Katılaşma süreci olan poliüretan köpük akışına güre yeni bir buzdolabı kabini tasarımı

There are many advantages of using polyurethane materials, including low cost, light weight, enhanced thermal and electrical insulation, and high impact strength and, therefore, it has many applications, as for example, producing various kinds of complex parts including automobile interior furnitures, household appliances and housing industry. Use of polyurethane foam is also spreading rapidly in refrigerators as insulation material. Reaction injection molding of polyurethane foam is a process in that two or more chemical components mix, chemically react and finally form a foam which flows into the mold cavity where the polymerization is initiated. Energy efficiency of modern refrigerators demands a very effective insulation and, hence, the foam is required to fill complex cavities in very short time scales. In order to increase cavity filling efficiency while shorten the injection molding process, it is necessary to understand the phenomena of mixing, reaction kinetics, bubble nucleation and growth and two-phase flow behaviour during mold filling. Lack of control on reactive injection molding parameters results in variations from load to load and even from part to part, leading to serious quality degradation and, thus, the whole process becomes labor-intesive at elevated material costs.International competition between companies is rapidly growing. Hence companies race in the energy efficiency field and invest large amount of money on R&D activities for having more efficient products. For refrigerators; energy efficiency is highly relative to its insulation performance. Rigid polyurethane foam is used as insulation material between the refrigerators cabinet walls. Good insulation performance depends on the homogeneity of foam in the cabinet. Another function of the foam is the mechanical support to thin cabinet walls. Short injection time and minimized chemical costs are desired in mass production. To provide these requirements air outlets orientation, numbers, diameters and progress of chemical reactions, the temperature of the injected mixture and cabinet temperature are important parameters. If we want to find these optimum parameters we have to understand the nature of the polyurethane injection process. Thus polyurethane injection process become more controllable and we can predict process parameters for new designs before the manufacturing. In the light of these informations the aims of the thesis obtained as; •Decreasing the usage of the foaming materials for single cabinet volume •Decreasing the costs due to change of the initial conditions of the process, •Decreasing the foam filling time of the cabinet, •Increasing the insulation and structural strength performance of the foam with minimizing the air traps in it, •Optimization positions, sizes and the numbers of air outlets to make the polyurethane injection procces more efficient, •Understanding the nature of polyurethane flow and getting a solid scientific knowledge about it. From this point of view a project started by ARCELIK Inc. and ITU Fluids Group with the support of the Ministry of Science Industry and Technology Commissary. A refrigerator with two doors chosen for the computational fluid dynamics (CFD) simulations. Flow of the rigid polyurethane foam in the cabinet is three dimensional, reactive, multiphase and time dependent. Also solidification occurs due to chemical reactions. Chemical reactions effect the flow very strongly. Except the CFD simulations, a chemical kinetics study has been done without flow to obtain optimum initial reaction conditions locally such as initial mass fractions of the species and initial temperature. ANSYS Meshing and ICEM CFD were used for mesh generation. CATIA and SOLIDWORKS were used for CAD and geometry refinements. On the other hand a FORTRAN code were used for modeling the chemical kinetics. Chemistry code was developed in the ITU Fluids Group. CFD simulations were done with the FLUENT software. Chemistry code was implemented in FLUENT by using the user defined functions (UDF) and they run simultaneously. Post processing had been done with the TECPLOT and MATLAB. Furthermore, EXCEL and some FORTRAN codes which were written during the project, are used for converting the physical, chemical and thermodynamic data for calculations. The validation of the chemical kinetics with real process is done by comparison between an experimental data. Gelling and blowing reaction rates are adjusted with the calibration of the Arrhenius parameters. Thus a similar behavior obtained with real reactions.