| Compared with the direct cooling refrigerator, the frost free refrigerator reduces the complexity of the cooling system. However, due to the configuration of the air duct system, the energy consumption and noise level may be increased. The performance of air duct system determines the air supply efficiency, while the working fan increases the energy consumption and noise of refrigerator. Compared with the common conditions, axial fans in frost free refrigerator usually work in off-design conditions, and the performance of the fans will be decreased. Due to the relative short history of the frost free refrigerator, air duct performance have not been systematically studied. Therefore, research on air duct characteristics and noise reduction technology is significant.Based on the current research, including refrigerator performance, air duct design, aerodynamic and acoustic performance of fan, the dissertation mainly studied on the components design for air duct system and overall performance of the frost free refrigerator. The main contents and conclusions including:(1) The aerodynamic performance of air duct components and thermal uniformity of the chambers have been studied. For the storage chamber, a design method based on flow characteristics has been proposed and divergent cross-section structure air duct has been designed, which makes the flow field smoother; combined with the structure and thermal load distribution characteristics of the storage chamber, the volume flow rates for each part of space in the chamber have been matched, and the maximum temperature difference in the chamber is lower than 2.5 ℃ according to the design of enclosed air circulation.(2) The effect of different types of deflecting rings on the aerodynamic performance of condenser fan has been studied. The tip vortex is generated due to the pressure difference between the pressure and suction sides. With semi-open type deflecting ring, the vortex is formed in the blade tip region near deflecting ring; it is formulated in the whole blade tip region when closed type deflecting ring is used, and the turbulence intensity along the opposite rotating direction is enhanced or weakened with the pressure increased or decreased, and vortex is gradually moving from pressure side to suction side. The condenser fan can generate higher performance with semi open type deflecting ring.(3) The effect of different deflecting rings on the noise characteristics of the condenser fan has been investigated. The deflecting rings mainly affect the pressure fluctuation near blade tip and pressure side of condenser fan. With closed type deflecting ring, pressure fluctuation near the blade tip and pressure side is much stronger, and it has broadband characteristics. With semi open type deflecting ring, the noise is mainly composed of blade tip noise and discrete noise at the pressure side. Noise level generated by the pressure surface of the condenser fan is decreased according to the influence reduction of the semi open type deflecting ring, and the total sound pressure level (SPL) is decreased by3.4dB(A).(3) The flow field generated by freezer fan in condition of large pressure difference between blade pressure and suction sides has been studied. Under the large pressure difference conditions, the airflow at the outlet of axial fan moves along the radial direction, and axial flow is hindered due to the large pressure difference, the force on the air and the viscosity provides the circumferential velocity, while centrifugal force cause the air move towards the radial direction. When the pressure difference is reduced, the exit flow will move along the axial direction instead of radial direction, and large vortex appeared between the main flow and reverse flow, which dissipates rapidly with the air moved to the downstream.(4) Noise level at most frequency bands decreases to some extent when semi-open deflecting ring is used for condenser fan in frost free refrigerator, and noise level at medium and high frequency bands are obviously decreased. For the semi open type deflecting ring, the minimum noise level appears when the length is shortened, and the noise level reduced fluctuately while the length of closed type deflecting ring is shortened. The noise level of the refrigerator will be increased when increasing the length of deflecting ring for freezer fan, and this is due to the increasing pressure difference between inlet and outlet of the fan. The SPL and energy consumption of the frost free refrigerator have been reduced by 3dB(A) and 5% through matching the deflecting ring length and fan rotating speed. |
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