Modeling the Natural Convection Heat Transfer and Dryout Heat Flux in a Porous Debris Bed

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
R. Sinha ◽  
A. K. Nayak ◽  
B. R. Sehgal
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Severe Accident ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Wide Range ◽  
Particulate Debris ◽  
Limiting Condition ◽  
Good Agreement

An empirical model for natural convection heat transfer for film-boiling condition has been developed for volumetrically heated particulate debris beds when flooded with water at the top of the bed. The model has been derived from the quenching data generated in the POMECO facility located at KTH, Stockholm. A dryout model is also developed for countercurrent flooding limiting condition when the heat generating saturated debris bed is flooded with water from the top. The model is in good agreement with the experimental data over a wide range of particle size and porosity as compared to the existing models. The implication of the models with respect to quenching of porous debris bed formed during postulated severe accident condition is discussed.

Natural Convection Heat Transfer and Entropy Generation From a Horizontal Cylinder With Baffles

2000 ◽  
Vol 122 (4) ◽  
pp. 679-692 ◽  
Author(s):  
B. A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Entropy Generation ◽  
Convection Heat Transfer ◽  
Horizontal Cylinder ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Wide Range

The problem of laminar natural convection heat transfer from a horizontal cylinder with multiple, equally spaced, low conductivity baffles on its outer surface was investigated numerically. The effect of several combinations of number of baffles and baffle height on the average Nusselt number was studied over a wide range of Rayleigh numbers. The computed velocity and temperature fields were also used to calculate the local and global entropy generation for different cylinder diameters. The results showed that there was an optimal combination of a number of baffles and baffle height for minimum Nusselt number for a given value of the Rayleigh number. Short baffles slightly increased the Nusselt number at small values of the Rayleigh number. The global entropy generation increased monotonically with increasing Rayleigh number and decreased with increasing cylinder diameter, baffle height, and number of baffles. [S0022-1481(00)01203-2]

Natural Convection Heat Transfer in a Vertical Air Layer Partitioned Into Cubical Enclosures of Finite Wall Thermal Conductivity and Thickness

1999 ◽  
Author(s):  
Y. Yamaguchi ◽  
Y. Asako
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Wall Thickness ◽  
Finite Thickness ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Wide Range

Abstract Three-dimensional natural convection heat transfer characteristics in a vertical air layer partitioned into cubical enclosures of finite wall thermal conductivity and finite thickness were obtained numerically. The outer surfaces of the enclosure are prescribed at different temperatures. These walls are often encountered in applications such as door panels and thermal insulation boards. The analyses were performed for finite wall thickness and conductivity, for Ra = 104 and 105 and for a wide range of wall thickness and thermal. The results were presented in form of temperature distributions and contour plots of Num and Qwall/Qtotal. From comparison of the results with ideal boundary conditions, a correlation for heat transfer for partitioned walls was developed. It was shown from the results that the ratio of heat transfer into the partition walls to the total heat transfer from the hot wall is a function of the product of wall thermal conductivity and thickness.

scholarly journals Enhancement of Natural Convection Heat Transfer From A Horizontal Cylinder Due to Vertical Shrouding Surfaces

1984 ◽  
Vol 106 (1) ◽  
pp. 124-130 ◽  
Author(s):  
E. M. Sparrow ◽  
D. R. Pfeil
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Thermal Characteristics ◽  
Horizontal Cylinder ◽  
Channel Height ◽  
Natural Convection Heat Transfer ◽  
Measured Temperature ◽  
Convection Heat ◽  
Wide Range

A comprehensive experimental study has been performed to determine the natural convection heat transfer characteristics of a heated horizontal cylinder situated in a vertical channel in air. Fifteen different channel configurations were employed, encompassing a wide range of channel heights and of spacings between the channel walls. Shroud walls having various thermal characteristics (highly conducting, highly conducting/rear insulated, and insulating) were used to form the channel. For each configuration, the cylinder Rayleigh number ranged from 1.5 × 104 to 2 × 105. It was found that a cylinder situated in a channel experiences enhanced natural convection heat transfer compared with a cylinder situated in unbounded space. Enhancements of up to 40 percent were encountered for the parameter ranges of the experiments. The enhancement is accentuated as the interwall spacing is decreased and as the channel height is increased. There is no enhancement for interwall spacings of 10 diameters or more. It was also found that the Nusselt number was quite insensitive to the various types of shroud walls employed. Measured temperature distributions along the shroud walls displayed different degrees of uniformity depending on whether the wall was conducting or insulating.

Natural Convection Heat Transfer for a Concentric Tube Thermosiphon

1985 ◽  
Vol 107 (3) ◽  
pp. 583-588 ◽  
Author(s):  
J. L. Steimke
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Single Phase ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Flow Loop ◽  
Model Equations ◽  
Steady Laminar ◽  
Good Agreement

Natural convection heat transfer for a single-phase thermosiphon formed by two concentric tubes and a central rod filled with water is studied theoretically and experimentally. The two annuli between the tubes and the rod are joined at the top and bottom and form a flow loop. The middle tube is heated while the outer tube is cooled. In this one-dimensional model equations for continuity, momentum, and energy for steady laminar flow are written and solved numerically. There is reasonably good agreement between the analytically and experimentally determined temperatures and convective velocities in the thermosiphon.

Analysis and Measurements of Interzonal Natural Convection Heat Transfer in Buildings

1986 ◽  
Vol 108 (3) ◽  
pp. 178-184 ◽  
Author(s):  
D. Hill ◽  
A. Kirkpatrick ◽  
P. Burns
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Rate ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Bernoulli Model ◽  
Convection Heat ◽  
Important Process ◽  
Temperature Distributions ◽  
Good Agreement

Natural convection heat transfer through doorways can be an important process by which thermal energy is transferred from one zone to another zone of a building. The topic of this paper is interzonal natural convection in a two zone and a three zone multilevel full scale building. Aperture velocity and temperature distributions are measured and the experimental interzonal mass flow rate and heat transfer are determined. A Bernoulli model is derived to predict the neutral heights, velocity profiles, and interzonal heat transfer. The measured and predicted interzonal flow rate and heat transfer are compared and found to be in good agreement.

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