.Sc. Thesis Sharif University of Technology ; Shafii, Mohammad Behshad (Supervisor)
Abstract
This research study presents an experimental investigation on forced convection heat transfer of an aqueous ferrofluid flow passing through a circular copper tube in the presence of a magnetic field. Both constant magnetic field and alternating magnetic field was examined. Moreover magnetic field layout and strength and modes of alternating magnetic field was investigated. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by...
Numerical Solution of Flow and Heat Transfer in Micro Heat Pipes
, M.Sc. Thesis Sharif University of Technology ; Farhanieh, Bijan (Supervisor) ; Afshin, Hossein (Co-Advisor)
Abstract
One of the important issues that increasing development of electronic systems has caused is how to transfer the generated heat out of the system. Heat pipes can transfer large amount of heat because of using latent heat of evaporation and condensation. In micro scales using micro heat pipes is popular that in this instrument liquid returns to evaporator by means of surface tension force. So numerical solution is essential for verifying experimental results and increasing performance of this instrument. In this research has been planned to develop a comprehensive model for numerical solution of flow and heat transfer in micro heat pipes. For this reason surface evaporation and …,...
Multi-objective Optimization of Internal Cooling Passages for a Turbine Blade
, M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim (Supervisor)
Abstract
In the present work, the shape and position of internal cooling passages within an axial turbine blade have been optimized to achieve a uniform temperature distribution with the minimum cooling air flow while the maximum temperature is below the allowable value. Four cooling passages are made within the blade. The cross section shape of each passage is parameterized using a new method based on an 8-order Bezier curve. This curve which is represented in terms of Bezier control points has much flexibility and can produce a large variety of shapes. The shape of the blade surface profile remains unchanged during the optimization process. The numerical simulation has been carried out using...
Thermal Simulation of Sponge Iron Production by Höganäs Method
, M.Sc. Thesis Sharif University of Technology ; Halali, Mohammad (Supervisor)
Abstract
Sponge Iron production is conducted in various methods that one of them is using coal as a reduction agent. Hoganas process is a different coal-based method that has not been investigated in details. Therefore, the heat transfer method in the system is one of the basic steps to a better recognition of this process (with special Hoganas charging). The present paper investigates the temperature distribution method in the Hoganas cylinder through a numerical model using finite elements. The effects of different parameters, namely preheating and porosity were studied on ceramic crucible made from silicon carbide and it was observed that the consumption energy decreases with the increase of...
An applicable method for efficiency estimation of operating tray distillation columns and its comparison with the methods utilized in HYSYS and Aspen Plus
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 51, Issue 10 , October , 2015 , Pages 1393-1402 ; 09477411 (ISSN) ; Sharif University of Technology
Springer Verlag
2015
Abstract
Developing general methods that rely on column data for the efficiency estimation of operating (existing) distillation columns has been overlooked in the literature. Most of the available methods are based on empirical mass transfer and hydraulic relations correlated to laboratory data. Therefore, these methods may not be sufficiently accurate when applied to industrial columns. In this paper, an applicable and accurate method was developed for the efficiency estimation of distillation columns filled with trays. This method can calculate efficiency as well as mass and heat transfer coefficients without using any empirical mass transfer or hydraulic correlations and without the need to...
An experimental study on the effect of ultrasonication on thermal conductivity of ferrofluid loaded with carbon nanotubes
, Article Thermochimica Acta ; Volume 617 , October , 2015 , Pages 102-110 ; 00406031 (ISSN) ; Salimpour, M. R ; Saghafian, M ; Shafii, M. B ; Sharif University of Technology
Elsevier
2015
Abstract
Nanofluids containing Fe3 O4 and carbon nanotubes nanoparticles emulsified and dispersed using gum arabic (GA) and tetramethylammonium hydroxide (TMAH) were made and characterized for potential use as heat transfer fluids. Due to the interaction between the TMAH and GA molecules, the magnetic nanoparticles and CNTs were physically adsorbed. This paper reports an experimental work on the effect of ultrasonication on thermal conductivity of this aqueous suspension. The characterization and surface morphology of the dried samples were studied by using XRD and TEM measurements. Experiments were conducted in the magnetic nanoparticles mass concentration range 0.494-2.428%,...
Experimental investigation of the thermal management of flat-plate closed-loop pulsating heat pipes with interconnecting channels
, Article Applied Thermal Engineering ; Volume 90 , 2015 , Pages 838-847 ; 13594311 (ISSN) ; Shafii, M. B ; Bijarchi, M. A ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Abstract A desired circulatory flow in flat-plate closed-loop pulsating heat pipes (FP-CLPHPs), which may ameliorate electronic thermal management, was achieved by using the new idea of interconnecting channels (ICs) to decrease flow resistance in one direction and increase the total heat transfer of fluid. In order to experimentally investigate the effects of the IC, two aluminum flat-plate thermal spreaders - one with ICs (IC-FP-CLPHP) and one without them - were fabricated. The FP-CLPHPs were charged with ethanol as working fluid with filling ratios of 35%, 50%, 65%, and 80% by volume. Performance of interconnecting channels in different heat inputs was explored, and the results...
Heat transfer and pressure drop characteristics of nanofluid in unsteady squeezing flow between rotating porous disks considering the effects of thermophoresis and Brownian motion
, Article Advanced Powder Technology ; Volume 27, Issue 2 , March , 2016 , Pages 564–574 ; 09218831 (ISSN) ; Tamim, H ; Sharif University of Technology
Elsevier
2016
Abstract
In this study, the unsteady three dimensional nanofluid flow, heat and mass transfer in a rotating system in the presence of an externally applied uniform vertical magnetic field is investigated. This study has different applications in rotating magneto-hydrodynamic (MHD) energy generators for new space systems and also thermal conversion mechanisms for nuclear propulsion space vehicles. The important effects of Brownian motion and thermophoresis have been included in the model of nanofluid. The governing equations are non-dimensionalized using geometrical and physical flow field-dependent parameters. The velocity profiles in radial, tangential and axial directions, pressure gradient,...
Two-dimensional free convection heat transfer below a horizontal hot isothermal flat strip
, Article Journal of Heat Transfer ; Volume 137, Issue 5 , May , 2015 ; 00221481 (ISSN) ; Nouri Gheimassi, A ; Salari, A ; Behshad Shafii, M ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2015
Abstract
Convection heat transfer below a horizontal, hot, and isothermal strip of infinite length and width of 2L embedded in fluids with different Prandtl number (Pr) and Nusselt number (Nu) is analyzed with the aid of integral method. A new concept is utilized to determine the boundary layer thickness at the strip's edge, which is based on matching the flow rate of the boundary layer below the strip at its edge and the flow rate of the plume, which forms after the heated fluid detaches from the strip's edge. In addition to these novelties, a numerical model is developed to verify the analytical framework, and an excellent agreement is observed between the analytical and numerical models
Different methods for calculating a view factor in radiative applications: Strip to in-plane parallel semi-cylinder
, Article Journal of Engineering Thermophysics ; Volume 24, Issue 2 , April , 2015 , Pages 169-180 ; 18102328 (ISSN) ; Mirhosseini, M ; Saboonchi, A ; Moosavi, A ; Sharif University of Technology
Maik Nauka-Interperiodica Publishing
2015
Abstract
Determining the shape factor is essential for solving radiative heat transfer problems. An important case that has various applications in the heat power plant systems is calculation of the configuration factor between the fins and the in-plane parallel semi-cylinder. In the present work, Monte Carlo method, Cross string method, and analytical solutions were implemented for this problem. Several simulations were performed by varying semi-cylinders radius and different lengths of the fin. Also, the influence of the number of emitting rays and the number of strips was studied. Considering a fin between two tubes, it is found that calculating the view factor between one tube and a fin is...
Simple and rapid determination of effective Murphree component efficiencies for operating absorbers, strippers and distillation columns filled with any type of trays
, Article Separation and Purification Technology ; Volume 139 , January , 2015 , Pages 104-108 ; 13835866 (ISSN) ; Sharif University of Technology
Elsevier
2015
Abstract
Estimating efficiency of an operating column has to be distinguished from that of a column being designed. This crucial point has been totally overlooked in the literature. All the methods and models available for predicting the Murphree efficiencies of tray columns have been developed for the design case. They generate their own mass and heat transfer rates and empirical parameters rather than produce true transfer rates by using operating column (realistic) data, especially the specifications of outlet streams. In addition, most of these methods are limited in application and insufficient in accuracy, especially if applied outside the range of conditions under which they were formulated....
Porous media approach in thermohydraulic analysis of high temperature reactors in pressurized/depressurized cooldown: An improvement
, Article Progress in Nuclear Energy ; Volume 80 , 2015 , Pages 119-127 ; 01491970 (ISSN) ; Tabatabai Ghomsheh, S. I ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
The current study aims at introducing a 2D and fast-running code for the issues pertinent to design, analysis and safety in modular high temperature reactors. While the porous media approach is only applied to pebble bed type, the analysis in this paper covers both pebble bed and prismatic reactor. A time-dependent mass equation along with energy conservation equation for the cooling gas and a time-dependent energy conservation equation for the solid was solved. Appropriate series of constitutive equations (e.g. heat transfer coefficient, effective heat conductivity of solid, heat transfer coefficient, pressure drop etc.) has been recruited as well. In addition a finite-volume method is...
Analytical solution of classic coupled thermoelasticity problem in a rotating disk
, Article Journal of Thermal Stresses ; Volume 38, Issue 11 , Sep , 2015 , Pages 1269-1291 ; 01495739 (ISSN) ; Entezari, A ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
A fully analytical solution of the classic coupled thermoelasticity problem in a rotating disk subjected to thermal and mechanical shock loads is presented. Axisymmetric thermal and mechanical boundary conditions are considered in general forms of arbitrary heat transfer and traction, respectively, at the inner and outer radii of the disk. To solve the governing system of equations, an analytical procedure based on the Fourier-Bessel transform is employed. Closed form formulations are presented for temperature and displacement fields. The results of the present formulations are in good agreement with the numerical results available in the literature. The radial distribution and time history...
An improved porous media approach to thermal-hydraulics analysis of high-temperature gas-cooled reactors
, Article Annals of Nuclear Energy ; Volume 76 , February , 2015 , Pages 485-492 ; 03064549 (ISSN) ; Tabatabai Ghomsheh, S. I ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
A precise thermal-hydraulics model is of great importance for developing more effective designs of High Temperature Gas Cooled Reactors (HTGR). Recently, several advancements have been made in the methods of analysis of porous media which could be of significant value in the development of more precise and robust codes. The objective of this research is to incorporate some of the most recent improvements in the development of a new 2D program for thermal-hydraulics analysis of modular high temperature reactors. The program is mainly based on the solution of a coupled set of mass, energy and momentum conservation equations for the gas flow, along with the energy conservation equation in the...
Temperature distribution on a gas turbine shaft exposed to swirl combustor flue
, Article Journal of Thermophysics and Heat Transfer ; Volume 29, Issue 2 , 2015 , Pages 319-328 ; 08878722 (ISSN) ; Saidi, M. H ; Mozafari, A. A ; Keshavarz, P ; Sharif University of Technology
Abstract
A gas turbine shaft is generally exposed to high-temperature gases and may seriously be affected and overheated duetotemperature fluctuationsinthe combustion chamber. Vortex flow inthe combustion chamber may increase the heat release rate and combustion efficiency, as well as control the location of energy release. However, this may result in excessive temperature on the combustor equipment and gas turbine shaft. In this study, a new gas turbine combustion chamber implementing a liner around the shaft and the liquid-fuel feeding system is designed and fabricated. The influences of parameters such as the Reynolds number and the equivalence ratio are studied. Experimental results are compared...
Heat transfer enhancement in shell-and-tube heat exchangers using porous media
, Article Heat Transfer Engineering ; Volume 36, Issue 3 , 2015 , Pages 262-277 ; 01457632 (ISSN) ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
A numerical simulation has been carried out to investigate the heat transfer enhancement in a shell-and-tube heat exchanger using a porous medium inside its shell and tubes, separately. A three-dimensional geometry with k-ε turbulent model is used to predict the heat transfer and pressure drop characteristics of the flow. The effects of porosity and dimensions of these media on the heat exchanger's thermal performance and pressure drop are analyzed. Inside the shell, the entire tube bundle is wrapped by the porous medium, whereas inside the tubes the porous media are located in two different ways: (1) at the center of the tubes, and (2) attached to the inner wall of the tubes. The results...
Heat transfer analysis of a porously covered heated square cylinder, using a hybrid Navier-Stokes-lattice Boltzmann numerical method
, Article International Journal of Thermal Sciences ; Volume 91 , May , 2015 , Pages 59-75 ; 12900729 (ISSN) ; Taeibi Rahni, M ; Jam, F ; Sharif University of Technology
Elsevier Masson SAS
2015
Abstract
In this work, two-dimensional laminar flow and heat transfer across a heated square cylinder, covered by a porous layer in a plane channel have been numerically investigated. The flow and thermal fields inside the porous layer were simulated using BrinkmaneForchmeyer extended Darcy model. Simulations were performed in different Reynolds numbers (Re = 60, 120, 160, and 200), porosities (ω = 0.7, 0.87, and 0.96), solid to fluid thermal conductivity ratios (λR = 10, 200, and 2000) and blockage ratios (BR = 0.5, 0.25 and 0.125). The effects of the mentioned parameters on pressure drop and heat transfer rate were investigated in detail. Also, the contribution of each side of the central squared...
Low computational-complexity model of EAF Arc-heat distribution
, Article ISIJ International ; Volume 55, Issue 7 , October , 2015 , Pages 1353-1360 ; 09151559 (ISSN) ; Saboohi, Y ; Škrjanc, I ; Logar, V ; Sharif University of Technology
Iron and Steel Institute of Japan
2015
Abstract
The paper presents a computational model and the corresponding algorithm for estimating the arc energy distribution to conductive, convective and radiative heat transfer in an electric arc furnace (EAF). The proposed algorithm uses channel arc model (CAM) in order to compute the distribution of the arc energy through empirical equations (to approximate arc radius), ideal gas law (to approximate arc density) and results of magneto-hydro-dynamic (MHD) models (to approximate arc pressure, temperature and velocity). Results obtained using the proposed algorithm are comparable with other similar studies; however, in contrast to other arc-energy distribution models, this model requires only two...