scholarly journals Numerical Investigation of Natural Convection and Entropy Generation of Water near Density Inversion in a Cavity Having Circular and Elliptical Body

2020 ◽  
Author(s):  
Nguyen Minh Phu ◽  
Nguyen Van Hap
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Convection Heat Transfer ◽  
Convection Current ◽  
Cold Wall ◽  
Convection Heat ◽  
Density Inversion ◽  
Transfer Coefficients ◽  
Impingement Heat Transfer

In this chapter, a water-filled square cavity with left hot wall and right cold wall was numerically investigated. The hot and cold wall temperatures are 10°C and 0°C respectively to examine the density inversion of natural convection water, i.e. water at 4°C. In the middle of the square, there are circular and elliptical bodies to study fluid–structure interaction in terms of the thermohydraulic behavior and entropy generation. 2D numerical simulation was performed using finite volume method in Ansys fluent software with the assumption of laminar flow. The simulation results are compared with benchmark data to determine reliability. The results indicate that the body insertions increase the convection heat transfer coefficients at the best heat transfer positions due to impingement heat transfer. An increase in heat transfer rate of 1.06 times is observed in the case of circular body compared to none. There are three primary eddies in the cavity with bodies, whereas the cavity without body has two primary eddies. Maximum entropy generation was found in the upper right corner of cavity mainly due to high horizontal temperature gradient. Bodies of circle and vertical ellipse have almost the same thermohydraulic and entropy generation characteristics due to the same horizontal dimension which mainly effects on the downward natural convection current. The entropy generation of cavity with circular body is 1.23 times higher than that of the cavity without body. At positions y/L = 1 on the hot wall and y/L = 0.74 on the cold wall, the convection heat transfer coefficient is close to zero due to stagnant fluid.

Experimental Investigation of Natural Convection Heat Transfer in Volumetrically Heated Spherical Segments

1996 ◽  
Vol 118 (1) ◽  
pp. 31-37 ◽  
Author(s):  
F. J. Asfia ◽  
B. Frantz ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Reactor Vessel ◽  
Core Material ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
External Cooling

External cooling of a light water reactor vessel by flooding of the concrete cavity with subcooled water is one of several management strategies currently being considered for accidents in which significant relocation of core material is predicted to occur. At present, uncertainty exists with respect to natural convection heat transfer coefficients between the pool of molten core material and the reactor vessel wall. In the present work, experiments were conducted to examine natural convection heat transfer in internally heated partially filled spherical pools with external cooling. In the experiments, Freon-113 was contained in a Pyrex bell jar, which was cooled externally with subcooled water. The pool was heated using a 750 W magnetron taken from a conventional microwave. The pool had a nearly adiabatic free surface. The vessel wall temperature was not uniform and varied from the stagnation point to the free surface. A series of chromel–alumel thermocouples was used to measure temperatures in both steady-state and transient conditions. Each thermocouple was placed in a specific vertical and radial location in order to determine the temperature distribution throughout the pool and along the inner and outer walls of the vessel. In the experiments, pool depth and radius were varied parametrically. Both local and averages heat transfer coefficients based on pool maximum temperature were obtained. Rayleigh numbers based on pool height were varied from 2 × 1010 to 1.1 × 1014. Correlations for the local heat transfer coefficient dependence on pool angle and for the dependence of average Nusselt number on Rayleigh number and pool depth have been developed.

Natural Convection Heat Transfer of Water Within a Horizontal Cylindrical Annulus With Density Inversion Effects

1983 ◽  
Vol 105 (1) ◽  
pp. 117-123 ◽  
Author(s):  
P. Vasseur ◽  
L. Robillard ◽  
B. Chandra Shekar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Cold Water ◽  
Freezing Point ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Density Inversion ◽  
Cylindrical Annulus

The effect of density inversion on steady natural convection heat transfer of cold water, between two horizontal concentric cylinders of gap width, L, is studied numerically. Water near its freezing point is characterized by a density maximum at 4°C. Numerical solutions are obtained for cylinders with nonlinear Rayleigh numbers RA ranging from 2 × 103 to 7.6 × 104, a radius ratio 1.75 ≤ ra ≤ 2.6 and an inversion parameter γ, relating the temperature for maximum density with the cavity wall temperatures, between −2 and 2. The results obtained are presented graphically in the form of streamline and isotherm contour plots. The heat transfer characteristics, velocity profiles, and local and overall Nusselt numbers are studied. The results of the present study were found qualitatively valid when compared with an experimental investigation carried out in the past.

Natural Convection Heat Transfer of Cold Water Within an Eccentric Horizontal Cylindrical Annulus

1988 ◽  
Vol 110 (4a) ◽  
pp. 894-900 ◽  
Author(s):  
C. J. Ho ◽  
Y. H. Lin
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Cold Water ◽  
Convection Heat Transfer ◽  
Orientation Angle ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Density Inversion ◽  
Cylindrical Annulus ◽  
Isothermal Cylinders

Natural convection heat transfer of cold water, encompassing a density inversion, within an eccentric horizontal annulus made of two isothermal cylinders, is numerically studied via a finite difference method. Numerical results have been obtained for an annular radius ratio 2.6 with Rayleigh number ranging from 103 to 106, the inversion parameter being 0.0 to 1.0, the eccentricity varying from 0 to 0.8, and the orientation angle of the inner cylinder between 0 and π. Results indicate that the flow patterns and heat transfer characteristics are strongly influenced by the combined effect induced by the density inversion of water and the position of the inner cylinder of the annulus. For the cases considered in the present study, a minimum in heat transfer arises with the inversion parameter between 0.4 and 0.5 depending primarily on the position of the inner cylinder.

Natural convection and thermal radiation analysis inside the square cavity filled with non-Newtonian fluid via heatlines and entropy generation

2022 ◽  
Author(s):  
Babar Iftikhar ◽  
Muhammad Arshad Siddiqui ◽  
Tariq Javed
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Radiation ◽  
Entropy Generation ◽  
Convection Heat Transfer ◽  
Bejan Number ◽  
Convection Heat ◽  
Flux Lines ◽  
Side Walls ◽  
Penalty Technique

Abstract In the present analysis, natural convection heat transfer coupled with thermal radiation of bi-viscosity fluid contained inside the cavity has been studied through heatlines and entropy generation. Heat is provided to the cavity through heated source with length L/2, which is placed at the middle of bottom wall. Side walls of the enclosure at low temperature i.e. T_c ad rest of the walls are kept an adiabatic. The idea of Bejan heatlines and average Bejan number have been used to visualized the convective heat folw and dominant irreversibility due to fluid flow or heat transfer, respectively. Finite element method with penalty technique has been applied to obtain the solution of governing equations. Results are obtained through numerically and displayed in terms of streamlines, heat flux lines , isotherms, velocity, temperature, entropy, Nusselt number and average Bejan number against the extensive range of bi-viscosity β=0.002-1 and thermal radiation N_R=0-5, at fixed Rayleigh Ra=〖10〗^5 and Prandtl number Pr=10. It is observed that there exist a direct relation between bi-viscosity parameter and convection heat transfer due to buoyancy-driven flow. Moreover, the dominant entropy generation has been reported through heat transfer in the lower region of the cavity with and without thermal radiation.

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