Paulo Smith Schneider

Application of inverse analysis to illumination design

This work investigates the application of the inverse analysis to the illumination design of a three-dimensional rectangular enclosure. The illumination design is inherently an inverse problem, in which the design surface is subjected to two conditions–the prescribed luminous flux and null luminous power–while the light sources are left unconstrained. It is considered that all surfaces emit and reflect diffusely, and that the hemispheric spectral emissivities are wavelength independent in the visible region of the spectrum. The illumination design is treated by two different approaches: by an explicit formulation that is regularized by the truncated singular value decomposition due to its ill-conditioned nature; and by an implicit formulation that is treated as an optimization problem using the generalized extremal optimization method, a stochastic algorithm. Both approaches are capable of providing design solutions that satisfy the prescribed luminous flux on the design surface with maximum errors that are less than 3.0%. † Preliminary versions of this work were presented in the 10th Brazilian Congress of Thermal Sciences and Engineering (ENCIT 2004) and in the 19th International Congress of Mechanical Engineering (COBEM 2007).

Strategies for solving the air flow—Thermal problem in multiroom buildings

Abstract Iterative and direct methods for solving the coupled problem of heat and mass transfers in buildings are presented and compared. Numerical problems often trouble the resolution of this problem and a choice between different strategies can be a way to overcome instabilities of calculus and runningtime difficulties. The state of the zones of air is represented as a function of temperature and pressure. The iterative method consists of separating the problem into two sub-sets, the first being a function of temperature and the other a function of pressure. The direct method simultaneously carries out the resolution of the original set. Two simulation codes were developed based on the ‘coupling method’, which is a method of solving the thermal problem by splitting it into levels of coupling. The direct option needs more computational effort, but is easier to run by non-experts. In contrast, the iterative method is better adapted to the connection of different programs. Simulation results are presented, and the performances of the two strategies are compared and discussed.

A comparison of experimental results of soot production in laminar premixed flames

Abstract Soot emission has been the focus of numerous studies due to the numerous applications in industry, as well as the harmful effects caused to the environment. Thus, the purpose of this work is to analyze the soot formation in a flat flame burner using premixed compressed natural gas and air, where these quasi-adiabatic flames have one-dimensional characteristics. The measurements were performed applying the light extinction technique. The air/fuel equivalence ratiowas varied to assess the soot volume fractions for different flame configurations. Soot production along the flamewas also analyzed by measurements at different heights in relation to the burner surface. Results indicate that soot volume fraction increases with the equivalence ratio. The higher regions of the flamewere analyzed in order to map the soot distribution on these flames. The results are incorporated into the experimental database for measurement techniques calibration and for computational models validation of soot formation in methane premixed laminar flames, where the equivalence ratio ranging from 1.5 up to 8.

Diffusion Flame Stability of Low Calorific Fuels

Mechanisms related to diffusion flame stabilization have been the subject of several studies within the last decades due the industrial and scientific interests. Information on flame stability is of fundamental importance in energy efficiency and safety regarding industrial applications. Thus, an experimental study was performed in order to examine the flame characteristics and regions of stability limits. In this study, a representative burner of industrial applications was employed, which allows the stabilization of several combustion regimes. The lift-off and blow-out flame regimes were investigated for different proportions of carbon dioxide in natural gas. In this way, an analysis of the calorific fuel influence on the flame stability was performed based on the measurements and a comparison with classical literature models was done. The fuel dilution by adding carbon dioxide was found to decrease the soot production, leading to lower flame heights and also, lower lift-off and blow-out limits. Results obtained from this study encourage future works which consider flames in large scale, in order to equate to industrial applications.

Experimental Assessment of Heat Transfer Correlations for a Small-Scale Evaporative Condenser

This work presents an experimental analysis of a small-scale evaporative condenser, performed on a calorimetric test facility, where heat transfer coefficients are measured and compared to some well-known correlations from the literature. The external flow of air and spray water ranged from 2.2 kg/min to 8.7 kg/min and 4.8 kg/min to 15.0 kg/min, respectively, keeping an average air to water ratio of approximately 1:2, followed by condensation temperatures ranging from 26 to 36°C. The flow pattern map is first determined, followed by the identification of the transition regions based on the void fraction concept. The overall heat transfer coefficient for the condensation zone calculated after the experimental data acquired in the present research was compared to six literature correlations, and the one developed by Tovaras, Bykov, and Gogolin in 1984 provided the better agreement. Local and mean values of the refrigerant heat transfer coefficients did not vary significantly for both single-phase superheated vapor and subcooling liquid. Results are still particular to the evaporative condenser assessed in the present work, and full-scale analysis must be performed in order to build more general correlations.

Evaluation of Air -- Water Flow in an Evaporative Condenser

Evaporative condensers present a hard problem fornumerical modeling because of the complex phenomena of heatand mass transfer outside of the bundle tubes in turbulent flows. The goal of this work is to study the air and water behavior inside an evaporative condenser operating with ammonia as the refrigerant fluid. A commercial CFD software package (FLUENT) is employed to predict the two-phase flow of air and water droplets in this equipment. The air flow is modeled as a continuous phase using the Eulerian approach while the droplets water flow is modeled as a disperse phase with Lagrangian approach. The coupling between pressure and velocity fields is performed by the SIMPLE algorithm. The pressure, velocity and temperature fields are used to perform qualitative analyses toidentify functional aspects of the condenser, while thetemperature and the relative humidity evolution contributed to verify the agreement between the results obtained with the numerical model and those presented by equipmentmanufacturer.

Optimization of a Sensible Thermal Storage System by a Lumped Approach

This study is focused on the optimization of a sensible thermal storage system subjected to a cyclic energy source. The objective is to minimize the system heat storage mass and its geometry to guarantee its operation within an admissible temperature range. The storage medium is modeled as a Lumped system and the working fluid by a non-capacitive energy balance. The storage medium is composed of an array of parallel flat plates submitted to an air stream. The optimization is based on an exhaustive search method. It is observed that the minimum heat storage mass is proportional to the mass airflow rate. An optimal relationship between the superficial heat transfer rate and the fluid flow inertia, given by the dimensionless parameter NTU, is found to be constant (4.03) and independent in respect to the mass flow rate. The system time constant was invariable (3,230 s) for the optimal relationship between the interface heat transfer rate and the system inertia.

Experiments on Inverse Method to Illumination by Optimization Technique IMIbyOPTIM with Fixed Light Source Power

The present work reports an experimental procedure designed to validate a particular solution for the distribution of artificial light sources in the sealing of an enclosure obtained by the inverse method IMIbyOPTIM. An illumination design assuming the free placement of purely diffuse light sources aims to generate a uniform illumination field on a work plane. A reduced scale enclosure is built to validate the method effectiveness, by comparing the experimental results to an illuminance target. An equally non-optimized light source distribution is placed on the enclosure and measurements confirm the hypothesis of distortion of the illumination field, already predicted by simulations. After the optimization of the light sources distribution, the measured illumination field becomes closer to the dimensionless unitary target, with a standard deviation of less than 0.021. This particular experiment verifies IMIbyOPTIM predictions and allows continuing the validation process of the method for a broad variety of design combinations.

Guidance on choosing a measuring instrument for indoor particle pollution studies

The possibility of acquiring real-time concentration data is leading many indoor air quality and health researchers to the use of particle measuring instruments instead of the classic filtration approach. This paper summarizes a checklist of characteristics that have to be considered on the selection of such instruments and checks the compliance of three air monitoring devices suitable for environmental exposure researches. An evaluation table with desirable instrument technical, economic, and logistics characteristics was summarized in a checklist, and spec sheets of three air monitoring devices suitable for environmental exposure researches were checked. Technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. Only one instrument was in comply with it. A popular air monitoring device among environmental exposure researchers was checked and it failed the accuracy check. When selecting a particle measuring instrument, technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. When selecting an instrument for a study, a lack of information on the quality of results is a strong indication that it should not be considered, as studys response may be compromised.The possibility of acquiring real-time concentration data is leading many indoor air quality and health researchers to the use of particle measuring instruments instead of the classic filtration approach. This paper summarizes a checklist of characteristics that have to be considered on the selection of such instruments and checks the compliance of three air monitoring devices suitable for environmental exposure researches. An evaluation table with desirable instrument technical, economic, and logistics characteristics was summarized in a checklist, and spec sheets of three air monitoring devices suitable for environmental exposure researches were checked. Technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. Only one instrument was in comply with it. A popular air monitoring device among environmental exposure researchers was checked and it failed the accuracy check. When selecting a particle measuring instrument, technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. When selecting an instrument for a study, a lack of information on the quality of results is a strong indication that it should not be considered, as studys response may be compromised.