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thermal-boundary-layer
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Empirical correlation for performance evaluation of electric/corona wind on natural convection
, Article Journal of Electrostatics ; Vol. 72, issue. 1 , February , 2014 , pp. 82-90 ; ISSN: 03043886 ; Shabahang-Nia, E ; Merdasi, A ; Sharif University of Technology
Abstract
The effect of the corona wind on the natural convection at a rectangular channel was investigated experimentally. The results indicate that the natural convection in the absence of electric/corona wind at obtuse angles outperforms than acute angles and keeps improving by increasing the angle. However, the efficiency of the electric/corona wind at acute angles is higher than obtuse angles. Generally, in the presence of electric/corona wind, heat transfer coefficient was increased. The effect of the electric/corona wind was decreased by raising heat flux. This mainly stems from the fact that the temperature gradient raises the thermal boundary layer and reduces the secondary flow power....
Turbulent decaying swirling flow in a pipe
, Article Heat Transfer Research ; Volume 49, Issue 16 , 2018 , Pages 1559-1585 ; 10642285 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Begell House Inc
2018
Abstract
In this work, a solution is applied to investigate the heat transfer characteristics in a pipe with turbulent decaying swirling flow by using the boundary layer integral scheme. The governing equation is solved using the forth-order Runge-Kutta scheme resulting in thermal boundary-layer thickness and dimensionless heat transfer coefficient, namely, the Nusselt number. Both forced- and free-vortex profiles are considered for the tangential velocity component. A comparison of the results obtained for the Nusselt number with available experimental data shows that this scheme has good capability in predicting the heat transfer parameters of swirling flow especially in the entrance region of a...
Theoretical and Experimental Investigation of NOx Reduction in a CNG Turbocharged Internal Combustion Engines
, Ph.D. Dissertation Sharif University of Technology ; Mozaffari, Ali Asghar (Supervisor) ; Hajilouy Benisi, Ali (Supervisor)
Abstract
Combustion and NOx emissions were simulated by quasi-dimensional and ratereaction methods respectively in a turbocharged CNG engine. Mean-value turbulence modeling was carried out during compression and combustion processes to simulate combustion process better. The most appropriate NG flame speed for the CNG turbocharged engine was applied and ignition delay was ended when flame radius became more than turbulence integral length scale. Hemispherical flame propagated from spark gap center and its intersection with reciprocating Mexican-hat piston bowl was calculated analytically. Thermal boundary layer, as a novel approach, was considered in the simulation and a better agreement of predicted...
Simulation and experimental investigation of performance and emissions of a turbocharged lean-burn natural gas engine considering thermal boundary layer
, Article Scientia Iranica ; Vol. 21, issue. 4 , 2014 , pp. 1424-1439 ; ISSN: 10263098 ; Mozafari, A ; Hajilouy-Benisi, A ; Sharif University of Technology
Abstract
Emission characteristics of pure natural gas is fairly known, however more experimental investigation of natural gas combustion is necessary. In this research, emission and performance of a turbocharged natural gas SI engine are investigated experimentally at WOT and lean burn conditions. A computer code is also developed in MATLAB environment for predicting engine performance and NO emission and the results are validated with experimental data. Thermal boundary layer, as a novel approach, is considered in the simulation and a better agreement of predicted mass fraction burned was achieved at end part of combustion process when compared with experimental results. Experimental results have...
Effects of insulated and isothermal baffles on pseudosteady-state natural convection inside spherical containers
, Article Journal of Heat Transfer ; Volume 132, Issue 6 , April , 2010 , Pages 1-10 ; 00221481 (ISSN) ; Hosseinizadeh, S. F ; Khodadadi, J. M ; Sharif University of Technology
2010
Abstract
The effects of insulated and isothermal thin baffles on pseudosteady-state natural convection within spherical containers were studied computationally. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables. Natural convection effect is modeled via the Boussinesq approximation. Parametric studies were performed for a Prandtl number of 0.7. For Rayleigh numbers of 104, 105, 106, and 107, baffles with three lengths positioned at five different locations were investigated (120 cases). The fluid that is heated adjacent to the sphere rises replacing the colder fluid, which sinks downward through the stratified stable thermal layer. For...
A new approach to thermo-fluid behavior through porous layer of heat pipes
, Article Scientia Iranica ; Volume 25, Issue 3B , 2018 , Pages 1236-1242 ; 10263098 (ISSN) ; Sharif University of Technology
Sharif University of Technology
2018
Abstract
This paper developed a new mathematical model to investigate the heat transfer as well as wick's thickness of a heat pipe. The model was established by conservative equations of continuity, momentum, and energy in the thermal boundary layer. Using a similarity variable, the governing equations were changed to a set of ordinary differential equations and were solved numerically by the forth-order Runge-Kutta method. The flow variables, such as velocity components, wick's thickness, and Nusselt number, were obtained. The results show that the Nusselt number is proportional to the square root of the Darcy-modified Rayleigh number and to the distance from the edge of the condenser surface....
Performance intensification of turbulent flow through heat exchanger tube using double V-cut twisted tape inserts
, Article Chemical Engineering and Processing - Process Intensification ; Volume 141 , 2019 ; 02552701 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier B.V
2019
Abstract
This paper aims to present a numerical model for heat transfer intensification in a heat exchanger tube equipped with novel double V-cut twisted tape. The effects of different cut ratios (0.6 < b/c<1.8)on the turbulent flow characteristics and thermal performance of the system are investigated over the Reynolds number range from 5000 to 15,000. The accuracy of (RNG)k-ε turbulence model used in the present study is validated by comparing with experimental results. The tube equipped with double V-cut twisted tape shows improved thermal performance in comparison with conventional twisted tape. This improvement is due to the additional vortex flow induced by the V-cuts which leads to more...
Forced-convection heat transfer of ferrofluids in a circular duct partially filled with porous medium in the presence of magnetic field
, Article Journal of Magnetism and Magnetic Materials ; Volume 475 , 2019 , Pages 304-315 ; 03048853 (ISSN) ; Shahrokhi, M ; Molaei Dehkordi, A ; Abbasi, Z ; Sharif University of Technology
Elsevier B.V
2019
Abstract
In this article, effects of magnetic fields induced by a finite length solenoid on the forced-convection heat transfer in a pipe partially filled with porous medium have been investigated. In this regard, two-dimensional steady-state fluid flow in the pipe was considered and the Darcy–Brinkman equation of motion was applied to model the fluid flow in the porous medium, as well as the thermal equilibrium was assumed between the solid phase and the magnetic nanofluid. Effects of electric current passing through the solenoid and the solenoid dimensions (i.e.; diameter and length) on the forced-convection heat transfer were studied carefully. The combined effects of the magnetic field and the...
Theoretical comparative assessment of single- and two-phase models for natural convection heat transfer of Fe3O4/ethylene glycol nanofluid in the presence of electric field
, Article Journal of Thermal Analysis and Calorimetry ; 2020 ; Tavakoli, S ; Pishvaie, M. R ; Sharif University of Technology
Springer Netherlands
2020
Abstract
Natural convective heat transfer of Fe3O4/ethylene glycol nanofluids around the platinum wire as a heater in the absence and presence of the high electric field was investigated, numerically. The control volume finite element method was employed for the numerical simulation. Effects of the flow model, the volume fraction of nanoparticles, Rayleigh number, and the electric field intensity on the natural heat transfer coefficient (NHTC) of nanofluid were studied. Simulation results of single-phase and two-phase flow models showed that the two-phase model could better predict experimental data than the single-phase model due to take into account the velocity of each phase in the mixture. The...
Theoretical comparative assessment of single- and two-phase models for natural convection heat transfer of Fe3O4/ethylene glycol nanofluid in the presence of electric field
, Article Journal of Thermal Analysis and Calorimetry ; Volume 146, Issue 2 , 2021 , Pages 981-992 ; 13886150 (ISSN) ; Tavakoli, S ; Pishvaie, M. R ; Sharif University of Technology
Springer Science and Business Media B.V
2021
Abstract
Natural convective heat transfer of Fe3O4/ethylene glycol nanofluids around the platinum wire as a heater in the absence and presence of the high electric field was investigated, numerically. The control volume finite element method was employed for the numerical simulation. Effects of the flow model, the volume fraction of nanoparticles, Rayleigh number, and the electric field intensity on the natural heat transfer coefficient (NHTC) of nanofluid were studied. Simulation results of single-phase and two-phase flow models showed that the two-phase model could better predict experimental data than the single-phase model due to take into account the velocity of each phase in the mixture. The...
Analytical approximate solution of the cooling problem by Adomian decomposition method
, Article Communications in Nonlinear Science and Numerical Simulation ; Volume 14, Issue 2 , 2009 , Pages 462-472 ; 10075704 (ISSN) ; Sedighi, K ; Farhadi, M ; Ebrahimi Kebria, H. R ; Sharif University of Technology
2009
Abstract
The Adomian decomposition method (ADM) can provide analytical approximation or approximated solution to a rather wide class of nonlinear (and stochastic) equations without linearization, perturbation, closure approximation, or discretization methods. In the present work, ADM is employed to solve the momentum and energy equations for laminar boundary layer flow over flat plate at zero incidences with neglecting the frictional heating. A trial and error strategy has been used to obtain the constant coefficient in the approximated solution. ADM provides an analytical solution in the form of an infinite power series. The effect of Adomian polynomial terms is considered and shows that the...