Study On Inlet Flow Distribution Characteristics And Structure Optimization Of Evaporator

Dry shell and tube evaporator is an important basic equipment in the refrigeration field.More than 80% of central air conditioning uses dry shell and tube evaporator.The evaporator performance plays a critical role in energy saving and consumption reduction of air conditioning.The uneven distribution of refrigerant is the most important element affecting the evaporator performance.The uneven distribution will cause the evaporator can not take full advantage of the the heat exchange area,which seriously affects its heat transfer performance.To address this issue of uneven refrigerant distribution,three kinds of improved evaporator structures were conceived based on the traditional evaporator flow distribution research,and their liquid separation performance was researched by numerical simulation and experimental validation.The research contents and conclusions of this thesis are as follows:(1)Numerical simulation was applied on the single-phase and two-phase refrigerant distribution in the traditional structure evaporator,and the causes of uneven liquid separation were analyzed.At the same time,the evaporator flow field,pressure and liquid volume fraction were analyzed.When the refrigerant is in single-phase state,the change of inlet mass flow rate has very small effect on the overall refrigerant distribution uniformity of the evaporator.When the refrigerant is two-phase state,the increase of inlet dryness will lead to the increase of the overall distribution uniformity of the gas phase,and the decrease of the liquid phase uniformity.In the wake of inlet mass flow increase,the overall distribution uniformity of gas phase and liquid phase is improved.The evaporator pressure drop increases along with dryness and mass flow increase.The eddy current in the tube box and the heat exchange tube is an key factor for the uneven flow distribution.(2)Under the conditions of different inlet mass flow and dryness,the distribution uniformity of two-phase refrigerant in the evaporator under the structure of flat-shaped shunt plate,bow-shaped shunt plate and distributor was studied,and compared with the traditional structure.At the same time,the flow field of the evaporator with different structures is analyzed.Among them,the two-phase refrigerant distribution in the distributor structure is the most uniform.Compared with the traditional structure,the overall distribution uniformity in the evaporator with the distributor structure is increased by 87.35% and 97.70%,respectively.(3)The structural optimization of the distributor is researched.The optimization parameters are the outlet diameter D of the distribution pipe,the inclination Angle θ of the distribution pipe,and the distance between the reflector head and the inlet end L.A total of fourteen designs were calculated and compared with the distributor samples,the eleventh scheme is the best.(4)Laser Doppler velocimeter is used to measure the velocity of the main stream at a specific position in the evaporator of the arch split plate structure,and the error is less than 18% compared with the simulation value,which certificates the dependability of the simulation.