An Experimental Study On Refrigeration System For Ultra-Low Temperature Freezer Using Mixed Refrigerant

Multi-component mixed refrigerant is employed and only single compressor is required in the rectification type auto-cascade refrigeration system.A rectification device is also used in this system to separate the refrigerants with different boiling point.Due to effect of the refrigeration,the system can obtain a higher efficiency as well as a stable performance.The aim of this paper is to apply the rectification type auto-cascade refrigeration cycle to the refrigeration system for low temperature freezers.Based on theoretical calculation and optimization,experiment has been conducted on this cycle in the -85℃～-125℃temperature range.The optimum compositions of the mixed refrigerant have been obtained and optimization of the structure of the system parts has been achieved.The refrigeration system for low temperature could operate steadily in long period.The main research contents of this thesis are as follow:1.The development and present status of the auto-cascade refrigeration system using mixed refrigerant are reviewed.2.Thermodynamics calculation and design calculation of he rectification type auto-cascade refrigeration system are conducted for the -125℃temperature range low temperature freezers.3.The experimental rig has been modified for researches in -85℃,-105℃,-125℃temperature ranges.The optimum compositions of the mixed refrigerant have been obtained and optimization of the structure of the system parts has been achieved respectively after many experimental optimizations.4.The rectification column which is the key component of the system has been improved and designed.A free rectification effect has been showed in the 30 days no-failure on-off reliability testing.5.Double capillary design has been used and the primary start failure which accompanied with single capillary design when the box temperature is very low in designed operation condition has been solved satisfactorily.