Scaling of Transient Natural Convection Cooling in a Side-Cooled Cavity: The Effect of Variable Viscosity

2011 ◽  
Author(s):  
Obai Younis ◽  
Feng Xu ◽  
Chengwang Lei ◽  
John C. Patterson ◽  
Jordi Pallares ◽  
...  
Keyword(s):  
Natural Convection ◽  
Transient Flow ◽  
Variable Viscosity ◽  
Initial Growth ◽  
Transient Natural Convection ◽  
Constant Viscosity ◽  
Side Walls ◽  
Convection Cooling ◽  
Cubical Cavity ◽  
Good Agreement

The transient natural convection of variable and constant viscosity fluids in a side cooled cubical cavity is studied experimentally. The convective flow in the cavity is visualized by the shadowgraph technique. The fluid was initially preheated and enough time is allowed to assure uniform temperature distribution. Temperature difference is introduced by a sudden cooling of the two side walls. The results indicate that the transient flow development is characterized by the following distinct processes: the initial growth of the vertical boundary layer and horizontal intrusions, the interaction of the horizontal intrusions and the stratification. New scaling relations are introduced to include the effect of the viscosity variation with temperature. The new suggested scalings showed good agreement with the measurements based on the shadowgraph images.

New benchmark solutions for transient natural convection in partially porous annuli

2016 ◽  
Vol 26 (3/4) ◽  
pp. 1187-1225 ◽  
Author(s):  
Nicola Massarotti ◽  
Michela Ciccolella ◽  
Gino Cortellessa ◽  
Alessandro Mauro
Keyword(s):  
Natural Convection ◽  
Free Convection ◽  
Transient Flow ◽  
Flow Behavior ◽  
Outer Radius ◽  
Temperature Fields ◽  
Content Type ◽  
Transient Natural Convection ◽  
Velocity And Temperature Fields ◽  
Benchmark Solutions

Purpose – The purpose of this paper is to focus on the numerical analysis of transient free convection heat transfer in partially porous cylindrical domains. The authors analyze the dependence of velocity and temperature fields on the geometry, by analyzing transient flow behavior for different values of cavity aspect ratio and radii ratio; both inner and outer radius are assumed variable in order to not change the difference ro-ri. Moreover, several Darcy numbers have been considered. Design/methodology/approach – A dual time-stepping procedure based on the transient artificial compressibility version of the characteristic-based split algorithm has been adopted in order to solve the transient equations of the generalized model for heat and fluid flow through porous media. The present model has been validated against experimental data available in the scientific literature for two different problems, steady-state free convection in a porous annulus and transient natural convection in a porous cylinder, showing an excellent agreement. Findings – For vertically divided half porous cavities, with Rayleigh numbers equal to 3.4×106 for the 4:1 cavity and 3.4×105 for the 8:1 cavity, the numerical results show that transient oscillations tend to disappear in presence of cylindrical geometry, differently from what happens for rectangular one. The magnitude of this phenomenon increases with radii ratio; the porous layer also affects the stability of velocity and temperature fields, as oscillations tend to decrease in presence of a porous matrix with lower value of the Darcy number. Research limitations/implications – A proper analysis of partially porous annular cavities is fundamental for the correct estimation of Nusselt numbers, as the formulas provided for rectangular domains are not able to describe these problems. Practical implications – The proposed model represents a useful tool for the study of transient natural convection problems in porous and partially porous cylindrical and annular cavities, typical of many engineering applications. Moreover, a fully explicit scheme reduces the computational costs and ensures flexibility. Originality/value – This is the first time that a fully explicit finite element scheme is employed for the solution of transient natural convection in partially porous tall annular cavities.

Transient Natural Convection of Water in a Horizontal Pipe With Constant Cooling Rate Through 4°C

1976 ◽  
Vol 98 (4) ◽  
pp. 581-587 ◽  
Author(s):  
K. C. Cheng ◽  
M. Takeuchi
Keyword(s):  
Natural Convection ◽  
Transient Flow ◽  
Temperature Fields ◽  
Freezing Process ◽  
Horizontal Pipe ◽  
Transfer Rates ◽  
Transient Natural Convection ◽  
Anomalous Density ◽  
Horizontal Cylinders ◽  
Relationship Of

A theoretical analysis is carried out to study the influence of an anomalous density-temperature relationship of water on the transient natural convection in horizontal cylinders with wall temperature decreasing at a uniform rate. Numercial solutions are obtained for three cases involving different cooling rates, pipe diameters, and initial uniform water temperatures for temperature conditions between 0 and 7°C. The transient flow and temperature fields, and local and overall heat transfer rates are presented to study the inversion of flow patterns caused by the maximum density at 4°C. The numerical results are compared with the experimental measurements and predictions of a quasi-steady boundary-layer model reported by Gilpin [2], and generally a good agreement is observed. Some implications on the subsequent freezing process are pointed out.

Experimental Study of Transient Natural Convection in an Inclined Porous Enclosure With Time-Periodically-Varying Wall Temperature

2011 ◽  
Author(s):  
M. Zeng ◽  
G. Wang ◽  
Y. C. Ren ◽  
H. Ozoe ◽  
Q. W. Wang
Keyword(s):  
Heat Flux ◽  
Porous Media ◽  
Natural Convection ◽  
Wall Temperature ◽  
Side Wall ◽  
Average Temperature ◽  
Transient Natural Convection ◽  
Inclined Enclosure ◽  
Side Walls ◽  
Inclined Angle

The transient natural convection in an inclined enclosure filled with porous media is studied experimentally and numerically for the time-periodically-varying wall temperature on one side wall and constant average temperature on the opposing side wall. This system has no temperature difference between the opposing two side walls in time-averaged sense. The porous media with three kinds of porosity consist of water and three kinds of glass ball with different diameter. The temperature and heat flux across the two above-mentioned walls are measured by a heat flux meter. The effects of inclined angles and porosity of the enclosure on heat transfer characteristics have also been studied. The experimental results show that, with the upper wall temperature oscillating, the heat flux across the enclosure is also periodically varied with time. However, the net heat flux is always from the lower wall to the upper wall and reaches maximum at a certain inclined angle. Numerical computations are also conducted and numerical results are qualitatively assured by the experimental measurements.

scholarly journals Transient Cooling of Waxy Crude Oil in a Floating Roof Tank

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Jian Zhao ◽  
Yang Liu ◽  
LiXin Wei ◽  
Hang Dong
Keyword(s):  
Natural Convection ◽  
Crude Oil ◽  
Test Results ◽  
Cooling Process ◽  
Local Cooling ◽  
Waxy Crude Oil ◽  
Waxy Crude ◽  
Transient Natural Convection ◽  
Temperature Test ◽  
Good Agreement

The transient cooling of waxy crude oil stored in a floating roof tank located in alpine region is studied by means of numerical simulation, accomplished with a two-dimensional model in cylindrical coordinates with the finite volumes method. The typical evolution of transient natural convection and temperature distribution is investigated which can be divided into four stages. For the transient natural convection, it is concluded as the formation, expansion, degradation, and vanishing stage, along with it is the evolution of temperature field regarded as the local cooling, integral cooling, the thermal stratification, and heat conduction course. Special attention is given to the solidified process of waxy oil and its influence on the cooling process of crude oil. Moreover, the effect of tank size, the temperature gradient between oil and ambient, viscosity, and Cp of waxy crude oil on the cooling rate is investigated. The main characteristic of cooling process obtained from numerical results shows a good agreement with the temperature test results from a large floating tank in the oil depot.

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