I. Bajsić

DNS of Turbulent Heat Transfer in Channel Flow With Heat Conduction in the Solid Wall

The Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in the two-dimensional turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed at constant friction Reynolds number 150 and Prandtl numbers between 0.71 and 7 considering the fluid temperature as a passive scalar. The obtained statistical quantities like root-mean-square temperature fluctuations and turbulent heat fluxes were verified with existing DNS studies obtained with ideal thermal boundary conditions. Results of the present study were compared to the findings of Polyakov (1974), who made a similar study with linearization of the fluid equations in the viscous sublayer that allowed analytical approach and results of Kasagi et al. (1989), who performed similar calculation with deterministic near-wall turbulence model and numerical approach. The present DNS results pointed to the main weakness of the previous studies, which underestimated the values of the wall temperature fluctuations for the limiting cases of the ideal-isoflux boundary conditions. With the results of the present DNS it can be decided, which behavior has to be expected in a real fluid-solid system and which one of the limiting boundary conditions is valid for calculation, or whether more expensive conjugate heat transfer calculation is required. @DOI: 10.1115/1.1389060#

Phase-locking control of the Coriolis meter’s resonance frequency based on virtual instrumentation

The Coriolis meter is a resonant-type sensor that is used for measuring the mass flowrate and the density of fluids. Its regular operation is conditional on the resonance vibration of its measuring tube. This paper presents the characteristics of a resonance-control system that is based on maintaining the proper phase difference between the detection and the excitation signals (phase-locked loop (PLL)). The controller was realized as a virtual instrument and programmed in the LabVIEW environment, which was also used for performing the theoretical simulations.

An analytical estimation of the Coriolis meter’s characteristics based on modal superposition

Abstract The aim of this paper is to derive approximate, analytically expressed, theoretical characteristics for a straight, slender-tube Coriolis meter, which can be applied to any of its working modes. The mathematical model is based on the theories of the Euler beam and one-dimensional fluid flow, and includes the effects of axial force, added masses, damping and excitation. The analytical approximations are evaluated by applying a Taylor-series expansion to the solutions of the Galerkin method, which are considered as a superposition of the Euler-beam modal functions. On the basis of the obtained analytical expressions, the properties of the meter’s characteristics are discussed, with the emphasis being on particular nonidealities.

Response Time of a Pressure Measurement System with a Connecting Tube

Abstract A connecting tube between the measured object and the pressure sensing element is a common component part of pressure measurement systems. Dynamic characteristics of the resulting fluid oscillator may significantly influence the magnitudes of dynamic measurement errors. This paper presents an experimental analysis of dynamic characteristics of connecting tubes of different lengths and diameters. Inlet step pressure changes were generated by a system of two loudspeakers, and pressure responses were measured by a piezoelectric measurement system. Using the measured responses, the characteristic natural frequencies and damping of the system under discussion were determined. The results were further employed to estimate the response settling time, which is required to sufficiently reduce dynamic measurement errors.

Identification of the dynamic properties of temperature-sensors in natural and petroleum gas

Abstract This paper presents a theoretical and experimental investigation of the dynamic properties of contact temperature-sensors in air as well as in natural and petroleum gas. Particularly with gas-supply systems, which can operate either with natural or petroleum gas, a knowledge of a sensor’s dynamic properties and sensitivity to different pressure and velocity conditions can be a crucial factor in the regulation and control of the system. The frequency characteristics of contact temperature-sensors in dynamic processes with air were analysed. The experimental results are presented for real Pt-resistance temperature-sensors, with an evaluation of the time-dependent uncertainty from different uncertainty sources. In real gas-supply systems, strict protective measures and a hazardous environment tend to prevent any standard experimental identification of the dynamic properties of temperature-sensors. This was the reason for our theoretical approach to the identification of the dynamic properties of the investigated temperature-sensors in natural and petroleum gas with the use of a computational calibration model, which was experimentally verified in an air-flow. Our experimental and theoretical investigation has shown that different gas compositions, pressures and velocities in the gas-supply system result in considerable variations which could lead to the applicability of the procedure in evaluating dynamic properties in highly hazardous systems.

Stability-boundary effect in Coriolis meters

Abstract The Coriolis meter is used for measuring the mass flowrate and density of fluids. If a measuring range is not sufficiently far from the stability boundary of its measuring tube (critical flowrate), both measuring effects can no longer be independent. This paper discusses a mathematical model of the straight, slender tube meter, solved by the Galerkin method. Utilizing a power series expansion in fluid velocity, theoretical characteristics are derived, including the stability-boundary effect. Based on theoretical findings, a procedure is suggested to make corrections of the interaction between the mass flowrate and density measurement.

SOFTWARE SENSOR FOR BIOMASS CONCENTRATION MONITORING DURING INDUSTRIAL FERMENTATION

For the on-line monitoring of the parameters and states of aerobic fermentation batch processes three parallel software sensors for biomass concentration monitoring were developed, which use mutually independent measured input signals: the oxygen uptake rate, the carbon dioxide excretion rate and the reaction heat flow. The software sensors are based on a linear model, where the parameters of the model are estimated using the recursive least squares method. The model was upgraded with a mechanism for a time-varying forgetting factor to enable good tracking of the estimated parameters during rapid and large changes in the non-linear and, in certain phases of the production, very dynamic process. The estimates given by all three software sensors are in good agreement with the measurements acquired off-line. The developed software sensors make it possible to achieve accurate process identification, mutual control of individual sensors and fault detection in the process. In this way, better supervision and more accurate monitoring of the industrial fermentation process is possible, where reliability of the operation is of key importance.

AUTOMATION OF INDUSTRIAL SPRAY DRYER

In this article, we illustrate some basic principles of spray drying which is, by definition, the transformation of feed from the fluid state into a dried particulate form by spraying the feed into a hot drying medium. It is a one step, continuous particle-processing operation involving drying. The aim of a spray-dryer control system is the maintenance of desired dried product quality, irrespective of what disturbances occur within the drying operation and variations of feed supply. With our counter-current spray dryer (diameter 5.5 m, height 20 m), we produce zeolite (granulate form). It is manually controlled with fully automated equipment for continuous measurement of process parameters. With the implementation of Fuzzy control,1-3 we would like to increase process stability and, above all, reach constant product quality.

Improved probe geometry for fluorescence-based fibre-optic temperature sensor

Abstract A fluorescent fibre probe with high collection efficiency for fluorescence-lifetime measurements is presented. A numerical model for calculating the collection efficiency for different probe designs has been employed. The position and number of fibres, crystal geometry, crystal-fibre gap and the backside crystal reflectivity are used as evaluation parameters for probe optimization. A possible three-fold increase in collected fluorescent light intensity is predicted in comparison with the classical two-fibre configuration. The model has been confirmed by constructing a seven-fibre probe with alexandrite crystal as the sensing element. An accuracy of ±0.3 K is achieved in the 20–90°C temperature range.

A one-dimensional numerical model of heat and mass transfer in air-water droplet flow

This paper presents a one-dimensional numerical model of the heat, mass and momentum transfer between water droplets and humid air in the disperse process device. The model merges a model of the disintegration of a water sheet presented by Dombrowski et al. [1] and a one-dimensional numerical model of the transport phenomena in the air washer presented by Demirdžić et al. [10]. Numerical results are compared with the available experimental results. Numerical simulations can predict one-dimensional analysis of the geometrical and thermophysical parameters in the disperse process device.ZusammenfassungEin numerisches Modell für die eindimensionale Impuls-Wärme-und Stoffübertragung zwischen Wassertropfen und feuchter Luft in einer Zerstäuberapparatur wird vorgestellt. Das Modell umfaßt zwei Konzepte: (1) Zerfall einer Wasserlamelle nach Dombrowski et al [1]. (2) Eindimensionales Modell für den Transportmechanismus im Luftwäscher nach Demirdžić et al [10]. Die Validierung der numerischen Simulationen, welche die eindimensionale Analyse einzelner geometrischer und thermophysikalischer Parameter der Zerstäuberapparatur ermöglichen, erfolgte durch Vergleich mit experimentell belegten Resultaten aus der Literatur.