Natural Convection Due to Thermal Buoyancy of Centrifugal Body Forces

2015 ◽  
pp. 41-55
Author(s):  
Peter Vadasz
Keyword(s):  
Natural Convection ◽  
Thermal Buoyancy ◽  
Body Forces

Natural Convection in Binary Gases Due to Horizontal Thermal and Solutal Gradients

1991 ◽  
Vol 113 (1) ◽  
pp. 141-147 ◽  
Author(s):  
J. A. Weaver ◽  
R. Viskanta
Keyword(s):  
Natural Convection ◽  
Unsteady Flow ◽  
Buoyancy Force ◽  
Measured Temperature ◽  
Concentration Gradients ◽  
Thermal Buoyancy ◽  
Smoke Flow ◽  
Numerical Predictions ◽  
Body Forces ◽  
Thermal Buoyancy Force

The influence of augmenting and opposing thermal and solutal buoyancy forces on natural convection of binary gases due to horizontal temperature and concentration gradients is examined through comparison of smoke flow visualization and measured temperature and concentration distributions with numerical predictions. The observed flow at the cold wall was unsteady for opposing body forces. The same basic flow structure was observed, but the unsteady flow intensifies as the opposing solutal buoyancy force increases as compared to the thermal buoyancy force. Comparison of predicted and measured temperatures and concentrations is fair overall, but the steady-state analytical model fails to predict the unsteady flow and heat and mass transport for opposing body forces.

scholarly journals Natural Convection from Four Circular Cylinders in Across Arrangement within Horizontal Annular Space

2020 ◽  
Vol 14 (2) ◽  
pp. 98-102
Author(s):  
Houssem Laidoudi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Prandtl Number ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Initial Conditions ◽  
Fluid Motion ◽  
Circular Cylinders ◽  
Thermal Buoyancy

AbstractNumerical investigation is accomplished to study the roles of governing parameters of natural convection on the fluid motion and heat transfer rate of four heated circular cylinders placed inside a circular enclosure of cold surface. The cylinders are positioned in across arrangement. The representative results are obtained within the ranges of initial conditions as: Prandtl number (Pr = 7.1 to 1000) and Rayleigh number (Ra = 103 to 105). The average Nusselt number of each inner cylinder is computed. The effects of thermal buoyancy strength on the fluid motion and temperature are also illustrated. It was found that the heat transfer rate of cylinders depends significantly on the position inside the enclosure. Moreover, the role of Prandtl number on flow and thermal patterns is negligible. The values of Nusselt number are also given, which can be useful for some engineering applications.

Numerical Modeling of Turbulent Natural Convection in a Concentrating Photovoltaic System

2010 ◽  
Author(s):  
K. M. Nazmul Ahsan ◽  
Robert F. Boehm ◽  
Yitung Chen ◽  
Jianhu Nie
Keyword(s):  
Natural Convection ◽  
Photovoltaic System ◽  
Published Data ◽  
Wall Functions ◽  
Turbulent Natural Convection ◽  
Thermal Buoyancy ◽  
Model Predictions ◽  
The Impact ◽  
Asymmetric Heating ◽  
Good Agreement

A Concentrating Photovoltaic (CPV) system arranged in an asymmetrically heated inclined parallel plate configuration is numerically simulated to investigate the turbulent natural convection inside the system. The flow is induced by the thermal buoyancy force. A low-Reynolds-number k-ε model with modified near wall functions from the Yang-Shih turbulence model has been adapted to numerically solve transport equations for k and ε. The model predictions are validated with available numerical and experimental data given in the literature. The comparison with the published data indicates a good agreement. The calculations are performed for asymmetric heating and assuming the fixed value for CPV cell temperature. The aspect ratio (L/W) and Rayleigh number are kept constant at 36.75 and 2.49×108 respectively. The current study is focused on evaluating the impact of variation of channel inclination and Nusselt number on the thermal profile inside the CPV system.

scholarly journals Air Flow Model for Mixed-Mode and Indirect-Mode Natural Convection Solar Drying of Maize

2020 ◽  
Vol 10 (2) ◽  
pp. 1
Author(s):  
Isaac N. Simate
Keyword(s):  
Natural Convection ◽  
Flow Rate ◽  
Mixed Mode ◽  
Flow Model ◽  
Air Flow ◽  
Solar Drying ◽  
Air Flow Rate ◽  
Thermal Buoyancy ◽  
Early Stages ◽  
Grain Moisture

An air flow model for mixed-mode and indirect-mode natural convection solar drying of maize to help understand the factors that influence air flow in the dryer is presented. Temperatures at various sections of the dryer obtained from drying experiments were input to the air flow model to predict the respective thermal buoyancies. The air flow rate was determined by balancing the sum of the buoyancy pressures with the sum of the flow resistances in the various sections of the dryer. To validate the model, the predicted air flow was compared with measured air flow from experiments. For both the mixed-mode and indirect-mode, the biggest driver of the air flow is the thermal buoyancy created in the collector, while the grain bed is the dominant pressure drop. Thermal buoyancy on top of the grain bed is largely responsible for the variation in air flow, translating into low mass air flow during the early stages of drying when grain moisture is high, and higher air flow in the later stages when grain moisture is low. The heating of the grain bed by direct radiation in the mixed-mode translates into a slightly higher air flow rate than the indirect-mode. The implications are that a thinner grain bed results in shorter drying time as it has a higher air flow rate than a thicker one. To mitigate the low air flow at the early stages of drying, the collector length should be appropriately designed for a desired air flow.

scholarly journals Thermal Buoyancy Effects in Rotating Non-Isothermal Flows

2001 ◽  
Vol 7 (6) ◽  
pp. 435-446 ◽  
Author(s):  
C. Y. Soong
Keyword(s):  
Temperature Field ◽  
Isothermal Flow ◽  
Fluid Temperature ◽  
Thermal Buoyancy ◽  
Rotating Systems ◽  
Body Forces ◽  
Flow Mechanisms ◽  
Scaling Analyses ◽  
Theoretical Results ◽  
Open Issues

The present paper is concerned with the non-isothermal flow mechanisms in rotating systems with emphasis on the rotation-induced thermal buoyancy effects stemming from the coexistence of rotational body forces and the nonuniformity of the fluid temperature field. Non-isothermal flow in rotating ducts of radial and parallel modes and rotating cylindrical configurations, including rotating cylinders and disk systems, are considered. Previous investigations closely related to the rotational buoyancy are surveyed. The mechanisms of the rotation-induced buoyancy are manifested by the author's recent theoretical results and scaling analyses pertaining to the rotation-induced buoyancy in rotating ducts and two-disk systems. Finally, the open issues for future researches in this area are proposed.

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