Jan Stasiek

Transformational-zone method of calculation of complex heat exchange during flow of optically active medium inside tube of diffuse grey surface

The paper presents analytical and experimental investigations of influence of radiative heat transfer on complex heat exchange during flow of optically active gas inside a pipe of diffusegrey properties. It was assumed that the pipe is heated from the outside by a constant heat flux and gas flowing inside is both absorbing and emitting and of small optical density. The influence of length and radiative properties of the pipe surface and of the gas temperature distribution on the wall and in the gas were analysed. The influence of radiative energy transfer on overall heat transfer coefficient was estimated. Mathematical model of radiative convective heat exchange in a system of one-dimensional temperature field, based on zone division method of Hottel and surface transformation, was verified numerically and experimentally. The results of numerical calculations were compared with experimental results obtained during carbone dioxide (CO2) flow inside electrically heated ceramic tube. The set of nonlinear differential equations was solved by Runge-Kutta method with Hamming modification and with the use of separable-kernel method.ZusammenfassungIm Artikel werden analytisch-experimentale Untersuchungen zum Einfluß der radiativen Energieübertragungsform auf den komplexen Wärmeaustausch bei Strömung eines optisch aktiven Gases im Inneren eines Rohres mit grau-diffusen Eigenschaften dargestellt. Es wird vorausgesetzt, daß das Rohr von außen mit ständigem Wärmestrahl beheizt ist, und das innen fließende Gas hat emittierende und absorbierende Eigenschaften mit geringer optischer Dichte. Analytisch wurde der Einfluß von Länge und Strahlungseigenschaften der Rohroberfläche sowie des Gases auf den Temperaturverlauf an Wand und im Gas untersucht. Der Einfluß der Strahlungsübertragung der übertragenen Energie auf den Gesamt-Wärmekoeffizienten wurde schätzungsweise angenommen. Gestützt auf das Prinzip der Zonenaufteilung nach Hottel und der Oberflächenübertragung wurde ein mathematisches Modell der Strahlungs-Konvektionsübertragung von Wärme in einem System mit eindimensionalem Temperaturfeld erarbeitet und der numerisch-experimentellen Überprüfung unterzogen. Die numerischen Rechenergebnisse wurden mit den experimentellen, bei Strömung von CO2 im Inneren eines elektrisch beheizten (keramischen) Rohres erhaltenen, verglichen. Ein System von nichtlinearen Differentialgleichungen wurde nach dem Runge-Kutta-Verfahren mit Modifikationen nach Hamming gelöst, wobei die Separable-Kernel-Methode zur Anwendung kam.

Application of generalized Pythagoras theorem to calculation of configuration factors between surfaces of channels of revolution

Abstract The generalized Pythagoras theorem is used to derive new forms of formulae for configuration factors in cylindrical and conical channels. The equations are then approximated by an exponential function which simplifies the calculation of radiation heat transfer in nonisothermal enclosures.

Generalized net-radiation method for open and closed enclosure filled with isothermal optical medium

The paper presents new engineering method of calculation of radiating heat exchange in open and closed enclosures filled with isothermal grey gas or with gas of known selective emissivity. The method of determination of generalized configuration factors was also presented. A number of new relations between temperature, heat fluxes and effective energy flux of surfaces was derived. A formula for dissipation loss of open system was presented. Two-surface open system was analysed in details. The new method was illustrated with a calculation example.ZusammenfassungIm Artikel ist ein neues Rechenverfahren für den Wärmeaustausch über Strahlung in offenen und geschlossenen, mit isothermem Grau-Gas oder mit Gas bestimmter selektiver Strah-lung gefüllten Systemen vorgestellt. Es werden das Bildungsprinzip der verallgemeinerten Konfigurationsparameter sowie eine Reihe von Abhängigkeiten zwischen Temperatur, Wärmestrahlung und Flächenhelligkeiten angegeben. Ebenfalls wird eine Gleichung für den Streuungsverlust des offenen Systems gegeben, ferner ein zweiflächiges offenes System in Einzelheiten analysiert. Das neue Verfahren wird in einem Rechenbeispiel dargestellt.

Thermochromic liquid crystals in heat transfer research

In recent years Thermochromic Liquid Crystals (TLC) have been successfully used in non-intrusive heat transfer and fluid mechanics studies. Thin coatings of TLCs at surfaces is utilized to obtain detailed heat transfer data of steady or transient process. Application of TLC tracers allows instantaneous measurement of the temperature and velocity fields for two-dimensional cross-section of flow. Computerized flow visualization techniques allow automatic quantification of temperature of the analyzed surface or the visualized flow cross-section. Here we describe our experience in applying the method to selected problems studied in our laboratory. They include modeling flow configurations in the differentially heated inclined cavity with vertical temperature gradient simulating up-slope flow as well as thermal convection under freezing surface. The main aim of these experimental models is to generate reliable experimental database on velocity and temperature fields for specific flow. The methods are based on computerized true-color analysis of digital images for temperature measurements and modified Particle Image Velocimetry and Thermometry (PIVT) used to obtain the flow field velocity.

Experimental and theoretical study on the radiation of gases containing dust particles

The attenuation of thermal radiation within a dilute cloud of pulverised coal and ash is investigated experimentally and theoretically, for different ranges of particle size. An empirical expression is developed for obtaining the absorptivity and emissivity of a coal/ash cloud. A new nomogram is also presented on the basis of this expression.ZusammenfassungEs wird die Abschwächung thermischer Strahlung in einer verdünnten Wolke aus pulverisierter Kohle und Asche experimentell und theoretisch für verschiedene Bereiche der Partikelgröße untersucht. Zur Bestimmung des Absorptions- und Emissionsvermögens einer Kohle/Asche-Wolke wird ein empirisch gefundener Ausdruck entwickelt, der außerdem Grundlage eines neuen Nomogramms ist.

Liquid Crystals, PIV and IR-Photography in Selected Technical and Biomedical Applications

Thermochromic liquid crystals (TLC), Particle Image Velocimetry (PIV), Infrared Imaging Themography (IR) and True-Colour Digital Image Processing (TDIP) have been successfully used in non-intrusive technical, industrial and biomedical studies and applications. These four tools (based on the desktop computers) have come together during the past two decades to produce a powerful advanced experimental technique as a judgment of quality of information that cannot be obtained from any other imaging procedure. The brief summary of the history of this technique is reviewed, principal methods and tools are described and some examples are presented. With this objective, a new experimental technique have been developed and applied to the study of heat and mass transfer and for biomedical diagnosis. Automated evaluation allows determining the heat and flow visualisation and locate the area of suspicious tissue of human body.

Heat transfer augmentation using liquid crystal

A visualization technique is used to measure the heat transfer to a plane surface with obstacles. Liquid crystal coated on a mylar sheet is used to locate isotherms on a cooled plate. The isotherms on the plate surface are recorded by JVC-camera and true-color image processing system. Experimental procedure cover full-field flow patterns in heat exchanger element (flat plate with discs in-line, staggered and with vortex generators) describing local heat transfer coefficient and Nusselt number on the surface.