Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
10
4
2018
NUMERICAL STUDY OF NON-REACTIVE CONFINED THERMAL JET WITH VARIABLE DENSITY
297-305
Mohamed El Amine
Fodil
Aeronautical and Propulsive Systems Laboratory, USTO University, B.P. 1500 El Mnaouer
Oran, Algeria
Sidi Mohamed Amine
Meftah
Aeronautical and Propulsive Systems Laboratory, USTO University, B.P. 1500 El Mnaouer
Oran, Algeria
Bachir
Imine
Aeronautical and Propulsive Systems Laboratory, USTO University, B.P. 1500 El Mnaouer
Oran, Algeria
This study deals with the density impact on the turbulence's structure in a confined and mobile atmosphere with
slow velocity. The variable density is gotten by heating or cooling the air jet, expending in an atmosphere at ambient
temperature. The jet temperature is regulated in order to relate the similar density Rρ to the mixed jet (CO2/air, air/air, CH4/air, and He/air). The finite volume method is adopted for the numerical resolution of elliptic equations governing these flows. The standard (k-ε) turbulence model is used. The computational predictions are compared with experimental observations in order to validate the mathematical model. There is no large difference between the computed average variables and those of experimental results. Also, different injection ratios are used in order to find a good correlation between a limit of the potential core and the density ratio.
DOUBLE DIFFUSIVE NATURAL CONVECTION IN A SQUARE ENCLOSURE FILLED WITH COPPER-WATER NANOFLUID INDUCED BY OPPOSITE TEMPERATURE AND CONCENTRATION GRADIENTS
307-320
Natesan
Saritha
School of Mechanical Engineering, VIT University, Vellore, India
A. Senthil
Kumar
School of Mechanical Engineering, VIT University, Vellore, India
Double-diffusive natural convection in a Cu–water nanofluid-filled square enclosure neglecting the effect of Soret and
Dufour is studied numerically. The horizontal walls are well insulated and impermeable, while the vertical walls are
imposed to opposite temperature and concentration gradients. Brinkman, Maxwell–Garnett models are used to determine
the effective dynamic viscosity and thermal conductivity of Cu–water nanofluid, respectively. A computational
code based on the SIMPLE algorithm is used to solve the system of conservation equations of mass, momentum, energy,
and species. Simulations are performed using the thermal Rayleigh number, the buoyancy ratio, and the solid
volume fraction as independent variables. The numerical results are studied in terms of velocity profiles, streamlines, isotherms, iso-concentrations, local and average Nusselt numbers, and Sherwood number for a wide range of Rayleigh number Ra = 104–105, the buoyancy ratio N = 0.1–10 and the solid volume fraction (0 ≤ φ ≤ 0.1) with Prandtl number Pr = 5.0 and Lewis number Le = 1. It is found that utilizing Cu–water nanofluid enhances the heat transfer
sufficiently while the enhancement is marginal for the mass transfer. It is also observed that the fluid flow behavior
increases with increasing Rayleigh number but decreases with increasing solid volume fraction.
NUMERICAL SIMULATION OF FILM CONDENSATION FROM GAS–VAPOR MIXTURES IN VERTICAL PARALLEL PLATE CHANNELS
321-335
Foad
Hassaninejadfarahani
University of Manitoba, Deptartment of Mechanical Engineering, 75A Chancellors Circle,
Winnipeg, Manitoba, Canada
Scott J.
Ormiston
University of Manitoba, Deptartment of Mechanical Engineering, 75A Chancellors Circle,
Winnipeg, Manitoba, Canada
The present work performs a numerical analysis of steady-state, laminar film condensation from a downward flow
of a vapor–gas mixture in vertical parallel plate channels. A finite volume method and a co-located variable storage
scheme were used with a structured non-orthogonal mesh. Relative to previous approaches the present work has the
following new aspects: the complete elliptic two-dimensional governing equations are solved in both phases, a dynamically
determined sharp interface is used between the phases, and the algebraic equations are solved in a pressure-based
coupled approach. Two velocities, pressure, and temperature in both phases plus non-condensing gas mass fraction and
interface locations are determined simultaneously for the entire solution domain. The results presented for steam–air
mixtures include axial velocity, pressure, and gas mass fraction profiles as well as axial variations of film thickness, condensation rate, local Nusselt number, and interface gas mass fraction. Detailed comparisons are made with results from an established parabolic (marching) model. Two cases are presented for which the parabolic model terminated because of a negative axial velocity. In those cases, the present elliptic model obtained solutions with predictions of small regions of reverse flow extending to the channel outlet.
CFD SIMULATION OF FLOW FIELD AND HEAT TRANSFER IN A SINGLE-CYLINDER HCCI ENGINE AT DIFFERENT BOUNDARY CONDITIONS
337-354
Renganathan
Manimaran
Thermal and Automotive Research Group, School of Mechanical and Building Sciences, VIT
University Chennai Campus, Tamilnadu, India 600127
Rajagopal Thundil Karuppa
Raj
Department of Automotive Engineering, VIT University Vellore Campus, Tamilnadu, India
632014
The evolution of the flow field inside a homogenous charge compression ignition (HCCI) diesel engine during the intake
stroke is studied using a computational fluid dynamics (CFD) model. The conditions of air and fuel at different inlet
pressures and temperatures are modified to study the suitability in an HCCI engine. These sets of conditions correspond to the simulation of turbocharging and preheating systems involved in the development of a homogeneously charged compression ignition engine. Two-phase flow is assumed between air and fuel. The fuel used here is diesel. The Reynolds stress model is used to close the Navier-Stokes equations due to turbulent flow field. The SIMPLE algorithm is used in the solution convergence in which the residuals of the governing equations are reduced with second-order convection schemes. Mesh scales are changed to arrive at grid-independent results of velocity in the intake stroke. Time steps are reduced to less than a degree of crank angle in obtaining a time-independent solution. The inlet pressure of air is varied from 0 to 1 bar (gauge) for modeling the turbocharging operation. Fuel injection at different flow rates is attempted to maintain the identical air-fuel ratio. Fuel at elevated temperatures (less than flash point) is employed for better mixing with air. The condition of preheated air with fuel at room temperature is also explored. The effect of air-fuel mixing due to different inlet pressures and temperatures is studied in this work.
NUMERICAL ANALYSIS OF CONCENTRIC DOUBLE PIPE LATENT THERMAL ENERGY STORAGE UNIT USING TWO PHASE CHANGE MATERIALS FOR SOLAR WATER HEATING APPLICATIONS
355-374
Fouzi
Benmoussa
LESEI Laboratory, Faculty of Technology,Mechanics Department, University of Batna-2,
Batna, Algeria
Riadh
Ouzani
LESEI Laboratory, Faculty of Technology,Mechanics Department, University of Batna-2,
Batna, Algeria
Ahmed
Benzaoui
Université des Sciences et de la technologie Houari Boumedienne, Faculté de Physique, Dépt.
Energétique. B.P. 32 El-Alia, 16111 Bab-Ezzouar, Alger, Algeria
Hocine
Benmoussa
LESEI Laboratory, Faculty of Technology,Mechanics Department, University of Batna-2,
Batna, Algeria
This paper presents a numerical study based on the energy equations for the transient thermal behavior of a concentric
double pipe latent thermal energy storage (LTES) unit for solar water heating applications. The annular space between
tubes is filled with two paraffin wax phase change materials (PCMs), named PCM1 and PCM2. A heat transfer
fluid (HTF: saturated water) flows through the inner tube and transfers the heat to the PCMs. Several numerical
investigations were conducted in order to examine the effects of the HTF inlet temperatures on the variation of the temperature of PCM1 and PCM2, melting fraction, melting and solidification time, HTF outlet temperature, heat
transfer rate, and total energy stored. Numerical results show that charging and discharging processes have three
distinct periods for the change of PCMtemperature and melting fraction.When the temperature difference between the
HTF inlet temperature and PCM increase, the variation of the temperature and melting fraction in different locations
in the PCM increases considerably, and then the charging and discharging process is rapidly reached. The melting
times of PCM1 and PCM2 decrease with an increase in the HTF inlet temperature. Moreover, the decreasing degree
of their melting times is different. The present analysis provides theoretical guidance for designing optimization of a concentric double pipe LTES unit filled with two PCMs.
BIOMASS FAST PYROLYSIS IN A SHAFTLESS SCREW REACTOR: RESIDENCE TIME DISTRIBUTION AND HEATING EVALUATION BY MEANS OF A DEM APPROACH
375-388
Stefano
Cordiner
Department of Industrial Engineering, University of Rome Tor Vergata, Via Del Politecnico 1,
Roma, 00133, Italy
Alessandro
Manni
Department of Industrial Engineering, University of Rome Tor Vergata, Via Del Politecnico 1,
Roma, 00133, Italy
Vincenzo
Mulone
Department of Industrial Engineering, University of Rome Tor Vergata, Via Del Politecnico 1,
Roma, 00133, Italy
Vittorio
Rocco
Department of Industrial Engineering, University of Rome Tor Vergata, Via Del Politecnico 1,
Roma, 00133, Italy
Screw reactors may be designed for small-scale fast pyrolysis processes, but few models have been available so far for design and optimization. In this work, an analysis of specific aspects such as solid residence time and heating processes is proposed for this type of reactor, studying the system via a 3D computational fluid dynamics model. The screw reactor where the pyrolysis process takes place has been modeled with a discrete element model (DEM) approach based on the multiphase code MFiX. The interactions between the gaseous phase and particles are taken into account, while the evaporation process and chemical reactions are neglected. This approach allows for investigating in more detail some characteristic effects related to the perturbation of operating parameters to compare numerical and experimental data. The numerical heat flux is in line with experimental results at an average value of about 100 W, corresponding to 1 kg/h biomass flow rate with a 7% moisture content wet basis (w.b.). The residence time of the solid particles in the pyrolysis region (less than half of the whole reactor length) is on the order of 6 seconds, which is typical for such applications. A 1D model based on the 3D data evaluation has then been set up with the aim of calibrating such effects by a simplified axial diffusion coefficient evaluated at 1 × 10-5 m2/s.