| Under the background of"emission peak"and"carbon neutrality",efficient natural gas heat-driven heat pumps has huge application prospects and market value in the residential heating field.Natural gas heat-driven Vuilleumier cycle(VM)heat pump has the advantages of high heating efficiency,environmentally friendly and high safety working medium,simple and compact structure,high reliability,long life,low operating noise and so on,which is very suitable for residential heating field,and has gradually attracted people’s attention in recent years.The Hofbauer-Vuilleumier heat pump is a new type of natural gas heat-driven VM heat pump with free pistons,which changes the pistons’sinusoidal motion pattern(simple as“S-type motion”)in the traditional free piston VM heat pump,and produces a novel“Dwell-based Motion”(simple as“D-type motion”)mode for the free pistons.However,in the current mature commercial numerical simulation softwares(such as SAGE,GT-Suite,etc.),which are mainly based on pistons’sinusoidal motion pattern,there is a lack of functions and modules that can be flexibly used in the numerical simulation study for the novel VM heat pump with D-type motion.It has been limiting the research and engineering development of the novel VM heat pump.Therefore,taking the novel VM heat pump’s system structure as reaserach object,this paper has developed analysis models that can be flexibly used in the numerical simulation of the novel VM heat pump with D-type motion.The performance simulation and multi-objective optimization were carried out,based on the experimental data and numerical analysis model of the novel VM heat pump prototype.The main research contents and achievements of this paper are as follows:(1)Based on the system structure and working principle of the novel VM heat pump,the second-order and third-order thermodynamic analysis models and a third-order dynamics model were built.The differences between different thermodynamic analysis models were compared and analyzed based on MATLAB software.And based on the novel VM heat pump’s experimental data,the dynamic and thermodynamic performance of the third-order simulation model were calibrated,which match well with the experimental data and have a high simulation accuracy.(2)Based on the force analysis of the novel heat pump’s hot and cold pistions,the pistions’s motion was simplified into a damped single degree of freedom vibration system,and the system’s damping coefficient C_d and spring coefficient K for piston’s movement were defined.The effects of different operating temperatures on the hot and cold pistons’C_d and K values at different working phases were analyzed qualitatively and quantitatively,based on the experimentally calibrated third-order1D CFD dynamics model.The results show that the variation rates of C_d and K values of hot piston are 8.71%-9.05%and 7.78%-7.84%,while those of cold piston are8.87%-9.38%and 16.56%-19.54%.Based on the analysis of the influence on the hot and cold pistons’s C_d and K values,the quantitative relationships between different operating temperatures and the hot and cold pistons’C_d or K values in different phases were established by response surface method.Coupled with the analytical solution of the damped single degree of freedom vibration equation,a simplified piston kinematics model was established,which is used to substitute the third-order1D CFD dynamics model for rapid prediction of piston’s free stroke,with substitution accuracy within 0.5%.Based on this simplified piston’s kinematics model,the effects of the hot chamber temperature T_h,the warm chamber temperature T_w,and the cold chamber temperature T_c on the pistons’s free stroke in different working phases were analyzed.The results show that the free stroke of both cold and hot pistons increases with the increase of T_h.With the increase of T_w,the free stroke of cold piston decreases gradually,while that of hot piston increases gradually.With the increase of T_c,the change law of free stroke of hot and cold piston is opposite to that of T_w.(3)Experimental researches were carried out on the novel VM heat pump’s principle prototype.The cycle working process,the cold and hot pistons’abnormal movement process,and the switching process between the S-type movement and D-type movement were analyzed,and the typical characteristics of the cold and hot pistons’abnormal movement were given.In addition,the effects of different operating temperature conditions and heating load regulation on performance were analyzed,based on the experimentally calibrated third-order 1D CFD dynamics model.The results show that different operating temperatures have a great influence on the heating performance coefficient COP_h,and the heating output power is mainly affected by the hot chamber temperature T_h.In addition,the heating output power was positively correlated with the working frequency of the cold and hot pistons’movement,and by changing dwell time in the D-type motion mode of the novel VM heat pump to change the working frequency,the load regulation function of reducing the heating output power was realized without worsening COP_h.Compared with the traditional free piston VM heat pump with S-type motion mode,the novel VM heat pump has great energy-saving advantages in partial load regulation.(4)Coupling the novel VM heat pump numerical simulation models established in this paper with NSGA-Ⅱ algorithm,the multi-objective optimization designs were carried out for the pistons’kinematic performance and thermodynamic performance.Based on the summary and analysis of experimental data,the novel VM heat pump numerical simulation models selected for multi-objective optimizations were simplified and processed to improve calculation speed,which can save the time cost of NSGA-Ⅱ algorithm optimization’s calculation.And taking Beijing heating season as an example,the comprehensive energy saving potential of the novel VM heat pump in all working conditions was analyzed.The research results show that,the piston kinematic performance and thermodynamic performance of the new VM cycle heat pump were greatly improved by the multi-objective optimization research carried out in this paper.Compared with the original machine,the electromagnetic power loss was greatly reduced for the optimization scheme,and the comprehensive COP_h was improved by 5.03%,while the heating output power was only reduced by 1.71%.In the whole operation condions of Beijing heating season,the comprehensive energy consumption of the novel VM heat pump’s structure optimization scheme was reduced by 3.88%compared with that of the original machine.Compared with the natural gas boiler,the comprehensive energy consumption of the structure optimization scheme and original machine scheme of novel VM heat pump were reduced by 34.64%and 32.00%respectively,which have a great energy-saving advantage.The research in this paper provides a wealth of thermodynamic and dynamics numerical simulation models for the study of VM heat pump,and deeply analyzes the pistons’dynamic characteristics and thermodynamic performance of the novel VM heat pump,which are providing theoretical guidance for the optimization design and engineering development of VM heat pump.Besides,it lays a foundation for the application of digital twins technology in the field of VM heat pump in future. |
PDF Full Text Request