The Influence Of Holes Opened In The Capillary Inserted In The Tube On The Performance Of The Evaporator

The heat exchanger was widely used and had received a lot of attention. Study on heat transfer enhancement technology, had always been a hot issue. This paper was mainly based on the field synergy principle and the enhancement of heat transfer characteristics of jet impingement, to design a heat exchanger device with a new type. In the heat exchanger, a capillary with opening holes was placed into a evaporation tube, and refrigerant R134 a flowed into evaporating pipe with direct impact from different orifices of the throttle capillary and absorbed heat by evaporation on the surface of evaporating pipe, in which the heat transferring efficiency was extremely high because of the best cooperativity between velocity field and temperature gradient field. In order to study the influence of opening characteristics of built-in capillary on the performance of the whole refrigeration system, simulation and experimental research were mainly included in this paper.First of all, COMSOL4.4 software was used for numerically simulate the process of impact on jet, and analyzed the influence of the hole diameter, internal capillary and entrance velocity on the heat transfer performance. The results were considered as a reference for making research plan of subsequent experiments.Then began experiments, which including two visualization experiments and one copper tube heat exchanger experiment. The experiments were carried out under different evaporation pressures of 0 MPa and 0.08 MPa respectively, and compared with conventional capillary throttle system.Through comparative analysis of condensing pressure change, temperature field distribution of evaporation on the surface of the tube, suction and exhaust temperature of compressor, inlet and outlet temperature of condenser, changes of fluid temperature and power consumption of compressor, the characteristics of open hole testing system and the effect of hole characteristics were summed up. According to the results of the three comparative experiments with different diameter, different hole spacing, and analysis of infrared thermal images and high speed camera images on the surface of heat exchange tubes, the following conclusions were summarized:(1) In view of large diameter and small coefficient of thermal conductivity of chemical glass tubes, the liquid supply temperature of visualization experiments mainly depended on the amount of flash gas, while the capillary experiments had a lower liquid supply temperature for larger throttling pressure drop and more flash gas;(2) In the opening experiments, temperature field on the surface of the evaporation tube, and other temperature measuring points and pressure measuring points were more stable, while there was a big fluctuation in contrast capillary experiment due to its poor ability of flow adjustment;(3) In the same evaporating pressure, heat exchange area and other conditions, the condensing pressures of capillary experiments were much larger than opening experiments, which indicated that the coefficient of performance of opening experiments system was larger than capillary experiments;(4) It can be considered that the refrigerating capacity of the opening experiment and capillary experiment are equal under the same evaporating pressure, heat transfer area and other conditions; while refrigerant charge amount in the opening experiment was generally less than 50% of capillary experiment because of its higher heat transfer efficiency;(5) Compared with the capillary experiment, the refrigerant in opening experiment flowed through compressor and took away less heat, and there was a larger temperature difference in the inlet and outlet of the condenser for less refrigerant charge, which led to a better heat transfer effect in condenser;(6) There was back liquid in the suction pipe of conventional capillary experiment, which increased power consumption without effective cooling; while there was no back liquid produced in opening experiment;(7) With the same refrigerating capacity, compressor power consumption in conventional capillary experiment was 6.2% to 9.1% higher than that of opening experiment, which was verified the higher efficiency of the experimental system;(8) In opening experiment, too small hole spacing and too large aperture would lead to more residual liquid, while too large hole spacing and too small aperture could produce uneven temperature distribution on the surface of heat exchange tubes; researches had shown that with the aperture between Φ0.5 mm to Φ0.8 mm, hole spacing between 8 cm to 12 cm, temperature field distribution was relatively uniform and the size of aperture and hole spacing within this scope had smaller impact.;(9) The research of numerical simulation and analysis of thermal infrared holograms and high-speed video in the heat transfer process found that, there were several orifices used for liquid supply in opening experiment, and the flow field and temperature gradient field of the jet medium field had the best coordination in the jet impingement area and could significantly strengthen the heat transfer, which made the temperature field formed on the surface of the evaporating tubes more uniform.