Development of a Predictive Equation for Ventilation in a Wall-Solar Chimney System

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
David Park ◽  
Francine Battaglia
Keyword(s):  
Mathematical Model ◽  
Relative Error ◽  
Natural Ventilation ◽  
Thermal Conditions ◽  
Ambient Air ◽  
Maximum Error ◽  
Scale Model ◽  
Small Scale ◽  
Maximum Relative Error ◽  
Solar Chimney

A solar chimney is a natural ventilation technique that has potential to save energy consumption as well as to maintain the air quality in a building. However, studies of buildings are often challenging due to their large sizes. The objective of this study was to determine the relationships between small- and full-scale solar chimney system models. Computational fluid dynamics (CFD) was employed to model different building sizes with a wall-solar chimney utilizing a validated model. The window, which controls entrainment of ambient air for ventilation, was also studied to determine the effects of window position. A set of nondimensional parameters were identified to describe the important features of the chimney configuration, window configuration, temperature changes, and solar radiation. Regression analysis was employed to develop a mathematical model to predict velocity and air changes per hour, where the model agreed well with CFD results yielding a maximum relative error of 1.2% and with experiments for a maximum error of 3.1%. Additional wall-solar chimney data were tested using the mathematical model based on random conditions (e.g., geometry, solar intensity), and the overall relative error was less than 6%. The study demonstrated that the flow and thermal conditions in larger buildings can be predicted from the small-scale model, and that the newly developed mathematical equation can be used to predict ventilation conditions for a wall-solar chimney.

Small and Full-Scale Modeling for the Application of Wall Solar Chimneys

2016 ◽  
Author(s):  
David Park ◽  
Francine Battaglia
Keyword(s):  
Natural Ventilation ◽  
Velocity Ratio ◽  
Thermal Conditions ◽  
Ambient Air ◽  
Full Scale ◽  
Scale Model ◽  
Small Scale ◽  
Solar Chimney ◽  
Window Position ◽  
Pi Theorem

A solar chimney is a natural ventilation technique that has a potential to save energy consumption as well as to maintain the air quality in the building. However, studies of buildings are often challenging due to their large sizes. The objective of the current study was to determine relationships between small- and full-scale solar chimney system models. In the current work, computational fluid dynamics (CFD) was utilized to model different building sizes with a solar chimney system, where the computational model was validated with the experimental study of Mathur et al. The window, which controls entrainment of ambient air, was also studied to determine the effects of window position. Correlations for average velocity ratio and non-dimensional temperature were consistent regardless of window position. Buckingham pi theorem was employed to further non-dimensionalize the important variables. Regression analysis was conducted to develop a mathematical model to predict a relationship among all of the variables, where the model agreed well with simulation results with an error of 2.33%. The study demonstrated that the flow and thermal conditions in larger buildings can be predicted from the small-scale model.

scholarly journals NUMERICAL EXPERIMENTS WITH AN ALGORITHM FOR PROCESSING EXPERIMENTAL DATA TO DETERMINE THE PARAMETERS OF A RHEOLOGICAL MODEL OF A LIQUID WITH THE EFFECT OF «SOLIDIFICATION»

2021 ◽  
pp. 206-211
Author(s):  
В.Н. Колодежнов ◽  
А.В. Колтаков ◽  
С.С. Капранчиков ◽  
А.С. Веретенников
Keyword(s):  
Experimental Data ◽  
Polyethylene Glycol ◽  
Calcium Carbonate ◽  
Relative Error ◽  
Rheological Model ◽  
Numerical Experiments ◽  
Maximum Error ◽  
Viscoplastic Fluid ◽  
Maximum Relative Error ◽  
Hardening Effect

Предложена методика обработки экспериментальных данных и алгоритм для ее реализации по определению параметров реологической модели вязкопластической жидкости, которая демонстрирует проявление эффекта «отвердевания». С целью проверки работоспособности алгоритма проведены численные эксперименты с наборами генерируемых случайным образом “псевдоэкспериментальных” данных с заранее заданной величиной максимальной относительной погрешности. Проведен анализ влияния максимальной относительной погрешности исходных “псевдоэкспериментальных” данных на величину относительной погрешности определяемых в ходе численных экспериментов параметров реологической модели. По итогам проведенных экспериментов показано, что относительная погрешность определения параметров реологической модели соизмерима с максимальной погрешностью генерируемых “псевдоэкспериментальных” данных. Рассмотрен пример обработки экспериментальных данных для суспензии частиц карбоната кальция на основе полиэтиленгликоля. A technique for processing experimental data and an algorithm for its implementation to determine the parameters of a rheological model of a viscoplastic fluid, which demonstrates the manifestation of the "hardening" effect, are proposed. In order to test the algorithm's operability, numerical experiments were carried out with sets of randomly generated "pseudo-experimental" data with a predetermined maximum relative error. The analysis of the influence of the maximum relative error of the initial “pseudo-experimental” data on the value of the relative error of the parameters of the rheological model determined during numerical experiments was carried out. Based on the results of the conducted experiments, it is shown that the relative error in determining the parameters of the rheological model is commensurate with the maximum error of the generated “pseudo-experimental” data. An example of processing experimental data for a suspension of calcium carbonate particles based on polyethylene glycol is considered.

A Parametric Study of Conjugate Heat Transfer of Solar Chimney

2009 ◽  
Author(s):  
J. Arce ◽  
J. P. Xaman ◽  
G. Alvarez ◽  
M. J. Jime´nez ◽  
M. R. Heras
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Parametric Study ◽  
Solar Irradiance ◽  
Natural Ventilation ◽  
Numerical Study ◽  
Ambient Air ◽  
Computer Code ◽  
Solar Chimney ◽  
Conservation Equations

Recently, new buildings are being designed considering natural sources such as natural ventilation as a passive technique. Solar chimneys are among those techniques of passive ventilation systems in buildings, to enhance the air quality and some times the thermal comfort. In this work, a numerical study of a solar chimney for forced ventilation is carried out. Also a parametric study varying the ambient air temperature, the solar irradiance and Reynolds number is considered. The dimensions of the solar chimney are 4.0 m high, and 0.35 m deep, the absorber surface of the solar chimney was 0.15 m thick of reinforced concrete. The conservation equations of mass, momentum, energy and two turbulence equations are solved under some simplifications such as: 2-D, incompressible, steady state turbulent air flow and conjugated heat transfer (conduction, forced convection and radiation). k-ω turbulent model was implemented and finite volume technique was applied to solve the conservation equations. In order to guarantee the right performance of the computer code, it was reduced to cases reported in the literature and verified; also, it was validated with an experiment. The variation of ambient temperature, solar irradiance and Reynolds number are analyzed in the parametric study. The heat transfer correlations for total Nusselt number (convective plus radiative) are introduced. From the results, it was found that the heat transfer increases as the Reynolds number increases for the hot surface of the solar chimney.

Application of a Wall-Solar Chimney for Passive Ventilation of Dwellings

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
David Park ◽  
Francine Battaglia
Keyword(s):  
Flow Regime ◽  
Natural Ventilation ◽  
Energy Use ◽  
Current Model ◽  
Numerical Data ◽  
Thermal Conditions ◽  
Solar Chimney ◽  
Airflow Distribution ◽  
Ventilation Technique ◽  
Save Energy

The solar chimney is a natural ventilation technique that has the potential to save energy use in buildings as well as maintain comfortable indoor quality. The objective of the current study was to examine the effects of the wall-solar chimney on airflow distribution and thermal conditions in a room. In the current work, computational fluid dynamics (CFD) was used to model a solar chimney. The solar chimney was modeled three-dimensionally for a more realistic simulation of fluid and thermal conditions. Experimental and numerical data from literature were used to validate the current model, and the results agreed very well. The current study showed that the flow in the solar chimney system can be either laminar or turbulent depending on the parameters of the system, and that the effect of the chimney inlet was more significant than that of the chimney width (air gap between the glass and absorber) on the flow regime. This study also developed a new characteristic Rayleigh number (Ra*) relating the chimney inlet and width, which showed good consistency with the prediction of the flow regime. The investigations of Ra* and the flow regime indicated that the flow becomes turbulent for Ra* ∼ 0.8 × 108. Finally, the potential improvements of the designs were discussed by observing the flow and thermal conditions of the room.

scholarly journals Noncontact Measurement for Radius of Curvature of Unpolished Lens

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Haifeng Liang
Keyword(s):  
Mathematical Model ◽  
Relative Error ◽  
Prediction Error ◽  
Convex Surface ◽  
Separation Distance ◽  
Radius Of Curvature ◽  
Maximum Relative Error ◽  
Spherical Lens ◽  
Parallel Lines ◽  
Lens Surface

A noncontact mathematical model to measure radius of curvature (ROC) of an unpolished spherical lens was proposed and also proved by experiments. This model gives ROC as a function of arcs radii and their separation distance, where the radii of the corresponding arcs could be acquired by taking coordinates of points on the arcs when two parallel lines of light project onto a lens surface. Our experiments demonstrated that the measured maximum relative error was 0.027% for a concave surface with a 38.19 mm ROC and 0.021% for a convex surface with a 97.75 mm ROC, which were all in agreement with those of theory prediction error. The suggested method presented a fast noncontact method for testing ROC of lens during coarse grinding and fine grinding.

A LES Study of Ventilation Flow Through a 3-D Room Fitted With Solar Chimney

2020 ◽  
Author(s):  
B. Phuoc Huynh
Keyword(s):  
Solar Radiation ◽  
Natural Ventilation ◽  
Boussinesq Approximation ◽  
Scale Model ◽  
Navier Stokes ◽  
Solar Chimney ◽  
3 Dimensional ◽  
Fluid Properties ◽  
Flow Through ◽  
Volume Method

Abstract Solar chimney (thermal chimney) is a device which absorbs solar radiation to heat the air. The heated air, becoming buoyant, rises through the chimney’s passage and induces further air currents. When fitted to a building, solar chimney can thus induce fresh outside air to flow through the building for ventilation. Because only natural means (solar radiation here) are involved to cause the air flow, solar chimney is considered a natural-ventilation device. This work investigates computationally natural ventilation induced by a roof-mounted solar chimney through a real-sized 3-dimensional room, using a commercial CFD (Computational Fluid Dynamics) software package which employs the Finite Volume Method. A LES (Large-Eddy Simulations) formulation with Smagorinsky SGS (Sub-Grid Scale) model is used. All fluid properties are assumed to be constant and corresponding to those of air at 300K (27°C, constant ambient temperature) and standard pressure at sea level (101.3kPa); but Boussinesq approximation (wherein temperature change affects only the fluid density pertaining to buoyancy force) is also assumed. Comparison is made with computational results obtained from a RANS (Reynolds-Averaged Navier-Stokes) formulation. Agreement between LES and RANS results indicate the trustworthiness of CFD methods used.

Robustness of a Neural Network Model for Power Peak Factor Estimation in Protection Systems

2006 ◽  
Author(s):  
Rose Mary G. P. Souza ◽  
Joa˜o M. L. Moreira
Keyword(s):  
Neural Network ◽  
Relative Error ◽  
Safety Margin ◽  
Maximum Error ◽  
Maximum Relative Error ◽  
Peak Factor ◽  
Protection Systems ◽  
Power Peak ◽  
Input Variables ◽  
Factor Estimation

This work presents results of robustness verification of artificial neural network correlations that improve the real time prediction of the power peak factor for reactor protection systems. The input variables considered in the correlation are those available in the reactor protection systems, namely, the axial power differences obtained from measured ex-core detectors, and the position of control rods. The correlations, based on radial basis function (RBF) and multilayer perceptron (MLP) neural networks, estimate the power peak factor, without faulty signals, with average errors between 0.13%, 0.19% and 0.15%, and maximum relative error of 2.35%. The robustness verification was performed for three different neural network correlations. The results show that they are robust against signal degradation, producing results with faulty signals with a maximum error of 6.90%. The average error associated to faulty signals for the MLP network is about half of that of the RBF network, and the maximum error is about 1% smaller. These results demonstrate that MLP neural network correlation is more robust than the RBF neural network correlation. The results also show that the input variables present redundant information. The axial power difference signals compensate the faulty signal for the position of a given control rod, and improves the results by about 10%. The results show that the errors in the power peak factor estimation by these neural network correlations, even in faulty conditions, are smaller than the current PWR schemes which may have uncertainties as high as 8%. Considering the maximum relative error of 2.35%, these neural network correlations would allow decreasing the power peak factor safety margin by about 5%. Such a reduction could be used for operating the reactor with a higher power level or with more flexibility. The neural network correlation has to meet requirements of high integrity software that performs safety grade actions. It is shown that the correlation is a very simple algorithm that can be easily codified in software. Due to its simplicity, it facilitates the necessary process of validation and verification.

Application of a Wall-Solar Chimney for Passive Cooling of Dwellings

2015 ◽  
Author(s):  
David Park ◽  
Francine Battaglia
Keyword(s):  
Energy Consumption ◽  
Flow Regime ◽  
Thermal Condition ◽  
Natural Ventilation ◽  
Energy Use ◽  
Current Model ◽  
Numerical Data ◽  
Thermal Conditions ◽  
Air Gap ◽  
Solar Chimney

Energy consumption is an important issue and has become a great concern during last the few decades, where most energy consumption is utilized for conditioning buildings. The solar chimney is a natural ventilation technique that has the potential to save energy use in buildings as well as maintain comfortable indoor quality. The objective of the current study is to examine the effects of the wall-solar chimney on airflow distribution and thermal conditions in a room. In the current work, computational fluid dynamics was used to model a solar chimney. The time-dependent conservation equations for mass, momentum and energy were solved with the k-ε turbulence equations using ANSYS Fluent. Previous literature, that utilized numerical modeling to study the solar chimney for different dimensions of chimney geometry, only considered a two-dimensional solar chimney with one-directional heat transfer. In the current study, the solar chimney was modeled three-dimensionally for a more realistic simulation of actual flow and thermal condition of the room. Experimental and numerical data from literature were used to validate the current model, and the results agreed very well. The current study showed that the flow in the solar chimney system can be either laminar or turbulent depending on the parameters of the system, and that the effect of the chimney inlet is more significant than that of the air gap on the flow regime. This study also developed a new characteristic Rayleigh number Ra* relating the chimney inlet and the air gap, which showed good consistency with the prediction of the flow regime. The investigations on Ra* and the flow regime indicated that the flow becomes turbulent for Ra* ∼ 0.8 × 108. Lastly, the potential improvements of the designs were discussed by observing the flow and thermal condition of the room.

scholarly journals Method of integro-differential equations for interpreting the results of vertical electrical sounding of the soil

2021 ◽  
pp. 67-70
Author(s):  
D. G. Koliushko ◽  
S. S. Rudenko ◽  
A. N. Saliba
Keyword(s):  
Mathematical Model ◽  
Relative Error ◽  
Power Plants ◽  
Current Source ◽  
Soil Surface ◽  
Observation Point ◽  
Practical Significance ◽  
Maximum Relative Error ◽  
Algebraic Equations ◽  
Linear Algebraic Equations

The paper is devoted to the problem of determining the geoelectric structure of the soil within the procedure of testing the grounding arrangements of existing power plants and substations to the required depth in conditions of dense development. To solve the problem, it was proposed to use the Schlumbergers method , which has a greater sounding depth compared to the Wenner electrode array. The purpose of the work is to develop a mathematical model for interpreting the results of soil sounding by the Schlumberger method in the form of a four-layer geoelectric structure. Methodology. To construct a mathematical model, it is proposed to use the solution of a particular problem about the field of a point current source, which, like the observation point, is located in the first layer of a four-layer soil. Based on this expressions, a system of linear algebraic equations of the 7-th order with respect to the unknown coefficients ai and bi was compiled. On the basis of its analytical solution, an expression for the potential of the electric field was obtained for conducting VES (the point current source and the observation point are located only on the soil surface). Results. Comparison of the results of soil sounding by the Schlumberger installation and the interpretation of its results for the same points shows a sufficient degree of approximation: the maximum relative error does not exceed 9.7 % (for the second point), and the average relative error is 3.6 %. Originality. Based on the obtained expression, a test version of the program was implemented in Visual Basic for Applications to interpret the results of VES by the Schlumberger method. To check the obtained expressions, the interpretation of the VES results was carried out on the territory of a 150 kV substation of one of the mining and processing plants in the city of Kriviy Rih. Practical significance. The developed mathematical model will make it possible to increase the sounding depth, and, consequently, the accuracy of determining the standardized parameters of the grounding arrangements of power stations and substations.

scholarly journals Test Verification and Application of a Longitudinal Temperature Force Testing Method for Long Seamless Rails Using FBG Strain Sensor

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Ping Wang ◽  
Kaize Xie ◽  
Rong Chen ◽  
Liyang Shao ◽  
Lianshan Yan ◽  
...  
Keyword(s):  
Temperature Variation ◽  
Relative Error ◽  
Test Specimen ◽  
Single Point ◽  
Maximum Error ◽  
Sensitivity Coefficient ◽  
Maximum Relative Error ◽  
Longitudinal Temperature ◽  
Temperature Force ◽  
Theoretical Results

In order to evaluate the health status of continuous welded rail accurately, a deduction on the FBG sensing principle has been made with regard to the temperature variation of test specimens under different constraint conditions. A long seamless rail testing solution and its on-site application are designed based on this deduction. According to the verification experiments of sensing principle inside, the effect of the reference temperature on the FBG temperature and strain sensitivity coefficient within −30°C~30°C is not higher than 0.05%; the maximum relative error of single point between the tested and theoretical results of test specimen under constrained condition is 3.2%; and the maximum relative error of slopes of fitted straight lines based on the tested and theoretical results within the entire test temperature range is 2.3%, verifying the deduced FBG sensing principle with regard to the test specimen under constrained condition. The maximum error of the longitudinal temperature force between the on-site tested results and calculated results in long seamless rails is only 6.1 kN, the corresponding rail temperature variation is 0.3°C, and the accumulated error is controllable within 5%.

Sign in / Sign up

Export Citation Format

Share Document