| The combination of the fan and heat exchanger is widely used in the heat exchange structure of modern mechanical and electrical products, and is integrated in the commonly used rectangular flow channel. In order to reduce energy consumption, axial fan is often arranged as the driving component of airflow in the flow channel. But the dual resistance of rectangular flow channel and heat exchanger produced great impact on the operating conditions of axial fan, to make it work under off-design condition, leading to the flow characteristics of fan and the heat transfer characteristics of heat exchanger affected by different degrees. In order to reasonably match the fan flow field and heat transfer characteristics of heat exchanger, and ensure high efficiently heat-transfer, in this paper, the rectangular channel which is set with evaporator and axial fan and used in air cooled refrigerator was taken as research object, the fan flow field characteristics under off-design conditions caused by different channel resistances, and the heat transfer characteristics of heat exchanger in the corresponding flow field were studied.First, the performance of axial fan was tested, which provided the basis for determining the actual operating condition of fan under different resistances. Then the flow field of fan at downstream under different flow resistances was studied using Particle Image Velocimetry technique (PIV), it is qualitatively concluded that the outlet flow field of fan presents radial motion characteristics under the larger flow resistance, and is changed from radial to axial direction with the decrease of flow resistance. On the basis of experimental study, numerical simulation was carried out by fluent software to quantitatively describe the flow resistance characteristics, the inner and outlet flow field of fan, and determine the actual operating condition of fan. The tip clearance flow field of fan under different operating conditions was studied, the results show that the operating conditions have great influence on the generation, the circumferential and axial distribution, and the strength of tip clearance vortex. At last, through analysis on the surface and internal pressure, and based on the radial equilibrium equation, the radial motion mechanism of fan flow field under large flow resistance was explained. It is concluded that the large pressure difference between inlet and outlet of fan, and the destruction of radial equilibrium are the main reasons for the radial flow.The low speed air flow and refrigeration experiment table was built, the overall heat transfer of evaporator and the distribution based on the different fan flow characteristics was studied by experiment. On the basis of experimental study, numerical simulation was carried out for studying the single fin channel, quantitative parameters such as heat flux, heat transfer coefficient and Nusselt number were used to determine the local heat transfer performance of evaporator under different flow states. Finally, the cooperative relationship between flow field and temperature field in heat exchange channel under different operating conditions was considered from the field synergy viewpoint, the results show that the cooperativeness is improved when the centrifugal flow field is changed to axial direction, but has no obvious change. |
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