Nevzat Onur

An experimental study on the effect of opposing wall on natural convection along an inclined hot plate facing downward

Abstract The results of an experimental study on natural convection between inclined plates are presented in this paper. Hot plate is facing downwards and heated isothermally. The lower plate is insulated and unheated. The plate inclinations were chosen to be 0°, 30°, 45° and measured with respect to vertical position. Experiments were performed for various temperature differences in air to determine the effect of plate spacing and inclination on natural convection heat transfer. It was observed that plate spacing and inclination influence the heat transfer rate.

An experimental study on air window collector having a vertical blind for active solar heating

Abstract In this study, an air window collector having vertical black blinds was investigated experimentally under actual outdoor conditions. The vertical blind was installed between two 120 × 80 cm glass panes. It can rotate about the vertical axis. The fully open position makes a 90° angle with the vertical plane. A commercially available blind made of cloth and coated with black paint was tested. The air circulation in the system is provided by a fan parallel to blinds. Various parameters were measured and recorded using a data acquisition system. The effect of these parameters on the thermal performance of the system were determined experimentally.

Forced convection heat transfer from a flat-plate model collector on roof of a model house

Presented in this abstract are the considerations and results of an investigation of forced convective heat loss from the surface of flat-plate model collectors flush mounted on the roof of a model residential house. Forced convection with air as the external fluid was treated.The study was motivated by the need to better understand heat transfer from the top surface of flat-plate solar energy collectors. The experimental work dealt with heat transfer from the top of rectangular parallelpipeds flush mounted on roof of a model residential house. The smallest collector was 7.62×10−2 m long by 7.62×10−2 m wide by 3.3×10−2 m deep, and the largest collector was 15.875×10−2 m long by 15.875×10−2 m wide by 3.3×10−2 m deep. These small scale units are expected to simulate heat loss pattern from a flat-plate solar collector placed over the roof of a residential dwelling. Experiments were performed to determine the average heat transfer coefficients for forced convective air flow over the surface of the model collector which was inclined and yawed relative to the incoming air flow. The wind speeds varied approximately from 2.5 m/sec to 15 m/sec, the flow was laminar for all wind speeds.ZusammenfassungEs werden Vorüberlegungen und Ergebnisse bezüglich einer Untersuchung mitgeteilt, deren Ziel es war, die Wärmeverluste infolge Zwangskonvektion von Flachplatten-Kollektoren auf den Dächern von Wohnhäusern im Kleinmodell zu bestimmen. Angeregt wurde die Studie durch den Bedarf an genaueren Berechnungsunterlagen für den Wärmeübergang an Flachplatten-Solarkollektoren. Die für das Experiment verwendeten zwei Kollektoren waren quadratisch, mit den Seitenlägen 7,62 bzw. 15,9 cm, bei jeweils 3,3 cm Tiefe. Die Versuche lieferten unter Zwangskonvektion mittlere Wärmeübergangskoeffizienten an den Oberflächen der Modellkollektoren, welche zur ankommenden Luftströmung sowohl geneigt als auch gedreht orientiert waren. Bei laminarer Strömung lagen die Anströmgeschwindigkeiten zwischen 2,5 and 15 m/s.

Transient heat conduction with uniform heat generation in a slab subjected to convection and radiation cooling

A finite difference scheme with fourth order Runge-Kutta method is employed to determine the unsteady state temperature distribution in a plane slab with uniform heat generation. The plane slab is insulated on one face and subjected to convective and radiative cooling at the other face. The plane slab has a uniform initial temperature and the ambient environment as well as the fluid temperatures are assumed to be constant. Heat conduction is considered to be one dimensional. Results are presented in dimensionless charts over a wide range of parameters.ZusammenfassungZur Ermittlung der instationären Temperaturverteilung in einer Platte mit gleichförmiger Wärmeerzeugung wird ein Differenzverfahren vierter Ordnung nach Runge-Kutta angewendet. Die ebene Platte ist einseitig isoliert und wird auf der anderen Seite durch Konvektion und Abstrahlung gekühlt. Zu Beginn befindet sich die Platte gleichförmig auf einer bestimmten Anfangstemperatur, die Temperaturen der umgebenden Objekte sowie des Fluids sind ebenfalls konstant. Der Wärmeleitungsvorgang sei eindimensional. Die Ergebnisse sind in dimensionsloser Form für einen weiten Parameterbereich in Diagrammform dargestellt.