Search

Development of a model that allows performance and combustion characteristics for a supercharged diesel engine was the main objective sought by the present work. Thus, the developed model is used, to examine the impact of start combustion, combustion duration, compression ratio, and heat flux, as well as intake conditions such as pressure and temperature, on the combustion characteristics of the supercharged diesel. For this purpose, a one zone thermodynamic prediction model was adopted with Wiebe function for combustion sub-model. The heat transfer was correlated using Woschni correlation. A numerical simulation is developed considering the crankshaft angle as the independent variable. Validation of the computational code has been favorably evaluated using our experimental data. To give a more general aspect to the developed model, experimental data found in the literature, are also used for this purpose. The results show that the addition of a turbocharger increases low-speed airflow and hence fuel consumption. In addition, an increase in intake pressure contributes to the rise of the heat flux released during combustion, while an increase in intake temperature leads to a strong increase in combustion temperature. Moreover, an increase in the compression ratio leads in a remarkable increase in all parameters simultaneously. However, maximum combustion pressure limits must not be exceeded. This is because the pressure has an effect with the engine mechanical strength. [ABSTRACT FROM AUTHOR]

AbstractThis article presents a numerical investigation and analysis of the cooling effectiveness of thermomagnetic transient natural convection in a long channel, equipped with four cylindrical heat-generating blocks. A non-Newtonian power-law ferrofluid was employed for the present investigation to achieve optimum cooling. The governing equations are the continuity equation, the momentum equation and the energy equation. The finite volume method was used to solve the resulting algebraic system. From an energy-saving point of view, this configuration can provide a good approximation for selecting effective physical and geometrical parameters to design a reliable thermal system. For this purpose, the study was carried out for various geometric and thermophysical parameters. Different values of thermal conductivity, power law index, Rayleigh number, Hartmann number and ferrofluid volume fraction, were considered. The results are illustrated in the form of streamlines, isotherms, average Nusselt and a spatio-temporal characterization of the mean ferrofluid velocity. From the results presented, we can conclude that the choice of non-Newtonian, pseudoplastic ferrofluid with a low thermal conductivity ratio subjected to a uniform magnetic field proves to be a crucial solution for efficient and stable cooling of heat-generating cylindrical blocks, which will have to be close to the cold walls of the channel. [ABSTRACT FROM AUTHOR]

This work groups a set of numerical results on the investigation of the external magnetic field effect on mixed convection in a ventilated square cavity with a heat source located in the middle of its bottom wall and filled with a ferrofluid. The behavior of the magnetic field was treated according to three different scenarios illustrated by magnetic Reynolds number value (Rm = 0.1, 0.001, and 0.00001). The dimensionless governing equations were solved numerically by the finite volume method and the SIMPLE algorithm was chosen for the treatment of coupling between the momentum and continuity equations using the QUICK scheme of Leonard. The numerical results for a large range of Hartmann numbers and volume fractions and for horizontal and vertical magnetic field directions are discussed in terms of streamlines, isotherms, Nusselt numbers, and maximal temperature of fluid and heat source. The results highlighted different scenarios showing the heat exchange rate enhancement and heat source cooling as a function of the magnetic field strength and direction and as a function of the internal fluid constitution and behavior. The diversity of these results as a function of the magnetic Reynolds number also underlines the limitation of theory based on low-Rm model in the treatment of MHD flows. [ABSTRACT FROM AUTHOR]

This article presents a numerical study of horizontal ring mixed convection with a heated inner cylinder equipped with two fins. Thermal buoyancy forces are maintained by considering the inner and outer cylinders at different uniform temperatures. The flow is generated by the rotation of the inner cylinder with a constant angular velocity (ω) in the counter-clockwise direction while the outer cylinder is held fixed. A finite volume scheme is adopted using the SIMPLE algorithm to solve the transport equations for continuity, momentum and energy. Simulations are made for various combinations of rotating Reynolds (Re = 0 to 1500) and Grashof numbers (Gr = 10 to 106). First, we focused on the criteria and parameters controlling the fully developed periodic regime. Thereafter, the heat transfer rates analyzed through the averaged Nusselt number (instant and over a period) highlights a complex phenomenon. For moderate Grashof numbers (Gr ≤ 103) the overall Nusselt number is not affected by Gr further, Re = 750 constitute a limit for the improvement of the heat transfer beyond which it decreases strongly. For larger Gr (>103), the reverse phenomenon occurs, i.e., the overall mean Nusselt number grows with Gr as Re < 750, then decreases for higher values. [ABSTRACT FROM AUTHOR]

This work present numerical simulation results of mixed convection in lid-driven “T” shallow cavity, filled by two immiscible fluids layers of air and Al2O3-water nanofluid. Mixed convection condition is created by the upper wall movement and temperature difference between the alveolus bottom and upper wall. Hydrodynamic and thermal characteristics of the flow have been predicted by solving the Navier- Stokes and energy equation using finite volume method. Coupling between two fluids layers are achieved using continuity of temperature and velocity at the interface air-nanofluid. Nano-particle volume fraction effect and geometrical shape of alveolus sidewalls (plane shape, concave shape and convex shape) have been chosen as discussed parameters. Analysis of obtained results shows that the heat transfer rate decreased with increasing volume fraction of solid inside the nanofluid layer. In addition, geometrical shape of alveolus sidewalls has a poor effect on flow structure and isotherms distribution in the physical domain.

This work is focused on corrugated bottoms role as a means to improving heat performance of cavities filled by two superimposed fluid layers. Physical models examined are square cavities with bottoms subjected to a constant heat flow and sidewalls maintained at cold temperatures. Cavities treated here have been filled with two different fluids. Computational code based on finite volume method has been used to solve two fluid region equations and predict thermal and hydrodynamic fields in two-layer system. Interface between two fluids was assumed to be fixed with null velocities and to be thermally conductive across two fluid regions, where heat flow continuity at this domain boundary was adopted. Mesh has been treated using curvilinear mesh grid in order to take into account corrugated bottoms. Different Rayleigh number values "(103 ≤ Ra ≤ 106)" and different filling rates of two flu ids "(1/3 ≤ h/L ≤ 2/3)" are included in this parametric study. Main objective of our research is focused on corrugated bottoms as a way to improve thermal performance of cavities filled by two fluids, we have opted to examined various forms of corrugation, based on wavelength effects "(0.1 ≤ b ≤ 0.5)" and amplitudes effect "(0 ≤ a ≤ 0.1)" of corrugated backgrounds. Results shows that corrugated bottoms provide an efficient means to improve thermal performances of cavities filled by two fluids. Also, it has been shown that optimal values of wave length and amplitude of corrugated bottoms exist where heat transfer rate reaches its maximum. [ABSTRACT FROM AUTHOR]

This study presents a series of numerical simulations of conjugate heat transfer within square cavity horizontally divided into two regions by a conductive wall. The two fluids are subjected to different boundary conditions. Cold fluid (Pr1) enters the upper part through an inlet (h1) and exits it via an outlet (h2), while the lower part has been heated from bellow and filled with another fluid (Pr2 = 7). The finite volume method has been used to predict thermal and hydrodynamic mechanisms in both fluid regions of cavity and at partition wall. Effect of inlet/outlet location has been considered according to two configurations. Influence of Reynolds number (50 ⤠Re ⤠1000), Grashof number (Gr=104 and Gr = 5 Ã-- 105), fluid-1 Prandtl number (Pr1), and thermal conductivity ratio (0.0001 ⤠k = k1/ks ⤠5) has been investigated. Analysis of results was done based on isotherms, streamlines, local, and average Nusselt number. The results show that one of two configurations guarantee a higher Nusselt number. Higher heat transfer rate was obtained by increasing Reynolds and Grashof numbers. Also, it has been found that the effect of upper fluid flow regime on lower fluid flow is more pronounced with a very low thermal conductivity ratio. [ABSTRACT FROM AUTHOR]

The main objective of this article is to study the effect of coupled mode free convection with surface radiation on the fluid flow behavior inside a tilted solar collector having a flat glass cover and a wavy bottom absorber. The cavity is subject to vertical gradient temperature while its top sidewalls remain thermally insulated. The dimensionless governing equations under Boussinesq approximation are coupled with a radiative model through the boundary conditions and solved by the Finite Volume Method. The numerical results are discussed in terms of streamlines, isotherms, convective and radiative Nusselt number along the cover plate for various aspect ratios, inclination angle, emissivity and Rayleigh number. These results highlighted the condition of the enclosure performance and revealed that the heat and fluid flow fields are affected by surface radiation and the above parameters. In the end, correlations for predicating the convection heat loss in term of averaged Nusselt numbers are developed in both pure free convection and coupled convection-surface radiation modes. [ABSTRACT FROM AUTHOR]

The study goes further to investigate numerically the effect of a finned plate on the heat transfer and fluid flow in a square enclosure with isothermal boundary conditions for a range of the Rayleigh numbers 103-106. The governing equations under Boussinesq approximation are solved in their dimensionless form by means of the finite volume method. Results for the cases computed are presented in terms of streamlines, isotherms and Nusselt numbers and show the condition of the enhancement of heat transfer from the finned plate to the surrounding cavity walls. They reveal that the heat and flow fields are dependent on the Rayleigh number and several geometrical ratio parameters. [ABSTRACT FROM AUTHOR]

The main objective of this article is to study the effect of 2D coupled mode free convection with surface radiation on the fluid flow behavior in an air filled partitioned and shallow cavity subjected to isothermal or insulated boundary conditions. The dimensionless governing equations under Boussinesq approximation are coupled with a radiative model through the boundaries conditions and solved by the finite volume method. The numerical results are discussed in terms of streamlines, isotherms, convective and radiative Nusselt numbers along the cover plate for various aspect ratios (a, b and c), emissivities and Rayleigh number. These results highlighted the condition of the enclosure performance and revealed among other that isothermal boundaries induce better convective heat exchange compared to adiabatic cases. Also, it is noticed that varying aspect ratio (a) causes strong influence on both Nusselt numbers compared to the aspect ratios (6) and (c). The increase of (ϵ0) raises Nuconv and decreases Nurad slightly. Whereas, an increase of (ϵc) leads to minor changes in Nurad when (b) or (c) vary, this effect becomes appreciable with increasing (a). [ABSTRACT FROM AUTHOR]