Experimental and numerical investigation of temperature distribution on ice maker system inlet section of built-in freezer

In the white goods industry, the refrigerator quality and efficiency expectations increase day by day. There are many research and development studies to answer these expectations about quality and efficiency improvements for the refrigerators. In this study, the heat transfer in the water inlet plastic section of the back wall of a built-in single door freezer was investigated by numerical analysis by using the ANSYS Fluent program, which is used for the analysis of computational fluid dynamics, in order to increase the product quality and to prevent the condensation which may occur in the freezer outer body. Verification of the numerical model was made by comparing the numerical temperature values at the points representing the standard thermocouples in the model with the experimental average temperature values. As a thermocouple temperature value, the average temperature values during the periodic operation of the freezer were taken. Therefore, while the numerical model is being developed, it was accepted as steady state, that is the temperature on the surfaces, does not change depending on the time. In the experiments which were performed to confirm the model, a test, which is similar to the water vapor condensation test in IEC 62552-2:2015 'Household Refrigerating Appliances - Characteristics and Test Methods' standard was performed. However, unlike the standard test, the test was applied to simulate heavier conditions. The test was performed by testing the freezer at a temperature of 25 ˚C with 80% relative humidity. The cabinet temperature in the freezer is set at -18 ° C. Numerical analysis has been carried out for three different situations. In the first case, the initial design for the water inlet area was evaluated and the temperature distributions on the aluminium tape, which is adhered to the back cover on the back wall of the freezer, were examined. The temperature of the center of the aluminium tape (x=75.1mm), where the thermocouples were placed in the experiments, was determined as 19.22°С. The minimum temperature value on the aluminum tape was found at 19.15 ° С at x = 135mm. Also, the minimum temperature at the freezer back sheet was 19.12 ° С at x = 172mm. All these values are lower than 21.31°C, which is the dew point temperature for 25°C and 80% relative humidity test conditions. According to numerical analysis result, it was determined that there would be condensation in this region. After numerical analysis, an experimental study was conducted for the first case. The minimum temperature value, found at the end of the test, was 19.1°C. In order to visualize this temperature distribution, the thermal photo was taken from the relevant area. As a result of this experiment, condensation was observed in relevant region because the temperature values on the aluminium tape and back sheet were lower than the critical dew point temperature. During the experiment, the temperature values, which were obtained from the thermocouples where were placed in specific regions, were compared with numerical analysis results. The numerical model was verified according to the results of comparison. In the first case results, the temperature values on the aluminium tape was lower than expected. Therefore, the solution proposals have been researched in order to increase the temperature values. In the second case, first solution proposal was investigated. In order to increase the temperature values on the aluminium tape and back sheet, unlike the first case, vacuum insulation panel (VIP), which has a lower thermal conductivity coefficient than polyurethane, was added on the air channel in the freezer body. Numerical analysis was performed for the second case. The temperature distribution on the back sheet and the aluminium tape, which is adhered to the back cover, was also examined for the second case. With the addition of the VIP, the expected temperature increment was occurred in the temperature distribution but could not be increased above the dew point temperature of 21.31°C. Unlike the temperature distribution in the first case, the VIP added model showed that temperature increase in the x direction. The temperature has increased towards the air channel. However, according to numerical analysis results, in the most critical region of the water inlet area, the minimum temperature was found 20.36°С at x=65mm. This value is lower than 21.31°C, which is the dew point temperature for 25°C and 80% relative humidity test conditions. According to the numerical analysis result, it was determined that there would be condensation in this region. The cost of the appliance was increased by the addition of the VIP but the desired temperature values could not be obtained according to numerical analysis results. For this reason, no experimental study has been done for the VIP added model. Finally, in the third case, the feature of the condenser, known as 'concealed', 'hot wall', 'flat-back' or 'skin kondenser' in the literature, has been utilized. This condenser has a feature which increases the wall temperatures. In order to increase the wall temperature by this way, the heating tube was added to the back sheet to remain in the polyurethane. The heating tube was fixed by using aluminium tape, which conducts the heat of the hot fluid passing through the tube more effectively to the back sheet. Numerical analysis has been done for the third case. As a result of the numerical analysis, the minimum temperature value at the center of the aluminium tape, which is adhered to the back cover, was found as 24.8°C at x=75.1mm. This value is sufficiently higher than the dew point temperature for 25°C and 80% relative humidity test conditions. In order to verify the temperature values which was found in the numerical analysis, the experiment was performed. During the experiment, temperature measurements were made in the water inlet area, where condensation is expected, by using thermocouples. In the experiment, the temperature in the center of the aluminium tape, which is adhered to the back cover, was found as 24.6°С at 75.1mm. In order to visualize this temperature distribution, the thermal photo was taken from the relevant area. At the end of the experiment, the temperature values, which was found on the aluminium tape and the back sheet, were compared with the numerical results. Numerical temperature values were confirmed by the experimental results. Since the minimum temperature values, which were found in the experimental and numerical analysis results, are higher than the dew point temperature value at 25°C and 80% relative humidity conditions, condensation is completely prevented in the relevant region. As a result, single door freezer back wall minimum temperature value is increased to the desired level by adding the heating tube which is passing through the back sheet similar to the hot wall condenser, the numerical results were supported by the experimental results.