Quantitative Experiment And Theoretical Research On Irreversible Loss In Heat Pump Cycle Expansion Process

With the implementation of the national energy-saving and emission-reduction policies,the energy-saving and consumption-reduction of heat pump systems with large temperature and pressure differences is one of the current research hotspots in the field of HVAC.At present,the research on the energy loss of the compressor and heat exchanger in the heat pump system is relatively mature,and there is not enough attention to the irreversible loss in the expansion process of the heat pump system,and the energy consumption of the expansion process in the heat pump system with a large pressure difference cannot be ignored.Therefore,this paper studies the irreversible loss of the heat pump cycle expansion process through simulation,theoretical analysis and experimental research.Firstly,this article uses Fluent simulation software to numerically simulate the evolution of the refrigerant’s thermal state in the electronic expansion valve,and reasonably simplifies the model,focusing on the study of the bubble generation mechanism,and exploring the impact of expansion valve opening changes on the refrigerant velocity field,pressure field,volume field and density field in the expansion valve,accumulate experience for subsequent heat pump cycle experiments and provide help for subsequent theoretical analysis of the expansion process.Secondly,a theoretical analysis of the irreversible loss in the expansion process is carried out.Because of the heat pump cycle in the expansion process is a typical process of non-equilibrium process,this article first introduces the basics of non-equilibrium thermodynamics,summarizes the three common definition of entropy and analysis on its nature,the introduction of non-equilibrium entropy balance equation in thermodynamics.Then the entropy balance equation of the expansion process is simplified,and a brand new entropy balance equation suitable for the expansion process is proposed.Finally,on the basis of previous research results,numerical experiments verify that there is a linear relationship between the entropy increase per unit mass of the refrigerant expansion process and the gas content at the outlet of the expansion valve,and the rationality of the entropy balance equation derived during the expansion process is verified.Subsequently,the irreversible loss experiment of the heat pump cycle expansion process is designed and an experiment platform is built.Designing the experimental schematic diagram and formulating the experimental plan,carrying out the specific selection of each component of the experimental platform,and selecting the appropriate measuring instrument.According to the experimental principle diagram and the size parameters of each component,the Revit software is used to establish the threedimensional drawing of the experimental platform,and the experimental platform is built according to the three-dimensional drawing.Finally,the experimental results of irreversible losses in the heat pump cycle expansion process are analyzed.Four kinds of expansion valve groups are used for experiments,and experiments are carried out under different temperature conditions and different flow conditions.The adjustment performance of the four expansion valve groups is compared,and the changes in compressor operating parameters and heat exchanger operating parameters are analyzed.Analysis of energy consumption of expansion valve.Compare the regulating performance of the valve when it goes up and down,and analyze the difference of the valve curve in the two cases.All the experimental results are classified according to the pressure difference before and after the expansion valve,and it is found that the entropy increase per unit mass of the refrigerant expansion process is linearly related to the mass fraction of the gas phase at the outlet of the expansion valve.It is not affected by the evaporation(condensation)temperature,the type of expansion valve,the expansion valve,opening degree,refrigerant flow rate and pressure difference between the inlet and outlet of the expansion valve.