Performance Analysis And Optimization Of Refrigeration Cycle Based On Three Classes Of New Working Substances

With the development of science and technology,refrigeration technology has become more and more important one.The traditional gas compression refrigeration technology is of the mainstream in the present field of refrigeration and air-condition,but it has some disadvantages such as greenhouse effect,noise,and limited cooling efficiency.For this reason,a number of scholars and engineers are exploring some potential green energy-saving refrigeration technologies.Some new refrigeration technologies such as magnetic,electrocaloric,and semiconductor thermoelectric ones,which use solid as the working substance,have distinct advantages of energy conservation and environmental protection and more and more attention have been attracted.In this thesis,the performances of the refrigeration cycles with the three classes of new working substances mentioned above are investigated and the main research contents are as follows:In chapters 2 and 3,based on the experimental data of Gds(Si2 Ge2),Gd5(Si0.985Ge0.985Ga0.003),La(Fe0.88Si0.12)13H1(Chapter 2)and LaFe11.6Si1.4(Chapter 3),different regenerative Ericsson refrigeration cycles using these magnetic materials as the working substance are established.The influences of magnetic field,nonperfect regeneration,the temperatures of heat sources,and the thermal hysteresis on the cooling quantity and COP of the refrigeration cycles are analyzed and evaluated and the optimal operating temperature range and refrigeration temperature span of the refrigeration cycles are obtained.The further calculation results show that in the temperature range[T0,T0+10K]and magnetic field change from 0 to 2T,the net cooling quantity and COP of the refrigeration cycle using Gd5(Si0.985Ge0.985Ga0.003)as the working substance are larger than those using Gd5(Si2Ge2),where T0 is the Curie temperature of magnetic material;Due to the thermal hysteresis of the working substance,the net cooling quantity of the refrigeration cycle and the temperature range with large net cooling capacity decrease,the COP of the refrigeration cycle also decreases obviously,and the maximum difference between the COPs of the refrigeration cycles with and without thermal hysteresis reaches up to more than 5 times.In chapter 4,we study the performance of intercooling Brayton refrigeration cycle using an electrocaloric material as the working substance.Based on the thermodynamic properties of electrocaloric materials,a new Brayton refrigeration cycle model is set up and the mathematical expressions of the cooling quantity,COP and work input of the refrigeration cycle are derived,and the impacts of the regeneration,irreversible adiabatic factor,ratio of high and low electric fields,heat sources' temperatures on the main performance parameters of the refrigeration cycle are explored.Then,the performances of electrocaloric refrigeration cycles with and without intercooling processes are compared.The results indicate that the work input of the refrigeration cycle with intercooling process decreases but the COP increases with the increase of the electric field ratio(?)H,;When(?)H>2.5,the difference between the work inputs or the COPs of the two refrigeration cycles with or without intercooling process gradually become small.In chapter 5,employing non-uniform doping nanostructure material,one constructs a new the semiconductor thermoelectric refrigerator model.By combined the energy balance equation and Domenicali's equation and employing finite difference method,we computed the heat flow and temperature distributions along the device legs such that the mathematical expressions of the cooling rate and COP of the refrigerator are obtained.The effects of the current density,lattice thermal conductivity,and width of the energy selective electron channel on the performance of the refrigerator are discussed.The results obtained here are compared with those of the uniform doping thermoelectric refrigerator.It shows that for the thermoelectric refrigerator with non-uniform doping nanostructure material,the quantum effects are capable of significantly reducing the irreversible energy losses due to the electron transport,and consequently,the cooling rate and thermodynamic perfect degree have obviously improved.For example,the maximum COP reaches to 32.78%of the COP of the reversible Carnot refrigerator when the channel width of the energy selective electron ?E=10meV.The results obtained can provide some theoretical guidance for the optimal parameter design and performance improvement of magnetic,electrocaloric,and semiconductor thermoelectric refrigerators.