Orhan Aydin

Natural convection in enclosures with localized heating from below and symmetrical cooling from sides

Natural convection of air in a two‐dimensional, rectangular enclosure with localized heating from below and symmetrical cooling from the sides has been numerically investigated. Localized heating is simulated by a centrally located heat source on the bottom wall, and four different values of the dimensionless heat source length, 1/5, 2/5, 3/5 and 4/5 are considered. Solutions are obtained for Rayleigh number values from 103 to 106. Local results are presented in the form of streamline and isotherm plots as well as the variation of local Nusselt number on the heated wall. Finally, the average Nusselt number at the heated part of the lower wall, \overline Nu, was shown to increase with an increase the Rayleigh number, Ra, or of the nondimensional heat source thickness, e.

Natural convection in rectangular enclosures heated from one side and cooled from the ceiling

Abstract Steady natural convection of air in a two-dimensional enclosure isothermally heated from one side and cooled from the ceiling is analyzed numerically using a stream function–vorticity formulation. Based on numerical predictions, the effects of Rayleigh number and aspect ratio on flow pattern and energy transport are investigated for Rayleigh numbers ranging from 103 to 107, and for five different aspect ratios of 0.25, 0.50, 1.0, 2.0 and 4.0. The effect of Rayleigh number on heat transfer is found to be more significant when the enclosure is shallow (ar > 1) and the influence of aspect ratio is stronger when the enclosure is tall and the Rayleigh number is high.

Determination of optimum air-layer thickness in double-pane windows

In this study, heat transfer through a double-pane window is numerically analyzed by a finite difference technique. The aim of the study is to determine the thermally optimum air-layer thickness between the two panes for different climates. Four different cities of Turkey, representing different climate conditions are considered: Ankara, Antalya, Kars and Trabzon. The height of the window, H is chosen 80 cm. The effect of air-layer thickness varies between 3 and 40 mm on the average Nusselt number and the heat flux through the inner pane. It was shown that energy losses through the double-pane windows can be considerably reduced by optimizing the thickness of air layer.

MIXED CONVECTION IN CAVITIES WITH A LOCALLY HEATED LOWER WALL AND MOVING SIDEWALLS

A numerical study is conducted to investigate the transport mechanism of laminar mixed convection in a shear - and buoyancy-driven cavity having a locally heated lower wall and moving cooled sidewalls. Effort is focused on the interaction of forced convection with natural convection. Localized heating is simulated by a centrally located heat source on the bottom wall, and four different values of the dimensionless heat source length, epsilon, 1 / 5, 2 / 5, 3 / 5, and 4 / 5 of the nondimensional length of the bottom wall, are considered. Parametric studies on the effect of mixed convection parameter, Gr Re2 (also referred to as Richardson number, Ri), in the range 0.1 ? 10, on the fluid flow and heat transfer are performed for each epsilon. Local results are presented in the form of streamline and isotherm plots as well as the variation of local Nusselt number on the heated wall. Three different regimes are observed with increasing Gr Re2: forced convection (with negligible natural convection), mixed convection (comparable forced and natural convection), and natural convection (with negligible forced convection).

A numerical study on buoyancy-driven flow in an inclined square enclosure heated and cooled on adjacent walls

Buoyancy-driven flows in enclosures play a vital role in many engineering applications such as double glazing, ventilation of rooms, nuclear reactor insulation, solar energy collection, cooling of electronic components, and crystal growth in liquids. Here, numerical study on buoyancy-driven laminar flow in an inclined square enclosure heated from one side and cooled from the adjacent side is conducted using finite difference methods. The effect of inclination angle on fluid flow and heat transfer is investigated by varying the angle of inclination between 0{degree} and 360{degree}, and the results are presented in the form of streamlines and isotherms for different inclination angles and Rayleigh numbers. On the basis of the numerical data, the authors determine the critical values of the inclination angle at which the rate of the transfer within the enclosure is either maximum or minimum.

Mixed Convection in a Vertical Parallel Plate Microchannel

In this study, fully developed mixed convective heat transfer of a Newtonian fluid in an open-ended vertical parallel plate microchannel is analytically investigated by taking the velocity slip and the temperature jump at the wall into account. The effects of the mixed convection parameter, Gr/Re, the Knudsen number, Kn, and the ratio of wall temperature difference, r T , on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Gr/Re,Kn,r T ) expression is developed.

Numerical Modeling of Forced-Convection Drying of Cylindrical Moist Objects

This study deals with simultaneous heat and mass transfer during drying of cylindrical moist objects through an implicit finite-difference method. Instantaneous temperature and moisture distributions inside the moist material as well as all local convective heat and mass transfer coefficients are also studied via the Fluent computational fluid dynamics (CFD) package. It is found that the convective heat transfer coefficients vary from 4.65 to 59.33 W/m 2 K, while the convective mass transfer coefficients range between 3.59 × 10−7 and 4.58 × 10−6 m/s, respectively. Remarkably good agreement is obtained between the predicted results and experimental data taken from the literature to validate the present model.

Mixed Convection in a Vertical Parallel Plate Microchannel With Asymmetric Wall Heat Fluxes

In this study, exact analytical results are presented for fully developed mixed convective heat transfer of a Newtonian fluid in an open-ended vertical parallel plate microchannel with asymmetric wall heating at uniform heat fluxes. The velocity slip and the temperature jump at the wall are included in the formulation. The effects of the modified mixed convection parameter, Gr q /Re, the Knudsen number, Kn, and the ratio of wall heat flux, r q =q 1 /q 2 , on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu= f(Gr q /Re,Kn,r q ) expression is developed. For, the limiting case of Kn=0, the results are found to be in an excellent agreement with those in the existing literature.

Laminar boundary layer flow over a horizontal permeable flat plate

An analysis is performed to study the laminar boundary layer flow over a porous flat plate with injection or suction imposed at the wall. Two different analyses techniques are used for the solution of boundary layer equations: similarity solution and numerical solution. The effect of uniform suction/injection on the heat transfer is discussed. The constant surface temperature thermal boundary condition is used for the horizontal flat plate. The effect of Prandtl number on heat transfer is also investigated. A scale analysis is performed to get more insight into the Prandtl effect. Friction coefficients and Nusselt numbers are calculated for constant fluid injection/suction along the plate. The results indicate that the suction enhances the heat transfer coefficient while injection causes a decrease in heat transfer.

Mixed Convection in a Vertical Microannulus Between Two Concentric Microtubes

In this study, fully developed mixed convective heat transfer of a Newtonian fluid in a vertical microannulus between two concentric microtubes is analytically investigated by taking the velocity slip and the temperature jump at the wall into account. The effects of the mixed convection parameter Gr/Re, the Knudsen number Kn, and the aspect ratio r* on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu = f (Gr/Re, Kn,r*) expression is developed. It is disclosed that increasing Gr/Re enhances heat transfer while rarefaction effects considered by the velocity slip and the temperature jump in the slip flow regime decreases it.