Study on a Multi-Layer Analytical Model of Natural Ventilation in Large Single-Cell Buildings

Solar Energy ◽  
2005 ◽  
Author(s):  
Jun Gao ◽  
Jia-Ning Zhao ◽  
Fu-Sheng Gao ◽  
Jing Liu ◽  
Zhao-Jun Wang
Keyword(s):  
Single Cell ◽  
Analytical Model ◽  
Flow Rate ◽  
Thermal Stratification ◽  
Natural Ventilation ◽  
Cfd Simulation ◽  
Thermal Plume ◽  
Boundary Treatment ◽  
Vertical Walls ◽  
Basic Equations

In large single-cell buildings, a multi-layer analytical model of natural ventilation is presented in this paper. The fluid mechanics of a plume developing in multi-layer environment is investigated based on the plume theory. Using the basic equations for a thermal plume, a mathematical model demonstrating this mechanics is established. Multi-layer thermal stratification of air density or temperature is considered driven by heat flux along wall surfaces. Airflow along vertical walls is modeled with two separate methods, one considering separate wall plumes for each layer and another modeling continuous airflow along the whole wall surface. A multi-layer model is established through balance equations for mass flow rate and heat in each layer. Two separate multi-layer models are presented and then are used to predict the ventilation flow rate and vertical temperature profiles. CFD simulation is also carried out using the RNG κ-ε model, together with an enhanced wall boundary treatment. Results of both present models are compared with those of CFD simulation. Comparisons of the results show that one model using turbulent boundary layer to calculate continuous airflow along vertical walls gives more reasonable and reliable predictions than the other one.

A Computational and Experimental Investigation of the Human Thermal Plume

2006 ◽  
Vol 128 (6) ◽  
pp. 1251-1258 ◽  
Author(s):  
Brent A. Craven ◽  
Gary S. Settles
Keyword(s):  
Velocity Distribution ◽  
Thermal Stratification ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Disease Spread ◽  
Thermal Plume ◽  
Centerline Velocity ◽  
Air Pollution Control ◽  
Human Form ◽  
Flow Rates

The behavior of the buoyant plume of air shed by a human being in an indoor environment is important to room ventilation requirements, airborne disease spread, air pollution control, indoor air quality, and the thermal comfort of building occupants. It also becomes a critical factor in special environments like surgery rooms and clean-rooms. Of the previous human thermal plume studies, few have used actual human volunteers, made quantitative plume velocity measurements, or considered thermal stratification of the environment. Here, a study of the human thermal plume in a standard room environment, including moderate thermal stratification, is presented. We characterize the velocity field around a human volunteer in a temperature-stratified room using particle image velocimetry (PIV). These results are then compared to those obtained from a steady three-dimensional computational fluid dynamics (CFD) solution of the Reynolds-averaged Navier-Stokes equations (RANS) using the RNG k‐ε two-equation turbulence model. Although the CFD simulation employs a highly simplified model of the human form, it nonetheless compares quite well with the PIV data in terms of the plume centerline velocity distribution, velocity profiles, and flow rates. The effect of thermal room stratification on the human plume is examined by comparing the stratified results with those of an additional CFD plume simulation in a uniform-temperature room. The resulting centerline velocity distribution and plume flow rates are presented. The reduction in plume buoyancy produced by room temperature stratification has a significant effect on plume behavior.

scholarly journals Model of thermal buoyancy in cavity-ventilated roof constructions

2021 ◽  
pp. 174425912098418
Author(s):  
Toivo Säwén ◽  
Martina Stockhaus ◽  
Carl-Eric Hagentoft ◽  
Nora Schjøth Bunkholt ◽  
Paula Wahlgren
Keyword(s):  
Analytical Model ◽  
Flow Rate ◽  
Numerical Study ◽  
Air Flow ◽  
Wind Pressure ◽  
Air Flow Rate ◽  
Test Set ◽  
Air Cavity ◽  
Thermal Buoyancy ◽  
The Impact

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

scholarly journals Geometrical Optimization of a Venturi-Type Microbubble Generator Using CFD Simulation and Experimental Measurements

Designs ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 4
Author(s):  
Dillon Alexander Wilson ◽  
Kul Pun ◽  
Poo Balan Ganesan ◽  
Faik Hamad
Keyword(s):  
Water Flow ◽  
Flow Rate ◽  
Cfd Simulation ◽  
Air Flow ◽  
Bubble Diameter ◽  
Diameter Ratio ◽  
Experimental Measurements ◽  
Cfd Model ◽  
Flow Rates ◽  
Throat Diameter

Microbubble generators are of considerable importance to a range of scientific fields from use in aquaculture and engineering to medical applications. This is due to the fact the amount of sea life in the water is proportional to the amount of oxygen in it. In this paper, experimental measurements and computational Fluid Dynamics (CFD) simulation are performed for three water flow rates and three with three different air flow rates. The experimental data presented in the paper are used to validate the CFD model. Then, the CFD model is used to study the effect of diverging angle and throat length/throat diameter ratio on the size of the microbubble produced by the Venturi-type microbubble generator. The experimental results showed that increasing water flow rate and reducing the air flow rate produces smaller microbubbles. The prediction from the CFD results indicated that throat length/throat diameter ratio and diffuser divergent angle have a small effect on bubble diameter distribution and average bubble diameter for the range of the throat water velocities used in this study.

Fabrication and Characterization of Anode-Supported SDC Film Electrolyte and its Single Cell

2010 ◽  
Vol 177 ◽  
pp. 407-410
Author(s):  
Xi Bao Li ◽  
Jian Wang ◽  
Xiao Hua Yu ◽  
Hong Xing Gu ◽  
Gang Qin Shao
Keyword(s):  
Single Cell ◽  
Power Density ◽  
Flow Rate ◽  
Current Density ◽  
Tape Casting ◽  
Threshold Value ◽  
Interface Layer ◽  
Open Circuit ◽  
Discharge Performance ◽  
Film Electrolyte

NiO-YSZ (NiO-yttria stabilized zirconia, 3:2, wt.%) and samaria doped ceria (SDC) tapes were prepared by aqueous tape casting. NiO-YSZ anode-supported SDC film electrolyte half-cell was fabricated by laminating and co-sintering at 1400°C for 2 h. The single cell was prepared after LSCF-SDC (lanthanum strontium cobalt ferrite-SDC, 1:1, wt.%) cathode was coated on the electrolyte surface and sintered at 1300 °C for 2 h. The discharge performance of the single cell was tested from 500 °C to 800 °C at different H2 flow rate. Results showed that the relationship between current (I) of and H2 flow rate (ν) was I = 8 × 106 ν. Before reaching the threshold value of H2 flow rate, the current density of single cell increased with the increasing of H2 flow rate. However, the current density did not change with increasing of H2 flow rate over the threshold value. The open circuit voltage (OCV) of single cell at 500°C, 600°C, 700°C, 800°C was 0.978, 0.921, 0.861, 0.803 V, respectively. The maximum power density reached 93.03 mW/cm2 at 800°C. The resistance of interface layer between Ni-YSZ anode and SDC electrolyte was the key impact on the power density.

A Verification and Validation Study of CFD Simulation of Wind-Induced Ventilation on Building with Single-Sided Opening

2014 ◽  
Vol 554 ◽  
pp. 696-700 ◽  
Author(s):  
Nur Farhana Mohamad Kasim ◽  
Sheikh Ahmad Zaki ◽  
Mohamed Sukri Mat Ali ◽  
Ahmad Faiz Mohammad ◽  
Azli Abd Razak
Keyword(s):  
Open Source Software ◽  
Natural Ventilation ◽  
Cfd Simulation ◽  
Previous Experiment ◽  
Experimental Methods ◽  
Verification And Validation ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Computational Fluid Dynamics Cfd ◽  
Model Approach

Wind-induced ventilation is widely acknowledged as one of the best approaches for inducing natural ventilation. Computational fluid dynamics (CFD) technique is gaining popularity among researchers as an alternative for experimental methods to investigate the behavior of wind-driven ventilation in building. In this present paper, Reynolds averaged Navier-Stokes equation (RANS) k-ε model approach is considered to simulate the airflow on a simplified cubic building with an opening on a single façade. Preliminary simulation using models from previous experiment indicates the reliability of OpenFOAM, the open source software that will be used in this study. The results obtained in this study will better define options for our future study which aims to explore how different buildings arrays modify the airflow inside and around a naturally ventilated building.

Experimental Evaluation of the Thermal Behavior of a Vertical Solar Tank Using Energy and Exergy Analysis

2005 ◽  
Author(s):  
Ali A. Dehghan ◽  
Mohammad H. Hosni ◽  
S. Hoda Shiryazdi
Keyword(s):  
Temperature Distribution ◽  
Flow Rate ◽  
Storage Tank ◽  
Thermal Stratification ◽  
Exergy Analysis ◽  
Hot Water ◽  
Second Law ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Hot Water Supply

The thermal performance of a Thermosyphon Domestic Solar Water Heater (DSWH) with a vertical storage tank is investigated experimentally. The system is installed on a roof - top of a four person family house and its thermal characteristics is evaluated by means of carefully measuring the temperature distribution of water inside the storage tank, solar collector flow rate and its inlet and outlet temperatures as well as load/consumption outlet and inlet temperatures and the corresponding water flow rate under a realistic operating conditions. The measurements are conducted every hour starting from morning until late night on a daily basis and continued for about 120 days during August until November 2004. It is seen that thermal stratification is well established inside the tank from 11 AM until 10 PM especially during August to September enabling the tank to provide the necessary amount of hot water at an acceptable temperature. However, thermal stratification is observed to start degrading from mid-night until morning when there is no hot water supply from the collector and due to the diffusion of heat from the top hot water layers to the bottom cold region and conduction through tank’s wall. The thermal behavior of the storage tank is also assessed based on both energy and exergy analysis and its first and second law efficiencies are calculated. It is observed that the storage tank under study has an average first law efficiency of 47.8% and is able to supply the required amount of hot water at a proper temperature. The average second law efficiency of the storage tank is observed to be 28.7% and, although is less than its first low efficiency, but is high enough to ensure that the quality of the hot water supply is well preserved. The proper level of second law efficiency is due to the preservation of the thermal stratification inside the storage tank, leading to supply of hot water at highest possible temperature and hence highest possible energy potential. Experiments are also done for no-load conditions when the storage tank only interacts with the collector, without hot water withdrawal from the tank. It is seen that for no-load condition, thermal stratification continuously develops from morning until around 16 PM after which no noticeable changes in the temperature distribution inside the tank is observed.

Lactation in the Human Breast From a Fluid Dynamics Point of View

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
S. Negin Mortazavi ◽  
Donna Geddes ◽  
Fatemeh Hassanipour
Keyword(s):  
Fluid Dynamics ◽  
Clinical Data ◽  
Flow Rate ◽  
Cfd Simulation ◽  
Geometric Model ◽  
Milk Intake ◽  
Vacuum Pressure ◽  
Cfd Modeling ◽  
Human Breast ◽  
Milk Flow

This study is a collaborative effort among lactation specialists and fluid dynamic engineers. The paper presents clinical results for suckling pressure pattern in lactating human breast as well as a 3D computational fluid dynamics (CFD) modeling of milk flow using these clinical inputs. The investigation starts with a careful, statistically representative measurement of suckling vacuum pressure, milk flow rate, and milk intake in a group of infants. The results from clinical data show that suckling action does not occur with constant suckling rate but changes in a rhythmic manner for infants. These pressure profiles are then used as the boundary condition for the CFD study using commercial ansys fluent software. For the geometric model of the ductal system of the human breast, this work takes advantage of a recent advance in the development of a validated phantom that has been produced as a ground truth for the imaging applications for the breast. The geometric model is introduced into CFD simulations with the aforementioned boundary conditions. The results for milk intake from the CFD simulation and clinical data were compared and cross validated. Also, the variation of milk intake versus suckling pressure are presented and analyzed. Both the clinical and CFD simulation show that the maximum milk flow rate is not related to the largest vacuum pressure or longest feeding duration indicating other factors influence the milk intake by infants.

scholarly journals Spatial distributions of airborne dust in a cows barn exposed to influence of different ventilation rates

2013 ◽  
Vol 29 (2) ◽  
pp. 373-383
Author(s):  
G. Topisirovic ◽  
D.V. Petrovic ◽  
R. Maletic
Keyword(s):  
Flow Rate ◽  
Indoor Air ◽  
Rotation Rate ◽  
Natural Ventilation ◽  
Electronic Control Unit ◽  
Air Flow ◽  
Control Unit ◽  
Dust Particles ◽  
Airborne Dust ◽  
Stability And Instability

Information on the concentration of dust particles is an important microclimate parameter that characterizes the local environmental quality of each livestock building. Increased concentration of dust particles primarily affects the indoor air quality and, consequently, the animal and workers health. Among many others, ventilation rate is a vital parameter that controls the spatial distribution of airborne dust particles in livestock buildings. This was the main motive for authors of this paper to research the influence of rotation rate of under-roof axial fans (i.e. the air flow rate) on airborne dust particles distribution crossover the barn specified for tied cows breeding. During a series of performed experiments, six different air flow rates have been maintained in the range between 0 m3?h-1 and 48000 m3?h-1. Flow rate has been controlled by special electronic control unit, which provided six different rotation rates of two under-roof fans, including the neutral regime (natural ventilation only). Measurements have been performed at four typical height levels (0,5 m; 1,0 m; 1,5 m and 2,0 m), cross-over the three lateral and four longitudinal characteristic building sections. Consequently, 48 measuring points were appropriately selected, in order to cover the indoor space in adequate way. Comparative analysis of air flow velocities and dust concentrations showed that this fan setup may give satisfactory results under adequate operational regime. Certain working regimes were recommended for use, and the third rotation rate step, generating the airflow of 37300 m3?h-1 or indoor air exchange level of approximately 25 h-1, has been found as the most suitable. Projekat Ministarstva nauke Republike Srbije, br. TR31086: Optimization of technological procedures and zoo-technical resources on farmsin purpose of milk production sustainability improvement, br. TR 31051: Improvement of biotechnological procedures as a function of rational utilizationof energy, agricultural products productivity and quality increase, br. III46009: Improvement and development new technological procedures in production ofanimal products, to achieve high quality and safe competitive products inmarket i br. OI 174011: Dynamical stability and instability of mechanical systems exposed to stochasticdisturbances

Analytical Model Quantifying the Net Coolant Flow Rate to a Microstructured Copper Surface validated with Two-Phase PIV Measurements

2021 ◽  
Author(s):  
Matt Harrison ◽  
Joshua Gess
Keyword(s):  
Heat Transfer ◽  
Analytical Model ◽  
Flow Rate ◽  
Circular Disk ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Two Phase

Abstract Using Particle Image Velocimetry (PIV), the amount of fluid required to sustain nucleate boiling was quantified to a microstructured copper circular disk. Having prepared the disk with preferential nucleation sites, an analytical model of the net coolant flow rate requirements to a single site has been produced and validated against experimental data. The model assumes that there are three primary phenomena contributing to the coolant flow rate requirements at the boiling surface; radial growth of vapor throughout incipience to departure, bubble rise, and natural convection around the periphery. The total mass flowrate is the sum of these contributing portions. The model accurately predicts the quenching fluid flow rate at low and high heat fluxes with 4% and 30% error of the measured value respectively. For the microstructured surface examined in this study, coolant flow rate requirements ranged from 0.1 to 0.16 kg/sec for a range of heat fluxes from 5.5 to 11.0 W/cm2. Under subcooled conditions, the coolant flow rate requirements plummeted to a nearly negligible value due to domination of transient conduction as the primary heat transfer mechanism at the liquid/vapor/surface interface. PIV and the validated analytical model could be used as a test standard where the amount of coolant the surface needs in relation to its heat transfer coefficient or thermal resistance is a benchmark for the efficacy of a standard surface or boiling enhancement coating/surface structure.

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