Investigation of time dependent multi-surface heat transfer in a close cavity

This study represents a transient natural convection heat transfer inside a closed cavity formed at refrigerator fresh food volume by varying surface temperatures. For this aim, a controllable and reliable experimental setup including both cold air flow and water circulation for multi-surface temperature regulation was established. Parametric studies had been conducted reflecting cold air flow rate and water bath set temperature for the cold and hot surfaces respectively. Natural convection dynamics occurring due to finite temperature differences between the closed cavity surfaces were investigated in more detail regarding the temperature and velocity distributions inside the cavity. This thesis is composed of six main chapters. In chapter one, scope, motivation and aim of this study have been explained in more detail including the literature and patent research about master thesis subject. In chapter two; components and structure of the controllable and reliable experimental setup are explained, followed by the detailed information on experimental methodology. In chapter three; detailed comparison of parametric tests in terms of dimensionless expression of cooling time and temperature distribution have been provided along with the transient cooling performance capacities of the parametric conditions. In chapter four; detailed heat transfer investigation has been conducted by applying first law of thermodynamics aiming to analyze natural convection dynamics such as convection heat transfer coefficient, Nusselt and Rayleigh numbers for the parametric experiments and the transient Nu-Ra relationships are provided compared with the current literature. In chapter five; the transient temperature distribution conditons inside the closed cavity which are obtained from the experimental data are processed and visualized with SigmaPlot program. Transient natural convection analysis is performed with the experimental boundary conditions by ANSYS FLUENT® analysis software. Obtained results from the CFD analysis are also presented in comparison with experimental results along with the CFD flow characteristics determined by the visual aspects of intracavity. In the final chapter, results of this study have been evaluated and suggestions have been proposed. In conclusion, high-flow rate of cold air and the adjacent surface temperature close to the target temperature decreases the cooling time of the cavity. Increasing adjacent surface temperature of the cavity causes a decrease in net heat transfer (qnet) from the close cavity. In parallel to the increasing average heat transfer coefficient, Nu number and corresponding natural convection heat transfer increases. The temperature distribution in the cavity is determined by the CFD analysis, which is also confirmed by the experimental results. A counter-clockwise flow loop within the chamber is determined by CFD analysis which is coherent with literature results.