A refrigerator adaptable ice machine design that can make clear ice using fractional freezing method

A considerable number of consumers basically demand that the ice used to cool beverages should look more clear compared to standard ones since ice formations with more clear structure are perceived to be more quality. In addition, ice made by using clear ice making process will be tasteless and odor-free. Furthermore, they melt later compared to standard ice forms since clear ice is purified. Therefore, using clear ice to cool any beverages will not only keep their taste and smell as they are and but also cool them for longer time since they melt later. Commercial ice machines that can make clear ice at various capacity levels are available in markets. Although such machines can meet consumers' demands to a certain extent, considerable space they take up and extra expenses they cause are the disadvantages of such machines. If the functional features of these commercial machines such as quick and clear ice making can be adapted to standard refrigerators, it can be a compact solution to meet consumers' demands for a multi-purpose machine functioning both as a refrigerator and ice machine. The aim of this study is to carry out a preliminary study to design a refrigerator adaptable ice machine that can make clear ice using fractional freezing method and to contribute to the attempts to develop a new compact product to meet consumer demands accordingly. Within the scope of this dissertation, only the design of a machine that can make ice using fractional freezing method as physical principle is dealt with. In order to obtain a background for the study, the related literature was reviewed, and patent research and a series of further research on similar products in the market were carried out. The examination of the studies in the related literature mostly revealed that the reason lying behind the deterioration of ice clarity is the air bubbles that are formed between ice-water interface and that cannot diffuse to atmosphere and; therefore, are trapped in ice formation. It is also suggested that the reason of such air bubbles formation is the changes in the solubility of air in water depending on temperature and pressure differences. Some researchers examined the air bubbles that are formed in materials when metals melt and later solidify during certain manufacturing processes such as casting and welding. In order to simplify the examination process, researchers establish an analogical connection between two processes: melting and solidifying of metals; and ice formation from water. Similarly, patent research following the review of available research in the literature revealed a number of patented designs that are used to make various clear ice forms by using one or more different methods. These designs were adapted into refrigerators or ice machines. However, the methods used to make clear ice other than fractional freezing method were not examined in detail since they are not within the scope of this study. Only the details about the patents using fractional freezing method were provided in the study. According to information obtained from the examination of similar products available in the market, it was observed that the clear ice making cycle is completed in a shorter time when fractional freezing method is used. Whereas, the method using the lowering of freezing rates resulted in much longer clear ice making cycle, which was often mentioned in the related literature. There are two different perspectives to evaluate the limitations to be considered while designing a refrigerator-adaptable ice machine that makes clear ice by using fractional freezing method. The limitations in the first group consist of technical details necessary to apply fractional freezing method to have clear ice formations. The basic principle of fractional freezing method is to remove the air, whose solubility decreases while freezing and concentration on water-ice interface increases, by using flowing water. When this technique is applied, ice forms are clear since no air bubbles are formed in ice. In order to have clear ice forms by using fractional freezing method, it is necessary to have a cold surface on which water will flow. When considered from this perspective, it is possible to divide the system into two subsystems: a cooling cycle to obtain a cold surface; and a water feeding system to circulate the water that flows over the cold surface. In order to obtain more detailed information about similar technical systems, a series of measurements were made on commercial spray type and waterfall type ice machines whose design features were examined during market search phase of the current study. One of these measurements was to determine surface temperature in ice trays used to make ice forms. Heat sensors were used to measure these surface temperatures. The values obtained from these measurements were displayed as graphics to examine temperature changes on ice tray surfaces throughout ice making process. Later, a series of measurements were carried out on the pumps used in commercial ice machines. Various catalogues and manuals provide information about both pumps. In order to verify the accuracy of this information, pressure decreases were measured for different flow rate values and pump characteristics curve was obtained accordingly. After these measurements, another group of measurements were made by operating the pump together with the electronic system of ice machine in order to calculate the flow rate of water pumped on technical system and pressure decrease corresponding with the flow rate value. After that, the system used to remove ice cubes from the trays was examined. It was found that hot gas defrost cycle was applied to remove ice forms from the trays. Finally, clarity of ice made in spray and waterfall type ice machines were measured in order to be able to examine clarity of ice more scientifically. For the purposes of these measurements, a device was used that basically determines the changes in light transmittance. The values obtained from these measurements brought a quantitative dimension to clarity concept. Moreover, it was possible to establish criteria to compare clarity values to be obtained in future ice machines designs in a more scientific way. The second group of limitations to be considered while designing a machine to make clear ice forms by using fractional freezing method is about design limitations of refrigerator to which this ice making system will be adapted. The type of refrigerator to be used was determined after the feasibility studies carried out. Later, design limitations to be considered during the adaptation of the design to refrigerator were examined in detail. When all the limitations of the technical system were determined, the expectations from the design were listed with references to such limitations. Alternative designs were prepared based on these expectations. The cost-value analyses of alternative spray and waterfall type ice machines designed to make ice forms using fractional freezing method were compared, which revealed that waterfall type ice machine should be the design alternative to be focused in the current study. The design details of alternative waterfall type ice machine were modelled in computer environment in 3-D form. The structural changes with regards to the adaptation of the system to refrigerator were applied to these 3-D models. In addition, the necessary details regarding the adaptation of the ice machine onto refrigerator were worked on. After the alternative design details were applied on computer environment, a prototype and trial version of the design was prepared to test whether it fulfills the desired functions. The tests showed that the ice cubes on the first row were more clear than those on the other rows. It has been agreed that this situation results from the fact that neither flow characteristics nor the distribution of temperature on the surface had the desired form and value. Later, the clarity of the ice cubes on the first row, which were made by using the prototype of the design, was measured. The clarity values obtained from this measurement were very close to those of commercial ice machines available in the market. Therefore; it can be concluded that this preliminary design is successful in this sense. Another situation observed during these tests is the formation of thick ice bridges among the cells since water flow in the system fail to fill up the center points of the cells completely; and therefore, ice cubes are formed at the sides of the cells as a result of continuing ice formation. It is thought that the structural details of ice tray cause this situation. Another situation faced during the process is undesired water splashes while it flows over ice tray. Although water flow over ice tray has a smooth form, some of the water flowing from one ice cell to the other splashes to unwanted areas since it hits ice tray surface. It is clear that water splashes are an undesired consequence. It is possible to eliminate this negative situation by changing the inclination angle of fins or adding shields to the design. Thanks to this experimental prototype study, it was possible to determine some potential problems in the design and to test the durations planned to complete ice making cycle. In accordance with literature review and market research, it has been concluded that the use of refrigerator adaptable fractional freezing physical principle is a convenient alternative in terms of both the duration of ice making process and the practicality of the method. Thanks to the experimental application on a prototype, it was possible to make ice cubes with a quality level close to the desired one. However; it is necessary to examine water flow characteristics numerically and optimize cold surface temperatures so as to increase clarity values at a more homogenous structure.