Effect of thick horizontal partial partition attached to one of the active walls of a differentially heated square cavity

Natural convection in cavities with a thin fin on the hot wall

Abstract: A numerical study has been carried out in differentially heated square cavities, which are formed by horizontal adiabatic walls and vertical isothermal walls. A thin fin is attached on the active wall. Heat transfer by natural convection is studied by numerically solving equations of mass, momentum and energy. Streamlines and isotherms are produced, heat and mass transfer is calculated. A parametric study is carried out using following parameters: Rayleigh number from 104 to 109, dimensionless thin fin length from 0.10 to 0.90, dimensionless thin fin position from 0 to 0.90, dimensionless conductivity ratio of thin fin from 0 (perfectly insulating) to 60. It is found that Nusselt number is an increasing function of Rayleigh number, and a decreasing function of fin length and relative conductivity ratio. There is always an optimum fin position, which is often at the center or near center of the cavity, which makes heat transfer by natural convection minimized. The heat transfer may be suppressed up to 38% by choosing appropriate thermal and geometrical fin parameters.

Computation of combined natural-convection and radiation heat-transfer in a cavity having a square body at its center

Abstract: This paper describes a numerical study of the radiation-natural convection interactions in a differentially-heated cavity with an inner body. A specifically developed numerical model, based on the finite-volume method, is used for the solutions of the governing differential-equations. The SIMPLER algorithm for the pressure–velocity coupling is adopted. The fluid (air) is perfectly transparent to the radiation. The surface emissivity e , the Rayleigh number Ra , and the thermal conductivity ratio R k were varied parametrically. For Pr = 0.71 and relatively wide ranges of the other parameters, results are reported in terms of isotherms, streamlines, average Nusselt-numbers across the enclosure, local Nusselt-numbers at the hot and cold walls, vertical and horizontal median velocities and horizontal walls, temperature distributions. It is found that: (i) the radiation exchange homogenizes the temperature inside the cavity and produces an increase in the average Nusselt-number, particularly when R k and Ra are high and (ii) the average Nusselt-number increases with increasing surface emissivity, especially at high Rayleigh numbers.

Numerical study of laminar natural convection inside square enclosure with single horizontal fin

Abstract: A numerical study for laminar natural convection inside a square enclosure with a single horizontal fin attached to its hot wall has been carried out The enclosure horizontal surfaces are adiabatic, the left wall is hot while the right one is cold The Prandtl number for the flow inside the enclosure is 071 A parametric study has been carried out to investigate the effect of Rayleigh number, fin length, conductivity ratio, thickness and position on heat transfer The fin thickness showed negligible effect on the average Nusselt number for all values of fin conductivity ratios The fin efficiency and temperature distribution were examined The fin effectiveness was also studied and it was found that the fin effectiveness enhanced in general with the increase of fin length Also, the maximum fin effectiveness was found at the lowest Rayleigh number for a given fin conductivity ratio A correlation has been proposed for the relation between Nusselt number and the parameters of study

Three-dimensional natural convection in finned cubical enclosures

Abstract: Three-dimensional natural convection of air in a cubical enclosure with a fin on the hot wall is numerically investigated for Rayleigh numbers of 103–106. The fin, with a thickness of 1/10 of the cavity side, is placed horizontally on the hot wall. The solid to fluid thermal conductivity ratio (Rk) and the fin width are varied. Because the fin is shorter than the cavity side, the cold flow sweeps the lower fin face and the hot wall at the clearances between the fin sides and the lateral walls, where high vertical velocities are reached. The fin inhibits the frontal and lateral access of fluid to the upper fin face, especially at low Rayleigh numbers. Low values of Rk cause heat transfer reductions. The contribution of the fin faces increases at high Rk causing heat transfer enhancements above 20%, which exceed the ones obtained in most two-dimensional studies. In the range of Ra from 105 to 106, maximum heat transfer rates are found for dimensionless fin widths of 0.6 and 0.8 respectively. It is concluded that for 105 ⩽ Ra ⩽ 106 a fin of partial width is more effective in promoting heat transfer than a fin of full width.

Partitioning of solar still for performance recovery: Experimental and numerical investigations with cost analysis

Abstract: In this paper, the effects of partitioning in solar still on performance recovery are investigated experimentally and numerically. Two single slope solar stills containing conventional and modified by installing a partition are fabricated and tested, simultaneously. Two stills have a same basin area. All experiments were performed in Semnan with geographical coordinates of 35° 33′ N, 53° 23′ E, Iran. Hourly temperature, productivity, and efficiency for the modified and conventional stills are obtained and compared. Moreover, a numerical simulation based on SIMPLE algorithm is utilized and different contours are drawn to more discuss about the physics of this problem. Finally, a cost analysis is performed to investigate the modified still, economically. It is found that the partitioned still works at much higher temperature difference between water and the condensing area especially for afternoon hours. Moreover, the productivity increases by installing the partition in the still. These enhancements are about 4.81%, 4.82%, 5.62%, and 8.16% for first, second, third, and fourth days of the experiment, respectively. Finally, the cost analysis studies reveal that the costs per liter of the fresh water production for the conventional and modified stills are 0.0096 and 0.0104 $/L/m2, respectively.

Natural convection of air in a square cavity: A bench mark numerical solution

Abstract: Details are given of the computational method used to obtain an accurate solution of the equations describing two-dimensional natural convection in a square cavity with differentially heated side walls. Second-order, central difference approximations were used. Mesh refnement and extrapolation led to solutions for 103⩽Ra⩽10 6 which are believed to be accurate to better than 1 per cent at the highest Rayleigh number and down to one-tenth of that at the lowest value.

Natural convection in enclosures

Abstract: Publisher Summary This chapter discusses the complex nature of the natural convection phenomena in enclosures It discusses the two basic configurations of natural convection— that is, a rectangular cavity and a horizontal circular cylinder In rectangular cavities, consideration is given to the two-dimensional convective motion generated by the buoyancy force on the fluid in a rectangle and to the associated heat transfer The two long sides are vertical boundaries held at different temperatures and the short sides can either be heat conducting or insulated Particular attention is given to the different flow regimes that can occur and the heat transfer across the fluid space between the two plane parallel vertical boundaries Although heat transfer by radiation may not be negligible it is independent of the other types of heat transfer and can be fairly accurately calculated separately To formulate the boundary value problem that describes this phenomena it is assumed that: (a) the motion is two-dimensional and steady, (b) the fluid is incompressible and frictional heating is negligible, and (c) the difference between the hot wall and cold wall temperatures is small relative to the absolute temperatures of the cold wall In horizontal circular cylinder, consideration is given to the large Rayleigh number flow with the Prandtl number large and the Grashof number of unit order of the magnitude

Natural convection heat transfer in enclosures with multiple vertical partitions

Abstract: Laminar natural convection in rectangular enclosures divided by multiple vertical partitions is studied experimentally and by numerical calculation. In the boundary layer regime, the partition temperature approximately increases linearly in the vertical direction. The boundary layer solution predicting the heat transfer rate is derived on the basis of the numerical results. It is shown that the Nusselt number is inversely proportional (1 + N) where N is the number of partitions. This is also confirmed by the experiments.

Natural convection in a partially divided enclosure

Abstract: This paper describes an experimental and analytical study of the phenomenon of heat transfer by natural convection in a rectangular enclosure fitted with an incomplete internal partition. The experiments were carried out in a water-filled enclosure with adiabatic horizontal walls and vertical walls maintained at different temperatures. Heat transfer measurements and flow visualization studies were conducted in the Rayleigh number range 109–1010, for aperture ratios h/H = 1, 1/4, 1/8, 1/16, and 0, where h and H are the height of the internal opening (above the partition) and the height of the enclosure, respectively. It is demonstrated that the aperture ratio h/H has a strong effect on both the heat transfer rate and the flow pattern. The second part of the study consists of an asymptotic analysis of the same phenomenon, valid in the limit of vanishing Rayleigh numbers. The flow and temperature fields in this limit are reported graphically for H/L = 0.5, Pr = 0.71 and 0.3 < h/H < 0.7, where L and Pr are the enclosure length and the Prandtl number, respectively.