Benedito Dias Baptista Filho - bdbfilho@net.ipen.br
Walmir Maximo Torres - wmtorres@net.ipen.br
José Carlos de Almeida - abolafio@net.ipen.br
Luiz Alberto Macedo - lamacedo@net.ipen.br
Samuel Carraccioli Santos - samuelcs@net.ipen.br
Instituto de Pesquisas Energéticas e Nucleares: IPEN-CNEN/SP, Divisão de Termo-Hidráulica
Caixa Postal 11049 - CEP 05422-970 - São Paulo, SP, Brasil

The paper describes problems with a magnetic flow meter used in a natural circulation process, subjected to extremely low mass flows rates and temperature changes. The paper discuss the flow measurement principle, and also installation and operation issues. Experimental results with a sensor installed in a Natural Circulation Loop and with another sensor installed in a laboratory setup are presented. The results showed non-linear characteristics of the instrument, offset temperature dependence, and the need of an efficient grounding system. Additional tests with an electrical isolated system (batteries) will be performed to check if the drift variation is due grounding effect. Also the signal shielding integrity will be checked.

Keywords: Magnetic Flow Meters, Natural Circulation
 
 

Fernando Jorge Rodrigues Neves - fernando@enm.unb.br
Cristiano Viana Serra Villa - cvsv@uol.com.br
João Nildo de Souza Vianna - vianna@enm.unb.br
Universidade de Brasília, Departamento de Engenharia Mecânica
Campus Universitário Darcy Ribeiro, 70910-900 - Brasília, D.F., Brasil

Currently for the dynamic calibration of pressure transducers, a relatively simple model for the transducer has been used. The simplification may lead to distorted results. In this paper a model named 1 input / 2 outputs is proposed. This model is well suited to the possible three situations found in the calibration: the comparative calibration with or without knowing the Frequency Response Function of the reference transducer and the absolute calibration. The variables of the 1 input / 2 outputs model have their physical meaning based on the assumption that the dynamic pressure generator is a shock tube. The analysis of the proposed model showed that the simplification adopted is reasonable only when the reference transducer's Frequency Response Function assumes a unit value over the considered frequency range. In addition the given results depend on the validity of the hypothesis of independence between the noise and the transducers' responses.

Keywords: Frequency Response Function, dynamic calibration, shock tube
 
 

Sonia M. dos Santos - vnsantos@mikrus.com.br
Fundação Universidade Federal do Rio Grande - Departamento de Física
96201-900 - Rio Grande, RS, Brasil

Vilson C. da S. Ferreira - vferreir@vortex.ufrgs.br
Universidade Federal do Rio Grande do Sul, Departamento de Engenharia Mecânica
Cx. P. 17819 - 90035-972 - Porto Alegre, RS, Brasil

Flow around an obstacle sometimes happen with a vortex shedding produced with a defined frequency. The present work uses Laser Doppler Velocimetry (LDV) coupled to a synchronised system which allows individualise Doppler signals up to 1 MHz in order to characterise the size of the vortices produced by different generators. Two different obstacles were studied. The vortex frequencies measured experimentally allowed to perform the actual Strouhal number (Sr), characterist of the periodic flows, and these values were compared with data from specialised bibliography. The study may contribute to define new geometry for generator elements adopted in vortex type flowmeter design. The LDV measured two velocity components, the axial and the circumferential one which allowed visualise the flow field downstream the obstacle. The study was held in a gravimentric calibration rig for water flowmeters with an extended uncertainty of +0,4%.

Keywords: Vortex Shedding; Laser Doppler Velocimetry; Frequency of vórtices
 
 

Cleyton Senior Stampa - cleytonstampa@aol.com
Universidade Católica de Petrópolis, Departamento de Engenharia Mecânica
CEP: 25685-070 - Petrópolis, RJ, Brasil

Sergio Leal Braga - slbraga@mec.puc-rio.br
Pontifícia Universidade Católica do Rio de Janeiro, Departamento de Engenharia Mecânica
CEP: 22453-900 - Rio de Janeiro, RJ, Brasil

O conhecimento do índice de refração de uma substância composta pode ser utilizado na determinação indireta de muitas grandezas, tais como: viscosidade, concentração, condutividade, calor específico e outras. No estudo dos processos de mudança de fase de substâncias binárias, o conhecimento dos campos de concentração e temperatura têm importância fundamental. O fato do índice de refração de soluções aquosas de cloreto de amônia (NH4Cl-H2O), bastante utilizadas como modelos transparentes de ligas metálicas, variar com a temperatura e, principalmente, com a concentração, sugere um estudo experimental de comportamento entre estas três grandezas. No presente trabalho é reportado um experimento de resfriamento de soluções desta substância, com concentrações de 5%, 10%, 15%, 19,7%, 24%, 28% e 32%, em peso de NH4Cl, no qual se determinou uma relação funcional entre índice de refração e temperatura para cada uma delas. A partir destas relações, é possível determinar-se valores de concentração dentro da faixa analisada, medindo-se índices de refração e temperaturas.

Palavras chave: índice de refração, temperatura, substâncias multicomponentes, concentração
 
 

Sandro M. M. de Lima e Silva - metrevel@mecanica.ufu.br
Gilmar Guimarães - gguima@mecanica.ufu.br
Universidade Federal de Uberlândia, Faculdade de Engenharia Mecânica,
Campus Santa Mônica, CEP: 38400-089 - Uberlândia, MG, Brasil

This work describes an experimental technique for determining simultaneously the thermal diffusivity and thermal conductivity of the Polychloroethylene (PVC). This technique uses experimental data from one of the same samples surfaces. It means that the imposing heat flux and the temperature response are measured at the same surface of the sample. Two objective functions using experimental and calculated temperature are defined. An objective function representing the eigenvalue phase angle is used to determine the thermal diffusivity, while a least square error function is used for the thermal conductivity estimation. The sequential unconstrained optimization technique BFGS, is used to calculate the search direction. In each case the golden section method is used in the one-dimensional search, followed by a polynomial approximation. A comparison with the flash method and guarded hot plate method gives a deviation of 2,97 % and 0,63 % for thermal diffusivity and thermal conductivity respectively.

Keywords: Parameter estimation, Thermal properties measurements, Heat conduction, Inverse problem, Optimization.
 
 

Bruno Venturini Loureiro - bruno_vl@yahoo.com
Aristóteles Alves Lyrio - aalyrio@uol.com.br
Rogério Silveira de Queiroz - gradiva@zaz.com.br
Universidade Federal do Espírito Santo, Departamento de Engenharia Mecânica
CEP 29060-970 - Vitória, ES, Brasil

A pure convective environment is generated in a tank filled with eight hundred liters of water, by exchanging heat in its bottom surface with condensed steam. The temperature stratification through the water form a stable region, and a mixed-layer where 10 ml of inert contaminant are released (rhodamine 6G at 800 ppb). An open argon ion laser beam (4 W at 514 nm) is made to reach the region of contaminant evolution, generating light emissions from the rhodamine plume, due to its fluorescence (above 550 nm of wave lenght). By using a CCD camera and a longpass optic filter, images are taken at 1 Hz and are analyzed, leading to the description of the plume center of mass as a function of time. It is also obtained the density probability functions that better describe the vertical concentration of bands integrated horizontally through time considering two cases of different vertical heat fluxes.

Keywords: Convection, Turbulence, Induced fluorescence
 
 

Valdir Araújo de Souza - email:valdir@mec.ita.cta.Br
Edson Luiz Zaparoli - email:zaparoli@mec.ita.cta.br
CTA - ITA - Departamento de Energia
Pça Mal. Eduardo Gomes, 50 - Vila das Acácias
CEP: 12228-900 - São José dos Campos - SP - Brasil

Flat plates are widely used in a large variety of equipment such as satellites, aircraft, air cooled heat exchangers and etc. When thermocouples are used to measure the temperature of flat plate surfaces, which are exposed to fluids at different temperatures, errors occur because of the heat conduction along the wire. In this work the parameters which affect the error were analysed considering two-dimensional conduction through the plate and the thermocouple wires. This problem was numerically solved employing the finite element method with a triangular non-structured adaptive mesh with six nodes per element. The mesh refinement is automatically done and it is denser in regions, which have sharp curvature, tight geometries and high temperature gradient. Firstly the results from the previously mentioned analysis are compared with the analytical solution where is taken into account a one-dimensional conduction that is suitable for thin flat plates and long thermocouple wires. This comparison allows the validation of the numerical results and also to evaluate the parameters range in which the one-dimensional approach is suitable. The results obtained from this work enable us to quantify the error associated with conduction through the thermocouple wires in the flat plates temperature measurement evaluating the conditions that causes more significant errors.

Keywords: Temperature measurement, Thermocouple conduction error, Finite element.
 
 

Daniela V. F. M. Rey Silva - daniela@lttc.coppe.ufrj.br
Alexandre P. de Oliveira - alexandre@lttc.coppe.ufrj.br
Helcio R. B. Orlande - helcio@serv.com.ufrj.br
Roberto de Souza* - rs@serv.com.ufrj.br
Universidade Federal do Rio de Janeiro, Departamento de Engenharia Mecânica, EE/COPPE
Cx. Postal 68503 - 21945-970 - Rio de Janeiro, RJ, Brasil
* Also Universidade Estadual do Rio de Janeiro

This paper deals with the sequential estimation procedure for the identification of thermal conductivity and of volumetric heat capacity of solids. The experimental setup conceived consists of a heater symmetrically assembled between two pieces of the specimen with unknown properties. The sequential estimation procedure is described in detail, as applied to the present nonlinear parameter estimation problem. Transient simulated temperature measurements taken in the specimen are used in order to verify the accuracy of this estimation approach.

Keywords: Thermal Conductivity, Volumetric Heat Capacity, Sequential Parameter Estimation, Maximum a Posteriori Estimator
 
 

Sonia M. dos Santos - vnsantos@mikrus.com.br
Jorge A . Almeida - jorge@calvin.ocfis.furg.br
Fundação Universidade Federal do Rio Grande - Departamento de Física
Cx. P. 474 - 96201-900 - Rio Grande, RS, Brasil

Vilson C. da S. Ferreira - vferreir@vortex.ufrgs.br
Lucas L. Gutkoski - hukax@ct.ufrgs.br
Universidade Federal do Rio Grande do Sul, Departamento de Engenharia Mecânica
Cx. P. 17819 - 90035-972 - Porto Alegre, RS, Brasil

This work presents the behaviour of solid particles in an multi-phase flow (three phases: water, air and micro-algae) using Velocimetry by Processing Image of Particle. Samples of micro-algae, food of shrimps larvae, were set in a acrylic circular tank filled with sea water, stirred by air flow coming from the bottom. The flow field is illuminated by a laser sheet and filmed by a CCD video camera. The visualised images are captured and stored on the hard disk of a microcomputer. The recorded images shows the micro movement of the particles allowing to a mobility study. The velocity of the particles was performed by two approaches. The first was, based on the search for individual particles, identified in two subsequent moments and in two different images in order to measure the displacement and to calculate the velocity based on the time between two separated images. The second one uses a high concentration of tracer particles distributed in the flow. Images in two different instants was obtained and the flow velocity is calculated by cross correlation of functions corresponding to each image. The main objective was to measure a complete flow field in a two-dimensional area, seeking for an ideal concentration of particles in each method.

Keywords: PIV; Particle Tracking Velocimetry; High Density of Particles Velocimetry
 
 

Marcelo Mendes Vieira - mmendes@usp.br
Marcelo Silva Guimarães - marcsg@usp.br
José R. Simões-Moreira - jrsimoes@usp.br
Escola Politécnica da USP, Departamento de Engenharia Mecânica
SISEA - Laboratório de Sistemas Energéticos Alternativos
Caixa Postal 61548 - 05508-900 - São Paulo, SP, Brasil

The main goal of this paper is to present results of experiments with flashing jets. The experiments were carried out with a jet issuing from a conical convergent nozzle, 10º half-angle and 0,3 mm of exit diameter, into a low-pressure chamber. High degrees of metastability were obtained as the liquid jet expanded in the nozzle. Injection pressure and temperature were controlled to the desired values during about 1 s, which was found to be sufficient to reach and keep the steady state regime. Images from the phenomenon were obtained from a "schlieren" set up using CCD camera. The analyses of these images with mathematical filters enabled a qualitative visualisation of the flashing jet structure and geometry leaving in nozzle. Three jet regimes were observed: (1) continuous; (2) partially atomised and; (3) complete evaporation with shock waves. In latter case, we speculate that the evaporation takes part on the liquid jet surface, which takes the approximate form of a cone.

Keywords: Evaporation wave, Metastable liquid, Evaporation, Phase change, Schlieren.
 
 

Odenir de Almeida -odenir@dem.feis.unesp.br
Claudio Lindquist -lindquis@dem.feis.unep.br
Sérgio Said Mansur -mansur@dem.feis.unesp.br
UNESP -Faculdade de Engenharia de Ilha Solteira, Departamento de Engenharia Mecânica 15385-000 -Ilha Solteira, SP, Brasil

Aristeu da Silveira Neto -aristeus@mecanica.ufu.br
UFU -Faculdade de Engenharia Mecânica, Departamento de Engenharia Mecânica 38400-902 -Uberlândia, MG, Brasil

This work presents a numeric and experimental investigation of blockage ratio effects on the flow past over square cylinders, for Reynolds numbers equal to 500. The blockade ratio, defined as the relationship between the front area of the cylinder and the transverse area of the test section, was varied between 2,5% to 30%. The experimental tests were driven in a vertical hydrodynamic tunnel, operated in continuous way. The frequency of vortex shedding in the cylinder wake was determined using the hot film anemometry. Images of the von Kármán wake formed upstream of the cylinder was obtained with the aid of visualization techniques. The numerical simulations were accomplished using the computational program FLUENT .5.0, employing the volume finite method in the spatial discretization of the governing equations. The simulations were conducted with the algorithm SIMPLEC for the coupling pressure-velocity, associated with the scheme QUICK for the treatment of convective terms. The numerical and experimental results shown a good agreement, permitting to obtain fine characteristics of the flow.
 
 

Cláudio Lindquist -lindquis@dem.feis.uneps.br
Odenir de Almeida -odenir@dem.feis.unesp.br
Sérgio Said Mansur -mansur@dem.feis.unesp.br
UNESP -Faculdade de Engenharia de Ilha Solteira, Departamento de Engenharia Mecânica
15385-000 -Ilha Solteira, SP, Brasil

Aristeu da Silveira Neto - aristeus@mecanica.ufu.br
UFU -Faculdade de Engenharia Mecânica, Departamento de Engenharia Mecânica
38400-902 -Uberlândia, MG, Brasil

This work presents a numerical and experimental investigation on the influence of the side ratio over the flow past rectangular cylinders, for Reynolds numbers up to 10 3 . The side ratio, defined as the ratio between the height and the width of the cylinder rectangular cross section, has been varied from 1 to 16. The experimental tests have been conducted in a vertical water tunnel operated by gravity. The vortex shedding frequency in the wake has been determined using hot film anemometry. Images from the cylinder wake and the shear layers over the surfaces have been obtained with flow visualization techniques. The numerical simulations have been performed using the finite volumes method without turbulence models, using the QUICK scheme for convective transport and the SIMPLEC algorithm for the pressure-velocity coupling. The numerical and experimental results have shown good agreement with the literature data.
 
 

Idalberto Ferreira de Ataídes - ifa@facintr.com.br
Centro Universitário do Triângulo (UNIT)
38411-186 - Av. Rafael Marino Neto, 600

Jardim Karaíba - Uberlândia - MG
Carlos Roberto Ribeiro - cribeiro@mecanica.ufu.br
Aristeu da Silveira Neto - aristeus@mecânica.ufu.br
Universidade Federal de Uberlândia (UFU)
Faculdade de Engenharia Mecânica (FEMEC)
38400-902 - Santa Mônica - Uberlândia - MG

When hydroelectric plants are inaugurated it is necessary to obtain the curve of turbine efficiency and compare it with the design parameters. It is obligatory to get the flow rates in the turbines. The flow rate calculated using the Gibson method can be very accurate and not very expensive. This work presents some theoretical considerations and experimental results which allow observations about the feasibility and limitations of the method. The difficulties due to noise in the data acquisition system , filtering of the data and calibration procedures of transducer are analyzed. The experimental results obtained through the Gibson method were also compared with the flow rate measured with a direct method. In order to verify the validity of the procedures adopted in this work, statistical analysis were applied to the results obtained through direct measurements and also by the Gibson method. It was proved that the Gibson method is very precise, versatile and competitive.

Keywords: Flow rate, Gibson, Pressure - time, Calibration, Volume - time.
 
 

Paulo R. Souza Mendes - pmendes@mec.puc-rio.br
Márcio da Silveira Carvalho - msc@mec.puc-rio.br
Mônica F. Naccache - naccache@mec.puc-rio.br
Rodrigo B. O. Jardim - rjardim@mec.puc-rio.br
Pontifícia Universidade Católica, Department of Mechanical Engineering
Rio de Janeiro, RJ 22453-900, Brazil

In this paper we present and discuss the design of an experimental apparatus for measuring thermal conductivity and specific heat of liquids. The apparatus consists essentially of a long annular cavity, filled with the liquid sample. The theory of the cell employs the hypotheses of purely radial heat flux and no natural convection inside the annular space. Thermal conductivity is calculated from data obtained during the steady state, while for specific heat evaluation, data pertaining to the transient regime are needed. Numerical solutions for the natural-convection flow and heat transfer inside the cell were obtained with the aid of the finite volume method. The results obtained showed that thermal conductivity measurement data are good for Grashof numbers less than 10 4 only.

Keywords: Thermal conductivity measurement, Annular cavity, Natural convection.
 
 

B.A.A. Gomes, azevedo@mec.puc-rio.br
R. L. Thompson, roney@mec.puc-rio.br
L.F.A. Azevedo, lfaa@mec.puc-rio.br
Departamento de Engenharia Mecânica, Pontifícia Universidade Católica - PUC/Rio
R. Marquês de São Vicente 225- Gávea, 22453-900 Rio de Janeiro, RJ, Brasil

A solid body rotation flow experiment was constructed with the objective of calibrating a Particle Image Velocimetry system (PIV). The PIV system determines the velocity field based on the analysis of consecutive images of tracer particles dispersed in the fluid and illuminated externally by a pulsed laser light. In the present case the images are analyzed by a cross-correlation algorithm yielding particle displacement fields. In order to evaluate the influence of the several parameters that control the accuracy of the PIV technique, a solid body rotation flow was chosen as a simple two-dimensional flow of known velocity field. A cylindrical glass container was mounted on a rotating table of controlled angular speed. Metallic coated hollow glass spheres of mean diameter of 30 µm were used as tracers particles in water. A geometrical calibration tool was designed so as to allow the flow coordinate system to be transformed from the camera xy frame of reference to the cylindrical frame of reference of the rotating tank. An uncertainty analysis was performed on the variables that affect the calibration procedure. Excellent agreement was found between measured and predicted velocities.

Keywords:.Velocity measurements, Particle Image Velocimetry, Calibration