Improvement of condenser performance at cooling systems

In this doctorate thesis, heat transfer from horizontal tubes in free convection has been investigated experimentally and numerically. Simultaneous heat and mass transfer in free convection from the same tube has been investigated experimentally. Thesis consists of eight chapters. In the first chapter, the aim of the study and the results to be reached have been explained generally. In the second chapter, studies that are related to our subject in the literature have been reviewed. In the third chapter, fundamental concepts which are in scope of this thesis and the calculation method have been explained. According to airwater vapor mixture is an ideal gas mixture and potential, which forms flow around a tube, arises from density difference depending on temperature and concentration, a calculation table have been formed. In the fourth chapter, a numerical study of heat transfer in free convection has been carried out. Heat transfer rate, Nu number and convective heat transfer coefficient values obtained numerically have been compared to experimental results and average deviation has been calculated. Using numerical Nu values the results correlated in the form of Nu=c.Ran and compared to available literature results. The results are in good agreement with the literature. CFD Software Fluent 6.0 was used for numerical studies. In addition, in this chapter a study related to critical coating thickness in free convection has been done and it is concluded that critical diameter should be determined considering variation of convective heat transfer coefficient. In the fifth chapter, experiments have been performed in a conditioned room in Arçelik A.S. (Arastırma ve Gelistirme Merkezi). Experiments consist of three main parts. In the first part; in free convection and constant ambient temperature, electrical energy that has been given to horizontal tubes having two different diameters, which are smaller than the critical diameter, has been measured and heat transfer coefficients have been calculated. Experiments have been repeated for the different ambient temperature values by changing surface temperature values. In the second part, tube was coated with the diameter below critical diameter. Experiments have been repeated with the boundary conditions of the tube without coating and heat transfer coefficients have been calculated. In the third part, by wetting the coating material on the tube surface, simultaneous heat and mass transfer arising from evaporation has been provided. In order to determine the heat and mass transfer, amount of electrical energy and water evaporating from the surface have been measured and heat and mass transfer coefficients have been determined. Besides, in order to analyze the effect of concentration difference on convection, the experiments have been done for three different ambient relative humidity values. Defining a unique Grashof number depending on total density difference, Ra, Raı values have been calculated with respect to Gr. In addition, using measured values of electrical energy and mass of evaporated water, Nu, Sh numbers have been determined experimentally. In the sixth chapter, for three conditions of the horizontal tube at similar boundary conditions measured heat transfer rates have been compared and the increase has been indicated in graphics. Using the results obtained in the first and second parts at the experiments, Nu and Ra number values have been calculated. Results have been successfully correlated by the equation NuD=0,898.Ra0,201(7,462.101