Research On Improvement Of Refrigerant Distribution Performance Of Dry Evaporator

With the implementation of national energy saving and emission reduction policies,further reduction of energy consumption of refrigeration systems is an inevitable requirement.Increasing the efficiency of the main equipment of refrigerating system is one of the important measures.Dry evaporator is widely used in refrigerating system because of its well performance of oil return,less refrigerant charge and stability.But the imbalance of refrigerant distribution among each heat exchanging pipe has become a main factor that restricts the optimization of dry evaporator.For one thing,the imbalance makes it impossible for the heat exchange area to be taken full advatage of,directly reducing the refrigerating capacity and heat exchange efficiency,eventually lowering the effiency of the entire refrigerating system and the equipment economy.For another,the imbalance can also cause the oscillation of expansion valve in the refrigerating system.To solve this engineering problem,this project has done relavant research on improving the refrigerant distribution performance of dry evaporator by using CFD simulation.First,according to a typical dry evaporator sample,a numerical simulation of pure liquid refrigerant is conducted.In this simulation,the reason of distribution imbalance has been analyzed.Taking the enginnering application into consideration,a distribution pipe plan and a orifice plate plan are given to improve the distribution perfromance.Meanwhile,a detailed calculation method of orifice diameter is introduced in the orifice plan.Besides,research on pure liquid refrigerant distribution has been done,showing that the distribution uniformity of the distribution pipe plan and the orifice plate plan increases by 43.04% and 34.07% respectively compared to the sample,approving the feasibility of the plans.Second,a preliminary research on gas-liquid two-phase refrigerant distribution has been done under the conditions of the evaporator sample,the distribution pipe plan and the orifice plate plan.The distribution uniformity of these three conditions are compared and analyzed according to the numerical simulation.The uniformity of mixed phase and liquid phase see an increase of 43.81% and 37.74% respectively in the preliminary distribution pipe plan.The uniformity of mixed phase and liquid phase increase by 51.36% and 45.86% respectively in the preliminary orifice plate plan.For further optimization of distribution,the diameter and the structure of openings are optimized in the distribution pipe plan,and the diameter and the installation position are optimized in the orifice plate plan.Eventually,the uniformity of mixed phase and liquid phase see an increase of 56.60% and 51.34% respectively in the optimal distribution pipe plan and the uniformity of mixed phase and liquid phase increase by 60.80% and 56.61% respectively in the optimal orifice plate plan.In addition,researches on the optimal distribution pipe plan and the optimal orifice plan in varied conditions have also been conducted.The dryness varies from 0.1 to 0.3 and the flow varies from 0.34 to 0.85 kg/s in the typical conditions of the research.The result shows that when dryness varies,the uniformity index of mixed phase doesn’t change much while the uniformity index of the liquid phase increases with dryness increased,indicating the decrease of its uniformity.Besides,flow has less effect on the uniformity of both mixed phase and liquid phase.Lastly,a numerical calculation of heat transfer are presented for the final distribution plan and the sample,comparing and analyzing the improvement of heat transfer performance after adding distribution structrue.Compared to the sample,the optimal distribution pipe plan sees an increase of 19.69% of heat transfer and the optimal orifice plate plan sees an increase of 23.83% of heat transfer.The results indicate the praticability of the two plans.