Investigation of turbulent mixed convection of air flow in vertical tubes using a zonal turbulence model

This paper discusses laminar mixed convection of air flow through vertical tubes. Calculations were performed by solving the Navier-Stokes and energy equations for a number of heating lengths. The Reynolds number based on the fluid bulk velocity and diameter of the tube is Re = 500 and Grashof number based on wall heat flux is Gr = 106. The numerical results have been obtained using a finite-volume code which solves the governing equations in axi-symmetric coordinate system. The pressure field is obtained with the SIMPLE algorithm. The HYBRID scheme is used for the convective terms. The computer code was validated by comparing its predictions with the reported analytical, numerical and experimental results. For various heating lengths the values of Nusselt number and friction coefficient are presented and the effects of heating length on these parameters are studied. It was found that for the buoyancy-aided convection, the velocity in the vicinity of the wall increases while decreases in the core region. These result in an enhancement of wall heat transfer coefficient.

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NUMERICAL ANALYSIS OF FLOW REGIMES IN DEVELOPING MIXED CONVECTION OF AIR FLOW IN A VERTICAL TUBE WITH VARIABLE FLUID PROPERTIES

International Symposium on Advances in Computational Heat Transfer ◽

10.1615/ichmt.2008.cht.420 ◽

2008 ◽

Author(s):

Amin Behzadmehr ◽

Andre Laneville

Keyword(s):

Numerical Analysis ◽

Mixed Convection ◽

Air Flow ◽

Flow Regimes ◽

Vertical Tube ◽

Variable Fluid Properties ◽

Fluid Properties

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The Simulation of Natural Ventilation of Buildings With Different Location of Windows/Openings

Volume 6B: Energy ◽

10.1115/imece2015-51168 ◽

2015 ◽

Author(s):

A. Idris ◽

B. P. Huynh ◽

Z. Abdullah

Keyword(s):

Air Quality ◽

Flow Pattern ◽

Turbulence Model ◽

Natural Ventilation ◽

Air Flow ◽

Building Design ◽

Building Envelope ◽

Navier Stokes ◽

Computational Domain ◽

Numerical Predictions

Ventilation is a process of changing air in an enclosed space. Air should continuously be withdrawn and replaced by fresh air from a clean external source to maintain internal good air quality, which may referred to air quality within and around the building structures. In natural ventilation the air flow is due through cracks in the building envelope or purposely installed openings. Its can save significant amount of fossil fuel based energy by reducing the needs for mechanical ventilation and air conditioning. Numerical predictions of air velocities and the flow patterns inside the building are determined. To achieve optimum efficiency of natural ventilation, the building design should start from the climatic conditions and orography of the construction to ensure the building permeability to the outside airflow to absorb heat from indoors to reduce temperatures. Effective ventilation in a building will affects the occupant health and productivity. In this work, computational simulation is performed on a real-sized box-room with dimensions 5 m × 5 m × 5 m. Single-sided ventilation is considered whereby openings are located only on the same wall. Two opening of the total area 4 m2 are differently arranged, resulting in 16 configurations to be investigated. A logarithmic wind profile upwind of the building is employed. A commercial Computational Fluid Dynamics (CFD) software package CFD-ACE of ESI group is used. A Reynolds Average Navier Stokes (RANS) turbulence model & LES turbulence model are used to predict the air’s flow rate and air flow pattern. The governing equations for large eddy motion were obtained by filtering the Navier-Stokes and continuity equations. The computational domain was constructed had a height of 4H, width of 9H and length of 13H (H=5m), sufficiently large to avoid disturbance of air flow around the building. From the overall results, the lowest and the highest ventilation rates were obtained with windward opening and leeward opening respectively. The location and arrangement of opening affects ventilation and air flow pattern.

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Evaluation and Optimisation of Processes Time for the Hot Air Oven Containing Sleeves

International Journal for Research in Applied Science and Engineering Technology ◽

10.22214/ijraset.2021.38109 ◽

2021 ◽

Vol 9 (11) ◽

pp. 404-410

Author(s):

Bandaru Nithin Kumar Varma

Keyword(s):

Heat Transfer ◽

Mixed Convection ◽

Epoxy Resin ◽

Latent Heat ◽

Air Flow ◽

Whole Process ◽

Hot Air

Abstract: The Hot air producing Oven is used to heat the sleeves which are used as raiser in casting purpose. The sleeves that are being manufactured are made of epoxy resin which consists of approximately 75% water and 25% mineral mix before heating and once the processes are complete i.e. the sleeves getting heated in the oven the product would turn into 35% water + 65% mix. The whole process would estimate the time around 4.5 hours. The first 2.5 hours the water is being removed from the sleeves in form of latent heat vaporization. The next 2 hours is use as the time for curing the them because of the flow of hot air through the sleeves. The processes time is evaluated keeping in mind that the heat transfer is happening in mixed convection. As they are placed vertically to the direction of air flow. The amount of heat transfer in terms of energy is evaluated for 4.5 hours in actual practise. The energy which is utilised in 4.5 hours is found and the same amount is consumed in 2.5 hours which is a solution solved theoretically by considering datum values. Keywords: epoxy resin, sleeves, latent heat, heat transfer, mixed convection.

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MODELING AIR FLOW-LINING HEAT TRANSFER IN THE CONDITIONS OF MIXED CONVECTION IN A MINE SHAFT

Физико-технические проблемы разработки полезных ископаемых ◽

10.15372/ftprpi20210515 ◽

2021 ◽

pp. 160-171

Author(s):

E. V. Kolesov ◽

B. P. Kazakov ◽

M. A. Semin

Keyword(s):

Heat Transfer ◽

Mixed Convection ◽

Air Flow ◽

Mine Shaft

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Computational Fluid Dynamics Modeling of Mixed Convection Flows in Building Enclosures

ASME 2013 7th International Conference on Energy Sustainability ◽

10.1115/es2013-18026 ◽

2013 ◽

Cited By ~ 2

Author(s):

Alexander Kayne ◽

Ramesh Agarwal

Keyword(s):

Heat Transfer ◽

Fluid Dynamics ◽

Experimental Data ◽

Computational Fluid Dynamics ◽

Mixed Convection ◽

Turbulence Model ◽

Numerical Algorithm ◽

Navier Stokes ◽

Cfd Simulations ◽

Flow And Heat Transfer

In recent years Computational Fluid Dynamics (CFD) simulations are increasingly used to model the air circulation and temperature environment inside the rooms of residential and office buildings to gain insight into the relative energy consumptions of various HVAC systems for cooling/heating for climate control and thermal comfort. This requires accurate simulation of turbulent flow and heat transfer for various types of ventilation systems using the Reynolds-Averaged Navier-Stokes (RANS) equations of fluid dynamics. Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) of Navier-Stokes equations is computationally intensive and expensive for simulations of this kind. As a result, vast majority of CFD simulations employ RANS equations in conjunction with a turbulence model. In order to assess the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for accurate simulations, it is critical to validate the calculations against the experimental data. For this purpose, we use three well known benchmark validation cases, one for natural convection in 2D closed vertical cavity, second for forced convection in a 2D rectangular cavity and the third for mixed convection in a 2D square cavity. The simulations are performed on a number of meshes of different density using a number of turbulence models. It is found that k-epsilon two-equation turbulence model with a second-order algorithm on a reasonable mesh gives the best results. This information is then used to determine the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for flows in 3D enclosures with different ventilation systems. In particular two cases are considered for which the experimental data is available. These cases are (1) air flow and heat transfer in a naturally ventilated room and (2) airflow and temperature distribution in an atrium. Good agreement with the experimental data and computations of other investigators is obtained.

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