A T-RANS/VLES Approach to Indoor Climate Simulations

Author(s):  
S. Kenjeresˇ ◽  
K. Hanjalic´ ◽  
S. B. Gunarjo

For accurate prediction of flow, scalar transport and wall heat and mass transfer in complex building space we propose a time-dependent RANS (T-RANS) approach which resolves in time and space the large-scale convective motion and associated deterministic eddy structure. The residual (“subscale”) turbulence is modeled by a single-point closure. The method can be regarded as Very Large Eddy Simulations (VLES) since the deterministic and modeled contribution to the turbulence moments are of the same order of magnitude. The modeled part becomes dominant in the near-wall regions where there are no large eddies and the proper choice of the subscale model is especially important for predicting wall friction and heat transfer. We use an ensemble-averaged 〈k〉 - 〈ε〉 - 〈θ2〉 algebraic stress/flux/concentration closure as the subscale model which can provide information about the stress and heat/species flux anisotropies. The method is especially advantageous for predicting flows driven or affected by thermal buoyancy, for which the conventional eddy-viscosity/diffusivity RANS models and gradient transport hypotheses are known to fail even in simple generic configurations. The approach was validated in a series of buoyancy-driven flows for which experimental, DNS and LES data are available. Examples of full-scale application include computational simulations of real occupied and furnished residential or office space in which the furniture elements and persons are treated as passive blocking elements. The simulation showed that the T-RANS approach can be used as a reliable tool for a variety of applications such as optimization of heating and ventilation system, building space insulation, indoor quality, safety measures related to smoke and fire spreading, as well as for accurate wall heat and mass transfer predictions.

Author(s):  
Yuri Kornienko

The main goal of this paper is to describe new approach to constructing generalized closure relationships for pipe, annular and sub-channel transfer coefficients for wall friction, heat and mass transfer. The novelty of this approach is that it takes into account not only axial and transversal parameter distributions, but also an azimuthal substance transfer effects. These constitutive relations, which are primordial in the description of single- and two-phase one-dimensional (1D) flow models, can be derived from the initial 3D drift flux formulation. The approach is based on the Reynolds flow, boundary layer, and substance transfer generalized coefficient concepts. Another aim is to illustrate the validity of the “conformity principle” for the limiting cases. The method proposed in this paper is founded on the similarity theory, boundary layer model, and a phenomenological description of the regularity of the substance transfer (momentum, heat, and mass) as well as on an adequate simulation of the flow structures. With the proposed generalized approach it becomes possible to develop an integrated in form and semi-empirical in maintenance structure analytical relationships for wall friction, heat and mass transfer coefficients.


Author(s):  
Duc Hai Do ◽  
Eckehard Specht

A mathematical model of lime calcination process in normal shafts kiln has been developed to determine the heat and mass transfer between the gas and the solid. The model is one-dimensional and steady state. The transport of mass and energy of the gas and the solid is modeled by a system of ordinary differential equations. A shrinking core approach is employed for the mechanics and chemical reactions of the solid material. The model can be used to predict the temperature profiles of the particle bed, the gas phase along the length of kiln axis. The calcination behavior of the particle bed can be also investigated. The influences of operational parameters such as: energy input, the origin of feed limestone and the lime throughput on the kiln performance including pressure drop are considered. Additionally, the local heat loss through the kiln wall is studied. The results of this study are direct utility for optimization and design of large-scale technical shaft kilns.


1980 ◽  
Vol 102 (3) ◽  
pp. 538-543 ◽  
Author(s):  
T. S. Chen ◽  
F. A. Strobel

The combined effects of buoyancy forces from thermal and species diffusion on the heat and mass transfer characteristics are analyzed for laminar boundary layer flow over a horizontal flat plate. The analysis is restricted to processes with low concentration levels such that the interfacial velocities due to mass diffusion and the diffusion-thermo/thermo-diffusion effects can be neglected. Numerical results for friction factor, Nusselt number, and Sherwood number are presented for gases having a Prandtl number of 0.7, with Schmidt numbers ranging from 0.6 to 2.0. In general, it is found that, for the thermally assisting flow, the surface heat and mass transfer rates as well as the wall shear stress increase with increasing thermal buoyancy force. These quantities are further enhanced when the buoyancy force from species diffusion assists the thermal buoyancy force, but are reduced when the two buoyancy forces oppose each other. While a higher heat transfer rate is found to be associated with a lower Schmidt number, a higher mass transfer rate occurs at a higher Schmidt number.


Author(s):  
Obulesu Mopuri ◽  
Raghunath Kodi ◽  
Charankumar Ganteda ◽  
Ramu Srikakulapu ◽  
Giulio Lorenzini

In the presence of a diffusion thermal and coupled magnet field effect, this manuscript seeks continuous free convective motion by a viscous, incompressible fluid that conducts electrically past a sloping platform via a porous medium. The free flow speed may be compatible with the exponentially tiny disrupting law. Two-term harmonic and non-harmonic functions solve dimensional-less control equations analytically. Detailed graphs are used to determine the budgets for tempo, temperature, and concentration for various limit calculations. Also, the numbers of Nusselt and Sherwood are given and evaluated with the graphs. Its sketches illustrate that the velocity profiles get reduced by the increase of aligned magnetic field parameter (α) and inclined angle parameter (ξ). Temperature profile is accelerated by rising heat absorption, Dufour number and concentration distribution is decelerated by enhancing the chemical reaction and Schmidt number. Heat and mass transfer frequently occurs in chemically processed industries, distribution of temperature and moisture over agricultural fields, dispersion of fog and environment pollution and polymer production. Free convection flow of coupled heat and mass transfer occurs due to the temperature and concentration differences in the fluid as a result of driving forces. For example, in atmospheric flows, thermal convection resulting from heating of the earth by sunlight is affected differences in water vapour concentration.


2020 ◽  
pp. 227-227
Author(s):  
Florin Bode ◽  
Claudiu Patrascu ◽  
Ilinca Nastase

Heat and mass transfer can be greatly increased when using impinging jets, regardless the application. The reason behind this is the complex behavior of the impinging jet flow which is leading to the generation of a multitude of flow phenomena, like: large-scale structures, small scale turbulent mixing, large curvature involving strong normal stresses and strong shear, stagnation, separation and re-attachment of the wall boundary layers, increased heat transfer at the impinged plate. All these phenomena listed above have highly unsteady nature and even though a lot of scientific studies have approached this subject, the impinging jet is not fully understood due to the difficulties of carrying out detailed experimental and numerically investigations. Nevertheless, for heat transfer enhancement in impinging jet applications, both passive and active strategies are employed. The effect of nozzle geometry and the impinging surface macrostructure modification are some of the most prominent passive strategies. On the other side, the most used active strategies utilize acoustical and mechanical oscillations in the exit plane of the flow, which in certain situations favors mixing enhancement. This is favored by the intensification of some instabilities and by the onset of large scale vortices with important levels of energy.


2020 ◽  
pp. 89-101
Author(s):  
V. Trokhaniak ◽  

Keeping poultry in damp and cold rooms with poor ventilation system reduces the weight gain of the bird, reduces its egg production and increases the incidence of young animals, as well as excessive feed consumption and exceeding the growing period established by technical regulations. The aim of the study was to determine the effective placement of exhaust ventilation equipment at the height of the end wall of the poultry house to improve the ventilation system, reduce stagnant air zones and improve the microclimate. The numerical modeling of hydrodynamics, heat and mass transfer processes during air ventilation in poultry buildings is carried out. The analysis of the conditions of heat and mass transfer in the poultry house, depending on the placement of fans along the height of the house, and the efficiency of the location of such equipment was determined. The system for maintaining the microclimate in poultry houses was considered in the presence of a system for cooling the outside air with water from an underground well. The ventilation system uses exhaust ventilation equipment with a fan wheel diameter of 1.25 m. In the simulation, the fans were installed at a height of 1.125, 1.5 and 1.875 m from the floor to the center of the fan axis. Simulation was performed for 2D CFD models using ANSYS Fluent software. The results of CFD analysis of the air flow pattern and the thermal state inside the house are presented. As a result of numerous studies, the geometry of the location of the ventilation equipment has been found. It is shown that it is advisable to install ventilation equipment at a height of 1.5 m. At the same time, the size of stagnant zones and the uneven distribution of air velocity near the bird are reduced. Numerical modeling was carried out in order to minimize the size of stagnant zones, equalize the air flow and improve the temperature indicators in the poultry house.


2018 ◽  
Vol 16 (9) ◽  
pp. 701-721
Author(s):  
Shalini JAIN ◽  
Shweta BOHRA

In this paper, a steady free convective heat and mass transfer boundary layer flow of an electrically conducting viscous fluid from a sphere in a porous medium with thermal radiation is studied. Soret and Dufour effects, velocity slip, and thermal slip are considered at the boundary. The governing PDE is transformed into non-linear ODE using suitable similarity transformations and solved numerically using bvp4c solver of MATLAB. The effect of Schmidt number (Sc), concentration to thermal buoyancy ratio parameter (Nb), Dufour number (Du), Soret number (Sr), radiation parameter (N), permeability parameter (K), dimensionless velocity slip parameter (g), and dimensionless thermal jump parameter (j) on  velocity, temperature and concentration fields, skin friction, and heat and mass transfer rates are analyzed and presented through graphs and tables.


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