A General Dynamic Model Of Indirect Cooling Household Refrigeator And Its Validation

With development of social and improvement of people's living standards, the household refrigerator becomes a necessary appliance. The household refrigerator can provide the low temperature for saving food, meawhile it consumes a lot of energy during 24-hour running. Improving refrigerator performance, not only can contribute to electricity saving for families, but also contributes to the national advocated targets of ?energy-saving emission reduction'and ?low-carbon', even contribute to the environment sustainability. Since China has been a member of WTO and the export capacity of household refrigerator has been increasing significantly, the improvement of energy efficiency of refrigerator can make the refrigerator made in china more competitive in the global markets. Comparing with direct cooling household refrigerator, indirect cooling household refrigerator has advantages on auto-defrost, large storage capacity and multi-temperature compartment etc, and there are widly used. Therefore, it is necessary to improve the energy efficiency of indirect cooling household refrigerator.To improve the performance of household refrigerator, experiment and simulation are widely used. The experiment can provide the reliable result of refrigerator, so it becomes a necessary way to understand the refrigerator for the engineer. However, the experiment takes too much money and time due to a lot of back and forth testing. Meanwhile, the simulation can predict the refrigerator performance quickly, and obtain the optimal results for refrigerator too. Therefore, the simulation is a good way to design new refrigerator for engineer.The thesis focuses on the development and validation of a general dynamic model for indirect cooling household refrigerator, which includes:1.A general model based on Z-transfer function for cabinet of indirect cooling household refrigerator is proposed.a) By treating air ducts in an indirect cooling refrigerator cabinet as normalized cabinets, and considering the cabinet as a combination of several normalized cabinets in serial or/and in parallel according to the mode of air distribution among normalized cabinets, a general model of the indirect cooling refrigerator cabinet is established.b) Computation speed of Z-transfer function method is about 40000 times faster than that of normally direct differential equation solving method while the deviation between those can be ignored.c) The air temperature of an indirect cooling household refrigerator predicted by the proposed model agrees well with the experimental data, in which the maximum deviation is 1.32oC and the total mean deviation is 0.4oC.2.A model for supersaturation frost growth on evaporator of indirect cooling household refrigerator is developed.a) Applicance range of the existed water vapor supersaturation degree correlation for the frost surface is extended to the lower temperature difference of household refrigerator running condition. And basing on the extending water vapor supersaturation degree correlation, the frost growth model is developed.b) The frost accumulation predicated by the developed model agrees with experimental data well, and maximum deviation is within 10%.3.A novel calculation method for two-phase refrigerant mass is developed based on real distribution of refrigerant quality in heat exchanger.a) The refrigerant quality distribution is predicated with distributed heat exchanger model, firstly; then the dimensionless length is introduced to describe the position of arbitrary point at two-phase zone, secondly; and then a polynomial for quality distribution is obtained by curve fitting; consequently, the mean void fraction for two phase zone is obtained and the refrigerant mass can be calculated.b) The comparsion of the predicated results between that of a novel calculation method and that of method based on linear quality distribuon of two-phase refrigerant show that: when the refrigerant quality distribution is non intensively non-linear, the deviation of the two-phase refrigerant mass novel calculation method based on real quality distribution and the two-phase refrigerant mass calculation model based on linear quality distribution are similar; meanwhile, the refrigerant quality distribution is intensively non-linear, comparing with the two-phase refrigerant mass calculation model based on linear quality distribution, the two-phase refrigerant mass novel calculation model can decrease mean deviation and max deviation respectively to the 59% and 55% of the original ones.c) The calculation speed of the two-phase refrigerant mass novel calculation model based on real quality distribution and the two-phase refrigerant mass calculation model based on linear quality distribution are similar, while it is about three orders of magnitude faster than that based on distributed heat exchanger model.4.The compressor model used in the dynamic model of household refrigerator is developed and includes below two parts,a) A quasi-dynamic hermetical compressor model covering the suction refrigerant state from vapor to two-phase is developed. This model includes a dynamic model for the mixing process of inside refrigerant and sucked two-phase or vapor refrigerant, a dynamic model for heat transfer of the compressor shell, and a steady state model for the polytropic compression. The maximum deviation for steady state mass flow rate and input power of a hermetic compressor are within 5%, while the deviations of the predicted transient mass flow rate and input power from the experimental data are within 10%.b) A model based on double film theory to predicate dissolved refrigerant mass in the lubricant oil is presented. This model can reflect the dynamic releasing speed of dissolved refrigerant. And the trend of the predicated evaporating pressure agrees with the experimental data when the developed model isemployed in the dynamic model of refrigerator. 5.A general dynamic model for indirect cooling household refrigerator is developed and validated with experiment data.a) A general dynamic model for refrigerator is developed based on the procedure oriented and modularization. The procedure orientation divide the refrigerator system into some basic running procedures (R-Cycle, F-Cycle, PumpDown and Off-Cycle) according to its control algorithm and model their, so that the model for refrigerator can be set up easily and quickly based on these procedures sub-system models. The modularization is used to modularize the basic component model of sub-system model, so that the component model can be improved and extended easily. Meanwhile, the proper components sub-models and effective algorithm should be integrated in the dynamic model. These component models and algorithms include quasi-dynamic compressor model, effective enthalpy method integrated with approximate analytic capillary model, multi-zone heat exchanger sub-model, Z-transfer function based cabinet model and implicit curve-fitting method for refrigerant thermodynamic properties, predictor-corrector algorithm, adaptive time step algorithm and time step interpolation method.b) The developed dynamic model is validated with the experiment on dual-compartment and multi-compartment household refrigerator. The predicted results agree well with experimental data of a dual-compartment refrigerator, the deviation of condensing pressure and evaporating pressure are within 10%, and the deviation of input power is within 10%. The predicted results agree well with experimental data of a mulit-compartment refrigerator too. The deviation of compartment air temperature is within 2oC, the deviation of condensing temperature or evaporating temperature are within 2oC, and the deviation of input power is within 10%. A typical case for simulating 24-hour performance of a refrigerator on a PC (Intel Pentium D CPU 2.66GHz, 1024MB RAM) only costs computation time 178.3 seconds.Finally, the work of this thesis is summarized and some proposals are given for the further studies.