| The cascade refrigeration system with coupling characteristics can effectively improve the applicability of the cascade refrigeration system in the field of refrigeration and refrigeration.In order to meet the stable and high-efficiency operation when the refrigeration load changes,a cascade coupling refrigeration system has been developed.The switching strategy of the operating mode is proposed.Through the unit test,the best coupling relationship between the high and low temperature stage frequencies of the cascade refrigeration system is obtained.Under the best coupling characteristics of the high and low temperature stage frequencies,the variable working condition test is carried out,Studied the influence of the coupling relationship between high and low temperature levels on system performance,and explained the operating mode switching characteristics with coupling characteristics.First of all,based on the theoretical analysis of the cascade refrigeration system,combined with the existing research results in the laboratory,comprehensive safety,high efficiency,applicability and popularization and other factors,R410 A is determined as a circulating working fluid,and the effect of intermediate characteristics changes is studied.The impact of system performance is conducive to promoting the correct and rapid progress of the experiment.Secondly,based on the operating characteristics of the cascade coupled refrigeration system,the influence of adjustable parameters on the cascade refrigeration system is analyzed.The evaporation temperature is-36°C,the condensation temperature is 37°C,39°C,41°C,and 43°C,and the high-temperature frequency 180 Hz,low-temperature stage frequency 150Hz～220Hz,under fixed working conditions,when the high-temperature stage frequency is constant,the coefficient of refrigeration performance will first increase and then decrease with the increase of the low-temperature stage frequency,that is,mode one(two)operation There is the best low-temperature stage frequency that couples the high-temperature stage frequency to maximize the coefficient of performance COP value;the current high-temperature stage frequency makes the corresponding low-temperature stage frequency with the largest COP value are 190 Hz,180Hz,170 Hz,160Hz,mode two is in the high-temperature stage The COP value at 180 Hz is slightly higher than the operating mode 1.In order to reduce the repeatability of the experiment,for the change of the high-temperature stage frequency,the high-temperature stage frequency is coupled to make the low-temperature stage frequency whose performance coefficient COP value is the largest and the reference of the high-temperature stage frequency is linear The relationship and linearity coefficient are determined with reference to the test bench test conditions and actual equipment.Third,under the final coupling characteristics of the high and low temperature levels(dual frequency conversion),the coupling characteristics of the high and low temperature levels follow the principle of maximum COP value,and the frequency range of the high temperature level is 80Hz～220Hz.Under different working conditions,the exhaust temperature of mode one(two)is within the limit of the safe temperature of 120℃.The maximum compression ratio of the high-temperature stage is 6.14 and 6.43,the minimum is4.86 and 4.81,and the compression ratio of the low-temperature stage is reduced by the minimum 0.90 and 1.02.The maximum is 1.01 and 1.73,and the average variation range of the COP value of the mode one(two)performance coefficient is 7.6% and 5.6%respectively.The exhaust gas temperature and high-temperature stage pressure ratio increase with the increase of the coupling frequency,and the low-temperature stage pressure ratio decreases with the increase of the coupling frequency.The coefficient of performance COP value increases first,then decreases slowly,and its growth rate Greater than the reduced speed.Finally,based on the experimental results,the change rule of mode switching is analyzed,and the mode operation is performed under the working conditions of evaporation temperature-36℃,condensation temperature 37℃,39℃,41℃,43℃,and high-temperature frequency range 80Hz～220Hz.The cooling capacity increases with increasing frequency.When the condensing temperature rises from 37°C to 43°C,the cooling capacity at the mode switching point is 4.6 k W,4.24 k W,4.10 k W,4.05 k W.The test results show that the cascade coupled refrigeration system can solve the problem of low efficiency of the unit during operation to a certain extent.When the refrigeration capacity changes,the mode can be switched to improve the efficiency of the refrigeration system to reduce power consumption. |
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