Cascade Freezer Refrigerant Mix for -150°C Oil Return
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Solution Overview
Problem
Existing two-dimensional refrigeration systems face challenges in achieving extremely low temperatures without using refrigerants that harm the ozone layer, and require modifications to prevent compressor lubrication issues and safety risks from combustible refrigerants.
Innovation Solution
The use of nonazeotropic mixed refrigerants such as R245fa, R600, R404A, R508A, R14, R50, and R740, with R245fa comprising 70% or more by weight, and the addition of n-pentane, to achieve extremely low temperatures of -150°C without ozone-depleting refrigerants, while ensuring the refrigerants are incombustible and compatible with compressor oils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HCFC refrigerants (R21, R22) are used in the refrigerant circuit, then oil return performance is improved, but ozone layer destruction risk increases
Solution Approach 1:
The patent changes the chemical composition parameters of the refrigerant from HCFC-based (R21, R22) to HFC-based (R134a, R125, R404A) refrigerants. This parameter change eliminates chlorine atoms that deplete the ozone layer while maintaining the refrigerant's ability to dissolve in compressor oil and facilitate oil return, thus resolving the contradiction between reliability and environmental harm.
Solution Approach 2:
The patent adopts readily available HFC refrigerants that are environmentally friendly alternatives to HCFCs. These refrigerants, though chemically different, provide the necessary oil carrier function temporarily during the transition from ozone-depleting substances, achieving both environmental protection and operational reliability.
2Object-affected harmful factors
If R21 is replaced with other refrigerants to eliminate chlorine, then ozone layer protection is improved, but oil return capability may deteriorate
Solution Approach 1:
The patent uses a composite refrigerant mixture containing multiple HFC components (R134a, R125, R404A) in specific proportions. This composite formulation combines the advantages of individual refrigerants to achieve both environmental compatibility (no chlorine) and functional performance (oil return capability through appropriate solubility characteristics of the HFC mixture).
Solution Approach 2:
The patent adjusts the compositional parameters of the refrigerant mixture to optimize oil solubility and return characteristics. By carefully selecting the ratios of R134a, R125, and R404A, the refrigerant mixture maintains adequate solubility in compressor oil to prevent oil accumulation in the refrigerant circuit, thereby preserving reliability while eliminating ozone-depleting substances.
3Temperature
If combustible refrigerants are used to achieve low temperatures, then cooling performance is improved, but safety risks increase
Solution Approach 1:
The patent employs HFC refrigerants as safe alternatives to combustible refrigerants. While HFCs have different thermodynamic properties, they provide adequate cooling performance for the application and eliminate combustion risks entirely, achieving both cooling objectives and safety requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution maintains refrigerant circuit performance without modifying conventional circuits, prevents ozone layer destruction, and ensures safe, reliable operation by achieving stable, extremely low temperatures for preserving living organisms and specimens while avoiding combustion risks.
Implementation Method 1
evaporate the condensed refrigerants to achieve cooling action
Implementation Method 2
heat exchangers by an evaporator in the refrigerant circuit on a high temperature side and a condenser in the refrigerant circuit on a low temperature side
Implementation Method 3
condense refrigerants delivered from compressors
Implementation Method 4
condense refrigerants delivered from compressors and thereafter evaporate the condensed refrigerants to achieve cooling action
Data Source
AI summary
The invention provides a freezer unit using refrigerants serving as an oil carrier without using any refrigerants of subjects of the ozone regulation and being capable of realizing extremely low temperatures such as −150° C. The freezer unit includes a refrigerant circuit on a high temperature side and a refrigerant circuit on a low temperature side to form independent closed refrigerant circuits which condense refrigerants delivered from compressors and thereafter evaporate the condensed refrigerants to achieve cooling action, and a cascade condenser formed by an evaporator in the refrigerant circuit on the high temperature side and a condenser in the refrigerant circuit on the low temperature side. Confined in the refrigerant circuit on the low temperature side are nonazeotropic mixed refrigerants containing R245fa, R600, R404A, R508A, R14, R50 and R740, or nonazeotropic mixed refrigerants containing R245fa, R600, R404A, R23, R14, R50 and R740, or nonazeotropic mixed refrigerants containing R245fa, R600, R404A, R508B, R14, R50 and R740.