| As a condenser,micro-channel heat exchanger has been widely used.It has the advantages of low cost,high efficiency and energy saving,corrosion resistance and high pressure resistance.However,the technology used as evaporator is still immature.In view of the interaction of vapor-liquid two-phase flow in micro-channel evaporator and its influence on heat transfer efficiency,in this paper,the flow and heat transfer characteristics of microchannel evaporator are experimentally and simulated by setting up an experimental bench for heat transfer enhancement and simulation.This paper draws the following conclusions through experimental research:（1）When the volume flow rate is less than 0.3m/s,the temperature of bottom flat tube is lower than middle flat tube and lower than top flat tube,the temperature distribution in the low temperature zone of the flat tube presents a“right triangle”shape distribution;when the volume flow rate is more than 0.4m/s but less than 0.5m/s,the temperature of every flat tubes at the same position is close to each other,temperature of middle flat tube is slightly lower,the temperature distribution in the low temperature zone of the flat tube presents an“isosceles triangle”shape distribution.At the same time,with the increase of refrigerant volume flow rate,the heat transfer capacity of the system increases,and the refrigerant side heat transfer coefficient of micro-channel evaporator increases.（2）With the increase of wind speed,the low temperature distribution area of the flat tube of micro-channel evaporator decreases.And the shape of the low temperature distribution area also changes.When the wind speed is less than 1.5m/s,the temperature rise of each flat tube is very small,only about 2℃,the low temperature distribution area presents the shape of an“isosceles trapezoid”;when the wind speed is more than 2.0m/s,the temperature rise of each flat tube is larger,and the temperature rise is about 10℃,the low temperature distribution area presents the shape of an“isosceles triangle”.At the same time,with the increase of wind speed,the heat transfer coefficient of refrigerant side increases,and the total heat transfer capacity increases.But in this experiment,the cooling capacity of water chiller is limited.When the wind speed is greater than 2.0m/s,the heat transfer capacity and heat transfer coefficient of the system will not change.（3）The pressure at the inlet and outlet of microchannel evaporator fluctuates with time.When the flow rate increases from 0.3m/s to 0.5m/s,the fluctuation frequency increases from 2×10-3/s to 2.86×10-3/s.With the increase of refrigerant flow rate,the pressure drop at the inlet and outlet of microchannel evaporator increases by 66.7%.When the wind speed increases from 2.0m/s to 2.5m/s,the pressure fluctuation frequency at the inlet and outlet of microchannel evaporator decreases from 2.86×10-3/s to 1.67×10-3/s.With the increase of wind speed,the pressure drop at the inlet and outlet of microchannel evaporator increases by about 185.7%.（4）The effects of refrigerant flow rate and air cross-wind speed on the uniformity of refrigerant distribution in the first process of microchannel evaporator are analyzed.With the increase of refrigerant flow rate,the distribution of refrigerant tends to be more uniform,and the non-uniformity decreases from 0.33 to 0.22,with a decrease of about 33%.The non-uniformity of refrigerant flow distribution is much better than that of refrigerant flow rate,When the wind speed increases from 1.5m/s to 2.0m/s,the non-uniformity increases sharply,with an increase of about 83%.When the wind speed increases from 2.0m/s to3.0m/s,the increase of non-uniformity of refrigerant distribution decreases to 27%.This paper establishes a two-dimensional model of the first process of micro-channel evaporator,and uses ANSYS 16.0 simulation software to simulate the flow and heat transfer of R134a refrigerant in the microchannel evaporator with louvered fins under different refrigerant flow velocities.The conclusions are as follows:（1）When the refrigerant inlet velocity is 0.2m/s0.4m/s,the top flat tube has the largest flow velocity and the bottom flat tube has the second;when the refrigerant inlet velocity is 0.5m/s1.0m/s,the lower flat tube has the largest flow velocity,and the middle flat tube has the largest flow velocity.The refrigerant flow velocity in the flat tube upward from the middle flat tube decreases,but the flow velocity in the top flat tube increases slightly.（2）With the increase of refrigerant inlet flow rate,the pressure drop in the first process of microchannel evaporator increases from 0.2m/s to 1.0m/s,and the pressure drop increases by 1372Pa.（3）The inlet velocity of refrigerant has a great influence on the uneven distribution of refrigerant in microchannel evaporator.With the increase of refrigerant inlet velocity,the non-uniformity of refrigerant distribution in microchannel evaporator decreases.When the flow rate is greater than 0.8m/s,the refrigerant distribution in the first process of microchannel evaporator tends to be more uniform.When the inlet velocity of refrigerant is 0.5m/s,the temperature is 5℃the dryness is0,the inlet temperature of air in the duct is 3℃and the wind speed is 2.0m/s,the simulated value of refrigerant temperature in each flat tube is consistent with the experimental value of flat tube surface temperature,and the error is less than 4.5℃.Comparing the non-uniformity of refrigerant distribution in the first process of microchannel evaporator under different refrigerant inlet velocities,the trend of simulation value and experiment value is basically consistent,and the experimental value is slightly lower than the simulation value.The comparative analysis basically shows that the simulation calculation is reasonable.In this paper,the heat transfer enhancement performance of micro-channel evaporator has been simulated and experimentally studied,which has certain scientific research significance,hoping to provide reference for the related research and application of micro-channel evaporator. |
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